Large strain infrared quantum cascade laser and method of making same

Abstract

The present disclosure provides a large-strain infrared quantum cascade laser and a growth method thereof, which comprises, from bottom to top, an InP lower waveguide layer, a quantum well cascade layer, and an InP upper waveguide layer; wherein the quantum well cascade layer is a multi-period cascade, each period of which comprises 8-12 periods of quantum well layer / barrier layer, which is an InGaAs / InAlAs superlattice material; a low-strain InGaAs layer; and a matching InGaAs layer. The quantum cascade laser of the present disclosure blocks surface defects by inserting a low-strain InGaAs layer between multiple periods of quantum well layer / barrier layer, and improves the flatness of the material surface by inserting a matching InGaAs layer, thereby avoiding the accumulation of defects during the growth of large-strain materials, and ultimately preparing high-quality epitaxial materials.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of optoelectronic materials, in particular to a large-strain infrared quantum cascade laser and a preparation method thereof. BACKGROUND

[0002] As an important waveband of atmospheric window, 3-4 μm high-power semiconductor laser is a key device to support the development of photoelectric system in this wavelength range, but it faces great technical difficulties to achieve high-power output in this wavelength range. Limited by the intrinsic band gap of semiconductor material, there is no semiconductor material in nature that can directly achieve high-power lasing in this waveband. Interband cascade laser is a laser that uses interband transition of superlattice structure to achieve laser emission. It is a relatively mature type of semiconductor laser in this wavelength range, but it cannot achieve high-power output above watts due to the limitation of working principle. Quantum cascade laser (QCL) is a semiconductor laser based on inter-subband electron transition. Through the design of energy band structure, it can achieve full-spectrum coverage in the mid-infrared and far-infrared waveband (3-14 μm), which is an important alternative technical solution to achieve high-power output in the 3-4 μm range. However, when the QCL wavelength expands to 3-4 μm, the epitaxial material is a large-strain material, and the quality of the epitaxial material becomes a key factor limiting the performance of the device.

[0003] The working principle of QCL is based on the transition of electrons between the upper and lower energy levels in the transition region, and the energy difference between the upper and lower energy levels corresponds to the QCL lasing wavelength. When the lasing wavelength expands in the direction of short wavelength (high energy), the structure of the QCL needs to have a large enough conduction band step to provide a large enough design space for electron transition and extraction level design. The QCL is mainly InP-based InGaAs / InAlAs material system, and the conduction band step of the matching material is 520 meV. To increase the conduction band step, the conventional method is to increase the Al component in InAlAs and reduce the Ga component in InGaAs, which introduces tensile strain in InAlAs and compressive strain in InGaAs while increasing the band step. By precisely designing the material thickness, the tensile strain and the compressive strain are compensated for each other, and high-quality material epitaxy can be achieved. However, when the wavelength is shortened to 3-4 μm, the Al component in InAlAs needs to be increased to more than 0.7, resulting in a strain of more than 1.2%. This greatly increases the technical difficulty of material growth. Even through strain compensation technology, because of the large strain in the growth of a single layer, a large number of defects are caused, and it is difficult to achieve high-quality material epitaxy. In order to achieve high power, QCL generally needs to be connected in multiple stages (usually 30-50 stages), and the required growth material thickness is thick, which will cause serious accumulation of material defects, further increasing the difficulty of high-power material preparation, and the material quality becomes the key problem that limits the power performance improvement and application promotion of 3-4 μm QCL. SUMMARY

[0004] (I) Technical problems to be solved

[0005] To solve the above problems, the present disclosure provides a large-strain infrared quantum cascade laser and a preparation method thereof, which at least partially solves the technical problems that the conventional quantum cascade laser is prone to cause a large number of defects and is difficult to achieve high-quality material epitaxy.

[0006] (II) Technical solutions

[0007] In one aspect, the present disclosure provides a large-strain infrared quantum cascade laser, which comprises, from bottom to top: an InP lower waveguide layer, a quantum well cascade layer, and an InP upper waveguide layer; wherein the quantum well cascade layer is a multi-period cascade, each period of which comprises: 8-12 periods of quantum well layer / potential barrier layer, which is an InGaAs / InAlAs superlattice material; a low-strain InGaAs layer; and a matching InGaAs layer.

[0008] Further, the InGaAs / InAlAs superlattice material is strain-compensated, and the components thereof are In X Ga (1-X) As / In Y Al (1-Y)As, wherein X≥0.7, Y≤0.3.

[0009] Further, the composition of the low-strained InGaAs layer is In Z Ga (1-Z) As, wherein 0.4

[0010] Further, the thickness of the low-strained InGaAs layer is 1-3 nm.

[0011] Further, the composition of the matching InGaAs layer is In 0.53 Ga 0.47 As.

[0012] Further, the thickness of the matching InGaAs layer is 5-10 nm.

[0013] Further, the low-strained InGaAs layer and the matching InGaAs layer are doped, and the doping concentration is 2-5×10 17 cm -3 .

[0014] Further, the excitation wavelength of the quantum well cascade layer is 3-4 μm.

[0015] Another aspect of the present disclosure provides a preparation method of the large-strained infrared quantum cascade laser according to the foregoing, which sequentially performs material preparation by using a MOCVD method, comprising the following steps: S1, growing an InP lower waveguide layer by using trimethylindium and PH3; S2, growing 8-12 periods of quantum well layer / potential barrier layer by using trimethylindium and trimethylgallium, and the composition is InGaAs / InAlAs superlattice material; S3, growing a low-strained InGaAs layer and a matching InGaAs layer by using trimethylindium and trimethylgallium; S4, repeating the operations of S2-S3, and then performing the operation of S2 once again; and S5, growing an InP upper waveguide layer by using trimethylindium and PH3.

[0016] Further, the quantum well layer / potential barrier layer in S2 is grown at a slow speed, and the growth speed is 0.1-0.2 μm per second.

[0017] (Three) beneficial effects

[0018] The large-strained infrared quantum cascade laser and the preparation method thereof provided by the present disclosure block surface defects by inserting a low-strained InGaAs layer among multiple quantum well layer / potential barrier layer periods, and improve the flatness of the material surface by inserting a matching InGaAs layer, so as to avoid the accumulation of defects in the growth process of the large-strained material, and finally obtain high-quality epitaxial material, thereby improving the performance of the device. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1A structural schematic diagram of a large-strain infrared quantum cascade laser according to an embodiment of the present disclosure is shown schematically.

[0020] Figure 2 A flowchart of a preparation method of a large-strain infrared quantum cascade laser according to an embodiment of the present disclosure is shown schematically.

[0021] Figure 3 A large-strain QCL material structure (left) and a band structure (right) of 3.8 μm according to an embodiment of the present disclosure are shown schematically. DETAILED DESCRIPTION

[0022] For the purpose of the present disclosure, the technical solutions and advantages are more clearly and clearly understood, the present disclosure is further described in detail below, and the drawings are referred to.

[0023] The terms used herein are merely for the purpose of describing specific embodiments, and are not intended to limit the present disclosure. The terms "include", "contain" and the like used herein indicate the existence of the described features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0024] Various orientation words in the present disclosure, such as "front", "back", "left", "right", "up", "down" and the like, are only for the convenience of description, and are used to describe the relative position relationship between the components, but are not used to limit the present disclosure, and the product placement method of the present disclosure may change the various orientation descriptions.

[0025] The present disclosure provides a large-strain infrared quantum cascade laser and a preparation method thereof, aiming to reduce the influence of lattice strain on material growth quality and improve the quality of epitaxial material. The quantum cascade laser is a multi-stage series structure, and the light-emitting region material usually has 30-50 periods, which is several hundred to thousands of nanometer-level coupled multi-quantum wells. During the material growth process, the material quality will gradually deteriorate as the number of periods increases, especially for 3-4 μm quantum cascade laser materials, which need to increase the Al component and reduce the Ga component to improve the material band step, but at the same time, it will cause a large strain, which brings great challenges to the epitaxial growth of high-quality materials.

[0026] Based on this, an embodiment of the present disclosure provides a large-strain infrared quantum cascade laser, please see Figure 1 , from bottom to top, including: InP lower waveguide layer, quantum well cascade layer, InP upper waveguide layer; wherein the quantum well cascade layer is a multi-period cascade, each period of which includes: 8-12 periods of quantum well layer / potential barrier layer, which is InGaAs / InAlAs superlattice material; low-strain InGaAs layer; matching InGaAs layer.

[0027] The large-strain infrared quantum cascade laser of the present disclosure is grown on an InP substrate, comprising an InP lower waveguide layer, a quantum well cascade layer, and an InP upper waveguide layer; the quantum well cascade layer has a period number of 30-50, and a low-strain InGaAs layer and a matching InGaAs layer are inserted every 8-12 periods, and the number of periods between the low-strain InGaAs layer and the matching InGaAs layer in the same laser is the same, i.e., as shown in Figure 1 The low-strain InGaAs layer is used to suppress material surface defects, and the matching InGaAs layer is used to improve the material surface flatness, effectively reducing strain accumulation.

[0028] On the basis of the above embodiment, the InGaAs / InAlAs superlattice material is strain-compensated, and the composition is In X Ga (1-X) As / In Y Al (1-Y) As, wherein X≥0.7 and Y≤0.3.

[0029] When the operating wavelength of the large-strain infrared quantum cascade laser is 3-4 μm, the Al composition in InAlAs is increased to more than 0.7, and the strain is significantly increased, and the insertion of the low-strain InGaAs layer and the matching InGaAs layer can significantly reduce strain accumulation.

[0030] On the basis of the above embodiment, the composition of the low-strain InGaAs layer is In Z Ga (1-Z) As, wherein 0.4

[0031] The low-strain InGaAs layer is mainly used to block surface defects, and the thickness is only 1-3 nm. If the thickness is too thick, the material surface will deteriorate due to strain accumulation. In the composition, the proportion of Ga in this range makes the strain moderate, avoiding the release of defects when the thickness of 1-3 nm reaches the critical thickness, because the greater the strain, the thinner the critical thickness.

[0032] On the basis of the above embodiment, the composition of the matching InGaAs layer is In 0.53 Ga 0.47 As, and the thickness of the matching InGaAs layer is 5-10 nm.

[0033] The matching InGaAs layer is mainly used to improve the material surface flatness, and the thickness is thicker than that of the low-strain InGaAs layer, which is beneficial to reduce the strain of In Z Ga (1-Z)As caused by the unevenness, the proportion of Ga in the matching InGaAs layer is 0.47, which is matched with the InP substrate, and the matching InGaAs layer has the technical effect of flattening the surface of the material.

[0034] On the basis of the above-mentioned embodiments, the low-strain InGaAs layer and the matching InGaAs layer are doped, and the doping concentration is 2-5×10 17 cm -3 .

[0035] The low-strain InGaAs layer and the matching InGaAs layer are doped, which is beneficial for carrier transport when being made into a device; the doping concentration in this range has the advantages of realizing electrical conductivity while avoiding the loss caused by carrier absorption.

[0036] On the basis of the above-mentioned embodiments, the excitation wavelength of the quantum well cascade layer is 3-4 μm.

[0037] The excitation wavelength of the large-strain infrared quantum cascade laser of the present disclosure is 3-4 μm, so as to reduce the defect accumulation in the material epitaxial growth process, improve the quality of the multi-period large-thickness material of 30-50 periods, and realize high-quality material epitaxy, which can promote the power performance improvement and application promotion of 3-4 μm QCL.

[0038] The present disclosure also provides a preparation method of the large-strain infrared quantum cascade laser, please refer to Figure 2 , the material preparation is carried out in the following steps in sequence by using the MOCVD method, including: S1, growing the InP lower waveguide layer by using trimethylindium and PH3; S2, growing the 8-12 period quantum well layer / potential barrier layer by using trimethylindium and trimethylgallium, and the component is InGaAs / InAlAs superlattice material; S3, growing the low-strain InGaAs layer and the matching InGaAs layer by using trimethylindium and trimethylgallium; S4, repeating the operations of S2-S3, and then performing the operation of S2 again; S5, growing the InP upper waveguide layer by using trimethylindium and PH3.

[0039] The preparation method of the quantum cascade laser of the present disclosure adopts metal-organic chemical vapor deposition (MOCVD), which is an important technical means for epitaxial preparation of high-quality semiconductor materials. The quantum cascade laser is grown at low temperature, and the substrate temperature is 500-540℃; high V / III ratio (molar ratio of V group hydride source and III group MO source during growth) is adopted, and the V / III ratio is >500. Specifically, a large-strained QCL material composed of InGaAs / InAlAs coupled superlattice is grown on an N-type (001) InP substrate, 2 trimethyl gallium (TMGa), 2 trimethyl indium (TMIn) and 1 trimethyl aluminum (TMAl) are used as III group sources, arsine (AsH3) and phosphine (PH3) are used as V group sources, and high-purity hydrogen is used as carrier gas.

[0040] The growth QCL cycle number is 30-50, and a low-strained InGaAs layer and a matching InGaAs layer are inserted every 10 growth cycles; during the growth process, the composition transformation of InGaAs is realized through mutual switching between TMIn1, TMIn2, TMGa1 and TMGa2; the structure of the large-strained QCL material is precisely designed to have a lasing wavelength in the wavelength range of 3-4 μm; the InGaAs / InAlAs coupled superlattice is strain-compensated; the composition of the InGaAs / InAlAs coupled superlattice is In X Ga (1-X) As and InxAl (1-Y) As, wherein X≥0.7 and Y≤0.3; the thickness of the inserted low-strained InGaAs layer is 1-3 nm, and the composition is In X Ga (1-X) As, wherein 0.4 0.53 Ga 0.47 As; the low-strained InGaAs thin layer and the matching InGaAs layer are doped, and the doping concentration is 2-5×10 17 cm -3 ;

[0041] On the basis of the above embodiment, the quantum well layer / potential barrier layer in S2 is grown slowly, and the growth speed is 1 μm per second.

[0042] Slow growth has the technical effect of forming a steep interface and ensuring the photoelectric performance of the material.

[0043] The method for growing high-power large-strain quantum cascade laser material by MOCVD provided by the present disclosure reduces defect accumulation during the growth of QCL material and improves material quality by inserting a low-strain InGaAs layer and a matching InGaAs layer every 8-12 growth cycles. During the growth of superlattice material, the insertion of a strain buffer is an effective means of isolating defects and improving surface quality. In the present disclosure, a thin InGaAs strain layer is used to block surface defects, and a matching InGaAs layer is used to improve the flatness of the material surface, effectively blocking the transmission of defects during the epitaxial growth of large-strain material, thereby avoiding defect accumulation during the growth of 3-4 μm large-strain material and improving material quality.

[0044] The present disclosure will be further described below through specific embodiments. In the following embodiments, the large-strain infrared quantum cascade laser and the method for preparing the same are specifically described. However, the following embodiments are only used to exemplify the present disclosure, and the scope of the present disclosure is not limited thereto.

[0045] The present embodiment provides a large-strain quantum cascade laser with a design wavelength of 3.8 microns and a method for epitaxial growth of the material thereof:

[0046] (1) The design wavelength of the grown large-strain QCL material is 3.8 μm, and the superlattice material composition in the QCL active region is In 0.76 Ga 0.24 As and In 0.26 Al 0.74 As, and the material structure of one period is as shown in Figure 3 the left drawing, and the corresponding energy band structure is as shown in Figure 3 the right drawing. The energy difference between the electron transition energy levels is ~ 320 meV, and the corresponding wavelength is ~ 3.8 microns;

[0047] (2) The full structure of the grown material is as shown in Figure 1 , which requires the growth of N-type doped InP, different component InGaAs and InAlAs materials, respectively. The material growth is completed by a low-pressure (100 mbar) Aixtron CCS 3x2” MOCVD growth chamber equipped with a close-coupled showerhead. Trimethyl gallium 1 (TMGa1), trimethyl gallium 2 (TMGa1), trimethyl indium 1 (TMIn1), trimethyl indium 2 (TMIn2) and trimethyl aluminum (TMAl) are used as group III sources, arsine (AsH3) and phosphine (PH3) are used as group V sources, silane (SiH4) is used as a doping source for doping, and high-purity hydrogen is used as a carrier gas;

[0048] (3) N-type InP substrate is deoxidized at 680°C, and then N-type doped InP lower waveguide layer is grown at 600°C. TMInl and PH3 are used to grow the waveguide layer. The flow rate of TMInl is 200 sccm, the flow rates of SiH4 source, dilute and inject are 15 sccm, 185 sccm and 15 sccm respectively, the flow rate of PH3 is 400 sccm, the V / III ratio is 1500, the growth rate is 0.5 nm / s, and the doping concentration is 3x10 16 cm -3 . The growth thickness is 3.5 μm, and the growth time is determined according to the growth rate and the thickness;

[0049] (4) After the growth of the InP lower waveguide is completed, the flow rates of TMInl, TMIn2, TMGa1, TMGa2 and TMAll are adjusted to be 10 sccm, 28 sccm, 0.35 sccm (source 10 / dilute 590 / inject 21), 0.552 sccm (source 10 / dilute 590 / inject 33.12) and 7.15 sccm respectively, which correspond to In 0.43 Ga 0.57 As (TMInl, TMGa2 combined growth of inserted strain layer), In 0.53 Ga 0.47 As (TMInl, TMGa1 combined growth of inserted matching layer), In 0.76 Ga 0.24 As (TMIn2, TMGa1 combined growth of active region quantum well layer) and In 0.26 Al 0.74 As (TMInl, TMAl1 combined growth of active region barrier layer), the flow rate of AsH3 is 150 sccm, the V / III ratio is ~ 900, and the substrate temperature is adjusted to 520°C, ready for growth of the active region;

[0050] (5) After the flow rate and the substrate temperature are stabilized, TMIn2 and TMGa1 are combined to grow In 0.76 Ga 0.24 As quantum well layer of the active region, the growth rate is TMInl and TMAl1 are combined to grow In 0.26 Al 0.74 As barrier layer of the active region, the growth rate is The growth time is determined according to the growth rate and the thickness, and a program is written to grow 10 periods Figure 1 of QCL material shown in the left picture;

[0051] (6) After the growth of the 10-period active region material is completed, TMInl and TMGa2 are combined to grow 2 nm In 0.43 Ga0.57 As strain insertion layer, 8nm In 0.53 Ga 0.47 As matching insertion layer, In 0.43 Ga 0.57 As growth rate In 0.53 Ga 0.47 As growth rate According to the growth rate and thickness, the growth time is determined, and the program is written to complete the growth;

[0052] (7) Repeat (5) and (6) twice, and then repeat (5) once, complete a total of 3 layers of insertion layer and 40 cycles of QCL material growth;

[0053] (8) Adjust the substrate temperature to 600℃, and after the temperature is stable, grow the waveguide layer using TMIn1 and PH3, TMIn1 flow rate 200sccm, SiH4 source, dilute and inject flow rate 15sccm, 185sccm and 15sccm respectively, PH3 flow rate 400sccm, V / III ratio 1500, growth rate 0.5nm / s, doping concentration 3x10 16 cm -3 , growth thickness 4.0μm, according to the growth rate and thickness, the growth time is determined, and the program is written to complete the growth of the whole material structure.

[0054] In this embodiment, a low-strained InGaAs layer and a matching InGaAs layer are inserted every 10 growth cycles, the thin strained layer is used to block surface defects, the matching InGaAs s layer is used to improve the material surface flatness, thereby avoiding the accumulation of defects in the growth process of large-strained material, and finally obtaining high-quality epitaxial material and improving the device performance.

[0055] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present disclosure, and it should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A large strain infrared quantum cascade laser, characterized in that, From bottom to top, it comprises: InP lower waveguide layer, quantum well cascade layer, InP upper waveguide layer; wherein the quantum well cascade layer is a multi-period cascade, each period comprising: 8-12 periods of quantum cascade laser structure, which is a strained-compensated InGaAs / InAlAs superlattice material; low-strained InGaAs layer; matching InGaAs layer; The low-strain InGaAs layer and the matching InGaAs layer are doped, and the doping concentration is 2-5×10 17 cm -3 -3. The InGaAs / InAlAs superlattice material is strain-compensated, with a composition of In X Ga (1-X） As / In Y Al (1-Y） As, where X > 0.7 and Y < 0.

3. The low-strained InGaAs layer has a composition of In Z Ga (1-Z） As, where 0.4 < Z < 0.

45. The composition of the matching InGaAs layer is In 0.53 Ga 0.47 As; the thickness of the matching InGaAs layer is 5-10 nm; the excitation wavelength of the quantum well cascade layer is 3-4 μm.

2. The large strain infrared quantum cascade laser of claim 1, wherein, the thickness of the low-strained InGaAs layer is 1-3 nm.

3. A method of fabricating a large-strain infrared quantum cascade laser according to any one of claims 1-2, wherein, The material preparation is carried out in the following steps by using MOCVD method, comprising: S1, growing InP lower waveguide layer by using trimethylindium and PH3; S2, growing 8-12 periods of quantum well layer / potential barrier layer by using trimethylindium and trimethylgallium, which is a InGaAs / InAlAs superlattice material; S3, growing low-strained InGaAs layer and matching InGaAs layer by using trimethylindium and trimethylgallium; S4, repeating the operations of S2-S3 and then performing the operation of S2 again; S5, growing InP upper waveguide layer by using trimethylindium and PH3.

4. The method of claim 3, wherein the method further comprises: The quantum well layer / potential barrier layer in S2 is grown at a slow speed, and the growth speed is 0.8-1.5 Å per second.

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