A method for improving the epitaxial growth quality of a tunnel junction cascaded semiconductor laser

Abstract

The application relates to a method for improving the epitaxial growth quality of a tunnel junction cascade semiconductor laser, and innovatively proposes a strain superlattice gradient repair technology. A periodic superlattice buffer layer is introduced at a tunnel junction interface through a composite growth mode of "low-temperature low-speed nucleation-high-temperature high-speed epitaxy". In the low-temperature stage, lattice strain relaxation is realized at a speed of 0.5-2 A / s, and in the high-temperature stage, defect coverage is completed at a speed of 4-8 A / s. Through thermal dynamics regulation, dislocation lines are bent and terminated at the superlattice interface. Compared with the traditional process, the scheme can significantly improve the crystal quality, and meanwhile, does not increase the specific contact resistance of the tunnel junction interface.

Description

Technical Field

[0001] This invention relates to a method for improving the epitaxial growth quality of tunnel-connected cascaded semiconductor lasers, belonging to the field of optoelectronic technology. Background Technology

[0002] High-power semiconductor lasers, as core strategic components of third-generation semiconductor technology, have performance breakthroughs that directly impact the self-sufficiency and controllability of key fields such as high-precision machining, lidar, and advanced defense equipment. Since van der Ziel and Tsang achieved the first GaAs-based tunnel cascade laser prototype at Bell Labs, this technology has continuously led the development of high-power semiconductor lasers due to its unique current multiplexing characteristics. In 2007, Müller's team achieved a quasi-continuous wave peak power output of 615 W in a 940 nm triple-junction device through bulk series resistance optimization, verifying for the first time the engineering feasibility of cascade structures in terms of drive current compression. Currently, foreign manufacturers have achieved industrialization breakthroughs, with representative companies including LaserDiode Incorporated (USA), Laser Components (Germany), and Osram.

[0003] The core technical bottleneck lies in the exponential decay of epitaxial crystal quality as the number of tunnel junctions increases. The physical mechanism is that traditional tunnel junctions require low-temperature MOCVD growth to achieve heavy n++ / p++ doping (doping concentration > 1×10⁻⁶). 19 cm -3 Under this process window, a three-dimensional island growth mode is easily induced, resulting in through-type dislocation defects on the (001) crystal plane. Experiments show that for each additional pair of tunnel junction structures, the full width at half maximum (FWHM) of the epitaxial wafer X-ray bicrystalline diffraction (XRD) will deteriorate by 20-30 arcsec, that is, the epitaxial growth quality is significantly reduced, which in turn leads to a decrease in the performance of the prepared laser. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for improving the epitaxial growth quality of tunnel-connected cascaded semiconductor lasers.

[0005] Specifically, addressing the challenge of exponential degradation of epitaxial crystal quality in tunnel-cascaded semiconductor lasers due to the increasing number of tunnel junctions, this invention innovatively proposes a strain superlattice gradient repair technique. Through a composite growth mode of "low-temperature, low-speed nucleation - high-temperature, high-speed epitaxy," multiple periodic superlattice buffer layers are introduced at the tunnel junction interface. Specifically, lattice strain relaxation is achieved at a rate of 1 Å / s in the low-temperature stage, and defect coverage is completed at a rate of 5 Å / s in the high-temperature stage. Thermodynamic control causes dislocation lines to bend and terminate at the superlattice interface. This significantly improves crystal quality and the output characteristics of the tunnel-cascaded semiconductor laser, without increasing the specific contact resistance of the tunnel junction interface.

[0006] The technical solution of the present invention is as follows: In one aspect, a method for improving the epitaxial growth quality of a tunnel-connected cascaded semiconductor laser includes the following steps: A strained superlattice layer is introduced between the tunnel junction layer and the N-confined layer in a tunnel junction cascaded semiconductor laser structure. The strained superlattice layer is obtained by a composite growth mode of low-temperature, low-speed nucleation growth followed by high-temperature, high-speed epitaxial growth. The low-temperature, low-speed nucleation growth rate is 0.5-2 Å / s, and the high-temperature, high-speed epitaxial growth rate is 4-8 Å / s.

[0007] According to a preferred embodiment of the present invention, the strained superlattice layer is an N-type strained superlattice layer GaAsP / GaAs.

[0008] According to a preferred embodiment of the present invention, the N-strained superlattice layer GaAsP / GaAs comprises L tensile-strained GaAsP superlattices with a thickness of a nm and unstrained GaAs superlattices with a thickness of b nm, wherein the N-type doping is 1E19~5E19, and wherein 0.02%≤tensile strain coefficient≤0.1%, 1≤L≤30, 2≤a, b≤10.

[0009] According to a preferred embodiment of the present invention, the total thickness of the N-strained superlattice layer GaAsP / GaAs is 10~200 nm.

[0010] In this invention, the values ​​of L, a, and b are the sum of strained superlattice layers obtained by low-temperature, low-speed nucleation growth and high-temperature, high-speed epitaxial growth, or the values ​​of individual strained superlattice layers obtained by low-temperature, low-speed nucleation growth and high-temperature, high-speed epitaxial growth, without any particular limitation.

[0011] According to a further preferred embodiment of the present invention, the N-strained superlattice layer GaAsP / GaAs comprises 10 tensile-strained GaAsP superlattices with a thickness of 4 nm and unstrained GaAs superlattices with a thickness of 6 nm, with a total thickness of 100 nm, an N-type doping concentration of 3E19, and a tensile strain coefficient of 0.05%.

[0012] According to a preferred embodiment of the present invention, the tunnel junction cascaded semiconductor laser structure comprises, from bottom to top: a substrate, a buffer layer, an N-confinement layer, an N-waveguide layer, an active layer, a P-waveguide layer, a P-confinement layer, a tunnel junction layer, a strained superlattice layer, an N-confinement layer, an N-waveguide layer, an active layer, a P-waveguide layer, a P-confinement layer, and an ohmic contact layer.

[0013] According to a preferred embodiment of the present invention, the substrate is GaAs, the buffer layer is N-type GaAs, and the N-confinement layer is Al. 0.55 Ga 0.45 As, the N-waveguide layer is Al 0.35 Ga 0.65 As, the active layer is GaAlInAs, and the P-waveguide layer is Al. 0.35 Ga 0.65 As, P is a confinement layer of Al 0.55 Ga 0.45 As, the tunneling layer is GaAs, and the N-confining layer is Al. 0.55 Ga 0.45 As, the N-waveguide layer is Al 0.35 Ga 0.65 As, the active layer is GaAlInAs, and the P-waveguide layer is Al. 0.35 Ga 0.65 As, P is a confinement layer of Al. 0.55 Ga 0.45 As, the ohmic contact layer is GaAs.

[0014] According to a preferred embodiment of the present invention, the thickness of the N-type buffer layer is 100~500 nm, the doping source is a Si₂H₆ source, and the doping concentration is 0.5*10⁻⁶. 18 cm -3 -1*10 18 cm -3 ; More preferably, the N-type buffer layer has a thickness of 320 nm and a doping concentration of 1*10⁻⁶. 18 cm -3 ; According to a preferred embodiment of the present invention, the N-confining layer is Al. 0.55 Ga 0.45 The As thickness is 50~2000nm, the doping source is Si2H6, and the doping concentration is 0.5*10⁻⁶. 18 cm -3 -1*10 18 cm -3 ; More preferably, the N-confinement layer has a thickness of 1500 nm and a doping concentration of 1*10⁻⁶. 18 cm -3 ; According to a preferred embodiment of the present invention, the N-waveguide layer is Al. 0.35 Ga0.65 The thickness of As is 100~1000nm, the doping source is Si2H6 source, and there is no intentional doping; More preferably, the thickness of the N-waveguide layer is 600 nm; According to a preferred embodiment of the present invention, the active layer is GaAlInAs with a thickness of 3.5~15nm and is free of intentional doping; A further preferred embodiment has an active layer thickness of 6 nm; According to a preferred embodiment of the present invention, the thickness of the P-waveguide layer is 100~1000 nm, the doping source is a Si2H6 source, and there is no intentional doping; More preferably, the thickness of the P-waveguide layer is 500 nm; According to a preferred embodiment of the present invention, the thickness of the P-confining layer is 50~1000 nm, the doping source is a Si2H6 source, and the doping concentration is 1*10⁻⁶. 17 cm -3 -1*10 18 cm -3 ; More preferably, the P-confinement layer has a thickness of 500 nm and a doping concentration of 5*10⁻⁶. 17 cm -3 ; According to a preferred embodiment of the present invention, the tunnel junction is composed of heavily doped P-type GaAs and heavily doped N-type GaAs, both with a thickness of 10~20nm, wherein the doping concentration of P-type GaAs is 8E19~2E20 and the doping concentration of heavily doped N-type GaAs is 1E19~5E19. More preferably, the tunnel junction layer is composed of heavily doped P-type GaAs and heavily doped N-type GaAs, each with a thickness of 15 nm, wherein the P-type GaAs doping concentration is 1*10⁻⁶. 20 cm -3 The doping concentration of heavily doped N-type GaAs is 3*10⁻⁶. 19 cm -3 ; According to a preferred embodiment of the present invention, the thickness of the p-type ohmic contact layer GaAs is 1500~2500 nm, the doping source is a CP2Mg source, and the doping concentration is 0.5*10⁻⁶. 20 cm -3 -1*10 20 cm -3 .

[0015] More preferably, the GaAs thickness of the p-ohmic contact layer is 2100 nm, and the doping concentration is 1*10⁻⁶. 20 cm -3 .

[0016] In another aspect, a method for improving the epitaxial growth quality of tunnel-connected cascaded semiconductor lasers includes the following specific steps: (1) Place the substrate in the MOCVD reaction chamber, heat it to 840-850℃, introduce the AsH3 source, perform pretreatment for 4-10 minutes, then cool it to 680℃~710℃, introduce the TMGa and Si2H6 sources, and grow a buffer layer. (2) A TMAl source was introduced, and the ambient temperature was 700~750℃ to grow an N-confined layer; (3) Adjust the flow rates of TMAl and TMGa sources, turn off the Si2H6 source, and grow the N waveguide layer at an ambient temperature of 680~720℃. (4) Adjust the flow rates of TMAl and TMGa sources, introduce the TMIn source, and grow the active layer at an ambient temperature of 690~730℃. (5) Turn off the TMIn source, adjust the flow rates of the TMAl and TMGa sources, and maintain the ambient temperature at 680~720℃ to grow the P-waveguide layer; (6) Adjust the source flow rates of TMAl and TMGa, introduce the doped source Cp2Mg, and grow the P-confined layer at an ambient temperature of 700~750℃. (7) Turn off the TMA1 source flow rate, introduce the doping source CBr4, and grow the heavily doped P-type at an ambient temperature of 550~650℃; then turn off the doping source CBr4, introduce the doping source Te, and grow the heavily doped N-type. (8) Turn off the Te source flow and introduce the doped source Si2H6. The ambient temperature is 600℃~650℃ and the growth rate is 0.5-2Å / s. Low-temperature and low-speed nucleation growth of strained superlattice layers GaAsP / GaAs is carried out to obtain 5 tensile strained GaAsP layers with a thickness of 4 nm and a strain-free GaAs superlattice with a thickness of 6 nm. The total thickness is 50 nm. The N-type doping concentration is 3E19, and the tensile strain coefficient of GaAsP is 0.05%. Growth was then paused, and the temperature was raised to 700℃~730℃ at a growth rate of 4-8 Å / s to perform high-temperature, high-speed epitaxial growth of strained superlattice layers GaAsP / GaAs, resulting in five strained GaAsP layers with a thickness of 4 nm and an unstrained GaAs superlattice with a thickness of 6 nm, for a total thickness of 50 nm. The N-type doping concentration was 3E19, and the strain coefficient of GaAsP was 0.05%. (9) Repeat steps 2 to 6 above; (10) Turn off the TMA1 source flow and grow the P-ohm contact layer GaAs at an ambient temperature of 660~700℃.

[0017] According to a preferred embodiment of the present invention, in step (1), the reaction temperature in the reaction chamber is 690°C; According to a preferred embodiment of the present invention, in step (2), the ambient temperature is 740°C; According to a preferred embodiment of the present invention, in step (3), the ambient temperature is 710°C; According to a preferred embodiment of the present invention, in step (4), the ambient temperature is 690°C; According to a preferred embodiment of the present invention, in step (5), the ambient temperature is 710°C; According to a preferred embodiment of the present invention, in step (6), the ambient temperature is 740°C; According to a preferred embodiment of the present invention, in step (7), the ambient temperature is 570°C; According to a preferred embodiment of the present invention, in step (8), the low-temperature ambient temperature is 610°C and the high-temperature ambient temperature is 720°C; According to a preferred embodiment of the present invention, in step (10), the ambient temperature is 680°C.

[0018] The beneficial effects of this invention are as follows: To address the exponential degradation of epitaxial crystal quality in tunnel-cascaded semiconductor lasers due to the increasing number of tunnel junctions, this invention innovatively proposes a strain superlattice gradient repair technique. By designing a composite growth mode of "low-temperature, low-speed nucleation - high-temperature, high-speed epitaxy," multiple periodic superlattice buffer layers are introduced at the tunnel junction interface. The low-temperature stage achieves lattice strain relaxation at a rate of 0.5-2 Å / s, while the high-temperature stage completes defect coverage at a rate of 4-8 Å / s. Thermodynamic control causes dislocation lines to bend and terminate at the superlattice interface. This approach significantly improves crystal quality compared to traditional processes without increasing the contact resistance at the tunnel junction interface. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the tunnel junction cascaded semiconductor laser structure obtained in Example 1. In the figure: 1-GaAsP, 2-GaAs.

[0020] Figure 2 The diagram shows a comparison of the power and voltage output characteristics of the tunnel junction cascaded semiconductor lasers prepared by Example 1 and Comparative Example 1.

[0021] Figure 3 The graph shows a comparison of the electro-optical conversion efficiency of the tunnel junction cascaded semiconductor lasers prepared by Example 1 and Comparative Example 1. Detailed Implementation

[0022] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0023] Example 1: A method for improving the epitaxial growth quality of tunnel-connected cascaded semiconductor lasers, comprising the following specific steps: (1) Place the substrate in the MOCVD reaction chamber, heat it to about 845℃, introduce an AsH3 source, perform a pretreatment for about 5 minutes, then cool it down to 690℃, introduce TMGa and Si2H6 sources, and grow a 320nm thick N-type GaAs buffer layer with a doping concentration of 1*10. 18 cm -3 ; (2) A TMAl source was introduced, and the ambient temperature was 740℃ to grow a 1500nm thick N-confined Al layer. 0.55 Ga 0.45 As, doping concentration is 1*10 18 cm -3 ; (3) By changing the source flow rates of TMAl and TMGa, turning off the Si2H6 source, and setting the ambient temperature to 710℃, a 600nm thick N-waveguide layer Al was grown. 0.35 Ga 0.65 As; (4) Change the flow rates of TMA1 and TMAGa sources, introduce TMAIn source, and grow an active layer with an ambient temperature of 690℃. (5) Turn off the TMIn source, change the TMAl and TMGa source flow rates, and grow a 500nm thick P-waveguide layer Al at an ambient temperature of 710℃. 0.35 Ga 0.65 As; (6) By changing the source flow rates of TMAl and TMGa, a doped source Cp2Mg was introduced, and the ambient temperature was 740℃, resulting in the growth of a 500nm thick P-confined Al layer. 0.55 Ga 0.45 As, doping concentration is 5*10 17 cm -3 ; (7) Turn off the TMAl source flow and introduce the doping source CBr4. The ambient temperature is 570℃. A 15nm thick heavily doped p-type GaAs with a doping concentration of 1*10⁻⁶ is obtained. 20 cm -3 Subsequently, the doping source CBr4 was turned off, and the doping source Te was introduced to grow a 15 nm thick heavily doped N-type GaAs with a doping concentration of 3*10⁻⁶. 19 cm -3 ; (8) Turn off the Te source flow and introduce the doped source Si2H6. The ambient temperature is 600℃. Grow a strained superlattice layer GaAsP / GaAs, which consists of 5 tensile strained GaAsP layers with a thickness of 4 nm and a strain-free GaAs superlattice with a thickness of 6 nm, for a total thickness of 50 nm. The N-type doping concentration is 3E19, and the tensile strain coefficient of GaAsP is 0.05%. Then pause the growth and raise the temperature to 700℃ to grow a strained superlattice layer GaAsP / GaAs, which consists of 5 tensile strained GaAsP layers with a thickness of 4 nm and a strain-free GaAs superlattice with a thickness of 6 nm, for a total thickness of 50 nm. The N-type doping concentration is 3E19, and the tensile strain coefficient of GaAsP is 0.05%. (9) Repeat steps 2 to 6 above; (10) With the TMAl source flow turned off and the ambient temperature at 680℃, a 2100nm thick P-ohm contact layer GaAs with a doping concentration of 1*10 20 cm -3 .

[0024] The fabricated tunnel junction cascaded semiconductor laser structure, such as Figure 1 As shown, from bottom to top, it includes: substrate, buffer layer, N-confinement layer, N-waveguide layer, active layer, P-waveguide layer, P-confinement layer, tunnel junction layer, strained superlattice layer, N-confinement layer, N-waveguide layer, active layer, P-waveguide layer, P-confinement layer, and ohmic contact layer.

[0025] Comparative Example 1 The fabrication method of the tunnel-junction cascaded semiconductor laser structure without introducing a strained superlattice layer is as follows: (1) Place the substrate in the MOCVD reaction chamber, heat it to about 845℃, introduce an AsH3 source, perform a pretreatment for about 5 minutes, then cool it down to 690℃, introduce TMGa and Si2H6 sources, and grow a 320nm thick N-type GaAs buffer layer with a doping concentration of 1*10. 18 cm -3 ; (2) A TMAl source was introduced, and the ambient temperature was 740℃ to grow a 1500nm thick N-confined Al layer. 0.55 Ga 0.45 As, doping concentration is 1*10 18 cm -3 ; (3) By changing the source flow rates of TMAl and TMGa, turning off the Si2H6 source, and setting the ambient temperature to 710℃, a 600nm thick N-waveguide layer Al was grown. 0.35 Ga 0.65 As; (4) Change the flow rates of TMA1 and TMAGa sources, introduce TMAIn source, and grow an active layer with an ambient temperature of 690℃. (5) Turn off the TMIn source, change the TMAl and TMGa source flow rates, and grow a 500nm thick P-waveguide layer Al at an ambient temperature of 710℃. 0.35 Ga 0.65 As; (6) By changing the source flow rates of TMAl and TMGa, a doped source Cp2Mg was introduced, and the ambient temperature was 740℃, resulting in the growth of a 500nm thick P-confined Al layer. 0.55 Ga 0.45 As, doping concentration is 5*10 17 cm -3 ; (7) Turn off the TMAl source flow and introduce the doping source CBr4. The ambient temperature is 570℃. A 15nm thick heavily doped p-type GaAs with a doping concentration of 1*10⁻⁶ is obtained. 20 cm -3 Subsequently, the doping source CBr4 was turned off, and the doping source Te was introduced to grow a 15 nm thick heavily doped N-type GaAs with a doping concentration of 3*10⁻⁶. 19 cm -3 ; (8) Turn off the Te source flow rate, introduce the TMAl source and the doped source Si2H6, and grow a 1500nm thick N-confined Al layer at an ambient temperature of 740℃. 0.55 Ga 0.45 As, doping concentration is 1*10 18 cm -3 ; (9) Repeat steps 3 to 6 above; (10) With the TMAl source flow turned off and the ambient temperature at 680℃, a 2100nm thick P-ohm contact layer GaAs with a doping concentration of 1*10 20 cm -3 .

[0026] Experimental example: 1. The tunnel cascaded semiconductor laser epitaxial wafers prepared in Example 1 and Comparative Example 1 were fabricated and tested using the same process. The test results are as follows: Figure 2 As shown, the performance differences are significant. Compared with Comparative Example 1, Example 1 has higher output power and slope efficiency, while the voltage remains essentially unchanged. This indicates that the strained superlattice gradient repair technology can significantly improve crystal quality, reduce non-radiative recombination efficiency, and does not increase the specific contact resistance of the tunnel junction interface. The chip current-voltage curves show that after the turn-on voltage, the chip's internal differential resistance (the slope of voltage and current) is basically the same, proving that no additional resistance is introduced, i.e., the additional superlattice does not increase the chip's specific contact resistance.

[0027] 2. The tunnel cascaded semiconductor laser epitaxial wafers prepared in Example 1 and Comparative Example 1 were fabricated using the same process, and their electro-optical conversion efficiency was tested. The test results are shown in [Figure 1]. Figure 3 As can be seen, the electro-optical conversion efficiency of Example 1 is significantly higher than that of Comparative Example 1. This is because Example 1 introduces a strained superlattice layer, which significantly improves the crystal quality and results in better chip performance.

[0028] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving the epitaxial growth quality of a tunnel-connected cascaded semiconductor laser, comprising the following steps: A strained superlattice layer is introduced between the tunnel junction layer and the N-confinement layer in a tunnel junction cascaded semiconductor laser structure. The strained superlattice layer is obtained by a composite growth mode of low-temperature, low-speed nucleation growth followed by high-temperature, high-speed epitaxial growth. The low-temperature, low-speed nucleation growth rate is 0.5-2 Å / s, and the high-temperature, high-speed epitaxial growth rate is 4-8 Å / s. The strained superlattice layer is an N-type strained superlattice layer GaAsP / GaAs. The N-type strained superlattice layer GaAsP / GaAs contains L tensile strained GaAsP superlattices with a thickness of a nm and unstrained GaAs superlattices with a thickness of b nm. The N-type doping is 1E19~5E19, where 0.02%≤tensile strain coefficient≤0.1%, 1≤L≤30, 2≤a, b≤10. The total thickness of the N-type strained superlattice layer GaAsP / GaAs is 10~200 nm. The tunnel-junction cascaded semiconductor laser structure, from bottom to top, includes: Substrate, buffer layer, N-confinement layer, N-waveguide layer, active layer, P-waveguide layer, P-confinement layer, tunnel junction layer, strained superlattice layer, N-confinement layer, N-waveguide layer, active layer, P-waveguide layer, P-confinement layer, ohmic contact layer; The substrate is GaAs, the buffer layer is N-type GaAs, and the N-confinement layer is Al. 0.55 Ga 0.45 As, the N-waveguide layer is Al. 0.35 Ga 0.65 As, the active layer is GaAlInAs, and the P-waveguide layer is Al. 0.35 Ga 0.65 As, P is a confinement layer of Al 0.55 Ga 0.45 As, the tunneling layer is GaAs, and the N-confining layer is Al. 0.55 Ga 0.45 As, the N-waveguide layer is Al. 0.35 Ga 0.65 As, the active layer is GaAlInAs, and the P-waveguide layer is Al. 0.35 Ga 0.65 As, P is a confinement layer of Al 0.55 Ga 0.45 As, the ohmic contact layer is GaAs.

2. The method according to claim 1, characterized in that, The N-type buffer layer has a thickness of 100~500nm, and the doping source is Si2H6 with a doping concentration of 0.5*10. 18 cm -3 -1*10 18 cm -3 ; The N-confining layer is Al. 0.55 Ga 0.45 The As thickness is 50~2000nm, the doping source is Si2H6, and the doping concentration is 0.5*10. 18 cm -3 -1*10 18 cm -3 ; The N-waveguide layer is Al 0.35 Ga 0.65 The thickness of As is 100~1000nm, the doping source is Si2H6 source, and there is no intentional doping; The active layer is GaAlInAs with a thickness of 3.5~15nm and is not intentionally doped.

3. The method according to claim 1, characterized in that, The P-waveguide layer has a thickness of 100~1000nm, and the doping source is Si2H6 source, with no intentional doping. The P-confinement layer has a thickness of 50~1000 nm, the doping source is Si2H6, and the doping concentration is 1*10. 17 cm -3 -1*10 18 cm -3 ; The tunnel junction is composed of heavily doped P-type GaAs and heavily doped N-type GaAs, both with a thickness of 10~20nm. The doping concentration of P-type GaAs is 8E19~2E20, and the doping concentration of heavily doped N-type GaAs is 1E19~5E19. The thickness of the p-type ohmic contact layer in GaAs is 1500~2500 nm, the doping source is a CP2Mg source, and the doping concentration is 0.5 × 10⁻⁶. 20 cm -3 -1*10 20 cm -3 .

4. A method for improving the epitaxial growth quality of tunnel-connected cascaded semiconductor lasers, comprising the following specific steps: (1) Place the substrate in the MOCVD reaction chamber, heat it to 840-850℃, introduce the AsH3 source, perform pretreatment for 4-10 minutes, then cool it to 680℃~710℃, introduce the TMGa and Si2H6 sources, and grow a buffer layer. (2) A TMAl source was introduced, and the ambient temperature was 700~750℃ to grow an N-confined layer; (3) Adjust the flow rates of TMAl and TMGa sources, turn off the Si2H6 source, and grow the N waveguide layer at an ambient temperature of 680~720℃. (4) Adjust the flow rates of TMAl and TMGa sources, introduce the TMIn source, and grow the active layer at an ambient temperature of 690~730℃. (5) Turn off the TMIn source, adjust the flow rates of the TMAl and TMGa sources, and maintain the ambient temperature at 680~720℃ to grow the P-waveguide layer; (6) Adjust the source flow rates of TMAl and TMGa, introduce the doped source Cp2Mg, and grow the P-confined layer at an ambient temperature of 700~750℃. (7) Turn off the TMA1 source flow rate, introduce the doping source CBr4, and grow the heavily doped P-type at an ambient temperature of 550~650℃; then turn off the doping source CBr4, introduce the doping source Te, and grow the heavily doped N-type. (8) Turn off the Te source flow and introduce the doped source Si2H6. The ambient temperature is 600℃~650℃ and the growth rate is 0.5-2 Å / s. Low-temperature and low-speed nucleation growth of strained superlattice layers GaAsP / GaAs is carried out to obtain 5 strained GaAsP layers with a thickness of 4 nm and a strain-free GaAs superlattice with a thickness of 6 nm. The total thickness is 50 nm. The N-type doping concentration is 3E19, and the tensile strain coefficient of GaAsP is 0.05%. Growth was then paused, and the temperature was raised to 700℃~730℃ at a growth rate of 4-8 Å / s to perform high-temperature, high-speed epitaxial growth of strained superlattice layers GaAsP / GaAs, resulting in five strained GaAsP layers with a thickness of 4 nm and an unstrained GaAs superlattice with a thickness of 6 nm, for a total thickness of 50 nm. The N-type doping concentration was 3E19, and the strain coefficient of GaAsP was 0.05%. (9) Repeat steps 2 to 6 above; (10) Turn off the TMA1 source flow and grow the P-ohm contact layer GaAs at an ambient temperature of 660~700℃.

5. The method according to claim 4, characterized in that, In step (1), the reaction temperature in the reaction chamber is 690℃; in step (2), the temperature in the ambient chamber is 740℃; and in step (3), the ambient temperature is 710℃.

6. The method according to claim 4, characterized in that, In step (4), the ambient temperature is 690℃; in step (5), the ambient temperature is 710℃; and the ambient temperature is 740℃.

7. The method according to claim 4, characterized in that, In step (7), the ambient temperature is 570℃; in step (8), the low temperature ambient temperature is 610℃ and the high temperature ambient temperature is 720℃; in step (10), the ambient temperature is 680℃.

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