CN114552379A

CN114552379A - Resonant cavity, laser unit, laser and laser radar

Info

Publication number: CN114552379A
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: 2022-05-27
Anticipated expiration: 2040-11-25
Also published as: WO2022110914A1; CN114552379B

Abstract

A resonant cavity, laser unit, laser and lidar, the resonant cavity comprising: the first reflector and the second reflector 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 having a material with a tensile strain and one or more second active regions having a material with 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 waveband, the first active region with tensile strain can release the compressive stress introduced by the second active region, the stress accumulation is prevented, and the stress release is avoided; the first active region and the second active region are arranged, so that the gain of an active structure can be ensured, stress balance is realized, structural defects are inhibited, the quality of a resonant cavity is improved, the external quantum efficiency and power are improved, and the reliability of a device is improved.

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

Laser radar is a range finding sensor commonly used, has characteristics such as detection range is far away, resolution ratio is high, receive the environmental disturbance little, and the wide application is in fields such as intelligent robot, unmanned aerial vehicle, unmanned driving. In recent years, the automatic driving technology is rapidly developed, and the laser radar is unavailable or lack of the laser radar as a core sensor for distance perception. The performance of a laser, which is one of the core components of a laser radar, has a great influence on the performance of the laser radar.

A conventional Vertical Cavity Surface Emitting Laser (VCSEL) generally includes a lower DBR (Distributed Bragg Reflector), an active region, a current confinement layer, and an upper DBR, which are sequentially epitaxially grown on an N-type doped substrate. Wherein, the current is injected into the active region through the electrode; the material of the active region is excited by the excitation light, resonates in a resonant cavity formed by the upper DBR and the lower DBR, and forms strong light beams with the same propagation direction, frequency and phase.

In VCSELs, the active region is a Quantum well (MQWs) formed by the alternating growth of two thin films of material. 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 an energy band of the quantum well are achieved.

However, the introduction of strain increases the risk of the occurrence of lattice structure defects, and there occurs a problem of a decrease in external quantum efficiency and power or a decrease in device reliability.

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.

To solve the above problems, the present invention provides a resonant cavity, comprising:

the first reflector and the second reflector 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 having a material with a tensile strain and one or more second active regions having a material with a compressive strain.

Optionally, 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 includes barrier regions and well regions located 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 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 magnitude of the stress of the tensile strain of the barrier region material of the first active region is greater than the magnitude of the stress of the compressive strain of the well region material of the first active region.

Optionally, the 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 and AlGaAsP.

Optionally, the 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 magnitude of the stress of the compressive strain of the barrier region material of the second active region is smaller than the magnitude of the stress of the compressive strain of the well region material of the second active region.

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

Optionally, the well region material of the second active region has a 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 mirror includes N-type doped ions; one of the first active regions is located at the first mirror surface.

Optionally, the method further includes: a reflective layer between adjacent first and second active regions.

Optionally, the first active region is located at one side of the reflective layer, and the one or more second active regions are located at 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 stacked structure, and the reflective layer includes a first reflective sub-layer and a second reflective sub-layer, where a refractive index of the first reflective sub-layer is not equal to a refractive index of the second reflective sub-layer.

Optionally, the first reflective sublayers and the second reflective sublayers 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 comprises: a current confinement layer on at least the first surface.

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

Optionally, the method further includes: a substrate on a side of the first mirror distal from the active structure.

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

Accordingly, the present invention provides a laser unit comprising:

a resonant cavity, the resonant cavity being a resonant cavity of the present invention; a first electrode; 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 present invention also provides a laser including:

the laser unit is the laser unit of the invention.

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

In addition, the present invention also provides a laser radar including:

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 solution of the present invention, the active structure includes a first active region and a second active region, where 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 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 while ensuring the gain of the active structure, inhibit the generation of structural defects, and is favorable for improving the quality of a resonant cavity, improving the external quantum efficiency and power and improving the reliability of a device.

In an alternative aspect of the present 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 includes a barrier region and a well region located between adjacent barrier regions, that is, the first active region and the second active region have similar structures, 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 does not need to separately analyze and optimize factors such as resistance, energy band, diffusivity, defect generation, and the like, and the complexity of the design of the active structure for balancing stress can be greatly reduced.

In an alternative aspect of the present invention, the first active region includes: an overcompensated quantum well, the second active region comprising: a compressively strained quantum well. The quantum well overall structure of the first active region and the quantum well overall structure of the second active region are set to be different strain forms, so that the stress balance is met, the selection range of quantum well materials is expanded, the limitation of working wavelength is avoided, the height of a potential barrier can be guaranteed, and the gain of the active region is improved.

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

In an alternative embodiment of the present invention, the well region material of the second active region has compressive strain, the barrier region material of the second active region has compressive strain, and the magnitude of compressive strain stress of the barrier region material of the second active region is smaller than the magnitude of compressive strain stress of the well region material of the second active region, that is, the barrier region of the second active region is made of a material with no stress or little compressive stress, and the second active region is compressive strain as a whole to obtain a higher gain.

In an alternative aspect of the invention, the material of the first mirror comprises N-type doped ions; one of the first active regions is located on the first mirror surface. The material of the first reflector with N-type doped ions has compressive strain, so that the first active region with tensile strain is directly arranged on the first reflector, and the tensile strain of the first active region can balance partial compressive strain of the first reflector so as to avoid compressive stress accumulation.

In the alternative of the invention, the method also comprises the following steps: the reflecting layer is arranged between the adjacent first active region and the second active region, and the cavity loss of different active regions of the resonant cavity can be adjusted by the reflecting layer, so that the gain difference can be balanced, the two active regions can work under a proper condition, and the performance of the device can be further improved.

In an alternative aspect of the invention, the reflective layer is a distributed bragg mirror. Since the first mirror and the second mirror are generally bragg mirrors, the reflecting layer is set to be the same bragg mirror, and no additional structure needs to be introduced, so that the influence of the introduced reflecting layer on the structural complexity can be reduced.

In an alternative aspect of the 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 can balance the compressive strain of a portion of the current confinement layer, thereby reducing the effect 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 on one side of the first reflecting mirror far 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 is high in material quality, and a good growth surface can be provided for the formation of the resonant cavity so as to guarantee the quality of the resonant cavity.

Drawings

FIG. 1 is a schematic cross-sectional view of a VCSEL unit;

FIG. 2 is a schematic cross-sectional view of another VCSEL unit;

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

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

FIG. 5 is a schematic cross-sectional view of a resonant cavity according to an embodiment 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 the intensity of the optical field in the cavity in the embodiment of FIG. 6 without the provision of the reflective layer;

FIG. 8 is a graph showing the distribution of the intensity of the optical field within the cavity of the resonator in the embodiment of FIG. 6;

FIG. 9 is a graph showing the distribution of the intensity of an optical field in a cavity in a further embodiment of a resonant cavity in accordance with the present invention;

FIG. 10 is a graph showing the distribution of the intensity of an optical field in a cavity in a further embodiment of a resonant cavity in accordance with the present invention;

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

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

Detailed Description

It is known from the background art that introducing strain in the active region of a VCSEL increases the risk of lattice structure defects. The structure of the VCSEL is combined to analyze the reason of the problem that the risk of the defect of the crystal lattice structure is increased:

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

The VCSEL laser chip includes a plurality of VCSEL units. 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 DBR 11, an active region 12, a current confinement layer 13, and an upper DBR 14 epitaxially grown in this order on a substrate 10. 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 Chemical vapor Deposition (MOCVD) technique.

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

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

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

The

active regions

12, 22 are quantum wells formed by alternately growing two thin films of material, whether front-emitting or back-emitting VCSELs. Specifically, the

active regions

12 and 22 include small bandgap semiconductor thin films and large bandgap semiconductor thin films, which are alternately disposed in the

active regions

12 and 22 to form a quantum well structure. After the quantum well structure is formed, a layer of Al is formed on the surface of the

active region

12, 22_1-xGa_xAn As layer; the Al is obtained by adopting a chemical wet etching method_1-xGa_xThe As layer forms a circular hole; then, the formed structure is placed in a high-temperature wet nitrogen environment to react with the Al_1-xGa_xOxidizing the As layer to partially oxidize the Al layer_1-xGa_xConversion of As layer to Al_1-xGa_xAn O insulating layer to form the current confining

layers

13, 23. In the current limiting

layers

13 and 23, a circular hole obtained by chemical wet etching is used for forming a current injection window, and the Al_1-xGa_xThe O insulating layer plays a role in limiting the current injected through the upper electrode 15. In Al_1-xGa_xAmong As, x is preferably not more than 0.04, i.e., a high Al component, which ensures a high oxidation rate.

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

In an active region of the quantum well structure, a small band gap semiconductor film is arranged between two adjacent layers of large band gap semiconductor films. The conduction and valence bands of the quantum well structure thus exhibit the well-like potentials shown in figure 3. Wherein, the area of the small band gap thin film between two adjacent layers of the large band gap semiconductor thin films is called a potential Well (Well) area, and the areas of the large band gap semiconductor thin films at two sides of the small band gap semiconductor thin film are called Barrier (Barrier) areas.

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

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

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

Compressive strain tends to be introduced in the active region of the quantum well structure. The energy band shape of the quantum well region can be adjusted due to the introduction of compressive strain; compared with the method of introducing tensile strain, the quantum well structure with compressive strain can obtain higher gain of an active region, so that the size of a band gap can be adjusted to adjust the corresponding working optical band.

However, strain introduction also has its disadvantages, as previously mentioned, it creates stress in the epitaxial layers formed, which can build up as the epitaxial layers grow. When the energy of stress accumulation is sufficiently large, stress relaxation occurs, which results in structural defects such as dislocations in the formed epitaxial layer.

If the structural defect is formed in the active region, the non-radiative coincidence of electron-hole pairs in the active region is increased, so that the External Quantum Efficiency (EQE) and the power are reduced; if the structural defect is formed in a region other than the active region, the structural defect may grow and diffuse to enter the active region in an aging experiment or a practical application, resulting in a decrease in device reliability.

For EQE, the differential external quantum efficiency η can be used_d(Differential External quantity Efficiency) to measure,

the structural defects can trap carriers, generate heat and do not generate photons, so that the problems of increase of the amount of the excited photons and reduction of EQE are caused.

It is therefore often necessary to balance the stress while forming the active region of the strained-introduced quantum well structure. The existing stress balancing methods mainly comprise the following two methods:

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

An epitaxial layer with opposite strain is added near the quantum well structure, for example, a release layer with tensile strain is arranged near the quantum well structure with compressive strain, so that the compressive stress is released. However, the introduction of the stress release layer increases the complexity of the structure, and requires separate analysis and optimization of the release layer for resistance, energy band, diffusion, defect generation, and other factors. This greatly increases the complexity of the design.

2) Another way is to design the quantum well with different strain patterns for the potential well and the barrier.

As previously described, to achieve higher gain, the well region is typically set to a compressive strain, and thus the barrier region is set to a tensile strain to balance the stress created by the 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 satisfy the stress balance condition, the material selection range of the barrier region is limited, which further limits the operating wavelength condition of the formed laser; and the barrier region of tensile strain is generally smaller in band gap, and the corresponding barrier height is smaller, so that the gain of the active region is lower, and the performance of the device is also sacrificed.

To solve the above technical problem, the present invention provides a resonant cavity, a laser unit and a laser, including: the first reflector and the second reflector 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 having a material with a tensile strain and one or more second active regions having a material with a compressive strain.

The active structure includes a first active region having a material with a tensile strain and a second active region having a material with a compressive strain. 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 while ensuring the gain of the active structure, inhibit the generation of structural defects, and is favorable for improving the quality of a resonant cavity, improving the external quantum efficiency and power and improving the reliability of a device.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

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: the first reflector 110 and the second reflector 140 are oppositely arranged at intervals; an active structure (not shown) located between the first mirror 110 and the second mirror 140; the active structure comprises 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 the compressive stress introduced by the first mirror 110 and the second

active regions

122a and 122b, so that stress accumulation is prevented, stress release in the working process of the device is avoided, and the service life is shortened; therefore, the arrangement of the first active region 121 and the second

active regions

122a and 122b can realize stress balance while ensuring the gain of the active structure, suppress the generation of structural defects, and is beneficial to improving the quality of the resonant cavity, improving the external quantum efficiency and power, and improving 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 present invention will be described in detail below with reference to the accompanying drawings.

The first mirror 110 and the second mirror 140, which are oppositely spaced apart, serve as two reflecting surfaces of a resonant cavity, respectively, and light travels back and forth between the first mirror 110 and the second mirror 140.

In some embodiments of the present invention, the first mirror 110 and the second mirror 140 are Bragg reflectors (DBR), and the first mirror 110 and the second mirror 140 each include 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 disposed. The adjacent high refractive index film and low refractive index film constitute one period. The reflectivity of the distributed bragg mirror is related to the periodicity of the high and low index films therein. For example, the first reflector 110 and the second reflector 140 may be Al alternately arranged in sequence_xGa_1-xAs/Al_1-yGa_yAs thin films, where x and y may be different.

In order to ensure the gain of the resonator, the first mirror 110 and the second mirror 140 must have a considerable number of cycles to satisfy the requirement of high reflectivity. And in order to ensure a narrow line width of the emitted laser light, a standing wave is formed in the resonant cavity after the light is reflected by the first mirror 110 and the second mirror 140 for 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 mirror 110 is greater than or equal to 99.9%, and the number of cycles of the first 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 ensured, the first reflecting mirror 110 and the second reflecting mirror 140 can be ensured to meet the requirement of high reflectivity so as to form a resonant cavity, the gain of the resonant cavity can be ensured, and the luminous intensity is ensured.

In this embodiment, the reflectivity of the second mirror 140 is lower than the reflectivity of the first mirror 110, so that the direction of the first mirror 110 pointing to the second mirror 140 is consistent with the laser emitting direction. The reflectivity of the first reflector 110 is more than 99.9%, so that the optical energy loss caused by the generated laser light transmission can be avoided as much as possible.

The active structure is internally provided with a gain medium capable of realizing population inversion, and the stimulated radiation amplification effect 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 barrier regions and well regions between adjacent barrier regions.

The first active region 121 and the second

active regions

122a and 122b have similar structures, 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, and does not need to separately analyze and optimize factors such as resistance, energy band, diffusivity, defect generation and the like, thereby greatly reducing the complexity of the design of the stress-balanced active structure.

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 an antinode position of an optical field standing wave; in order to further enhance the overall gain of the laser and achieve high power output, one or more Quantum Wells (QW or MQWs) are respectively disposed at the positions of the antinodes. Specifically, the quantum well active region includes a plurality of quantum wells, and in this embodiment, in the first active region 121 and the second

active regions

122a and 122b in the active structure, each active region is a structure of a plurality of quantum wells.

It should be noted that a quantum well at an anti-node position is equivalent to a PN junction; the active structure is equivalent to a plurality of PN junctions connected in series. The potential barrier between N-P will increase the resistance of the active structure. In order to reduce the resistance, the resonant cavity further comprises: a tunneling layer located between adjacent active regions.

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, Tunnel junctions (Tunnel junctions) are formed between the adjacent first active regions 121 and the adjacent second active regions 122a, and between the adjacent second active regions 122a and the adjacent second active regions 122b, and the connection resistance between the adjacent active regions can be effectively reduced through the reverse biased Tunnel junctions.

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

active regions

122a and 122b to be different strain forms, the selection range of quantum well materials can be expanded while stress balance is met, the limitation of working wavelength is avoided, the barrier height can be ensured, and the gain of the active regions is improved.

In this embodiment, the well region material of the first active region 121 has a compressive strain, and the barrier region material of the first active region 121 has a tensile strain; the magnitude of the stress of the tensile strain of the barrier region material of the first active region 121 is greater than the magnitude of the stress of the compressive strain of the 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 well region of the first active region 121, so that the entire first active region 121 assumes a state of tensile strain, and is therefore referred to as an overcompensated quantum well. Corresponding to the accumulation of tensile stress, the first active region 121 which integrally presents tensile strain can realize certain balance on compressive strain, and can effectively reduce the stress accumulation of the active structure; and the larger tensile strain of the barrier region of the first active region 121 tends to have a higher barrier height, and the formed quantum well has a stronger quantum confinement effect than the barrier region of the compressive strain, so that a larger gain can be obtained.

In this embodiment, the well region material of the second

active regions

122a, 122b has a compressive strain, the barrier region material of the second

active regions

122a, 122b has a compressive strain, and the magnitude of the stress of the compressive strain of the barrier region material of the second

active regions

122a, 122b is less than the magnitude of the stress of the compressive strain of the well region material of the second

active regions

122a, 122 b. Specifically, the barrier regions of the second

active regions

122a and 122b are made of a material with a small amount of compressive stress. In other embodiments of the present invention, the well region material of the second active region has 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 compressive strained as a whole to obtain higher gain.

Specifically, based on the operating band of the resonant cavity, the potential well region material of the first active region 121 is one of InGaAs, GaAs, InGaAsN, and InGaAsN nsb, and the barrier region material of the first active region 121 is one of GaAsP, AlGaAsP, AlGaAsN, and GaAsN; the well region material of the second

active regions

122a, 122b is one of InGaAs, GaAs, InGaAsN nsb, 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 therefore 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 the compressive strain of a portion 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 a direction of the first surface pointing to the second surface is consistent with a current direction; the resonant cavity further comprises: a current confinement layer on at least 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 a light emitting area in the active area is increased to improve the gain.

Furthermore, in some embodiments of the present invention, a surface of the first active region facing the second active region has the current confinement layer thereon. 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 influence of the oxidation process on the compression strain of the second active region is reduced.

Specifically, in this embodiment, the resonant cavity includes three current confinement layers: a first current confinement layer, a second current confinement layer, and a third current confinement layer. Since the material of the first mirror 110 includes N-type doped ions and the second mirror 140 includes P-type doped ions in this embodiment, the direction of the second mirror 140 pointing to the first mirror 110 is consistent with the current direction; the direction of the second mirror 140 towards the first mirror 110 is thus identical to the direction of the first surface towards the second surface, the surface of the active area towards the second mirror 140 being the first surface and the direction of the active area towards 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 and 122b are arranged in the same order as 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 again. Therefore, the first, second, and third current confinement layers are respectively 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 122 b.

In addition, in the present embodiment, in order to simplify the process steps and improve the material quality, in the process of forming the current confinement layer, the semiconductor compound is oxidized after the growth of all the materials is completed, 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 at a first surface 1211 of the first active region 121, a second semiconductor compound 132 located at a first surface of the second active region 122a, and a third semiconductor compound 133 located at a 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 double epitaxy method, that is, after the semiconductor compound is formed, a machine is replaced to perform an oxidation step, which is not limited in the present invention.

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

The substrate 100 can provide a process platform during formation of the resonant cavity. In this embodiment, the substrate 100 is located on a side of the first reflector 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 N, P type doped GaAs, InP, GaSb, or InSb. 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 doping ions included in the first mirror 110 are N-type ions, and the doping ions included in the second 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, setting the material of the substrate 100 as the N-type doped semiconductor material (for example, N-type doped GaAs) can provide a good growth surface and a good 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 made of other semiconductor materials. When the substrate is made of other semiconductor materials, the material of the active structure can be selected according to the material of the substrate to realize stress balance.

In this embodiment, the number of the first active regions 121 is 1; the number of the second active regions 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 also be 2 to 4, and the number of the second active regions may also be 1 to 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.

It should be further noted that, in this embodiment, 1 first

active region

121 and 2 second

active regions

122a and 122b are sequentially formed on the substrate 100. This arrangement is merely exemplary. In other embodiments of the present invention, the second active region is 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 region, the second active region, and the first active region 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 and 222b, and a second mirror 240 sequentially on the substrate 200; a first current confinement layer 231, a first filling-up layer 271 and a first tunneling layer 251 sequentially positioned between the first active region 221 and the second active region 222 a; a second current confinement layer 232, a second fill-in layer 272 and a second tunneling layer 252 sequentially disposed 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 present embodiment is the same as the previous embodiment, and the description thereof is omitted; as shown in fig. 6, the difference between the present embodiment and the previous embodiment is that, in the present embodiment, the resonant cavity further includes: a reflective layer 280 located inside the active structure. The arrangement of the reflective layer 280 can adjust the cavity loss of different active regions in the resonant cavity active structure, so that the gain difference can be balanced, two active regions in the active structure can work under appropriate conditions, and the device performance can be further improved.

In this embodiment, a current confinement layer is further disposed on the active region, and 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 the second active region 222a, that is, the first active region 221 in the active structure is located on one side of the reflective layer 280, and the second

active region

222a, 222b in one or more of the active structures is located on the other side of the reflective layer.

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

active regions

222a, 222b are located on the side of the reflective layer 280 facing the second mirror 240.

Because the material of the first active region 221 and the material of the second

active regions

222a and 222b are different in strain type, 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 arrangement of the reflective layer 280 can balance the gain difference of the quantum wells of different junction designs, and can further improve the device performance.

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

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

Loss of cavity

Wherein R is₁、R₂Respectively, the reflectivities of the front and rear reflecting surfaces of the cavity of the resonant cavity, in particular, R₁Reflectance of reflection surface in light output surface direction, R₂The reflectance of the reflection surface in the non-light-emitting surface direction is shown.

The smaller the cavity loss, the longer the life (Lifetime) of the corresponding light in the cavity, i.e. the more times the light propagates back and forth in the cavity due to reflection before exiting the cavity, the more times it passes through the active region. The energy increment of light in the unit length of the active area is in direct proportion 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 region gain. The larger g represents the increased energy of the light passing through the active region.

Fig. 7 shows the distribution of the intensity of the optical field in the cavity in the embodiment of fig. 6 without the provision of the reflective layer. In the figure, the abscissa represents the distance between the light field position and the light-emitting surface of the resonant cavity, and the ordinate is the 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 disposed, the first mirror and the second mirror are used as reflective surfaces of the resonant cavity in different active regions, and the R corresponding to different active regions₁·R₂The values of (a) and (b) are the same, and thus, the cavity losses of the equivalent resonators for each active region are similar; the intensity distribution of the optical field is substantially uniform within the different active areas.

Fig. 8 shows the distribution of the intensity of the optical field in the cavity in the embodiment of fig. 6, i.e. the distribution of the intensity of the optical field in the cavity after the reflective layer is provided. In the figure, the abscissa 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 far from the substrate 200 and the position of the light field in fig. 6), and the ordinate is 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-type doped dbr, and the second mirror 240 far from the substrate 200 is a P-type doped dbr. In addition, the light is emitted in the direction of the first mirror 210 toward the second mirror 240, so the light is emitted from the second mirror 240, that is, the resonant cavity is a resonant cavity emitting light from the front, and therefore, 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, 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 a reflective surface of an equivalent resonant cavity, and the reflective layer 280 and the second mirror 240 are another reflective surface of the equivalent resonant cavity. In the first active region 221, the light reflected by the reflective layer has increased coherence with the light reflected by the second mirror 240. Therefore, for the first active region 221, the total reflectivity facing away from the laser emitting direction (i.e. the direction of the second mirror 240 pointing to the first mirror 210) is increased, and the reflectivity along the laser emitting direction (i.e. the direction of the first mirror 210 pointing to the second mirror 240) is not changed, i.e. the arrangement of the reflective layer 280 can significantly increase the R corresponding to the equivalent resonant cavity₁Value, while R₂Remains substantially unchanged and therefore R in the first active region 221 can be significantly increased₁·R₂So that the cavity loss of the resonant cavity equivalent to 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 illustrated in the circle 390 in fig. 8.

On the other hand, 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 not the sameAccordingly, the phase difference of the light reflected by the first reflecting mirror 210 and the reflective layer 280 is different from the phase difference of the light reflected by the second reflecting mirror 240 and the reflective layer 280, and thus the reflective layer cannot simultaneously enhance the coherence of the light in the active regions on both sides. Therefore, when the light in the first active region 221 is coherently enhanced, the light in the second active region 222, 223 cannot be coherently enhanced, and for the second

active region

222a, 222b, the second mirror 240 is a reflecting surface of the equivalent resonant cavity, and 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, so that the reflecting layer 280 is disposed to have the reflectivity R of the reflecting surface of the equivalent resonant cavity₂The influence of the value is small, and the influence on the cavity loss of the resonant cavity equivalent to 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 positioned 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 equivalent cavity loss of the active structure at one side part far away from the light-emitting surface, thereby increasing the intensity of the partial optical field and further realizing the compensation of the gain difference caused by different junction design quantum wells.

In some embodiments of the present invention, the refractive index of the material of the reflective layer 280 is different from the refractive index of the material of the first active region 221, and the refractive index of the material of the reflective layer 280 is different from the refractive index of the material of the second

active regions

222a and 222b, so that the reflective layer 280 and the adjacent material film layer can form a distributed bragg reflector structure.

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 reflecting layer 280 is configured as the same bragg mirror, and no additional structure needs to be introduced, so that the influence of the introduced reflecting layer on the structural complexity can be reduced.

Specifically, in this embodiment, the reflective layer 280 is a stacked structure, and the reflective layer 280 includes a first reflective sub-layer (not shown) and a second reflective sub-layer (not shown), where a refractive index of the first reflective sub-layer is not equal to a refractive index of the second reflective sub-layer. An interface with a certain reflectivity is formed in the reflective layer 280 by adding a first reflective sub-layer and a second reflective sub-layer with a high or low refractive index, and the phase difference of front and rear reflected lights is adjusted by adjusting the thickness of the first reflective sub-layer and the thickness of the second reflective sub-layer, thereby adjusting the total reflectivity of the reflective layer 280.

In some embodiments of the present invention, the reflective layer includes a plurality of first reflective sub-layers and a plurality of first reflective sub-layers, and the first reflective sub-layers and the second reflective sub-layers are alternately disposed, that is, the plurality of first reflective sub-layers and the plurality of first reflective sub-layers are alternately disposed, so as to adjust the overall reflectivity of the reflective layer.

The first reflecting sub-layer and the second reflecting sub-layer form a period, and when the optical path of light emitted by each material layer corresponding to the active region in the period is lambda/4, namely the optical paths of the light emitted by the first reflecting sub-layer and the light emitted by the second reflecting sub-layer are lambda/4, relatively large reflectivity can be obtained; when the optical paths generated by different material layers in one period deviate from lambda/4, namely, the optical paths of lambda/4 are generated when the first reflecting sublayer and the second reflecting sublayer are different, relatively small reflectivity can be obtained. In addition, the total reflectivity of the reflecting layer can be adjusted by increasing or decreasing the period number or changing the material of the two sub-layers to change the refractive index difference between the sub-layers.

The reflectance of the entire reflective layer 280 is adjusted by changing the thickness ratio of the first reflective sublayer and the second reflective sublayer, or increasing or decreasing the number of cycles (pair number).

In this embodiment, the actually required increase in the optical field intensity is small, and therefore the reflective layer is provided as a low refractive index layer (half pair DBR) of one λ/4 optical path length. The reflecting 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 optical field intensity at the position of the partial active structure far from the light-emitting surface relative to the optical field intensity at the position of the partial active structure near the light-emitting surface is about 0.83 unit.

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

The present embodiment is the same as the previous embodiments, and the present invention is not repeated herein, but the difference between the present embodiment and the previous embodiments is that, in the present embodiment, the actually required optical field intensity increase amount is smaller than that in the previous embodiment, so 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 smaller than λ/4, so as to reduce the reflectivity of the reflective layer, thereby obtaining a smaller optical field increase amount. Therefore, in the present embodiment, the reflective layer is provided as a low refractive index layer having a thickness smaller than the λ/4 optical path length.

As shown in fig. 9, the abscissa represents the distance between the light field position and the light-emitting surface of the resonant cavity, and the ordinate represents the normalized light 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 optical field intensity at the position of the partial active structure away from the light-emitting surface is about 0.64 unit relative to the optical field intensity at the position of the partial active structure close to the light-emitting surface.

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

The present embodiment is the same as the previous embodiments, and the present invention is not repeated herein, but the difference between the present embodiment and the previous embodiments is that, in the present embodiment, the actually required optical field intensity is increased by a larger amount compared to the previous embodiments, so the reflectivity of the reflective layer is mainly adjusted by changing the number of periods (i.e. pair number) of the reflective layer, for example, by adding a high refractive index layer after the low refractive index layer, thereby forming a complete period (DBR pair). Therefore, in the present embodiment, the reflective layer is configured as a distributed bragg mirror having only one period.

As shown in fig. 10, the abscissa represents the distance between the position of the optical field 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 optical field intensity at the position of the partial active structure away from the light-emitting surface is about 1.30 units relative to the optical field intensity at the position of the partial active structure close to the light-emitting surface.

In summary, comparing fig. 8 to 10, it can be known that the higher the reflectivity of the reflective layer is, the larger the difference between the optical field intensity at the position of the coherence enhancing partial active structure obtained by phase matching of the light reflected by the reflective mirror and the reflective layer and the optical field intensity at the position of the phase mismatch partial active structure is. Therefore, through the arrangement of 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 the intensity of any optical field can be obtained.

Therefore, by designing the reflective layer and disposing the reflective layer between the adjacent first active region 221 and the second active region 222a, it is possible to compensate for the lower gain of the first active region 221 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 appropriate conditions. In general, a region with a low gain value needs to have a larger light field intensity to reduce the threshold current of the device and suppress the heat generation of the active region. Therefore, through the arrangement and the reality of the reflecting layer, the working conditions of different active regions can be optimized respectively, and the purposes of reducing threshold current and improving the working state under the high-temperature condition are achieved.

It should be further noted that the way that the reflective layer enhances the intensity of the optical field at the active structure position on the side far from the light exit surface is only an example, and in other embodiments of the present invention, the reflective layer may also enhance the intensity of the optical field at the active structure position on the side near the light exit surface.

The present embodiment is the same as the foregoing embodiments, and the description of the present invention is omitted here, and the present embodiment is different from the foregoing embodiments in that the position where the reflective layer is disposed enables coherence between the light reflected by the reflective layer and the light reflected by the first reflector to be enhanced, so that in the active structure near the light exit surface, the total reflectivity toward the laser exit direction is increased, and the reflectivity along the laser exit direction is unchanged, so that the cavity loss in the active structure near the light exit surface is reduced; therefore, in this embodiment, the arrangement of the reflective layer can enhance the intensity of the optical field at the position of the active structure near the light exit surface.

Therefore, as shown in fig. 11, the abscissa represents the distance between the optical field position and the light-emitting 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, the intensity of the optical field in the active structure near the light-emitting surface is significantly increased compared to the active structure far from the light-emitting surface.

Other modes are explained as follows: the reflective layer material can be varied to vary the refractive index difference and thereby vary the reflectivity of the reflective layer; the width of the gradient layer is changed by adjusting the material (certain element composition) of the reflecting layer, and the wider the gradient layer is, the smaller the reflectivity is.

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 difference of quantum wells with different junction designs; and adjusting the gain difference of different positions in the active structure to reach a balanced position through the arrangement of the material, the position, the thickness and the number of layers of the reflecting layer. Correspondingly, the invention also provides a laser unit, which specifically comprises: the resonant cavity is provided by the invention; a first electrode; 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: a resonant cavity, the resonant cavity being a resonant cavity of the present invention; a first electrode 261; and a second electrode 262.

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

The technical solution of the embodiment of the laser unit of the present invention is described in detail below with reference to the accompanying drawings.

The resonant cavity (not labeled in the figures) is the resonant cavity of the present invention. Specifically, the specific technical solution of the resonant cavity refers to the aforementioned embodiment of the resonant cavity, and the present invention is not described herein again.

The first electrode and the second electrode enable connection of the resonant cavity to 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 a surface of the substrate 200, and the first electrode 261 is electrically connected to 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 is the same as the laser emitting direction, so the second electrode 262 includes a window (not shown), and the window penetrates the second electrode 262 along the laser propagation direction. The window is used for emitting laser.

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

In other embodiments of the present invention, the laser unit may also be a back-side light 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 is provided.

The resonant cavity is a resonant cavity of the present invention, and specifically includes a first mirror 310, an active structure, and a second mirror 340, which are sequentially located on the substrate 300; wherein the active structure includes 1 first active region 321 and 2 second

active regions

322a, 322b sequentially located on the first mirror 310; a first current confinement layer 331, a first filling-up layer 371 and a first tunneling layer 351 are sequentially arranged between the first active region 321 and the second active region 322 a; a second current confinement layer 332, a second fill-up layer 372 and a second tunneling layer 352 are sequentially arranged between the second active region 322a and the second active region 322 b; a third current confinement layer 333 is disposed between the second active region 322b and the second mirror 340.

Specifically, the specific technical solution of the resonant cavity refers to the aforementioned embodiment of the resonant cavity, and the present invention is not described herein again.

The present embodiment is the same as the previous embodiment, and the description of the present invention is omitted; the present embodiment is different from the previous embodiments in that 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 the same as the direction of the second reflecting mirror 340 pointing to the first reflecting mirror 310.

Therefore, the first electrode 361 is located on the 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 the surface of the second mirror 340 on the side away from the active structure. Wherein the surface of the substrate 300

In this embodiment, a first active region 321 with tensile strain is first formed on the substrate 300, and 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 formation of the first mirror 310 and the formation of the first current confinement layer can be balanced, thereby improving the quality of the second

active regions

322a and 322 b.

The fact that the reflective layer is not provided in the back-side light-emitting laser unit is merely an example, and in other embodiments of the present invention, the reflective layer may be provided in the back-side light-emitting laser unit.

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

The laser unit includes: a resonant cavity is provided.

The resonant cavity is a resonant cavity of the present invention, and specifically includes a first mirror 410, an active structure, and a second mirror 440 sequentially disposed on the substrate 400; wherein the active structure includes 1 first

active region

421 and 2 second

active regions

422a, 422b sequentially on the first mirror 410; a first current confinement layer 431, a first filling-up layer 471 and a first tunneling layer 451 are sequentially arranged between the first active region 421 and the second active region 422 a; a second current limiting layer 432, a second gap filling layer 472 and a second tunneling layer 452 are sequentially arranged between the second active region 422a and the second active region 422 b; 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 light emitting laser unit, that is, laser generated by the laser unit is emitted from the substrate 400, and the emitting direction of the laser is the same as the direction in which the second reflecting mirror 440 points to the first reflecting mirror 410.

The present embodiment is the same as the previous embodiment, and the description of the present invention is omitted; the difference between this embodiment and the foregoing embodiments is that in this embodiment, in the first active region 421, the tensile stress of the material of the barrier region is very large, so that the gain of the first active region 421 is larger than the gains of the second

active regions

422a and 422b, and therefore, in the active structure, the reflective layer 480 is disposed between the first active region 421 and the second active region 422a, so that the light in the second

active regions

422a and 422b can be coherently enhanced after being reflected by the first mirror 410, the second mirror 440, and the reflective layer 480, and the light in the first active region 421 cannot be coherently enhanced, so as to reduce the optical field intensity at the position of the first active region 421, thereby achieving the balance of energy gains of different active regions in the active structure.

As shown in fig. 12, in some embodiments of the present 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 is electrically connected 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 of the extension 402 facing the second mirror 440. The first electrode 461 is disposed on the surface of the extension region 402, where the first mirror 410 faces the second 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 coplanar electrodes, which is beneficial to reducing the packaging difficulty of the laser unit and improving the packaging quality.

In addition, the present invention also provides a laser, specifically comprising: the laser unit is the laser unit of the invention.

Since the laser unit is the laser unit of the present invention, the specific technical scheme of the laser unit refers to the foregoing embodiments of the laser unit, and the present invention is not described herein again.

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 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 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 while ensuring the gain of the active structure, inhibit the generation of structural defects, contribute to improving the quality of the resonant cavity, contribute to improving the external quantum efficiency and power and contribute to improving the reliability of the 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 the generation of structural defects while ensuring the gain of an active structure, so that the resonant cavity has high quality, high external quantum efficiency and power and high reliability; therefore, the laser provided by the invention is used as the light source of the laser radar, so that the quality, power and 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 the material of the first active region has a tensile strain, and the 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 waveband, the first active region with tensile strain can release the compressive stress introduced by the second active region, the stress accumulation is prevented, and the stress release is avoided; therefore, the arrangement of the first active region and the second active region can realize stress balance while ensuring the gain of the active structure, inhibit the generation of structural defects, and is favorable for improving the quality of a resonant cavity, improving the external quantum efficiency and power and improving 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 effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A resonant cavity, comprising:

the first reflector and the second reflector 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 having a material with a tensile strain and one or more second active regions having a material with 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 barrier regions and well regions 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 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 magnitude of the stress of the tensile strain of the barrier region material of the first active region is greater than the magnitude of the stress of the compressive strain of the well region material of the first active region.

5. The resonant cavity as set forth in any of claims 2-4, wherein the 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 and AlGaAsP.

6. The resonant cavity of claim 3, wherein the 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 magnitude of the stress of the compressive strain of the second active region barrier region material is less than the magnitude of the stress of the compressive strain of the second active region well region material.

7. The resonant cavity of claim 2 or 6, wherein the well region material of the second active region is InGaAs and the barrier region material of the second active region is AlGaAs.

8. The resonant cavity of claim 3, wherein the 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 resonator 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: a reflective layer between adjacent first and second active regions.

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

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

15. The resonant cavity according to claim 11 or 14, wherein the reflective layer is a stacked structure, the reflective layer comprises a first reflective sublayer and a second reflective sublayer, and the refractive index of the first reflective sublayer is not equal to the refractive index of the second reflective sublayer.

16. The resonant cavity of claim 15, wherein the first reflective sublayers and the second reflective sublayers alternate.

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

the resonant cavity further comprises: a current confinement layer on at least the first surface.

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

19. The resonant cavity of claim 1, further comprising: a substrate located on a side of the first mirror remote from the active structure.

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

21. A laser unit, comprising:

a resonant cavity according to any one of claims 1 to 20;

a first electrode;

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 away from the active structure.

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

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

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.