CN115224587A - Active region unit, active region, epitaxial structure and chip of quantum cascade laser - Google Patents

Abstract

The present disclosure provides an active region unit of a quantum cascade laser having a ramp transition property, the active region unit sequentially including from top to bottom: an implant region for providing an implant energy state; a gain region for providing a luminescence upper energy state and a luminescence lower energy state, wherein the luminescence upper energy state is greater than the luminescence lower energy state, a radiative transition from the luminescence upper energy state to the luminescence lower energy state is a ramp transition, and the injection energy state is greater than the luminescence upper energy state; and a relaxed region for providing relaxed energy states, the relaxed energy states including a top energy state and a bottom energy state, wherein the top energy state is less than the luminescence lower energy state; wherein the injection region, the gain region and the relaxation region adopt

A semiconductor material. The disclosure also provides an active region, an epitaxial structure and a chip of the quantum cascade laser.

Description

Quantum cascade laser active region unit, active region, epitaxial structure and chip

technical field

The present disclosure relates to the field of semiconductor technology, and more particularly, to a quantum cascade laser active area unit, an active area, an epitaxial structure and a chip.

Background technique

Quantum Cascade Laser (QCL) is the current miniaturized high-performance infrared laser light source, which is widely used in environmental monitoring, industrial process control and other fields. At present, QCL based on InP-based InGaAs/InAlAs material system has been able to achieve 3-12 Micron band room temperature continuous wave operation.

However, when the laser wavelength needs to be extended to the band above 12 microns or below 3 microns, since the internal loss is significantly higher than the 3-12 micron band, the active region gain of the mature InP-based InGaAs/InAlAs material system is not enough to compensate for the loss. Room temperature continuous wave operation cannot be achieved, and a high-gain active region needs to be designed to overcome the above shortcomings.

SUMMARY OF THE INVENTION

In view of this, the embodiments of the present disclosure provide a quantum cascade laser active region unit, an active region, an epitaxial structure and a chip.

半导体材料。According to a first aspect of the present disclosure, there is provided an active area unit of a quantum cascade laser with oblique transition properties, the active area unit including, from top to bottom, an injection area for providing an injection energy state; A gain region is used to provide a luminescence upper energy state and a luminescence lower energy state, wherein the luminescence upper energy state is greater than the luminescence lower energy state, and the radiation transition from the luminescence upper energy state to the luminescence lower energy state is inclined a transition, the implanted energy state is greater than the luminescent upper energy state; and a relaxation region for providing a relaxation energy state, the relaxation energy state includes a top energy state and a bottom energy state, wherein the top energy state is less than the energy state under the light emission; wherein, the injection region, gain region and relaxation region are all used

Semiconductor material.

半导体材料选自InAs、InSb、GaSb、AlSb、InAsSb中的至少一种，或者InAs、InSb、GaSb、AlSb、InAsSb中至少两种形成的合金中的至少一种。According to an embodiment of the present disclosure, the

The semiconductor material is selected from at least one of InAs, InSb, GaSb, AlSb, InAsSb, or at least one of an alloy formed by at least two of InAs, InSb, GaSb, AlSb, and InAsSb.

According to an embodiment of the present disclosure, the energy difference between the injection energy state and the emission upper energy state is 5-7 meV.

According to an embodiment of the present disclosure, the energy difference between the injection energy state and the luminescence upper energy state is equal to one optical phonon energy.

According to an embodiment of the present disclosure, the relaxation energy state includes a microstrip energy state or a localized energy state.

According to an embodiment of the present disclosure, the energy difference between the light-emitting lower energy state and the top energy state is 0-5 meV.

According to an embodiment of the present disclosure, an energy difference between the luminescent lower energy state and the top energy state is equal to one optical phonon energy.

According to a second aspect of the present disclosure, there is provided an active region of a quantum cascade laser, the active region comprising a plurality of active region units as described in any one of the above-mentioned series connected in series, wherein the series connected In the active area unit, the bottom energy state of the relaxation area of the previous active area unit is greater than the light-emitting upper energy state of the gain area of the next active area unit.

According to an embodiment of the present disclosure, the number of active area cells in the active area is greater than or equal to 10.

半导体材料。According to a third aspect of the present disclosure, an epitaxial structure of a quantum cascade laser is provided, the epitaxial structure comprising: a lower cladding layer, a lower superlattice waveguide layer, a lower isolation layer, and any of the above-mentioned layers grown on a substrate in sequence. The active region, the upper isolation layer, the upper superlattice waveguide layer, and the upper cladding layer described in one item, wherein the active region adopts

Semiconductor material.

According to an embodiment of the present disclosure, the substrate adopts a material that is lattice-matched with the material of the active region, and is selected from one of InAs, GaSb, and InSb.

According to an embodiment of the present disclosure, the lower cladding layer and the upper cladding layer adopt materials lattice-matched with the substrate material, including semiconductor materials of binary, ternary, and quaternary compounds, and narrow-band gap quantum wells Superlattice materials formed with wide bandgap barriers.

According to an embodiment of the present disclosure, the doping concentration of the lower cladding layer and the upper cladding layer is 1×10 ¹⁷ cm ⁻³ to 5×10 ¹⁸ cm ⁻³ .

According to an embodiment of the present disclosure, the thickness of the lower cladding layer is 100 nm˜4000 nm, and the thickness of the upper cladding layer is 100 nm˜4000 nm.

According to an embodiment of the present disclosure, the materials used for the lower superlattice waveguide layer and the upper superlattice waveguide layer are strained superlattice materials.

According to an embodiment of the present disclosure, the refractive index of the lower superlattice waveguide layer and the upper superlattice waveguide layer is smaller than that of the active region.

According to an embodiment of the present disclosure, the lower isolation layer and the upper isolation layer employ materials that are lattice-matched to the substrate material.

According to an embodiment of the present disclosure, the refractive index of the lower isolation layer and the upper isolation layer is greater than that of the active region.

According to an embodiment of the present disclosure, the thickness of the lower isolation layer is 100 nm˜4000 nm, and the thickness of the upper isolation layer is 100 nm˜4000 nm.

According to a fourth aspect of the present disclosure, there is provided a quantum cascade laser chip, the chip comprising: the epitaxial structure of the quantum cascade laser according to any one of the above, wherein the active region, the upper The isolation layer, the upper superlattice waveguide layer and the upper cladding layer form a ridge waveguide structure; the back electrode is formed on the back of the substrate of the epitaxial structure away from the lower cladding layer; the dielectric insulating layer is formed on the ridge waveguide structure and surface electrodes, which are formed on the surface of the upper cladding layer of the epitaxial structure away from the upper superlattice waveguide layer.

According to an embodiment of the present disclosure, the width of the ridge waveguide structure is 5 μm˜50 μm.

According to an embodiment of the present disclosure, the thickness of the dielectric insulating layer is 50 nm˜1000 nm.

According to an embodiment of the present disclosure, the material used for the dielectric insulating layer is one selected from SiO ₂ , Si ₃ N ₄ , and Si ₃ N ₄ /SiO ₂ .

According to an embodiment of the present disclosure, the material used for the surface electrode is one selected from Au, Ti/Au, and Ti/Pt/Au.

As can be seen from the above technical solutions, the beneficial effects of the quantum cascade laser active area unit, active area, epitaxial structure and chip provided by the present disclosure are as follows:

半导体材料和斜跃迁的结构，显著提高了发光上能态寿命，从而提高了有源区的增益，实现了高增益的有源区。1. The active region unit of the quantum cascade laser with oblique transition properties provided by the present disclosure, using

The semiconductor material and the structure of the oblique transition significantly increase the lifetime of the upper energy state of light emission, thereby increasing the gain of the active region and realizing a high-gain active region.

半导体材料和斜跃迁的结构的有源区单元串联得到的，提高了有源区的增益，降低了有源区的损耗。2. The active region of the quantum cascade laser with oblique transition properties provided by the present disclosure is obtained by adopting

The semiconductor material and the active area unit of the oblique transition structure are obtained in series, which improves the gain of the active area and reduces the loss of the active area.

3. The epitaxial structure of the quantum cascade laser with oblique transition properties provided by the present disclosure can effectively reduce the waveguide loss and improve the lifetime of the upper energy state of light emission through the design of the high-efficiency active region.

半导体材料和斜跃迁的结构，显著提高了发光上能态寿命，从而提高激光器的动态范围和输出功率。4. The chip of the quantum cascade laser with oblique transition properties provided by the present disclosure adopts the

The semiconductor material and the structure of the oblique transition significantly increase the lifetime of the upper energy state, thereby increasing the dynamic range and output power of the laser.

Description of drawings

The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of embodiments of the present disclosure with reference to the accompanying drawings, in which:

FIG. 1( a ) schematically shows a schematic diagram of the vertical transition of the local conduction band energy of the active region unit of the quantum cascade laser according to the embodiment of the present disclosure;

FIG. 1(b) schematically shows a schematic diagram of a local conduction band energy band slant transition of an active region unit of a quantum cascade laser according to an embodiment of the present disclosure;

FIG. 2 schematically shows the conduction band diagram of the active region unit of the quantum cascade laser according to the embodiment of the present disclosure when an electric field is applied;

FIG. 3 schematically shows a conduction band diagram of the active region unit of the quantum cascade laser according to another embodiment of the present disclosure when an electric field is applied;

FIG. 4 schematically shows a schematic diagram of a stack structure of an active region unit of a quantum cascade laser according to an embodiment of the present disclosure;

FIG. 5 schematically shows a schematic diagram of a quantum cascade laser epitaxy structure according to an embodiment of the present disclosure;

FIG. 6 schematically shows the high-resolution X-ray diffraction spectrum of the quantum cascade laser epitaxial structure according to the embodiment of the present disclosure;

FIG. 7 schematically shows the atomic force microscope morphology of the surface of the quantum cascade laser epitaxial structure according to the embodiment of the present disclosure;

FIG. 8 schematically shows the lasing spectrum of the quantum cascade laser chip according to the embodiment of the present disclosure under different injection currents.

Detailed ways

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood, however, that these descriptions are exemplary only, and are not intended to limit the scope of the present disclosure. In the following detailed description, for convenience of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. It will be apparent, however, that one or more embodiments may be practiced without these specific details. Also, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts of the present disclosure.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure. The terms "comprising", "comprising" and the like as used herein indicate the presence of stated features, steps, operations and/or components, but do not preclude the presence or addition of one or more other features, steps, operations or components.

Where expressions like "at least one of A, B, or C, etc.," are used, they should generally be interpreted in accordance with the meaning of the expression as commonly understood by those skilled in the art (eg, "has A, B, or C, etc." At least one of the "systems" shall include, but not be limited to, systems with A alone, B alone, C alone, A and B, A and C, B and C, and/or A, B, C, etc. ). The terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second" may expressly or implicitly include one or more of said features.

半导体材料体系取代InGaAs/InAlAs材料体系，可以将增益提高2倍以上，但是该新材料体系的外延生长难度明显高于成熟的InP基材料体系，同时缺乏高效率的有源区设计，因此基于

半导体材料体系的量子级联激光器至今没有实现室温连续波大功率激射。Quantum Cascade Laser (QCL) is based on inter-subband transitions, and its gain g and the effective mass m* of the material in the active region satisfy the following relationship: g∝(m*) ^-3/2 , that is, the smaller the effective mass is , the higher the material gain, the new effective mass can be considered

The semiconductor material system replaces the InGaAs/InAlAs material system, which can increase the gain by more than 2 times, but the epitaxial growth difficulty of this new material system is significantly higher than that of the mature InP-based material system, and it lacks high-efficiency active area design. Therefore, based on the

Quantum cascade lasers in semiconductor material systems have not yet achieved room temperature continuous wave high-power lasing.

An embodiment of the present disclosure provides an active region unit of a quantum cascade laser with oblique transition properties. The active region unit includes, from top to bottom, an injection region, a gain region, and a relaxation region.

The injection region is used to provide an injection energy state, and the wave function of the injection energy state and the wave function of the luminescence upper energy state of the gain region optionally have the characteristic of strong coupling.

A gain region is used to provide a luminescence upper energy state and a luminescence lower energy state, wherein the luminescence upper energy state is greater than the luminescence lower energy state, and the radiation transition from the luminescence upper energy state to the luminescence lower energy state is inclined transition, the injection energy state is greater than the luminescence upper energy state, the energy difference between the luminescence upper energy state and the luminescence lower energy state determines the wavelength of the laser, and the energy difference between the luminescence upper energy state and the luminescence lower energy state is given by The thickness of the quantum well and the potential barrier that provide the upper and lower luminescence energy states and the composition of the potential barrier are determined, and at least one potential barrier is set between the quantum well that provides the upper luminescence energy state and the quantum well that provides the lower luminescence energy state , optionally set 2 potential barriers, optionally set 3 potential barriers, so that the radiative transition of electrons from the luminescence upper energy state to the luminescence lower energy state has the property of oblique transition, and the property of the oblique transition makes the luminescence upper energy The lifetime of the state is at least greater than 0.5 ps, and optionally the lifetime of the luminescent upper energy state is greater than 1 ps.

半导体材料。所述

半导体材料体系指晶格常数在

附近的半导体材料。A relaxation region for providing a relaxation energy state, the relaxation energy state includes a top energy state and a bottom energy state, wherein the top energy state is smaller than the light-emitting lower energy state; wherein the injection region, the gain region and relaxation region using

Semiconductor material. said

The semiconductor material system refers to the lattice constant in

Nearby semiconductor materials.

半导体材料选自InAs、InSb、GaSb、AlSb、InAsSb中的至少一种，或者InAs、InSb、GaSb、AlSb、InAsSb中至少两种形成的合金中的至少一种。According to an embodiment of the present disclosure, the

The semiconductor material is selected from at least one of InAs, InSb, GaSb, AlSb, InAsSb, or at least one of an alloy formed by at least two of InAs, InSb, GaSb, AlSb, and InAsSb.

According to an embodiment of the present disclosure, the energy difference between the injection energy state and the light emission upper energy state is 5-7 meV, optionally, the energy difference is 6 meV, which is beneficial to realize resonant tunneling injection.

According to an embodiment of the present disclosure, the energy difference between the injection energy state and the luminescence upper energy state is equal to one optical phonon energy, which is beneficial to realize phonon-assisted injection.

According to an embodiment of the present disclosure, the relaxation energy state includes a microstrip energy state or a localized energy state.

According to an embodiment of the present disclosure, the energy difference between the light-emitting lower energy state and the top energy state is 0-5 meV, which is favorable for the relaxation of electrons in the light-emitting lower energy state through resonance tunneling. Optionally, the energy difference may be 2meV or 3meV.

According to an embodiment of the present disclosure, the energy difference between the luminescence lower energy state and the top energy state is equal to one optical phonon energy, which is beneficial to the relaxation of electrons in the luminescence lower energy state by means of phonon-assisted scattering.

Exemplarily, when the relaxation energy state is composed of a microstrip formed under an electric field, the energy state at the top of the microstrip is located below the luminescence lower energy state; the energy state at the top of the microstrip is the same as the luminescence lower energy state. The energy difference is not less than zero; the energy difference between the energy state at the bottom of the microstrip and the light-emitting upper energy state of the next active region unit is not less than zero, and can be smaller, so as to rapidly relax through resonance tunneling or electron scattering.

Exemplarily, when the relaxation energy state consists of a series of local energy states formed under an electric field, the energy difference between the series of local energy states is optionally the energy of one optical phonon; the one The highest energy state of the series of local energy states is located below the light-emitting energy state; the energy difference between the highest energy state of the series of local energy states and the light-emitting energy state is not less than zero; the series of local energy states The energy difference between the lowest energy state of the state and the luminescent upper energy state of the next active region unit is not less than zero, and may be small for fast relaxation through resonant tunneling or electron scattering.

半导体材料和斜跃迁的结构，显著提高了发光上能态寿命，从而提高了有源区的增益。The active region unit of the quantum cascade laser with oblique transition properties provided by the embodiment of the present disclosure adopts the

The semiconductor material and the structure of the oblique transition significantly increase the lifetime of the upper energy state of the luminescence, thereby increasing the gain of the active region.

FIG. 1( a ) schematically shows a schematic diagram of the vertical transition of the local conduction band energy of the active region unit of the quantum cascade laser according to the embodiment of the present disclosure. FIG. 1( b ) schematically shows a schematic diagram of a local conduction band energy band slant transition of an active region unit of a quantum cascade laser according to an embodiment of the present disclosure.

As shown in Fig. 1(a), the vertical transition of the prior art, in which the luminescence upper energy state and the luminescence lower energy state come from the same set of quantum wells, and the electron radiation transition is vertical in space, as shown by the vertical arrow in the figure .

As shown in FIG. 1( b ), in the oblique transition of the embodiment of the present disclosure, the quantum well providing the upper luminescence energy state and the quantum well providing the lower luminescence energy state are spatially separated, and the electron radiation transition is spatially oblique , as shown by the slanted arrow in the figure.

In the oblique transition energy band of the embodiment of the present disclosure and the vertical transition energy band in the prior art, the upper energy state lifetime of the oblique transition energy band is 1.6 ps, which is 3.3 times the upper energy state lifetime of the vertical transition. According to the known semiconductor laser theory , the upper energy state has a long lifetime, which means that a high electron concentration in the injection region is not required to achieve population inversion and lasing. The advantage of a lower electron concentration in the injection region is that the loss caused by the absorption of free carriers in the active region is less Small, it is beneficial to reduce the laser threshold and improve the output power of the laser.

FIG. 2 schematically shows a conduction band diagram of the active region unit of the quantum cascade laser according to an embodiment of the present disclosure when an electric field is applied.

As shown in FIG. 2 , the conduction band diagram includes a gain region 100 , an injection region 200 and a relaxation region 300 . The gain region 100 includes a light-emitting upper energy state 101 and a light-emitting lower energy state 102; the energy of the light-emitting upper energy state 101 is greater than the energy of the light-emitting lower energy state 102; the light-emitting upper energy state 101 and the light-emitting lower energy state 102 The energy difference of 102 is equal to the energy of the emitted photon of the quantum cascade laser, which determines the lasing wavelength of the laser; The thickness of the barrier layer, the composition of the barrier material, and the like vary, and therefore, the emission wavelength of the QCL varies depending on the thickness of the well layer, the thickness of the barrier layer, the composition of the barrier layer material, and the like. The positions of the electron wave functions and energy states in the band diagram are obtained by simulation. The electron lifetime of the luminescence upper energy state 101 is t1, and the electron lifetime of the luminescence lower energy state 102 is t2. According to the embodiment of the present disclosure, t1>t2; the maximum value of the wave function of the luminescence upper energy state 101 is located at In the quantum well U, the maximum value of the wave function of the energy state 102 under the luminescence is located in the quantum well L, and two potential barriers B1 and B2 are set between the quantum well U and the quantum well L, so that the upper energy state 101 in the luminescence is The radiative transition to the luminescent lower energy state 102 is an oblique transition.

The injection region 200 includes a degenerate injection energy state 201; the energy of the injection energy state 201 is greater than the luminescence upper energy state 101; the energy difference between the injection energy state 201 and the luminescence upper energy state 101 is about one optical The energy of the phonon is 30-35meV, and optionally, the energy difference is 32meV or 33meV.

The relaxation region 300 includes a series of energy states, and a microstrip is formed under an applied electric field, wherein the top 301 of the microstrip is located below the energy state 102 under light emission, and the energy difference between the top 301 of the microstrip and the energy state 102 under light emission is about one optical phonon The energy is 30-35meV, optionally, the energy difference is 32meV or 33meV; the microstrip bottom 302 is located above the implanted energy state 201 of the next active area unit, and the microstrip bottom 302 has The energy difference of the implanted energy states 201 of the source unit is 5-10 meV, optionally, the energy difference is 7 meV or 8 meV. The energy state 401 located above the injection energy state 201 and the closest distance may become the leakage energy state of the injected electron. The energy difference between the state 401 and the implanted energy state 201 is 40-80 meV, optionally, the energy difference is 55 meV or 60 meV.

FIG. 3 schematically shows a conduction band diagram of the active region unit of the quantum cascade laser according to another embodiment of the present disclosure when an electric field is applied.

As shown in FIG. 3 , the conduction band diagram includes a gain region 100 , an implantation region 200 and a relaxation region 300 . The gain region 100 includes a light-emitting upper energy state 101 and a light-emitting lower energy state 102; the energy of the light-emitting upper energy state 101 is greater than the energy of the light-emitting lower energy state 102; the light-emitting upper energy state 101 and the light-emitting lower energy state 101 The energy difference of the energy state 102 is equal to the energy of the emitted photon of the quantum cascade laser, which determines the lasing wavelength of the laser; The thickness of the barrier layer and the like vary, and therefore, the emission wavelength of the quantum cascade laser varies depending on the thickness of the well layer, the thickness of the barrier layer, and the like. The positions of the electron wave functions and energy states in the band diagram are obtained by simulation. The electron lifetime of the luminescence upper energy state 101 is t1, and the electron lifetime of the luminescence lower energy state 102 is t2. According to the embodiment of the present disclosure, t1>t2; the maximum value of the wave function of the luminescence upper energy state 101 is located at In the quantum well U, the maximum value of the wave function of the energy state 102 under the luminescence is located in the quantum wells L1 and L2, and two potential barriers B1 and B2 are set between the quantum well U and the quantum well L1, so that the luminous energy is The radiative transition from state 101 to luminescent state 102 is an oblique transition.

The injection region 200 includes an injection energy state 201 ; the energy of the injection energy state 201 is greater than the luminescence upper energy state 101 ; the energy difference between the injection energy state 201 and the luminescence upper energy state 101 is 5-10 meV.

The relaxation region 300 includes a series of energy states, and a microstrip is formed under an applied electric field, wherein the top 301 of the microstrip is located below the energy state 102 under light emission, and the energy difference between the top 301 of the microstrip and the energy state 102 under light emission is about one optical phonon The energy is 30-35 meV; the bottom 302 of the microstrip is located above the implanted energy state 201 of the next active region unit. The energy state 401 located above the injection energy state 201 and the closest distance may become the leakage energy state of the injected state electrons. According to the embodiment of the present disclosure, the energy difference between the energy state 401 and the injection energy state 201 is greater than the photon-phonon energy, which is 40 ~80meV.

FIG. 4 schematically shows a schematic diagram of a stack structure of an active region unit of a quantum cascade laser according to an embodiment of the present disclosure.

As shown in Figure 4, it is composed of a stack of active area units of the quantum cascade laser, in which the InAs layer constitutes the quantum well layer, and the AlSb layer constitutes the barrier layer; the active area of the quantum cascade laser consists of N The source area unit is superimposed and formed, in general, N is greater than or equal to 10. Optionally, N is greater than or equal to 10 and less than or equal to 100, optionally, N is equal to 80 or 90.

In this embodiment, the first 2.1 nm AlSb layer from top to bottom is the injection barrier; four undoped InAs quantum wells adjacent to it form a light-emitting region that provides oblique transitions between subbands; A doped InAs quantum well and two undoped InAs quantum wells below form a relaxation region, which is also an electron injection region for the next active region unit, and its electron energy state is related to the light emission of the next active region unit. The upper energy state forms strong coupling.

In another embodiment, the light-emitting region is formed by 3 or 5 undoped quantum wells, which form strong coupling with the electron injection energy state of the previous active region unit; in another embodiment, the potential barrier is optional is composed of AlAs _x Sb _1-x , and the ratio x of As makes the total strain of the quantum well and barrier layers in the whole epitaxial structure less than the critical strain value.

In another embodiment, the quantum well is optionally composed of InAs _x Sb _1-x , and the ratio x of As is such that the total strain of the quantum well layer and the barrier layer in the entire epitaxial structure is less than the critical strain value.

In another embodiment, the quantum well is optionally composed of In _1-y Ga _y Sb, and the ratio y of Ga makes the total strain of the quantum well layer and the barrier layer in the entire epitaxial structure less than the critical strain value.

In another embodiment, the quantum well is optionally composed of In _1-y Ga _y As _x Sb _1-x , the ratio y of Ga and the ratio x of As make the total strain of the quantum well layer and the barrier layer in the whole epitaxial structure less than the critical strain value.

An embodiment of the present disclosure provides an active region of a quantum cascade laser, the active region includes a plurality of active region units as described in any one of the above-mentioned series connected, wherein the serially connected active region In the unit, the bottom energy state of the relaxation region of the previous active region unit is greater than the light emitting upper energy state of the next active region unit gain region. Exemplarily, the relaxation region of the previous active area unit is also the electron injection area of the next active area unit.

According to an embodiment of the present disclosure, the number of active area cells in the active area is greater than or equal to 10.

半导体材料和斜跃迁的结构的有源区单元进行串联得到，增益区中发光量子阱的子带间跃迁采用斜跃迁方式，提供长的发光上能态寿命，有利于实现粒子数反转，降低注入区电子浓度，提高了有源区的增益，降低了有源区的损耗。The active region of the quantum cascade laser with oblique transition properties provided by the embodiments of the present disclosure will use

The semiconductor material and the active area unit of the oblique transition structure are connected in series, and the inter-subband transition of the light-emitting quantum well in the gain area adopts the oblique transition method, which provides a long luminescent upper energy state lifetime, which is conducive to the realization of particle number inversion and reduces the The electron concentration in the injection area increases the gain of the active area and reduces the loss of the active area.

半导体材料。其中，有源区由N个所述具有斜跃迁性质的量子级联激光器有源区单元串联构成，N＝10～100。所述下超晶格波导层和所述上超晶格波导层的总应变小于临界应变值。Embodiments of the present disclosure provide an epitaxial structure of a quantum cascade laser, the epitaxial structure includes: a lower cladding layer, a lower superlattice waveguide layer, a lower isolation layer, a lower cladding layer, a lower superlattice waveguide layer, a lower isolation layer, and any of the above grown sequentially on a substrate. The active region, the upper isolation layer, the upper superlattice waveguide layer and the upper cladding layer, wherein the active region adopts

Semiconductor material. Wherein, the active region is composed of N quantum cascade laser active region units with oblique transition properties in series, and N=10-100. The total strain of the lower superlattice waveguide layer and the upper superlattice waveguide layer is less than a critical strain value.

According to an embodiment of the present disclosure, the substrate adopts a material lattice-matched to the material of the active region, for example, the effective mass at the Γ point at room temperature is less than 0.03 m ₀ , where m ₀ is the mass of free electrons, exemplarily, One selected from InAs, GaSb, and InSb.

According to an embodiment of the present disclosure, the lower cladding layer and the upper cladding layer adopt materials lattice-matched with the substrate material, including semiconductor materials of binary, ternary, and quaternary compounds, and narrow-band gap quantum wells Superlattice materials formed with wide bandgap barriers. The upper isolation layer and the lower isolation layer are made of binary, ternary or quaternary semiconductor materials that are lattice-matched with the substrate material.

According to an embodiment of the present disclosure, the doping concentration of the lower cladding layer and the upper cladding layer is 1×10 ¹⁷ cm ⁻³ to 5×10 ¹⁸ cm ⁻³ . Optionally, the doping concentration of the lower cladding layer and the upper cladding layer is 1×10 ¹⁸ cm ⁻³ .

According to an embodiment of the present disclosure, the thickness of the lower cladding layer is 100 nm˜4000 nm, and the thickness of the upper cladding layer is 100 nm˜4000 nm. Optionally, the thicknesses of the lower cladding layer and the upper cladding layer are both 2000 nm or 3000 nm.

According to an embodiment of the present disclosure, the materials used for the lower superlattice waveguide layer and the upper superlattice waveguide layer are strained superlattice materials.

According to an embodiment of the present disclosure, the refractive index of the lower superlattice waveguide layer and the upper superlattice waveguide layer is smaller than that of the active region.

According to an embodiment of the present disclosure, the lower isolation layer and the upper isolation layer employ materials that are lattice-matched to the substrate material.

According to an embodiment of the present disclosure, the refractive index of the lower isolation layer and the upper isolation layer is greater than that of the active region.

According to an embodiment of the present disclosure, the thickness of the lower isolation layer is 100 nm˜4000 nm, and the thickness of the upper isolation layer is 100 nm˜4000 nm. Optionally, the thicknesses of the lower isolation layer and the upper isolation layer are both 2000 nm or 3000 nm.

According to an embodiment of the present disclosure, the refractive indices of the upper cladding layer and the lower cladding layer are less than or equal to the refractive indices of the upper superlattice waveguide layer and the lower superlattice waveguide layer.

According to an embodiment of the present disclosure, the upper cladding layer and the lower cladding layer are heavily doped, and the upper and lower spacer layers and the superlattice layer are lightly doped.

According to an embodiment of the present disclosure, the upper superlattice waveguide layer and the lower superlattice waveguide layer are strained superlattice materials, and the total strain of the strained superlattice is not greater than a critical strain value; the critical strain value is It means that after the accumulation of strain due to lattice mismatch between the epitaxial layer and the substrate reaches a critical value, defects such as dislocations will be generated in the epitaxial layer.

The epitaxial structure of the quantum cascade laser with oblique transition properties provided by the embodiments of the present disclosure can effectively reduce the waveguide loss and improve the lifetime of the upper energy state through the high-efficiency active region design, so as to improve the dynamic range and output power of the laser. .

FIG. 5 schematically shows a schematic diagram of a quantum cascade laser epitaxy structure according to an embodiment of the present disclosure.

As shown in FIG. 5, the substrate 600 adopts an InAs single crystal substrate;

The active region 604 is composed of an InAs/AlSb quantum well superlattice;

The lower cladding layer 601a and the upper cladding layer 601b are made of epitaxial InAs thin films, with a thickness of 100 nm to 4000 nm, an n-type doping concentration of 1×10 ¹⁷ cm ^-3 to 5×10 ¹⁸ cm ^-3 , and a refractive index smaller than that of the active region refractive index;

The lower superlattice waveguide layer 602a and the upper superlattice waveguide layer 602b use epitaxial InAs/AlSb superlattice, the thickness is 500nm-5000nm, and the refractive index is smaller than the refractive index of the active region;

According to the disclosed embodiments, the use of the lower superlattice waveguide layer 602a and the upper superlattice waveguide layer 602b can effectively reduce the waveguide loss compared with the use of the heavily doped InAs waveguide layer in the prior art, thereby improving the performance of the laser. Performance such as dynamic range and output power;

The lower isolation layer 603a and the upper isolation layer 603b are made of epitaxial InAs thin films, with a thickness of 500nm to 4000nm, an n-type doping concentration of 1×10 ¹⁶ cm ^-3 to 1×10 ¹⁷ cm ^-3 , and a refractive index greater than that of the active region Rate.

FIG. 6 schematically shows the high-resolution X-ray diffraction spectrum of the quantum cascade laser epitaxial structure of the embodiment of the present disclosure.

As shown in Figure 6, the spectrum contains clear satellite peaks, and the average full width at half maximum (FWHM) is 26 arcsec. According to the distance between adjacent satellite peaks, the thickness of a cascade cycle is calculated to be 98.5 nm, which is basically consistent with the designed 100 nm, indicating that the epitaxy The crystal quality of the layer is higher.

FIG. 7 schematically shows the atomic force microscope topography of the surface of the quantum cascade laser epitaxial structure according to the embodiment of the present disclosure.

As shown in Figure 7, it can be seen that there are clear atomic steps on the surface of the epitaxial structure of the quantum cascade laser, and the RMS is 0.17 nm, indicating that the surface flatness of the epitaxial layer is high.

An embodiment of the present disclosure provides a quantum cascade laser chip, the chip comprising: the epitaxial structure of the quantum cascade laser according to any one of the above, wherein the active region of the epitaxial structure, the upper isolation layer, the The upper superlattice waveguide layer and the upper cladding layer form a ridge waveguide structure; the back electrode is formed on the back of the substrate of the epitaxial structure away from the lower cladding layer; the dielectric insulating layer is formed on the sidewall of the ridge waveguide structure and a surface electrode, formed on the surface of the upper cladding layer of the epitaxial structure away from the upper superlattice waveguide layer.

According to an embodiment of the present disclosure, the width of the ridge waveguide structure is 5 μm˜50 μm. Optionally, the width is 30 μm or 35 μm.

According to an embodiment of the present disclosure, the thickness of the dielectric insulating layer is 50 nm˜1000 nm. Optionally, the thickness is 500 nm or 600 nm.

According to an embodiment of the present disclosure, the material used for the dielectric insulating layer is one selected from SiO ₂ , Si ₃ N ₄ , and Si ₃ N ₄ /SiO ₂ .

According to an embodiment of the present disclosure, the material used for the surface electrode is one selected from Au, Ti/Au, and Ti/Pt/Au.

半导体材料和斜跃迁的结构，显著提高了发光上能态寿命，有利于降低有源区的损耗，从而提高激光器的动态范围和输出功率，已经实现了由所设计的具有斜跃迁能带结构的QCL产生的15微米激射。The chip of the quantum cascade laser with the inclined transition property provided by the embodiment of the present disclosure adopts the

The semiconductor material and the structure of the oblique transition significantly increase the lifetime of the luminescent upper energy state, which is beneficial to reduce the loss of the active region, thereby improving the dynamic range and output power of the laser. 15-micron lasing generated by QCL.

FIG. 8 schematically shows the lasing spectrum of the quantum cascade laser chip according to the embodiment of the present disclosure under different injection currents.

As shown in Fig. 8, the lasing wavelength of the laser is located near 668cm ^-1 , which is 14.9 microns, which is consistent with the theoretical design of 15 microns. The depression of the single lasing spectrum below is caused by the absorption of _CO2 in the air.

It should be noted that the embodiments of the present disclosure provide the design of two active region energy band structures as non-limiting examples. It is conceivable that, in some embodiments of the present invention, the active region has an oblique transition band structure, and the relative position and energy difference between the luminescent upper energy state and the injected energy state can be designed in a similar manner. The relaxation region may not be in the form of a microstrip, but in the form of a local relaxation energy state.

Those skilled in the art will appreciate that various combinations and/or combinations of features recited in various embodiments and/or claims of the present disclosure are possible, even if such combinations or combinations are not expressly recited in the present disclosure. In particular, various combinations and/or combinations of the features recited in the various embodiments of the present disclosure and/or in the claims may be made without departing from the spirit and teachings of the present disclosure. All such combinations and/or combinations fall within the scope of this disclosure.

Embodiments of the present disclosure have been described above. However, these examples are for illustrative purposes only, and are not intended to limit the scope of the present disclosure. Although the various embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art can make various substitutions and modifications, and these substitutions and modifications should all fall within the scope of the present disclosure.

Claims (24)

1. An active area unit of a quantum cascade laser with a ramp transition property, characterized in that the active area unit comprises from top to bottom:

an implant region for providing an implant energy state;

a gain region for providing a luminescence upper energy state and a luminescence lower energy state, wherein the luminescence upper energy state is greater than the luminescence lower energy state, a radiative transition from the luminescence upper energy state to the luminescence lower energy state is a ramp transition, and the injection energy state is greater than the luminescence upper energy state; and

a relaxed region for providing relaxed energy states, the relaxed energy states including a top energy state and a bottom energy state, wherein the top energy state is less than the luminescence lower energy state;

wherein the injection region, the gain region and the relaxation region adopt

A semiconductor material.

2. The active area cell of claim 1, wherein the active area cell is configured to be connected to a power supply line

The semiconductor material is selected from at least one of InAs, inSb, gaSb, alSb and InAsSb, or at least one of alloys formed by at least two of InAs, inSb, gaSb, alSb and InAsSb.

3. The active area cell of claim 1, wherein the energy difference between the injected energy state and the light emitting upper energy state is 5-7meV.

4. The active area cell of claim 1, wherein the energy difference between the injected energy state and the light emitting upper energy state is equal to one optical phonon energy.

5. The active-area cell of claim 1, wherein the relaxed energy state comprises a microstrip energy state or a local energy state.

6. The active area cell of claim 5, wherein the energy difference between the lower energy state for light emission and the top energy state is 0-5meV.

7. The active area unit of claim 5, wherein the energy difference between the luminescence lower energy state and the top energy state is equal to one optical phonon energy.

8. An active region of a quantum cascade laser, wherein the active region comprises a plurality of active region units according to any one of claims 1 to 7 connected in series, wherein the bottom energy state of a relaxation region of a previous active region unit in the active region units connected in series is larger than the light emission upper energy state of a gain region of a next active region unit.

9. The active region of claim 8, wherein the number of active region cells in the active region is greater than or equal to 10.

10. An epitaxial structure for a quantum cascade laser, the epitaxial structure comprising:

a lower cladding layer, a lower superlattice waveguide layer, a lower isolation layer, an active region according to any one of claims 8-9, an upper isolation layer, an upper superlattice waveguide layer, and an upper cladding layer sequentially grown on a substrate, wherein the active region employs a lower cladding layer, a lower superlattice waveguide layer, and an upper isolation layer

A semiconductor material.

11. The epitaxial structure of claim 10 wherein the substrate is a material lattice matched to the active region material and is selected from one of InAs, gaSb, inSb.

12. The epitaxial structure of claim 11 wherein the lower and upper cladding layers are of a material lattice matched to the substrate material, semiconductor materials including binary, ternary, quaternary compounds, and superlattice materials formed with narrow bandgap quantum wells and wide bandgap barriers.

13. The epitaxial structure of claim 12, wherein the lower cladding layer and the upper cladding layer have a doping concentration of 1 x 10 ¹⁷ cm ^-3 ～5×10 ¹⁸ cm ^-3 。

14. The epitaxial structure of claim 13, wherein the lower cladding layer has a thickness of 100nm to 4000nm and the upper cladding layer has a thickness of 100nm to 4000nm.

15. The epitaxial structure of claim 10 wherein the material used for the lower superlattice waveguide layer and the upper superlattice waveguide layer is a strained superlattice material.

16. The epitaxial structure of claim 15, wherein the lower superlattice waveguide layer and the upper superlattice waveguide layer have refractive indices less than the active region.

17. The epitaxial structure of claim 11, wherein the lower and upper isolation layers are of a material lattice matched to the substrate material.

18. The epitaxial structure of claim 17, wherein the lower isolation layer and the upper isolation layer have a refractive index greater than the active region.

19. The epitaxial structure of claim 18, wherein the lower spacer layer has a thickness of 100nm to 4000nm and the upper spacer layer has a thickness of 100nm to 4000nm.

20. A quantum cascade laser chip, comprising:

an epitaxial structure of a quantum cascade laser of any one of claims 10 to 19, wherein the active region, the upper isolation layer, the upper superlattice waveguide layer and the upper cladding layer of the epitaxial structure form a ridge waveguide structure;

the back electrode is formed on the back surface, far away from the lower cladding layer, of the substrate of the epitaxial structure;

the dielectric insulating layer is formed on the side wall of the ridge waveguide structure; and

and the surface electrode is formed on the surface of the upper cladding layer of the epitaxial structure far away from the upper superlattice waveguide layer.

21. The quantum cascade laser chip of claim 20, wherein the ridge waveguide structure has a width of 5 μ ι η to 50 μ ι η.

22. The quantum cascade laser chip of claim 20, wherein the dielectric insulating layer has a thickness of 50nm to 1000nm.

23. Root of herbaceous plantThe quantum cascade laser chip of claim 22, wherein the dielectric insulating layer is made of a material selected from the group consisting of SiO ₂ 、Si ₃ N ₄ 、Si ₃ N ₄ /SiO ₂ One kind of (1).

24. The quantum cascade laser chip of claim 20, wherein the surface electrode is made of one material selected from Au, ti/Pt/Au.

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