CN114552379B

CN114552379B - Resonant cavity, laser unit, laser and laser radar

Info

Publication number: CN114552379B
Application number: CN202011344323.4A
Authority: CN
Inventors: 宣黎阳; 向少卿
Original assignee: Hesai Technology Co Ltd
Current assignee: Hesai Technology Co Ltd
Priority date: 2020-11-25
Filing date: 2020-11-25
Publication date: 2023-08-08
Anticipated expiration: 2040-11-25
Also published as: WO2022110914A1; CN114552379A

Abstract

A resonant cavity, a laser unit, a laser and a lidar, the resonant cavity comprising: the first reflecting mirror and the second reflecting mirror are arranged at intervals; an active structure located between the first mirror and the second mirror; the active structure includes one or more first active regions of a material having a tensile strain and one or more second active regions of a material having a compressive strain. The second active region with compressive stress has higher gain, the band gap can be regulated and controlled to adjust the working band, and the first active region with tensile strain can release the compressive stress introduced by the second active region, so that stress accumulation is prevented, and stress release is avoided; the arrangement of the first active region and the second active region can realize stress balance and inhibit structural defects while guaranteeing the gain of an active structure, is beneficial to improving the quality of a resonant cavity, the external quantum efficiency and the power and the reliability of a device.

Description

Resonant cavity, laser unit, laser and laser radar

Technical Field

The invention relates to the field of lasers, in particular to a resonant cavity, a laser unit, a laser and a laser radar.

Background

The laser radar is a commonly used ranging sensor, has the characteristics of long detection distance, high resolution, small environmental interference and the like, and is widely applied to the fields of intelligent robots, unmanned aerial vehicles and the like. In recent years, the development of automatic driving technology is rapid, and a laser radar is indispensable as a core sensor for distance perception. The performance of the laser, which is one of the core components of the laser radar, has a great influence on the performance of the laser radar.

Conventional vertical cavity surface emitting lasers (Vertical Cavity Surface Emitting Laser, VCSELs for short) typically include a lower bragg reflector (Distributed Bragg Reflector, DBR for short), an active region, a current confinement layer, and an upper DBR grown epitaxially on an N-doped substrate in sequence. Wherein current is injected into the active region through the electrode; the material of the active region is excited to emit light, and resonates in a resonant cavity formed by the upper layer DBR and the lower layer DBR to form strong light beams with the same propagation direction, the same frequency and the same phase.

In a VCSEL, the active region is a quantum well (Multi Quantum Wells, MQWs) formed by alternately growing thin films of two materials. In an active region using a quantum well, structural strain is often introduced, so that the purposes of improving the gain of the active region and regulating and controlling the energy band of the quantum well are achieved.

However, the introduction of strain increases the risk of lattice structure defects, and problems of reduced external quantum efficiency and power or reduced device reliability occur.

Disclosure of Invention

The invention solves the problem of providing a resonant cavity, a laser unit, a laser and a laser radar to overcome the problem caused by strain introduction.

In order to solve the above problems, the present invention provides a resonant cavity, comprising:

the first reflecting mirror and the second reflecting mirror are oppositely arranged at intervals; an active structure located between the first mirror and the second mirror; the active structure includes one or more first active regions of a material having a tensile strain and one or more second active regions of a material having a compressive strain.

Optionally, at least one of the first active region and the second active region is a quantum well active region, the quantum well active region including a barrier region and a potential well region between adjacent barrier regions.

Optionally, the first active region includes: an overcompensated quantum well, the second active region comprising: a compressively strained quantum well.

Optionally, the potential well region material of the first active region has a compressive strain, and the barrier region material of the first active region has a tensile strain; the tensile strain of the barrier region material of the first active region has a stress magnitude greater than the compressive strain of the potential well region material of the first active region.

Optionally, the potential well region material of the first active region is InGaAs, and the potential barrier region material of the first active region is at least one of GaAsP, alGaAsP.

Optionally, the potential well region material of the second active region has a compressive strain, the barrier region material of the second active region has a compressive strain, and the compressive strain of the barrier region material of the second active region has a stress magnitude that is less than the compressive strain of the potential well region material of the second active region.

Optionally, the potential well region material of the second active region is InGaAs, and the potential barrier region material of the second active region is AlGaAs.

Optionally, the potential well region material of the second active region has compressive strain and the barrier region material of the second active region is unstrained.

Optionally, the quantum well active region includes a plurality of quantum wells.

Optionally, the material of the first reflecting mirror includes N-type doping ions; one of the first active regions is located at the first mirror surface.

Optionally, the method further comprises: and the reflecting layer is positioned between the adjacent first active area and the second active area.

Optionally, the first active region is located on one side of the reflective layer, and the one or more second active regions are located on the other side of the reflective layer.

Optionally, the refractive index of the reflective layer material is different from the refractive index of the first active region material, and the refractive index of the reflective layer material is different from the refractive index of the second active region material.

Optionally, the reflective layer is a distributed bragg mirror.

Optionally, the reflective layer is a laminated structure, and the reflective layer includes a first reflective sub-layer and a second reflective sub-layer, where the refractive index of the first reflective sub-layer is not equal to the refractive index of the second reflective sub-layer.

Optionally, the first reflective sub-layer and the second reflective sub-layer are alternately arranged.

Optionally, the active region has a first surface and a second surface opposite to each other, and a direction of the first surface pointing to the second surface is consistent with a current direction; the resonant cavity further includes: and a current limiting layer at least on the first surface.

Optionally, the surface of the first active region facing the second active region has the current confinement layer thereon.

Optionally, the method further comprises: and the substrate is positioned on one side of the first reflecting mirror away from the active structure.

Optionally, the substrate is an N-type substrate, the doped ions contained in the first reflecting mirror are N-type ions, and the doped ions contained in the second reflecting mirror are P-type ions.

Accordingly, the present invention provides a laser unit comprising:

the resonant cavity is the resonant cavity of the invention; a first electrode; and a second electrode.

Optionally, the second electrode is located on a surface of the second mirror on a side away from the active structure.

Optionally, the first electrode is located on a side of the first mirror away from the active structure, and the first electrode is located on a surface of the substrate.

Optionally, the second electrode includes a window, and the window penetrates through the second electrode along the laser propagation direction.

In addition, the invention also provides a laser, comprising:

the laser unit is the laser unit of the invention.

Optionally, the laser is a vertical cavity surface emitting laser.

In addition, the invention also provides a laser radar, which comprises:

a light source comprising the laser of the present invention.

Compared with the prior art, the technical scheme of the invention has the following advantages:

in the technical scheme of the invention, the active structure comprises a first active region and a second active region, wherein the material of the first active region has tensile strain, and the material of the second active region has compressive strain. The first active region with tensile strain can release compressive stress introduced by the second active region, so that stress accumulation is prevented, and stress release is avoided; therefore, the arrangement of the first active region and the second active region can realize stress balance and inhibit the generation of structural defects while ensuring the gain of an active structure, thereby being beneficial to improving the quality of a resonant cavity, the external quantum efficiency and the power and the reliability of a device.

In an alternative scheme of the invention, at least one of the first active region and the second active region is a quantum well active region, and the quantum well active region comprises a potential barrier region and a potential well region positioned between adjacent potential barrier regions, that is, the first active region and the second active region are similar in structure, so that the arrangement of the first active region and the second active region does not increase the structural complexity of the active structure, and the complexity of the active structure design of stress balance can be greatly reduced without separately analyzing and optimizing factors such as resistance, energy band, diffusivity, defect generation and the like.

In an alternative embodiment of the present invention, the first active area includes: an overcompensated quantum well, the second active region comprising: a compressively strained quantum well. The quantum well integrated structures of the first active region and the second active region are set to be in different strain forms, so that the selection range of the quantum well material can be expanded while the stress balance is met, the limitation of working wavelength is avoided, the barrier height can be ensured, and the gain of the active region is improved.

In an alternative scheme of the invention, the potential well region material of the first active region has compressive strain, and the potential barrier region material of the first active region has tensile strain; the stress magnitude of the tensile strain of the barrier region material of the first active region is greater than the stress magnitude of the compressive strain of the potential well region material of the first active region, so that the whole of the first active region material presents the tensile strain corresponding to the accumulation of the tensile stress to realize the balance of the compressive strain of the second active region; and the larger tensile strain of the barrier region of the first active region tends to have higher barrier height, compared with the barrier region of compressive strain, the formed quantum well has stronger quantum confinement effect, and larger gain can be obtained.

In an alternative scheme of the invention, the potential well region material of the second active region has compressive strain, the potential barrier region material of the second active region has compressive strain, and the stress magnitude of the compressive strain of the potential barrier region material of the second active region is smaller than that of the compressive strain of the potential well region material of the second active region, namely the potential barrier region of the second active region adopts a material without stress or with a small amount of compressive stress, and the whole second active region is compressive strain so as to obtain higher gain.

In an alternative scheme of the invention, the material of the first reflecting mirror comprises N-type doping ions; one of the first active regions is located at the first mirror surface. The material of the first reflecting mirror with N-type doped ions has compressive strain, so that the first active region with tensile strain is directly arranged on the first reflecting mirror, and the compressive strain of the first reflecting mirror can be balanced by the first active region with tensile strain so as to avoid the accumulation of compressive stress.

In an alternative scheme of the invention, the method further comprises the following steps: the reflection layer is positioned between the adjacent first active area and the second active area, and the cavity loss of different active areas of the resonant cavity can be adjusted by the arrangement of the reflection layer, so that gain difference can be balanced, two active areas can work under proper conditions, and the device performance can be further improved.

In an alternative embodiment of the present invention, the reflective layer is a distributed bragg mirror. Since the first mirror and the second mirror are typically bragg mirrors, the reflective layers are arranged as identical bragg mirrors without introducing additional structures, so that the influence of introducing the reflective layers on the structural complexity can be reduced.

In an alternative embodiment of the present invention, the surface of the first active region facing the second active region has the current confinement layer thereon. Since the material of the current confinement layer has a compressive strain, the first active region is capable of balancing the compressive strain of a portion of the current confinement layer, thereby reducing the impact of the current confinement layer on the compressive strain of the second active region.

In an alternative scheme of the invention, the resonant cavity further comprises a substrate, and the substrate is positioned at one side of the first reflecting mirror away from the active structure; the substrate is an N-type substrate, the doped ions contained in the first reflecting mirror are N-type ions, and the doped ions contained in the second reflecting mirror are P-type ions. The N-type substrate has higher material quality, and can provide a good growth surface for the formation of the resonant cavity so as to ensure the quality of the resonant cavity.

Drawings

Fig. 1 is a schematic cross-sectional structure of a VCSEL unit;

fig. 2 is a schematic cross-sectional structure of another VCSEL unit;

FIG. 3 is a schematic diagram of the band structure of a quantum well;

FIG. 4 is a schematic illustration of the change in lattice structure before and after strain introduction during epitaxial growth;

FIG. 5 is a schematic cross-sectional view of an embodiment of a resonant cavity of the present invention;

FIG. 6 is a schematic cross-sectional view of another embodiment of a resonant cavity of the present invention;

FIG. 7 shows the distribution of optical field intensity in the cavity of the resonant cavity of the embodiment of FIG. 6 without the reflective layer;

FIG. 8 shows the distribution of optical field intensity within the cavity of the resonant cavity of the embodiment of FIG. 6;

FIG. 9 is a graph showing the distribution of optical field intensity in a cavity according to yet another embodiment of the present invention;

FIG. 10 is a graph showing the distribution of optical field intensity in a cavity according to yet another embodiment of the present invention;

FIG. 11 is a schematic cross-sectional view of another embodiment of the laser unit of the present invention;

fig. 12 is a schematic cross-sectional structure of a laser unit according to still another embodiment of the present invention.

Detailed Description

As is known from the background art, introducing strain into the active region of a VCSEL increases the risk of lattice structure defects. Analysis of the structure of a VCSEL now combined with the cause of the increased risk of lattice structure defects:

Referring to fig. 1, a schematic cross-sectional structure of a VCSEL unit is shown.

The VCSEL laser chip comprises a plurality of VCSEL cells. As shown in fig. 1, between the upper electrode 15 and the annular lower electrode 16, the device structure of the VCSEL unit includes: a lower layer DBR 11, an active region 12, a current confinement layer 13, and an upper layer DBR 14 are epitaxially grown on the substrate 10 in this order. Each epitaxial layer is obtained by epitaxial growth on a substrate 10 (at least one of a GaAs substrate, a doped Si substrate, and a doped C substrate) by a Metal-organic compound vapor deposition (Metal-Organic Chemical Vapour Deposition, MOCVD) technique.

In each VCSEL unit, a current is injected into the active region 12 through the upper electrode 15; the material of the active region 12 is excited to emit light, and resonates in a resonant cavity formed by the upper layer DBR 14 and the lower layer DBR 11 to form an intense light beam having the same propagation direction, frequency and phase. Fig. 1 shows a front side light emitting VCSEL unit in which the number of periods of the upper DBR 14 is small and the reflectivity is slightly lower than that of the lower DBR 11, so that part of the light is transmitted upward from the upper DBR 14 as usable laser light.

Referring to fig. 2, a schematic cross-sectional structure of another VCSEL unit is shown.

Similarly, the substrate 20 has a lower layer DBR 21, an active region 22, a current confinement layer 23, and an upper layer DBR 24 epitaxially grown thereon in this order. Fig. 2 shows a back side light emitting VCSEL unit, whereby the upper DBR 24 top layer of each VCSEL unit is provided with an upper layer electrode 25 and the VCSEL laser chip bottom is provided with a ring-shaped lower layer electrode 26. The laser light of the back side light emitting VCSEL exits the substrate 20 as compared to the front side light emitting VCSEL.

The active regions 12, 22 are quantum wells formed by alternately growing thin films of both materials, whether front-side or back-side emitting VCSELs. Specifically, the active regions 12, 22 include small band gap semiconductor thin films and large band gap semiconductor thin films that are alternately arranged within the active regions 12, 22 to form a quantum well structure. After the formation of the quantum well structure, a layer of Al is formed on the surface of the active regions 12, 22 _1-x Ga _x An As layer; the Al is obtained by adopting a chemical wet etching method _1-x Ga _x The As layer forms a circular hole; then the formed structure is placed in a high-temperature wet nitrogen environment, and the Al is treated _1-x Ga _x Oxidizing the As layer to make part of said Al _1-x Ga _x As layer conversionIs Al _1-x Ga _x O insulating layer to form said current confinement layers 13, 23. In the current confinement layers 13, 23, circular holes obtained by chemical wet etching are used to form current injection windows, the Al _1-x Ga _x The O-insulating layer serves to limit the current injected through the upper electrode 15. At Al _1-x Ga _x As, x is preferably less than or equal to 0.04, i.e., a high Al component, ensures a high oxidation rate.

Referring to fig. 3, a schematic diagram of the band structure of a quantum well is shown.

In the active region of the quantum well structure, a small band gap semiconductor film is arranged between two adjacent large band gap semiconductor films. The conduction and valence bands of the quantum well structure thus exhibit the well-like potentials shown in fig. 3. Among them, a region of the small band gap thin film between two adjacent large band gap semiconductor thin films is referred to as a potential Well (Well) region, and regions of the large band gap semiconductor thin films on both sides of the small band gap semiconductor thin film are referred to as Barrier (Barrier) regions.

Referring to fig. 4, a schematic diagram of the change in lattice structure before and after strain introduction during epitaxial growth is shown.

In the epitaxial growth process of the semiconductor structure, when the lattice constant of the material of the formed epitaxial layer is different from that of the growth surface (for example, the lattice constant of the material of the grown layer is different from that of the substrate), strain is generated in the formed epitaxial layer, and stress is introduced.

As shown in fig. 4, when the lattice constant of the material of the formed epitaxial layer is larger than the lattice constant of the growth surface (for example, when the lattice constant of the material of the grown layer is larger than the lattice constant of the material of the substrate), compressive strain (compressive strain) is generated in the formed epitaxial layer, and the lattice constant of the formed epitaxial layer is extruded to be close to the lattice constant of the growth surface, and accordingly, compressive stress is generated in the formed epitaxial layer; conversely, when the lattice constant of the material of the epitaxial layer is smaller than the lattice constant of the growth surface (e.g., when the lattice constant of the material of the growth layer is smaller than the lattice constant of the material of the substrate), a tensile strain (tensile strain) is generated in the epitaxial layer, and the lattice constant of the epitaxial layer stretches to a lattice constant close to the growth surface, and accordingly, a tensile stress is generated in the epitaxial layer.

Compressive strain is often introduced in the active region of the quantum well structure. Because the energy band shape of the quantum well region can be adjusted by introducing compressive strain; quantum well structures with compressive strain can achieve higher active region gain than those with tensile strain introduced, thereby enabling adjustment of the bandgap size to adjust the corresponding operating optical band at the same time.

However, strain introduction has the disadvantage that, as mentioned above, strain introduction causes stress to be generated in the epitaxial layer formed, and stress is accumulated as the epitaxial layer grows. When the energy of the stress accumulation is large enough, stress release occurs, so that structural defects such as dislocation and the like are generated in the formed epitaxial layer.

If structural defects are formed in the active region, non-radiative coincidence of electron-hole pairs in the active region is increased, resulting in a reduction in external quantum efficiency (External Quantum Efficiency, EQE for short) and power; if the structural defects are formed in the area outside the active area, the structural defects can grow and spread in the aging test or practical application, thereby entering the active area, and causing the reliability of the device to be reduced.

For EQE, the differential external quantum efficiency η may be employed _d (Differential External Quantum Efficiency) to be measured, The structural defect can capture carriers, heat is generated and photons are not generated, so that the problems of increased stimulated photon quantity and reduced EQE are caused.

It is often necessary to balance the stress while forming the active region of the strain-inducing quantum well structure. The existing stress balancing modes mainly comprise the following two modes:

1) One way is to provide a separate stress relief layer.

An epitaxial layer with opposite strain is added to the quantum well structure attachment, for example, a tensile strain-inducing release layer is provided to the quantum well structure attachment to induce compressive strain, thereby releasing compressive stress. However, the introduction of the stress release layer increases the complexity of the structure, and needs to analyze and optimize the factors of the release layer on resistance, energy band, diffusion, defect generation, and the like. This greatly increases the complexity of the design.

2) Another way is to arrange the potential well and the potential barrier of the quantum well into different strain forms when designing the quantum well.

As described above, in order to obtain a higher gain, the potential well region is generally set to compressive strain, and therefore the potential barrier region is set to tensile strain to balance the stress generated in the potential well region. The method has the advantages that the stress balance of the quantum well structure can be realized within the epitaxial growth range, so that the growth quality of the formed quantum well structure is ensured, and the reliability of the device is improved.

However, in order to meet the stress balance condition, the material selection range of the barrier region is limited, so that the working wavelength condition of the formed laser is limited; the tensile strained barrier region typically has a smaller bandgap and a corresponding smaller barrier height, which can result in lower gain in the active region and can also sacrifice device performance.

In order to solve the technical problem, the invention provides a resonant cavity, a laser unit and a laser, which comprises: the first reflecting mirror and the second reflecting mirror are oppositely arranged at intervals; an active structure located between the first mirror and the second mirror; the active structure includes one or more first active regions of a material having a tensile strain and one or more second active regions of a material having a compressive strain.

The active structure includes a first active region and a second active region, wherein a material of the first active region has a tensile strain and a material of the second active region has a compressive strain. The first active region with tensile strain can release compressive stress introduced by the second active region, so that stress accumulation is prevented, and stress release is avoided; therefore, the arrangement of the first active region and the second active region can realize stress balance and inhibit the generation of structural defects while ensuring the gain of an active structure, thereby being beneficial to improving the quality of a resonant cavity, the external quantum efficiency and the power and the reliability of a device.

In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.

Referring to fig. 5, a schematic cross-sectional structure of an embodiment of a resonant cavity of the present invention is shown.

As shown in fig. 5, the resonant cavity includes: a first reflecting mirror 110 and a second reflecting mirror 140, wherein the first reflecting mirror 110 and the second reflecting mirror 140 are arranged at opposite intervals; an active structure (not shown) located between the first mirror 110 and the second mirror 140; the active structure includes one or more first active regions 121 and one or more second active regions 122a, 122b, the material of the first active regions 121 having a tensile strain and the material of the second active regions 122a, 122b having a compressive strain.

The first active region 121 with tensile strain can release compressive stress introduced by the first reflecting mirror 110 and the second active regions 122a and 122b, so that stress accumulation is prevented, and the phenomenon that the service life is reduced due to stress release in the working process of the device is avoided; therefore, the arrangement of the first active region 121 and the second active regions 122a and 122b can realize stress balance while guaranteeing the gain of the active structure, inhibit the generation of structural defects, and facilitate the improvement of the quality of the resonant cavity, the improvement of external quantum efficiency and power and the improvement of the reliability of the device.

In this embodiment, the resonant cavity is a resonant cavity of a vertical cavity surface emitting laser.

Embodiments of the technical scheme of the present invention are described in detail below with reference to the accompanying drawings.

The first reflecting mirror 110 and the second reflecting mirror 140, which are arranged at opposite intervals, respectively serve as two reflecting surfaces of the resonant cavity, and light rays propagate back and forth between the first reflecting mirror 110 and the second reflecting mirror 140.

In some embodiments of the invention, the first mirror 110 and the second mirror 140 are bragg reflectors (Distributed Bragg Reflector, abbreviated as DBR), and the first mirror 110 and the second mirror Su Soudi each comprise a high refractive index film and a low refractive index film, and the high refractive index film and the low refractive index film are alternately arranged. Adjacent high refractive index films and low refractive index films constitute one cycle. The reflectivity of a distributed bragg mirror is related to the number of periods in which the high and low refractive index films are present. For example, the first and second reflecting mirrors 110 and 140 may be Al alternately arranged in order _x Ga _1-x As/Al _1-y Ga _y As film, where x and y may be different values.

In order to guarantee the gain of the resonant cavity, the first mirror 110 and the second mirror 140 must have a considerable number of cycles to meet the high reflectivity requirement. And in order to ensure that the outgoing laser light has a narrow linewidth, a standing wave is formed in the resonant cavity after the light is reflected by the first and second mirrors 110 and 140 a plurality of times. Therefore, the first mirror 110 and the second mirror 140 need to have a comparable reflectivity.

In this embodiment, the reflectivity of the first reflecting mirror 110 is greater than or equal to 99.9%, and the number of cycles of the first reflecting mirror 110 is greater than or equal to 30, so as to meet the requirement of high reflectivity of the resonant cavity; the reflectivity of the second mirror 140 is greater than or equal to 98%, and the number of cycles of the second mirror 140 is greater than or equal to 11. The number of the whole periods of the first reflecting mirror 110 and the second reflecting mirror 140 is guaranteed, the first reflecting mirror 110 and the second reflecting mirror 140 can be guaranteed to reach the high reflectivity requirement to form a resonant cavity, the gain of the resonant cavity can be guaranteed, and the luminous intensity is guaranteed.

In this embodiment, the reflectivity of the second mirror 140 is lower than the reflectivity of the first mirror 110, so that the direction in which the first mirror 110 points to the second mirror 140 coincides with the laser light emitting direction. The reflectivity of the first reflecting mirror 110 is up to 99.9% or more, so that the loss of light energy caused by the transmission of the generated laser light can be avoided as much as possible.

The active structure is internally provided with a gain medium capable of realizing the inversion of the particle number, and the amplification effect of stimulated radiation is generated.

In some embodiments of the present invention, at least one of the first active region 121 and the second active regions 122a, 122b is a quantum well active region including a barrier region and a potential well region between adjacent barrier regions.

The first active region 121 and the second active regions 122a and 122b are similar in structure, so that the arrangement of the first active region 121 and the second active regions 122a and 122b does not increase the structural complexity of the active structure, does not need to analyze and optimize factors such as resistance, energy band, diffusivity, defect generation and the like separately, and can greatly reduce the complexity of the active structure design of stress balance.

In this embodiment, the resonant cavity is a resonant cavity of a vertical cavity surface emitting laser. For a vertical cavity surface emitting laser, in order to improve the gain of the quantum well active region, a quantum well structure is generally arranged at the antinode position of the optical field standing wave; to further enhance the overall gain of the laser, high power output is achieved with one or more quantum wells (Quantum Well or Multi Quantum Wells, QW or MQWs) disposed at the locations of the multiple antinodes, respectively. Specifically, the quantum well active region includes a plurality of quantum wells, and in this embodiment, each of the first active region 121 and the second active regions 122a and 122b in the active structure is a structure of a plurality of quantum wells.

It should be noted that the quantum well at one antinode position corresponds to one PN junction; the active structure is equivalent to a plurality of PN junctions connected in series. The barrier between N-P increases the resistance of the active structure. In order to reduce the resistance, the resonant cavity further comprises: and the tunneling layer is positioned between the adjacent active areas.

In this embodiment, the resonant cavity includes a first tunneling layer 151 located between the first active region 121 and the second active region 122a, and a second tunneling layer 152 located between the second active region 122a and the second active region 122 b.

Therefore, a Tunnel Junction (Tunnel Junction) is formed between the adjacent first and second active regions 121 and 122a and between the adjacent second active regions 122a and 122b, and the connection resistance between the adjacent active regions can be effectively reduced by reverse biasing the Tunnel Junction.

It should be further noted that, in order to adjust the position of the quantum well structure so as to be located at the antinode position of the optical field standing wave, the resonant cavity further includes: and the gap filling layer is positioned between the adjacent quantum well active regions. In this embodiment, the resonant cavity includes a first fill layer 171 and a second fill layer 172 between adjacent active regions, wherein the first fill layer 171 is located between the first active region 121 and the second active region 122a, and the second fill layer 172 is located between the second active region 122a and the second active region 122 b.

In some embodiments of the present invention, the first active region 121 includes: overcompensated quantum well (Over-Compensated QW), the second active region 122a, 122b comprising: a compressively strained quantum well (Compressive Strain QW). By setting the quantum well overall structures of the first active region 121 and the second active regions 122a and 122b to different strain forms, the selection range of the quantum well material can be widened while the stress balance is satisfied, the limitation of the working wavelength is avoided, the barrier height can be ensured, and the gain of the active region is improved.

In this embodiment, the material of the potential well region of the first active region 121 has a compressive strain, and the material of the barrier region of the first active region 121 has a tensile strain; the tensile strain of the barrier region material of the first active region 121 has a stress magnitude greater than the compressive strain of the potential well region material of the first active region 121. The tensile stress of the barrier region of the first active region 121 is greater than the compressive stress of the potential well region of the first active region 121, so that the whole first active region 121 is in a tensile strain state, and thus is called an overcompensated quantum well. The first active region 121, which integrally presents tensile strain, can realize a certain balance of compressive strain corresponding to the accumulation of tensile stress, and can effectively reduce the stress accumulation of the active structure; and the greater tensile strain of the barrier region of the first active region 121 tends to have a higher barrier height, compared to the barrier region of compressive strain, the quantum well formed has a stronger quantum confinement effect, and thus a greater gain can be obtained.

In this embodiment, the potential well region material of the second active regions 122a and 122b has a compressive strain, and the barrier region material of the second active regions 122a and 122b has a compressive strain, and the stress magnitude of the compressive strain of the barrier region material of the second active regions 122a and 122b is smaller than the stress magnitude of the compressive strain of the potential well region material of the second active regions 122a and 122 b. Specifically, the barrier regions of the second active regions 122a, 122b are made of a material with a small compressive stress. In other embodiments of the present invention, the potential well region material of the second active region has a compressive strain and the barrier region material of the second active region is unstrained. The barrier region of the second active region is made of a material with little or no compressive stress, and the second active region is compressively strained as a whole to achieve higher gain.

Specifically, the GaAs is used as a resonant cavity of the substrate, based on the working band of the resonant cavity, the potential well region material of the first active region 121 is one of InGaAs, gaAs, inGaAsN, inGaAsNSb, and the potential barrier region material of the first active region 121 is one of GaAsP, alGaAsP, alGaAsN, gaAsN; the potential well region material of the second active regions 122a, 122b is one of InGaAs, gaAs, inGaAsN, inGaAsNSb, and the barrier region material of the second active regions 122a, 122b is AlGaAs or GaAs.

In this embodiment, the material of the first reflecting mirror 110 includes N-type doped ions; one of the first active regions 121 is located on the surface of the first mirror 110. The material of the first mirror 110 has a compressive strain, and thus, the first active region 121 having a tensile strain is directly disposed on the surface of the first mirror 110, so that the tensile strain of the first active region 121 balances a portion of the compressive strain of the first mirror 110 to avoid the accumulation of compressive stress.

In addition, in some embodiments of the present invention, the active region has a first surface and a second surface opposite to each other, and the direction of the first surface pointing to the second surface is consistent with the current direction; the resonant cavity further includes: and a current limiting layer at least on the first surface. The current limiting layer can limit the distribution range of current and inhibit the current dispersion effect, so that the current density of the light emitting area in the active area is increased to improve the gain.

Furthermore, in some embodiments of the present invention, the surface of the first active region facing the second active region has the current confinement layer thereon. Because the material of the current limiting layer has compressive strain, the first active region can balance the compressive strain of part of the current limiting layer, the current limiting layer is formed in an oxidation mode, the oxidation brings stronger compressive strain, the current limiting layer is formed on the surface of the first active region, the influence of an oxidation process on a subsequent second active region can be reduced, and the compressive strain of the second active region is reduced due to the oxidation process.

Specifically, in this embodiment, the resonant cavity includes three current limiting layers: a first current confinement layer, a second current confinement layer, and a third current confinement layer. Since in the present embodiment, the material of the first mirror 110 includes N-type doped ions, the second mirror 140 includes P-type doped ions, and the direction of the second mirror 140 pointing to the first mirror 110 is consistent with the current direction; the direction in which the second mirror 140 points to the first mirror 110 is identical to the direction in which the first surface points to the second surface, the surface of the active region facing the second mirror 140 being the first surface, and the direction in which the active region faces the first mirror 110 being the second surface. For example, the surface of the first active region 121 facing the second mirror 140 is a first surface 1211 of the first active region 121, and the surface of the first active region 121 facing the first mirror 110 is a second surface 1212 of the first active region 121. The first surface and the second surface of the second active regions 122a, 122b are consistent with the arrangement sequence of the first surface 1211 and the second surface 1212 of the first active region 121, that is, the surface facing the second mirror 140 is the first surface, and the surface facing the first mirror 110 is the second surface, which is not described herein. Therefore, the first, second and third current confinement layers are located at the first surface 1211 of the first active region 121, the first surface of the second active region 122a and the first surface of the second active region 122b, respectively.

In addition, in the present embodiment, in order to simplify the process steps and improve the material quality, the semiconductor compound is oxidized after the growth of all materials is completed in the process of forming the current confinement layer, that is, in the embodiment shown in fig. 5, the semiconductor compound used to form the current confinement layer is oxidized after the second mirror 140 is formed; only the semiconductor compound layer used to form the current confinement layer is shown in fig. 5. Specifically, the resonant cavity includes a first semiconductor compound 131 located on the first surface 1211 of the first active region 121, a second semiconductor compound 132 located on the first surface of the second active region 122a, and a third semiconductor compound 133 located on the first surface of the second active region 122 b. However, this is merely an example, and in other embodiments of the present invention, the resonant cavity may be formed by a secondary epitaxy method, that is, the step of oxidizing after the semiconductor compound is formed, and the present invention is not limited thereto.

It should be further noted that, in some embodiments of the present invention, the resonant cavity further includes: a substrate 100, the substrate 100 being located on a side of the first mirror 110 remote from the active structure, or the substrate 100 being located on a side of the second mirror 140 remote from the active structure.

The substrate 100 is capable of providing a process platform during the formation of the resonant cavity. In this embodiment, the substrate 100 is located on a side of the first mirror 110 away from the active structure. Thus, in the process of forming the resonant cavity, after providing the substrate 100, the first mirror 110, the active structure, and the second mirror 140 are sequentially formed on the substrate 100.

The material of the substrate may be one of GaAs, inP, gaSb or InSb doped N, P. Specifically, the substrate 100 is an N-type substrate, that is, the material of the substrate 100 is an N-type doped semiconductor material (for example, one of N-type doped GaAs, inP, gaSb or InSb), the doped ions contained in the first reflecting mirror 110 are N-type ions, and the doped ions contained in the second reflecting mirror 140 are P-type ions. Since the substrate process of the N-type doped semiconductor material is relatively mature and the material quality is relatively high, the material of the substrate 100 is set to be the N-type doped semiconductor material (for example, N-type doped GaAs), which can provide a good growth surface and process platform for the subsequent growth of the first mirror 110, the active structure and the second mirror 140, and can effectively improve the quality of the subsequent material film.

In this embodiment, the substrate 100 is a GaAs substrate. In other embodiments of the present invention, the substrate may be other semiconductor materials. When the substrate is of other semiconductor materials, the material of the active structure may be selected to achieve stress balance based on the material of the substrate.

Note that, in this embodiment, the number of the first active regions 121 is 1; the number of the second active areas is 2. However, the number of the first active regions and the second active regions is not limited in the present invention, and in other embodiments of the present invention, the number of the first active regions may be 2-4, and the number of the second active regions may be 1-3. For example, when the second active region has a higher gain than the first active region, a greater number of second active regions may be provided to increase the overall gain and output power of the resonant cavity.

In this embodiment, 1 first active region 121 and 2 second active regions 122a and 122b are sequentially formed on the substrate 100. But this arrangement is merely an example. In other embodiments of the present invention, the second active regions are located between adjacent first active regions, for example, in other embodiments of the present invention, active structures arranged in the order of the first active regions, the second active regions, and the first active regions may be sequentially formed on the substrate.

Referring to fig. 6, a schematic cross-sectional structure of another embodiment of the resonant cavity of the present invention is shown.

The resonant cavity includes: a first mirror 210, a first active region 221, 2 second active regions 222a, 222b, and a second mirror 240, which are sequentially located on the substrate 200; a first current confinement layer 231, a first fill layer 271, and a first tunneling layer 251 sequentially located between the first active region 221 and the second active region 222 a; a second current confinement layer 232, a second fill layer 272, and a second tunneling layer 252 sequentially between the second active region 222a and the second active region 222 b; and a third current confinement layer 233 on a surface of the second active region 222b facing the second mirror 240.

The embodiment is the same as the previous embodiment, and the present invention is not repeated; as shown in fig. 6, this embodiment is different from the previous embodiment in that in this embodiment, the resonant cavity further includes: a reflective layer 280, which is located inside the active structure. The reflection layer 280 is configured to adjust cavity loss of different active regions in the active structure of the resonant cavity, so as to balance gain difference, so that two active regions in the active structure can work under appropriate conditions, and device performance can be further improved.

In this embodiment, a current confinement layer is further disposed on the active region, specifically, as shown in fig. 6, the reflective layer 280 is located between the first current confinement layer 231 and the first active region 221; in other embodiments of the present invention, the reflective layer may also be disposed on a side of the first current confinement layer away from the first active region, that is, the first current confinement layer is located between the reflective layer and the first active region.

In some embodiments of the present invention, the active structure is divided into two parts, and the two parts of the active structure are respectively located at two sides of the reflective layer 280 on a straight line along the light propagation direction. In this embodiment, the reflective layer 280 is located between the adjacent first active region 221 and second active region 222a, i.e. the first active region 221 in the active structure is located on one side of the reflective layer 280, and the second active regions 222a, 222b of one or more of the active structures are located on the other side of the reflective layer.

As shown in fig. 6, the first active region 221 is located on a side of the reflective layer 280 facing the first mirror 210, and the second active regions 222a, 222b are located on a side of the reflective layer 280 facing the second mirror 240.

Because the material strain types of the first active region 221 and the second active regions 222a and 222b are different, the first active region 221 and the second active regions 222a and 222b of the quantum well structure adopt different types of junction designs, the gains of the quantum wells of different junction designs are different, and the reflective layer 280 is arranged to balance the gain differences of the quantum wells of different junction designs, so that the device performance can be further improved.

The effect of the reflective layer 280 in balancing the difference in quantum well gain for different junction designs is explained in detail below.

For the active structure, each active region may be equivalent to a cavity of one resonant cavity. The light field intensity I in each cavity is determined by the cavity gain and the cavity loss, and the larger the cavity gain is, the smaller the cavity loss is, and the larger the light field intensity in the corresponding resonant cavity is.

Cavity lossWherein R is ₁ 、R ₂ Respectively the reflectivity of the front and back reflecting surfaces of the resonant cavity, specifically R ₁ The reflectance of the reflecting surface in the direction of the light-emitting surface is represented by R ₂ The reflectance of the reflecting surface in the non-light-emitting surface direction is shown.

The smaller the cavity loss, the longer the Lifetime (Lifetime) of the corresponding light in the resonant cavity, i.e. the more times the light propagates back and forth in the cavity due to reflection before exiting the resonant cavity, the more times it passes through the active region. The energy increment of light in the unit length of the active area is proportional to I.g, wherein I is the intensity of an optical field in the resonant cavity, and the larger the loss is, the smaller the intensity of the optical field is; g is the active area gain. The larger g indicates the greater the increased energy of the light passing through the active region.

Fig. 7 shows the distribution of optical field intensity in the cavity of the resonant cavity in the embodiment of fig. 6 without the reflective layer. The abscissa in the graph represents the distance between the light field position and the light emitting surface of the resonant cavity, and the ordinate is normalized light field intensity I. Wherein the abscissa intercepts only the area near the active structure.

As shown in FIG. 7, if no reflective layer is provided, the first and second reflectors are used as reflective surfaces of the resonant cavity in different active regions, and R corresponds to different active regions ₁ ·R ₂ The values of (2) are the same, so that the cavity loss of the equivalent resonant cavity for each active region is close; the light field intensity distribution is substantially uniform in the different active regions.

Fig. 8 shows the distribution of the intensity of the optical field in the cavity of the resonant cavity in the embodiment shown in fig. 6, that is, the distribution of the intensity of the optical field in the cavity after the reflective layer is disposed. Wherein, the abscissa in the figure represents the distance between the light field position and the light emitting surface of the resonant cavity (i.e., the distance between the surface of the resonant cavity away from the substrate 200 in fig. 6 and the position of the light field), and the ordinate represents the normalized light field intensity I. Wherein the abscissa intercepts only the area near the active structure.

It should be noted that, in the embodiment shown in fig. 6, the first mirror 210 close to the substrate 200 is an N-doped distributed bragg mirror, and the second mirror 240 far from the substrate 200 is a P-doped distributed bragg mirror. In addition, the light is emitted along the direction in which the first mirror 210 is directed to the second mirror 240, so that the light is emitted from the direction of the second mirror 240, that is, the resonant cavity is a resonant cavity with front light, so that the reflectivity of the first mirror 210 is greater than the reflectivity of the second mirror 240.

Referring to fig. 6 and 8 in combination, the reflective layer 280 is located between the first active region 221 and the second active region 222a, and the reflective layer 280 and the first mirror 210 and the second mirror 240 respectively form a resonant cavity.

For the first active region 221, the first mirror 210 is one reflecting surface of the equivalent resonator, and the reflecting layer 280 and the second mirror 240 are the other reflecting surface of the equivalent resonator. Within the first active region 221, the light reflected by the reflective layer is coherently enhanced with the light reflected by the second mirror 240. Thus for the first active For the region 221, the total reflectance in the direction opposite to the laser light emitting direction (i.e. the direction in which the second mirror 240 points to the first mirror 210) is increased, and the reflectance in the laser light emitting direction (i.e. the direction in which the first mirror 210 points to the second mirror 240) is unchanged, i.e. the arrangement of the reflective layer 280 can significantly increase the R corresponding to the equivalent resonator ₁ Value of R at the same time ₂ Remains substantially unchanged, thus enabling a significant increase in R in the first active region 221 ₁ ·R ₂ So that the cavity loss of the equivalent resonant cavity of the first active region 221 can be significantly suppressed, the intensity of the optical field in the first active region 221 is significantly increased as described in circle 390 in fig. 8.

On the other hand, since the distance between the reflective layer 280 and the first mirror 210 and the distance between the reflective layer 280 and the second mirror 240 are different, the phase difference of light reflected by the first mirror 210 and the reflective layer 280 is different from the phase difference of light reflected by the second mirror 240 and the reflective layer 280, and thus the reflective layer cannot simultaneously enhance the coherence of light rays in the active regions on both sides. So that when the light in the first active region 221 is coherently enhanced, the light in the second active regions 222, 223 cannot be coherently enhanced, and for the second active regions 222a, 222b, the second mirror 240 is a reflecting surface of the equivalent resonant cavity, the reflecting layer 280 and the first mirror 210 are the other reflecting surface of the equivalent resonant cavity, wherein the reflectivity of the first mirror 210 is relatively high, and thus the reflecting layer 280 is arranged to reflect the light in the equivalent resonant cavity ₂ The effect of the values is small and the cavity loss of the equivalent resonant cavity of the second active region 222a, 222b is small, so that the intensity of the optical field in the second active region 222a, 222b does not change much as shown in fig. 8.

Therefore, when the active structure is divided into two parts which are respectively located at two sides of the reflecting layer on a straight line along the light propagation direction, the arrangement of the reflecting layer 280 can reduce the cavity loss of the equivalent resonant cavity of the active structure at one side far away from the light emitting surface, thereby increasing the light field intensity of the part and further realizing the compensation of gain difference caused by quantum wells with different junction designs.

In some embodiments of the present invention, the refractive index of the reflective layer 280 material is different from the refractive index of the first active region 221 material, and the refractive index of the reflective layer 280 material is different from the refractive index of the second active region 222a, 222b material, so that the reflective layer 280 can form a distributed bragg mirror structure with the adjacent material film layers.

In some embodiments of the present invention, the reflective layer 280 is a distributed Bragg reflector, i.e., the reflective layer 280 may be one or more periodic Bragg reflectors. Since the first mirror 210 and the second mirror 240 are generally bragg mirrors, the reflective layer 280 is configured as the same bragg mirror, and no additional structure is required to be introduced, so that the influence of the introduction of the reflective layer on the structural complexity can be reduced.

Specifically, in this embodiment, the reflective layer 280 is a laminated structure, and the reflective layer 280 includes a first reflective sub-layer (not labeled in the drawing) and a second reflective sub-layer (not labeled in the drawing), where the refractive index of the first reflective sub-layer is not equal to the refractive index of the second reflective sub-layer. By adding a first reflective sub-layer and a second reflective sub-layer with high refractive index or low refractive index, an interface with a certain reflectivity is formed in the reflective layer 280, and by adjusting the thickness of the first reflective sub-layer and the thickness of the second reflective sub-layer, the phase difference of the front and rear reflected light is adjusted, thereby adjusting the overall reflectivity of the reflective layer 280.

In some embodiments of the present invention, the reflective layer includes a plurality of first reflective sublayers and a plurality of first reflective sublayers, where the first reflective sublayers and the second reflective sublayers are alternately arranged, i.e., the plurality of first reflective sublayers and the plurality of first reflective sublayers are alternately arranged, so as to adjust the overall reflectivity of the reflective layer.

One period is formed by one first reflecting sub-layer and one second reflecting sub-layer, and when the optical path of light emitted by each material layer corresponding to the active area in one period is lambda/4, namely the optical path of lambda/4 is generated by the first reflecting sub-layer and the second reflecting sub-layer, relatively larger reflectivity can be obtained; a relatively small reflectivity can be obtained when the optical path created by the different material layers within a period deviates from lambda/4, i.e. the first reflective sub-layer and the second reflective sub-layer do not create a lambda/4 optical path at the same time. In addition, the overall reflectivity of the reflecting layer can be adjusted by increasing or decreasing the number of periods or changing the refractive index difference between the two sublayers by changing the materials of the two sublayers.

The reflectivity of the reflective layer 280 as a whole is adjusted by changing the thickness ratio of the first reflective sub-layer and the second reflective sub-layer, or increasing or decreasing the number of cycles (pairs).

In this embodiment, the actually required light field intensity increase amount is small, and therefore the reflection layer is set as a low refractive index layer (half pair DBR) of one λ/4 optical path. The reflective layer and the adjacent material film layer form a structure similar to a distributed Bragg reflector.

As shown in fig. 8, after the reflective layer is added, the increase D1 of the light field intensity at the active structure position on the side far from the light exit surface with respect to the light field intensity at the active structure position on the side near the light exit surface is about 0.83 unit.

Referring to fig. 9, a further embodiment of the resonant cavity of the present invention is shown with respect to the distribution of optical field intensity within the cavity.

The present embodiment is the same as the foregoing embodiment, and the present invention is not repeated herein, and the difference between the present embodiment and the foregoing embodiment is that the actually required light field intensity increase is smaller than that of the previous embodiment, so that the reflectivity of the reflective layer is adjusted mainly by changing the thickness of the reflective layer, for example, by reducing the thickness of the reflective layer, the optical path length of the reflective layer is made to be smaller than λ/4, so as to reduce the reflectivity of the reflective layer, thereby obtaining a smaller light field increase. Therefore, in this embodiment, the reflective layer is provided as a low refractive index layer having a thickness less than λ/4 optical path.

As shown in fig. 9, the abscissa represents the distance between the optical field position and the light exit surface of the resonant cavity, and the ordinate represents the normalized optical field intensity I. Wherein the abscissa intercepts only the area near the active structure. As can be seen from the figure, after the reflective layer is added, the increase D2 of the light field intensity at the portion of the active structure position away from the light exit surface with respect to the light field intensity at the portion of the active structure position near the light exit surface is about 0.64 units.

Referring to fig. 10, a further embodiment of the resonant cavity of the present invention is shown with respect to the distribution of optical field intensity within the cavity.

The difference between the present embodiment and the foregoing embodiment is that the actually required light field intensity increase is larger than that of the foregoing embodiment, so that the reflectivity of the reflective layer is adjusted mainly by changing the number of periods (i.e. the pair number) of the reflective layer, for example, by adding a high refractive index layer after the low refractive index layer, so as to form a complete period (DBR pair). Therefore, in this embodiment, the reflective layer is provided as a distributed bragg mirror having only one period.

As shown in fig. 10, the abscissa represents the distance between the optical field position and the light exit surface of the resonant cavity, and the ordinate represents the normalized optical field intensity I. Wherein the abscissa intercepts only the area near the active structure. As can be seen from the figure, after the reflective layer is added, the increase D3 of the light field intensity at the portion of the active structure position away from the light exit surface with respect to the light field intensity at the portion of the active structure position near the light exit surface is about 1.30 units.

In summary, as can be seen from comparing fig. 8 to 10, the higher the reflectivity of the reflective layer, the larger the difference between the light field intensity at the active structure position of the coherence enhancing part and the light field intensity at the active structure position of the phase mismatch part obtained by phase matching of the light reflected by the reflective mirror and the reflective layer. Therefore, by setting the reflecting layers with different thicknesses, the phase matching degree between the light emitted by the active structure and the light reflected by the reflecting mirror and the reflecting part is adjusted, and the difference value of any light field intensity can be obtained.

Therefore, by designing the reflective layer and disposing the reflective layer between the adjacent first active region 221 and second active region 222a, the lower gain of the first active region 221 can be compensated for when the gain of the first active region 221 is lower than that of the second active regions 222a and 222b, so that both the first active region 221 and the second active regions 222a and 222b can operate under suitable conditions. Generally, a region with a low gain value needs to set a larger optical field intensity to reduce the threshold current of the device and inhibit the heating of the active region. Therefore, through the arrangement and the reality of the reflecting layer, the working conditions of different active areas can be respectively optimized, and the purposes of reducing the threshold current and improving the working state under the high-temperature condition are realized.

It should be further noted that the method of enhancing the light field intensity of the active structure position on the side far from the light emitting surface by the reflective layer is merely an example, and in other embodiments of the present invention, the reflective layer may also enhance the light field intensity of the active structure position on the side near to the light emitting surface.

In an embodiment of the present invention, the reflective layer is disposed at a position capable of enhancing coherence between the light reflected by the reflective layer and the light reflected by the first reflecting mirror, so that total reflectivity in an active structure near a light emitting surface side is increased toward a laser emitting direction, and reflectivity in the laser emitting direction is unchanged, so that cavity loss in the active structure near the light emitting surface side is reduced; the arrangement of the reflecting layer can enhance the light field intensity at the position of the active structure near the light emergent surface side. Compared with the active structure at the side far away from the light emitting surface, the light field intensity in the active structure at the side near the light emitting surface is obviously enhanced.

Other modes are described: the reflective layer material may be varied to vary the refractive index difference, and thus the reflectivity, of the reflective layer; adjusting the reflective layer material (an elemental composition) changes the graded layer width, the wider the graded layer, the smaller the reflectivity.

In summary, the arrangement of the reflective layer can inhibit the loss of part of the active structure and enhance the gain of part of the active structure, thereby playing a role in balancing the gain differences of quantum wells designed by different junctions; and adjusting gain differences at different positions in the active structure to reach balanced positions through the arrangement of the materials, the positions, the thicknesses and the layer numbers of the reflecting layers. Correspondingly, the invention also provides a laser unit, which specifically comprises: the resonant cavity is provided by the invention; a first electrode; and a second electrode.

Referring to fig. 6, a schematic cross-sectional structure of an embodiment of the laser unit of the present invention is shown.

The laser unit includes: the resonant cavity is the resonant cavity of the invention; a first electrode 261; a second electrode 262.

In this embodiment, the laser unit is a laser unit of a vertical cavity surface emitting laser.

The following describes in detail the technical solution of the laser unit embodiment of the present invention with reference to the accompanying drawings.

The resonant cavity (not labeled in the figure) is the resonant cavity of the present invention. Specifically, the specific technical scheme of the resonant cavity refers to the foregoing embodiment of the resonant cavity, and the disclosure is not repeated herein.

The first electrode and the second electrode realize connection of the resonant cavity with an external circuit.

In this embodiment, the first electrode 261 is located on a side of the first mirror 210 away from the active structure, the first electrode 261 is located on the surface of the substrate 200, and the first electrode 261 is electrically connected with the active structure through the substrate 200 and the first mirror 210; the second electrode 262 is located on a surface of the second mirror 240 on a side away from the active structure, and the second electrode 262 is electrically connected to the active structure through the second mirror 240.

In this embodiment, the direction of the first mirror 210 pointing to the second mirror 240 coincides with the laser light emitting direction, so that the second electrode 262 includes a window (not labeled in the figure) that penetrates the second electrode 262 along the laser light propagation direction. The window is used for realizing the emergence of laser.

In this embodiment, the direction of the first mirror 210 pointing to the second mirror 240 is consistent with the laser emitting direction, and the first mirror 210 and the second mirror 240 are sequentially located on the substrate 200, so that the laser unit is a front-emitting laser unit.

In other embodiments of the present invention, the laser unit may be a back-side emitting laser unit.

Referring to fig. 11, a schematic cross-sectional structure of another embodiment of the laser unit of the present invention is shown.

The laser unit includes: a resonant cavity.

The resonant cavity is a resonant cavity of the present invention, and specifically includes a first reflecting mirror 310, an active structure, and a second reflecting mirror 340 that are sequentially located on the substrate 300; wherein the active structure comprises 1 first active region 321 and 2 second active regions 322a, 322b on the first mirror 310 in sequence; a first current limiting layer 331, a first filling layer 371 and a first tunneling layer 351 are sequentially disposed between the first active region 321 and the second active region 322 a; a second current confinement layer 332, a second fill layer 372, and a second tunneling layer 352 are sequentially disposed between the second active region 322a and the second active region 322b; a third current confinement layer 333 is disposed between the second active region 322b and the second mirror 340.

Specifically, the specific technical scheme of the resonant cavity refers to the foregoing embodiment of the resonant cavity, and the disclosure is not repeated herein.

The embodiment is the same as the foregoing embodiment, and the present invention is not repeated; the difference between this embodiment and the previous embodiment is that in this embodiment, the laser unit is a back-side-emitting laser unit, that is, the laser generated by the laser unit is emitted from the substrate 300 side, and the emitting direction of the laser is consistent with the direction in which the second mirror 340 points to the first mirror 310.

Therefore, the first electrode 361 is located on a side of the first mirror 310 away from the active structure, and the first electrode 361 is located on the surface of the substrate 300; the second electrode 362 is located on a surface of the second mirror 340 on a side away from the active structure. The first electrode 361 on the surface of the substrate 300 has a window penetrating along the laser direction, so as to realize the emission of the laser.

In this embodiment, the first active region 321 with tensile strain is formed on the substrate 300, and the second active regions 322a and 322b with compressive strain are formed on the first active region 321, so that the compressive strain generated by the first mirror 310 and the first current confinement layer can be balanced, and the purpose of improving the quality of the second active regions 322a and 322b is achieved.

The fact that no reflective layer is provided in the back-side emitting laser unit is merely an example, and in other embodiments of the present invention, a reflective layer may be provided in the back-side emitting laser unit.

Referring to fig. 12, a schematic cross-sectional structure of a further embodiment of the laser unit of the present invention is shown.

The laser unit includes: a resonant cavity.

The resonant cavity is a resonant cavity of the present invention, and specifically includes a first reflecting mirror 410, an active structure, and a second reflecting mirror 440, which are sequentially located on the substrate 400; wherein the active structure comprises 1 first active region 421 and 2 second active regions 422a, 422b located sequentially on the first mirror 410; a first current confinement layer 431, a first filling layer 471 and a first tunneling layer 451 are sequentially disposed between the first active region 421 and the second active region 422 a; a second current limiting layer 432, a second filling layer 472 and a second tunneling layer 452 are sequentially arranged between the second active region 422a and the second active region 422b; a third current confinement layer 433 is disposed between the second active region 422b and the second mirror 440.

In this embodiment, the laser unit is a back-side emitting laser unit, that is, the laser generated by the laser unit is emitted from the substrate 400 side, and the emitting direction of the laser is consistent with the direction of the second mirror 440 pointing to the first mirror 410.

The embodiment is the same as the foregoing embodiment, and the present invention is not repeated; this embodiment is different from the foregoing embodiment in that in this embodiment, the tensile stress of the barrier region material in the first active region 421 is very large, so that the gain of the first active region 421 is greater than the gain of the second active region 422a, 422b, so that in the active structure, the reflective layer 480 is disposed between the first active region 421 and the second active region 422a, so that after the light of the second active regions 422a and 422b is reflected by the first mirror 410, the second mirror 440 and the reflective layer 480, coherent enhancement can be achieved, but the light of the first active region 421 cannot be coherently enhanced, so as to reduce the light field intensity at the location of the first active region 421, thereby achieving balance of energy gains of different active regions in the active structure.

As shown in fig. 12, in some embodiments of the invention, the laser unit includes a core region 401 and an extension region 402 in a plane perpendicular to the propagation direction of the laser light; the resonant cavity is located within the core region 401; and the first mirror 410 extends to the extension 402; the first electrode 461 is in contact with the first mirror 410 of the extension 402. The first electrode 461 makes electrical connection to the active structure through the first mirror 410.

Specifically, in this embodiment, the first electrode 461 is located on the surface of the first mirror 410 facing the second mirror 440 of the extension region 402. The first electrode 461 is disposed on the surface of the first reflecting mirror 410 of the extension region 402 facing the second reflecting mirror 440, so that the first electrode 461 and the second electrode 462 face the same side, thereby providing a good foundation for the subsequent fabrication of the coplanar electrode, being beneficial to reducing the packaging difficulty of the laser unit and improving the packaging quality.

In addition, the invention also provides a laser, which specifically comprises: the laser unit is the laser unit of the invention.

Since the laser unit is a laser unit of the present invention, the specific technical scheme of the laser unit refers to the foregoing embodiment of the laser unit, and the disclosure is not repeated herein.

In this embodiment, the laser is a vertical cavity surface emitting laser.

In the laser, in a laser unit, an active structure of a resonant cavity comprises a first active region and a second active region, wherein a material of the first active region has tensile strain, and a material of the second active region has compressive strain. The first active region with tensile strain can release compressive stress introduced by the second active region, so that stress accumulation is prevented, and stress release is avoided; therefore, the arrangement of the first active region and the second active region can realize stress balance and inhibit the generation of structural defects while ensuring the gain of an active structure, thereby being beneficial to improving the quality of a resonant cavity, the external quantum efficiency and the power and the reliability of a device.

In addition, the invention also provides a laser radar, which specifically comprises: a light source comprising the laser of the present invention.

The resonant cavity of the laser can realize stress balance and inhibit structural defects while ensuring the gain of an active structure, so that the resonant cavity has high quality, high external quantum efficiency, high power and high reliability; therefore, the laser device provided by the invention is used as a light source of the laser radar, so that the quality, the power and the reliability of the light source can be effectively improved, the detection distance of the laser radar can be effectively expanded, the detection precision of the laser radar is ensured, and the reliability of the laser radar is improved.

In summary, in the resonant cavity of the present invention, the active structure includes a first active region and a second active region, wherein a material of the first active region has a tensile strain, and a material of the second active region has a compressive strain. The second active region with compressive stress has higher gain, the band gap can be regulated and controlled to adjust the working band, and the first active region with tensile strain can release the compressive stress introduced by the second active region, so that stress accumulation is prevented, and stress release is avoided; therefore, the arrangement of the first active region and the second active region can realize stress balance and inhibit the generation of structural defects while ensuring the gain of an active structure, thereby being beneficial to improving the quality of a resonant cavity, the external quantum efficiency and the power and the reliability of a device.

Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention, and the scope of the invention should be assessed accordingly to that of the appended claims.

Claims

1. A resonant cavity, comprising:

the first reflecting mirror and the second reflecting mirror are oppositely arranged at intervals;

An active structure located between the first mirror and the second mirror; the active structure includes one or more first active regions of a material having a tensile strain and one or more second active regions of a material having a compressive strain.

2. The resonant cavity of claim 1, wherein at least one of the first active region and the second active region is a quantum well active region comprising a barrier region and a potential well region between adjacent barrier regions.

3. The resonant cavity of claim 2, wherein the first active region comprises: an overcompensated quantum well, the second active region comprising: a compressively strained quantum well.

4. The resonant cavity of claim 3, wherein the potential well region material of the first active region has a compressive strain and the barrier region material of the first active region has a tensile strain;

the tensile strain of the barrier region material of the first active region has a stress magnitude greater than the compressive strain of the potential well region material of the first active region.

5. The resonant cavity of any of claims 2-4, wherein the potential well region material of the first active region is InGaAs and the barrier region material of the first active region is at least one of GaAsP, alGaAsP.

6. The resonant cavity of claim 3, wherein the potential well region material of the second active region has a compressive strain, the barrier region material of the second active region has a compressive strain,

the compressive strain of the second active region barrier region material has a stress magnitude that is less than the compressive strain of the potential well region material of the second active region.

7. The resonator according to claim 2 or 6, wherein the potential well region material of the second active region is InGaAs and the barrier region material of the second active region is AlGaAs.

8. The resonator of claim 3, wherein the potential well region material of the second active region has a compressive strain and the barrier region material of the second active region is unstrained.

9. The resonant cavity of claim 2, wherein the quantum well active region comprises a plurality of quantum wells.

10. The resonant cavity of claim 1, wherein the material of the first mirror comprises N-type dopant ions;

one of the first active regions is located at the first mirror surface.

11. The resonant cavity of claim 1, further comprising: and the reflecting layer is positioned between the adjacent first active area and the second active area.

12. The resonant cavity of claim 11, wherein the first active region is located on one side of the reflective layer and the one or more second active regions are located on the other side of the reflective layer.

13. The resonant cavity of claim 11, wherein the refractive index of the reflective layer material is different from the refractive index of the first active region material and the refractive index of the reflective layer material is different from the refractive index of the second active region material.

14. The resonant cavity of claim 11, wherein the reflective layer is a distributed bragg mirror.

15. The resonant cavity of claim 11 or 14, wherein the reflective layer is a laminated structure, the reflective layer comprising a first reflective sub-layer and a second reflective sub-layer, the refractive index of the first reflective sub-layer being unequal to the refractive index of the second reflective sub-layer.

16. The resonant cavity of claim 15, wherein the first reflective sub-layer and the second reflective sub-layer are alternately disposed.

17. The resonant cavity of claim 1, wherein the active region has first and second opposing surfaces, the first surface pointing in a direction coincident with the direction of the current flow;

The resonant cavity further includes: and a current limiting layer at least on the first surface.

18. The resonant cavity of claim 17, wherein the surface of the first active region facing the second active region has the current confinement layer thereon.

19. The resonant cavity of claim 1, further comprising: and the substrate is positioned on one side of the first reflecting mirror away from the active structure.

20. The resonant cavity of claim 19, wherein the substrate is an N-type substrate, the first mirror comprises doped ions of N-type and the second mirror comprises doped ions of P-type.

21. A laser unit, comprising:

a resonant cavity as claimed in any one of claims 1 to 20;

a first electrode;

and a second electrode.

22. The laser unit of claim 21 wherein the second electrode is located on a surface of the second mirror on a side remote from the active structure.

23. The laser unit of claim 21 wherein the first electrode is located on a side of the first mirror remote from the active structure, the first electrode being located on a substrate surface.

24. The laser unit of claim 23, wherein the second electrode includes a window extending through the second electrode in the direction of laser propagation.

25. A laser, comprising:

a laser unit according to any one of claims 21 to 24.

26. The laser of claim 25, wherein the laser is a vertical cavity surface emitting laser.

27. A lidar, comprising:

a light source comprising the laser of any one of claims 25 to 26.