Quantum well, multi-quantum well epitaxial structure and preparation method thereof

Abstract

The invention provides a quantum well, a multi-quantum well epitaxial structure and a preparation method thereof, and belongs to the field of semiconductor lasers. The invention provides a quantum well which is of a multi-layer structure and comprises alternate quantum barrier layers and quantum well layers. The array substrate further comprises a gradient buffer layer. The adjacent quantum barrier layer and quantum well layer are combined through a gradient buffer layer; the bottom layer and the top layer in the multi-layer structure are quantum barrier layers; in a unit formed by the connected quantum barrier layer, gradual change buffer layer and quantum well layer, with the quantum barrier layer as the beginning and the adjacent quantum well layer as the end, the size of the gradual change buffer layer in the horizontal direction is gradually reduced, the emission wavelength of the gradual change buffer layer is gradually increased in the direction from beginning to end, and the emission wavelength of the gradual change buffer layer is gradually increased. The initial emission wavelength of the gradient buffer layer is consistent with the emission wavelength of the quantum barrier, and the final emission wavelength of the gradient buffer layer is smaller than the emission wavelength of the quantum well. The quantum well has a high carrier migration rate, a high refractive index and a high optical confinement factor.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor lasers, and particularly to a quantum well, a multi - quantum well epitaxial structure and a preparation method thereof. Background Art

[0002] Semiconductor lasers are the core light sources in optical communication systems and are widely used in fields such as optical fiber communication, dense wavelength division multiplexing (DWDM), and 5G communication: in optical fiber communication, by converting electrical signals into optical signals (typical wavelengths 1310 / 1550 nm), they achieve high - speed (above 100 Gbps), low - loss long - distance transmission, supporting backbone network and fiber - to - the - home (FTTH) deployment; DWDM utilizes the narrow linewidth (<0.1 nm) and wavelength stability of semiconductor lasers to increase the capacity of a single optical fiber to dozens of Tbps, meeting the requirements of cloud computing and big data; in 5G communication, the optoelectronic conversion of high - frequency millimeter - wave signals relies on the integration of lasers and modulators to reduce the transmission delay between base stations. Among them, distributed feedback (DFB) lasers have become the first choice for long - distance transmission due to their single - longitudinal - mode characteristics.

[0003] In a multi - quantum well (MQW) epitaxial structure of a DFB (distributed feedback) laser, the multi - quantum well layer is usually composed of alternately grown nanoscale thin - layer materials, such as InGaAsP quantum well layers (thickness <10 nm) and InP barrier layers. This design localizes carriers (electrons and holes) in the well layer through the quantum confinement effect, enhancing the radiative recombination efficiency, and at the same time integrating a Bragg grating to achieve single - longitudinal - mode output. However, when pursuing high - power output, the problem of uneven carrier distribution in the multi - quantum well structure is prominent. Due to the difference in carrier migration rates between the quantum well and the barrier layer, the carrier filling efficiency of the middle quantum well is often lower than that of the edge well layers, resulting in the carrier spatial hole - burning effect and exacerbating mode instability.

[0004] Existing technologies have partially alleviated the problem through strain - compensated quantum wells or asymmetric waveguide designs, but there is still room for further optimization in maintaining carrier transport efficiency and optical confinement. Summary of the Invention

[0005] The present invention provides a quantum well, a multi - quantum well epitaxial structure and a preparation method thereof. While optimizing the carrier migration rate, the quantum well of the present invention maintains a high refractive index of the quantum well, improving the optical confinement factor.

[0006] The present invention provides a quantum well, which is a multi - layer structure including alternating quantum barrier layers and quantum well layers;

[0007] It further includes: a graded buffer layer;

[0008] Adjacent quantum barrier layers and quantum well layers are combined through the graded buffer layer;

[0009] Both the bottom layer and the top layer in the multi-layer structure are quantum barrier layers;

[0010] In a unit composed of an adjacent quantum barrier layer, a graded buffer layer, and a quantum well layer: starting from the quantum barrier layer and ending with an adjacent quantum well layer, in the direction from the start to the end, the horizontal dimension of the graded buffer layer gradually decreases, the emission wavelength of the graded buffer layer gradually increases, the initial emission wavelength of the graded buffer layer is consistent with the emission wavelength of the quantum barrier layer, and the final emission wavelength of the graded buffer layer is less than the emission wavelength of the quantum well layer.

[0011] Preferably, in one such unit: the thickness of the quantum barrier layer and the quantum well layer is 6 ± 0.18 nm; the maximum thickness of the graded buffer layer is 2 ± 0.06 nm;

[0012] The horizontal dimension of the quantum well layer is less than the horizontal dimension of the quantum barrier layer;

[0013] In the quantum well layer and the graded buffer layer in contact: the horizontal dimension of the surface of the graded buffer layer in contact with the quantum well layer is greater than the horizontal dimension of the quantum well layer.

[0014] Preferably, the final emission wavelength of the graded buffer layer is 1050 ± 10 nm;

[0015] The emission wavelength of the quantum well layer is 1330 ± 10 nm, and the emission wavelength of the quantum barrier layer is 1000 ± 10 nm.

[0016] Preferably, the number of layers of the quantum well layer is 3 to 10 layers.

[0017] The present invention also provides a multi-quantum well epitaxial structure, including the quantum well described in the above technical solution.

[0018] Preferably, it includes a substrate 1, an N-InP buffer layer 2, an N-AlInAs confinement layer 3, an undoped AlGaInAs lower waveguide layer 4, a quantum well 5, an undoped AlGaInAs upper waveguide layer 6, a P-AlInAs confinement layer 7, a P-InP graded buffer layer 8, a P-InGaAsP etch stop layer 9, a P-InP cladding layer 10, a P-InGaAsP grating layer 11, a P-InP connection layer 12, a first P-InGaAsP barrier graded buffer layer 13, a second P-InGaAsP barrier graded buffer layer 14, and a P-InGaAs ohmic contact layer 15 stacked in sequence;

[0019] The quantum well 5 includes the quantum well described in the above technical solution;

[0020] The composition of the quantum well layer in the quantum well 5 is: In0.701Ga0.110Al0.189As, and the composition of the quantum barrier layer is: In0.530Ga0.280Al0.190As; in the direction from beginning to end, the composition in the graded buffer layer gradually changes from In0.530Ga0.280Al0.190As to In0.310Ga0.280Al0.160As.

[0021] Preferably, the emission wavelength of the P-InGaAsP corrosion blocking layer 9 is 1100 ± 10 nm;

[0022] The emission wavelength of the P-InGaAsP grating layer 11 is 1150 nm ± 10 nm, the grating period is 196.2 ± 1 nm, and the depth is 40 ± 1.2 nm. The emission wavelength of the P-InP graded buffer layer 8 is 600 ± 18 nm;

[0023] The emission wavelength of the first P-InGaAsP barrier graded buffer layer 13 is 1300 ± 10 nm;

[0024] The emission wavelength of the second P-InGaAsP barrier graded buffer layer 14 is 1500 ± 10 nm.

[0025] The present invention also provides a preparation method for the multi-quantum well epitaxial structure described in the above technical solution, including the following steps:

[0026] Deposit an N-InP buffer layer 2, an N-AlInAs confinement layer 3, an undoped AlGaInAs lower waveguide layer 4, a quantum well 5, an undoped AlGaInAs upper waveguide layer 6, a P-AlInAs confinement layer 7, a P-InP graded buffer layer 8, a P-InGaAsP corrosion blocking layer 9, a P-InP cladding layer 10, and a P-InGaAsP grating fabrication layer on the substrate 1 in sequence;

[0027] Perform photolithography on the P-InGaAsP grating fabrication layer to obtain a P-InGaAsP grating layer 11;

[0028] Deposit a P-InP connection layer 12, a first P-InGaAsP barrier graded buffer layer 13, a second P-InGaAsP barrier graded buffer layer 14, and a P-InGaAs ohmic contact layer 15 on the P-InGaAsP grating layer 11 in sequence to obtain the multi-quantum well epitaxial structure.

[0029] Preferably, the temperature during the deposition of the quantum well layer in the quantum well 5 is 600 - 650 °C,

[0030] The temperature during the deposition of the quantum barrier layer in the quantum well 5 is 650 - 680 °C.

[0031] The present invention also provides a DFB laser, including the multi - quantum well epitaxial structure described in the above - mentioned technical solution or the multi - quantum well epitaxial structure prepared by the preparation method described in claim 8 or 9.

[0032] Starting from the quantum barrier layer and ending with the adjacent quantum well layer, in the direction from the start to the end, the size of the graded buffer layer in the horizontal direction gradually decreases, and the emission wavelength of the graded buffer layer gradually increases, forming a "boost - glide" energy - band path similar to ballistic flight. When carriers pass through the quantum barrier layer, they are accelerated, and after entering the quantum well layer, they complete recombination using inertia, reducing the tunneling resistance and helping the carriers to cross the quantum well layer smoothly. Moreover, the connection between the quantum barrier layer and the quantum well layer is no longer a vertical connection structure, but is connected through a graded buffer layer with a certain gradient slope (that is: in the direction from the quantum barrier layer to the adjacent quantum well layer, the size of the graded buffer layer in the horizontal direction gradually decreases), enabling the carriers to cross the quantum well region in a more stable manner, improving the carrier mobility to a certain extent, and improving the uneven distribution of carriers in the active region. And a uniform carrier distribution can enhance the optical confinement factor, enhance the overall radiative recombination efficiency, and avoid the leakage of hot carriers caused by local thermal effects, thereby reducing the threshold current; combined with the alternating design of the quantum barrier layer and the quantum well layer (the quantum well has tensile strain and the quantum barrier has compressive strain), it further suppresses the carrier overflow and enhances the radiative recombination probability.

[0033] Furthermore, a graded transition layer with a thickness of 2 nm is introduced at the quantum well / barrier interface. By the symmetric composition gradient of the adjacent two graded buffer layers (in the direction from the quantum barrier layer to the adjacent quantum well layer, the emission wavelength of the graded buffer layer gradually increases), the lattice mismatch stress and the inherent problem of uneven carrier distribution in the multi - quantum well structure are alleviated, the interface defect density is reduced, and the carrier injection uniformity and the luminescence efficiency are improved. Further, a temperature gradient regulation (600 - 650 °C for the quantum well and 650 - 680 °C for the quantum barrier) and the strategy of setting the graded buffer layer are adopted to match the thermal expansion coefficients, reduce defects such as interface dislocations, and improve the material crystallization quality and device reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a cross - sectional schematic diagram of the quantum well in the embodiment of the present invention;

[0035] Figure 2 It is a schematic diagram of the change in the emission wavelength of the graded buffer layer in the embodiment of the present invention;

[0036] Figure 3 It is a schematic diagram of the structure of the multi - quantum well epitaxial structure of the present invention;

[0037] Figure 4 It is a schematic diagram of the structure of the AlGaInAs quantum well in the embodiment of the present invention;

[0038] Figure 5 Schematic diagram of the epitaxial structure after forming a grating in the embodiment;

[0039] Figure 6 Schematic diagram of the multi - quantum well epitaxial structure in the embodiment;

[0040] Figure 7 Graph showing the relationship between the temperature, gas pulse injection mode and growth time in the MOCVD reaction chamber in the embodiment;

[0041] Figure 8 Stimulated emission recombination rate of a common DFB laser chip;

[0042] Figure 9 Stimulated emission recombination rate of the DFB laser chip in the embodiment;

[0043] Figure 10 Optical power - current curve of a common DFB laser chip;

[0044] Figure 11 Optical power - current curve of the DFB laser chip in the embodiment;

[0045] Figure 12 I - V curve of a common DFB laser chip;

[0046] Figure 13 I - V curve of the DFB laser chip in the embodiment;

[0047] Figure 14 Schematic diagram of the quantum well structure in a common DFB laser chip. Detailed implementation manners

[0048] The present invention provides a quantum well, which is a multi - layer structure including alternating quantum barrier layers and quantum well layers;

[0049] It further includes: a graded buffer layer;

[0050] Adjacent quantum barrier layers and quantum well layers are combined through the graded buffer layer;

[0051] Both the bottom layer and the top layer in the multi - layer structure are quantum barrier layers;

[0052] In a unit composed of an adjacent quantum barrier layer, graded buffer layer and quantum well layer: starting from the quantum barrier layer and ending with an adjacent quantum well layer, in the direction from the start to the end, the horizontal dimension of the graded buffer layer gradually decreases, the emission wavelength of the graded buffer layer gradually increases, the initial emission wavelength of the graded buffer layer is consistent with the emission wavelength of the quantum barrier layer, and the final emission wavelength of the graded buffer layer is less than the emission wavelength of the quantum well layer.

[0053] The quantum well provided by the present invention is a multi-layer structure, including alternating quantum barrier layers and quantum well layers, and both the bottom layer and the top layer of the quantum well are quantum barrier layers; the number of the quantum well layers is preferably 3 to 10 layers. In a specific embodiment of the present invention, the number of the quantum well layers can be 3 layers, 4 layers, 5 layers, 6 layers, 7 layers, 8 layers, 9 layers or 10 layers.

[0054] In the present invention, the emission wavelength of the quantum well layer is preferably 1330 ± 10 nm, and the emission wavelength of the quantum barrier layer is preferably 1000 ± 10 nm.

[0055] In the present invention, in one of the units: the thickness of the quantum barrier layer and the quantum well layer is preferably 6 ± 0.18 nm.

[0056] In the present invention, among adjacent quantum well layers and quantum barrier layers: the size of the quantum well layer in the horizontal direction is smaller than that of the quantum barrier layer in the horizontal direction. In the present invention, the horizontal direction refers to the direction parallel to the bottom layer of the quantum barrier layer.

[0057] The quantum well provided by the present invention includes a graded buffer layer, and adjacent quantum barrier layers and quantum well layers are combined through the graded buffer layer (that is: the graded buffer layer connects adjacent quantum barrier layers and quantum well layers).

[0058] In the present invention, in one of the units: starting from the quantum barrier layer and ending with the adjacent quantum well layer, in the direction from the start to the end, the size of the graded buffer layer in the horizontal direction gradually decreases; among the quantum well layer and the graded buffer layer in contact: the size of the surface of the graded buffer layer in contact with the quantum well layer in the horizontal direction is preferably larger than that of the quantum well layer in the horizontal direction; the size of the surface of the graded buffer layer in contact with the quantum barrier in the horizontal direction is preferably the same as that of the quantum barrier layer in the horizontal direction, and the maximum thickness of the graded buffer layer is preferably 2 ± 0.06 nm.

[0059] In the present invention, in one of the units: starting from the quantum barrier layer and ending with the adjacent quantum well layer, in the direction from the start to the end, the emission wavelength of the graded buffer layer gradually increases, the initial emission wavelength of the graded buffer layer is consistent with that of the quantum barrier, the final emission wavelength of the graded buffer layer is less than that of the quantum well, the initial emission wavelength of the graded buffer layer is preferably 1000 ± 10 nm, and the final emission wavelength of the graded buffer layer is preferably 1050 ± 10 nm.

[0060] The present invention also provides a multi-quantum well epitaxial structure, including the quantum well described in the above technical solution.

[0061] The multi-quantum well epitaxial structure provided by the present invention preferably includes a substrate 1; the substrate preferably includes InP, and the conductivity of the InP is preferably 0.16 to 0.64 S / m;

[0062] The multi-quantum well epitaxial structure provided by the present invention preferably includes an N-InP buffer layer 2 on the surface of a substrate 1;

[0063] The multi-quantum well epitaxial structure provided by the present invention preferably includes an N-AlInAs confinement layer 3 on the surface of the N-InP buffer layer 2;

[0064] The multi-quantum well epitaxial structure provided by the present invention preferably includes an undoped AlGaInAs lower waveguide layer 4 on the surface of the N-AlInAs confinement layer 3;

[0065] The multi-quantum well epitaxial structure provided by the present invention preferably includes a quantum well 5 on the surface of the undoped AlGaInAs lower waveguide layer 4; the quantum well (5) includes the quantum well described in the above technical solution; the composition of the quantum well layer in the quantum well (5) is: In 0.701 Ga 0.110 Al 0.189 As, and the composition of the quantum barrier layer is: In 0.530 Ga 0.280 Al 0.190 As; in the direction from beginning to end, the composition in the graded buffer layer gradually changes from In 0.530 Ga 0.280 Al 0.190 As to In 0.310 Ga 0.280 Al 0.160 As.

[0066] The multi-quantum well epitaxial structure provided by the present invention preferably includes an undoped AlGaInAs upper waveguide layer 6 on the surface of the quantum well 5;

[0067] The multi-quantum well epitaxial structure provided by the present invention preferably includes a P-AlInAs confinement layer 7 on the surface of the undoped AlGaInAs upper waveguide layer 6;

[0068] The multi-quantum well epitaxial structure provided by the present invention preferably includes a P-InP graded buffer layer 8 on the surface of the P-AlInAs confinement layer 7, and the emission wavelength of the P-InP graded buffer layer 8 is preferably 600 ± 18 nm;

[0069] The multi-quantum well epitaxial structure provided by the present invention preferably includes a P-InGaAsP corrosion barrier layer 9 on the surface of the P-InP graded buffer layer 8, and the emission wavelength of the P-InGaAsP corrosion barrier layer 9 is preferably 1100 ± 10 nm;

[0070] The multi-quantum well epitaxial structure provided by the present invention preferably includes a P-InP cladding layer 10 on the surface of the P-InGaAsP corrosion barrier layer 9;

[0071] The multi-quantum well epitaxial structure provided by the present invention preferably includes a P-InGaAsP grating layer 11 on the surface of the P-InP cladding layer 10. The emission wavelength of the P-InGaAsP grating layer 11 is preferably 1150 nm, the grating period is preferably 196.2 ± 1 nm, and the depth is preferably 40 ± 1.2 nm;

[0072] The multi-quantum well epitaxial structure provided by the present invention preferably includes a P-InP connection layer 12 on the surface of the P-InGaAsP grating layer 11; the P-InP connection layer 12 preferably includes a P-InP protection layer 12-1 and an InP secondary epitaxial layer 12-2;

[0073] The multi-quantum well epitaxial structure provided by the present invention preferably includes a first P-InGaAsP barrier graded layer 13 on the surface of the P-InP connection layer 12. The emission wavelength of the first InGaAsP barrier graded buffer layer is 1300 ± 10 nm;

[0074] The multi-quantum well epitaxial structure provided by the present invention preferably includes a second P-InGaAsP barrier graded buffer layer 14 on the surface of the first P-InGaAsP barrier graded layer 13. The emission wavelength of the second InGaAsP barrier graded buffer layer is 1500 ± 10 nm;

[0075] The multi-quantum well epitaxial structure provided by the present invention preferably includes a P-InGaAs ohmic contact layer 15 on the surface of the second P-InGaAsP barrier graded buffer layer 14.

[0076] The present invention also provides a preparation method for the multi-quantum well epitaxial structure described in the above technical solution, including the following steps:

[0077] Deposit an N-InP buffer layer 2, an N-AlInAs confinement layer 3, an undoped AlGaInAs lower waveguide layer 4, a quantum well 5, an undoped AlGaInAs upper waveguide layer 6, a P-AlInAs confinement layer 7, a P-InP graded buffer layer 8, a P-InGaAsP etch stop layer 9, a P-InP cladding layer 10, and a P-InGaAsP grating fabrication layer on the substrate 1 in sequence;

[0078] Perform photolithography on the P-InGaAsP grating fabrication layer to obtain a P-InGaAsP grating layer 11;

[0079] Deposit a P-InP connection layer 12, a first P-InGaAsP barrier graded buffer layer 13, a second P-InGaAsP barrier graded buffer layer 14, and a P-InGaAs ohmic contact layer 15 on the P-InGaAsP grating layer 11 in sequence to obtain the multi-quantum well epitaxial structure.

[0080] In the present invention, the temperature during the deposition of the quantum well layer in the quantum well 5 is preferably 600 - 650 °C;

[0081] The temperature during the deposition of the quantum barrier layer in the quantum well 5 is preferably 650 - 680 °C.

[0082] The present invention also provides a DFB laser, which is a multi - quantum well epitaxial structure described in the above technical solution or a multi - quantum well epitaxial structure prepared by the preparation method described in the above technical solution.

[0083] The following will describe in detail the quantum well, multi - quantum well epitaxial structure and their preparation methods provided by the present invention in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0084] Figure 3 The following is a schematic structural diagram of the multi - quantum well epitaxial structure of the present invention: 1 - substrate, 2 - N - InP buffer layer, 3 - N - AlInAs confinement layer, 4 - undoped AlGaInAs lower waveguide layer, 5 - quantum well, 6 - undoped AlGaInAs upper waveguide layer, 7 - P - AlInAs confinement layer, 8 - P - InP graded buffer layer, 9 - P - InGaAsP etch stop layer, 10 - P - InP cladding layer, 11 - P - InGaAsP grating layer, 12 - P - InP coupling layer, 13 - first P - InGaAsP barrier graded layer, 14 - second P - InGaAsP barrier graded buffer layer, 15 - P - InGaAs ohmic contact layer.

[0085] Example 1

[0086] Using InP with a conductivity of 0.4 S / m as the growth substrate, it is placed in the MOCVD system of Aixtron company for growth:

[0087] The reaction chamber pressure is 50 mbar, the growth temperature is 670 °C, using H2 as the carrier gas, trimethylindium (TMIn), trimethylgallium (TMGa), trimethylaluminum (TMAl), diethylzinc (DeZn), silane (SiH4), arsine (AsH3) and phosphine (PH3) as the reaction source gases, and successively growing an N - InP buffer layer (500 nm thick, Si - doped, doping concentration of 1×e 18 cm -3 of the N - InP buffer layer 2), an N - AlInAs confinement layer (50 nm thick, Si - doped, doping concentration of 1×e 18 cm -3 of the N - A l0.48 In 0.52 As confinement layer 3), an undoped refractive index - graded AlGaInAs lower waveguide layer (25 nm thick, undoped In 0.530 Ga 0.125Al 0.345 Lower waveguide layer of As), 5 periods of AlGaInAs quantum wells (5, non-doped In with a thickness of 6 nm 0.701 Ga 0.110 Al 0.189 As quantum wells), 6, non-doped In with a thickness of 6 nm 0.530 Ga 0.280 Al 0.190 As quantum barriers) and 10 graded buffer layers (non-doped with a thickness of 2 nm between each quantum barrier and quantum well

[0088] In 0.530 Ga 0.280 Al 0.190 As---In 0.310 Ga 0.280 Al 0.160 As graded buffer layer), the maximum thickness of the graded buffer layer is 2 nm; the horizontal dimension of the surface of the graded buffer layer in contact with the quantum barrier is the same as the horizontal dimension of the quantum barrier layer, the horizontal dimension of the quantum well layer is 1.27 times the horizontal dimension of the surface of the graded buffer layer in contact with the quantum well layer, and the final emission wavelength of the graded buffer layer is 1050 nm; the emission wavelength of the quantum well layer is 1330 nm, and the initial emission wavelengths of the quantum barrier layer and the graded buffer layer are 1000 nm), non-doped AlGaInAs upper waveguide layer with a refractive index gradient (25 nm thick, non-doped In 0.530 Ga 0.125 Al 0.345 As upper waveguide layer 6), P-AlInAs confinement layer (50 nm thick, Zn-doped, doping concentration of 2×e 17 cm -3 of P-Al 0.48 In 0.52 As confinement layer 7), P-InP graded buffer layer (85 nm thick, Zn-doped, doping concentration of 5×e 17 cm -3 of P-InP graded buffer layer 8), InGaAsP corrosion blocking layer with an emission wavelength of 1100 nm (10 nm thick, Zn-doped, doping concentration of 5×e 17 cm -3 of P-InGaAsP corrosion blocking layer 9), InP cladding layer (10 nm thick, Zn-doped, doping concentration of 5×e 17 cm -3P-InP), and an InGaAsP grating fabrication layer with an emission wavelength of 1150 nm and a P-InP protective layer. The thickness of the InGaAsP grating fabrication layer is 25 nm. Then, the grown epitaxial wafer is taken out, and a grating is formed by holographic lithography or electron beam lithography. The grating period is 196.2 nm, and the depth is 40 nm.

[0089] Figure 1 This is a schematic cross-sectional view of the quantum well in the embodiment of the present invention.

[0090] Figure 2 This is a schematic diagram showing the change in the emission wavelength of the graded buffer layer in the embodiment of the present invention;

[0091] Figure 4 This is a schematic structural diagram of the AlGaInAs quantum well in the embodiment of the present invention.

[0092] The schematic diagram of the epitaxial structure after forming the grating is as Figure 5 shown, that is: Figure 5 This is a schematic diagram of the epitaxial structure after forming the grating in the embodiment.

[0093] Among them, the growth temperature of the quantum well layer is controlled at 645 °C to suppress In component segregation at low temperature and stabilize the incorporation of Al; the temperature of the quantum barrier layer is raised to 655 °C to enhance the Al mobility and improve the barrier crystallization quality. The graded buffer layer realizes the component gradient by linearly adjusting the TMAl / TMIn flow rate to reduce interface defects.

[0094] After the epitaxial wafer is cleaned, it is then put into the MOCVD epitaxial furnace again to grow the InP secondary epitaxial layer by low-temperature pulse deposition method. The growth of the secondary epitaxial layer:

[0095] Under the protection of 900 sccm of PH3 gas, the reaction chamber is slowly heated to 560 °C, and then TMIn is introduced into the MOCVD reaction chamber in a pulsed manner to slowly grow an undoped InP capping layer of InP. Among them, the Source flow rate of TMIn is set to 10 sccm, and the growth rate of the InP secondary epitaxial layer is linearly related to the flow rate of In. Generally, it can be calculated by the following formula:

[0096]

[0097] Among them, V is the growth rate of InP, CInP is the concentration of TMIn introduced into the reaction chamber, and its value can be accurately measured by the Epison III gas concentration monitor connected to the MFC and the five-two valve on the MOCVD equipment. When the InP Souce flow rate is 10 sccm, its concentration is 87 molar concentration. It can be calculated that the growth rate of InP with an In flow rate of 10 sccm is 0.0028 nm / s. When the In flow rate increases to 720 sccm, the In concentration is 7300 molar concentration. The growth rate of InP is 0.2 nm / s.

[0098] Figure 7 It is a graph showing the relationship between the temperature, gas pulse injection mode and growth time in the MOCVD reaction chamber. At t1 = 2 s, the pulse is on, and TMIn (flow rate of 10 sccm) and DeZn (introduced into the reaction chamber through a double dilution pipeline, with its Source / Dilute / inject flow rates of 90 / 150 / 100, equivalent to a DeZn flow rate of 37.5 sccm introduced into the reaction chamber) are introduced to grow the InP nucleation layer; at t2 = 2 s, the pulse is off, allowing the atoms in the nucleation layer to have enough time to migrate to their lowest energy points; at t3 = 15 s, the pulse is on, and TMIn and DeZn are introduced again to grow an epitaxial layer of a certain thickness; at t4 = 2 s, the pulse is off to form a stable epitaxial layer. After t4, it enters the next cycle. In the pulse growth method, a high partial pressure ratio of PH3 (900 sccm) is always maintained, which is beneficial to reducing the volatilization of P during the heating process. First, TMIn and DeZn are introduced in short pulses to form a very thin nucleation layer on the substrate and make it form a stable state, reducing stacking faults and vacancies. Then, an epitaxial layer of a certain thickness is grown on the basis of the nucleation layer, which can significantly reduce the defect density of the semiconductor epitaxial layer.

[0099] Using this pulsed gas flow growth, each cycle takes 21 s and the growth thickness is about 0.048 nm. After growing 900 cycles, that is, t5 = 5.25 h, the thickness of the grown InP epitaxial layer is 43.2 nm;

[0100] Then, the temperature of the reaction chamber is raised to 670 °C, and the second step of the secondary epitaxy is carried out. At this time, a new TMIn line needs to be added, and its source flow rate is increased to 360 sccm, that is, the flow rate of In is increased to 720 sccm, and the concentration is 7300 molar concentration. DeZn is used as a dopant and introduced into the reaction chamber through a double-dilution pipeline. Its source / dilute / inject flow rates are 90 / 150 / 100 respectively, which is equivalent to a DeZn flow rate of 37.5 sccm introduced into the reaction chamber. At this time, the growth rate of the InP epitaxial layer is 0.2 nm / s, and the growth thickness in 50 min is 600 nm. After growing the InP secondary epitaxial layer, an InGaAsP barrier graded buffer layer (50 nm thick, Zn-doped, doping concentration of 3×e 18 cm -3 of the first P-In 0.821 Ga 0.179 As 0.391 P 0.609 barrier graded buffer layer 13, 100 nm thick, Zn-doped, doping concentration of 5×e 18 cm -3 of the second P-In 0.73 5Ga 0.265 As 0.574 P 0.426 barrier graded buffer layer 14) and an InGaAs ohmic contact layer (180 nm thick, Zn-doped, doping concentration of 2×e 19 cm -3 of the P-In 0.53 Ga 0.47 As ohmic contact layer 15) are formed, that is, a complete DFB epitaxial structure is formed.

[0101] Figure 6 It is a schematic diagram of the multi-quantum well epitaxial structure in the embodiment. Figure 6 In 12-1 is a P-InP protective layer (40 nm thick, InP, Zn doping concentration of 1.5×e 18 cm -3 ), 12-2 is an InP secondary epitaxial layer (1700 nm thick, InP, Zn doping concentration gradient from 1×e 18 cm -3 to 2×e 18 cm -3 gradually increasing).

[0102] After the epitaxial layer growth is completed, the ridge waveguide structure can be formed using photolithography and etching processes. The front electrode is then evaporated on the ridge waveguide structure, and the InP substrate is thinned. The back electrode is evaporated on the back of the thinned InP substrate; a high-reflection film (90% reflectivity) is evaporated at one end of the tube core, and a low-reflection film (10% reflectivity) is evaporated at the other end to complete the production of the DFB laser chip.

[0103] For further characterization, the DFB laser chip was simulated using Crosslight's software. The simulation results were compared with those of an ordinary DFB laser chip (the ordinary DFB laser chip differs from the DFB laser chip in Example 1 only in the quantum wells. The schematic diagram of the quantum well structure in the ordinary DFB laser chip is shown in FIG. Figure 14 As shown in the figure, compared with the quantum well of the present invention, there is no gradient buffer layer, the thickness of the quantum barrier is 10 mm, and the rest are the same), the stimulated radiation recombination rates of the two DFB laser chips are shown in the figure. Figures 8 - 9 As shown in the figure, the simulated optical power current curve is as follows Figures 10 - 11 As shown, the IV curve is as Figures 12 - 13 As shown. Among them, Figure 8 is the stimulated radiation recombination rate of a common DFB laser chip; Figure 9 is the stimulated radiation recombination rate of the DFB laser chip in the embodiment; Figure 10 This is the optical power current curve of a common DFB laser chip; Figure 11 is the optical power current curve of the DFB laser chip in the embodiment; Figure 12 This is the IV curve of a common DFB laser chip; Figure 13 FIG. 4 is the IV curve of the DFB laser chip of the embodiment.

[0104] Depend on Figures 8 - 9 It can be seen that the stimulated emission recombination rate in a conventional DFB laser chip decreases in a step-like manner, while in the DFB laser chip with a graded buffer layer, the stimulated emission recombination rate shows a more uniform distribution. In addition, the optical confinement factor of the conventional DFB laser chip is 0.0974, while the optical confinement factor of the DFB laser chip with a graded buffer layer is 0.0987. The uniform carrier distribution improves the overall optical confinement factor of the laser.

[0105] Depend on Figures 10 - 11 It can be seen that the threshold current of the DFB laser chip with a graded buffer layer multi-quantum well epitaxial structure is 2-3 mA smaller than that of an ordinary DFB laser chip, and the power increases slightly.

[0106] Depend on Figures 12 - 13It can be seen that the resistance of the DFB laser chip with a graded buffer layer multi-quantum well epitaxial structure has a slightly smaller decrease, indicating that the carrier mobility of the DFB laser chip with a graded buffer layer multi-quantum well epitaxial structure is higher.

[0107] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A quantum well, characterized in that, It is a multi-layer structure, including alternating quantum barrier layers and quantum well layers; It further includes: a graded buffer layer; Adjacent quantum barrier layers and quantum well layers are combined through the graded buffer layer; Both the bottom layer and the top layer in the multi-layer structure are quantum barrier layers; In a unit composed of an adjacent quantum barrier layer, graded buffer layer and quantum well layer: starting from the quantum barrier layer and ending with the adjacent quantum well layer, in the direction from the start to the end, the horizontal dimension of the graded buffer layer gradually decreases, the emission wavelength of the graded buffer layer gradually increases, the initial emission wavelength of the graded buffer layer is the same as the emission wavelength of the quantum barrier layer, and the final emission wavelength of the graded buffer layer is less than the emission wavelength of the quantum well layer.

2. The quantum well according to claim 1, wherein In one of the units: the thickness of the quantum barrier layer and the quantum well layer is 6 ± 0.18 nm; the maximum thickness of the graded buffer layer is 2 ± 0.06 nm; The horizontal dimension of the quantum well layer is smaller than the horizontal dimension of the quantum barrier layer; In the contacting quantum well layer and graded buffer layer: the horizontal dimension of the surface of the graded buffer layer in contact with the quantum well layer is larger than the horizontal dimension of the quantum well layer.

3. The quantum well according to claim 1, wherein, The final emission wavelength of the graded buffer layer is 1050 ± 10 nm; The emission wavelength of the quantum well layer is 1330 ± 10 nm, and the emission wavelength of the quantum barrier layer is 1000 ± 10 nm.

4. The quantum well according to claim 1, wherein The number of layers of the quantum well layer is 3 to 10 layers.

5. A multi-quantum well epitaxial structure, characterized in that, It includes the quantum well according to any one of claims 1 to 4.

6. The multi-quantum well epitaxial structure according to claim 5, wherein It includes a substrate (1), an N-InP buffer layer (2), an N-AlInAs confinement layer (3), an undoped AlGaInAs lower waveguide layer (4), a quantum well (5), an undoped AlGaInAs upper waveguide layer (6), a P-AlInAs confinement layer (7), a P-InP graded buffer layer (8), a P-InGaAsP corrosion blocking layer (9), a P-InP cladding layer (10), a P-InGaAsP grating layer (11), a P-InP connection layer (12), a first P-InGaAsP barrier graded buffer layer (13), a second P-InGaAsP barrier graded buffer layer (14), and a P-InGaAs ohmic contact layer (15) stacked in sequence; The quantum well (5) includes the quantum well according to any one of claims 1 to 4; The composition of the quantum well layer in the quantum well (5) is: In 0.701 Ga 0.110 Al 0.189 As, and the composition of the quantum barrier layer is: In 0.530 Ga 0.280 Al 0.190 As; in the direction from beginning to end, the composition in the graded buffer layer gradually changes from In 0.530 Ga 0.280 Al 0.190 As to In 0.310 Ga 0.280 Al 0.160 As.

7. The multi-quantum well epitaxial structure according to claim 6, wherein, The emission wavelength of the P-InGaAsP corrosion blocking layer (9) is 1100 ± 10 nm; The emission wavelength of the P-InGaAsP grating layer (11) is 1150 nm ± 10 nm, the grating period is 196.2 ± 1 nm, the depth is 40 ± 1.2 nm, and the emission wavelength of the P-InP graded buffer layer (8) is 600 ± 18 nm; The emission wavelength of the first P-InGaAsP barrier graded buffer layer (13) is 1300 ± 10 nm; The emission wavelength of the second P-InGaAsP barrier graded buffer layer (14) is 1500 ± 10 nm.

8. The method for preparing the multi-quantum well epitaxial structure according to any one of claims 6 to 7, characterized in that, It includes the following steps: An N-InP buffer layer (2), an N-AlInAs confinement layer (3), an undoped AlGaInAs lower waveguide layer (4), a quantum well (5), an undoped AlGaInAs upper waveguide layer (6), a P-AlInAs confinement layer (7), a P-InP graded buffer layer (8), a P-InGaAsP etch stop layer (9), a P-InP cladding layer (10), and a P-InGaAsP grating fabrication layer are sequentially deposited on a substrate (1); The P-InGaAsP grating fabrication layer is lithographed to obtain a P-InGaAsP grating layer (11); A P-InP connection layer (12), a first P-InGaAsP barrier graded buffer layer (13), a second P-InGaAsP barrier graded buffer layer (14), and a P-InGaAs ohmic contact layer (15) are sequentially deposited on the P-InGaAsP grating layer (11) to obtain the multi-quantum well epitaxial structure.

9. The preparation method according to claim 8, characterized in that, The temperature during deposition of the quantum well layer in the quantum well (5) is 600 - 650 °C, The temperature during deposition of the quantum barrier layer in the quantum well (5) is 650 - 680 °C.

10. A DFB laser, characterized in that, Comprising the multi-quantum well epitaxial structure according to any one of claims 5 to 7 or the multi-quantum well epitaxial structure prepared by the preparation method according to claim 8 or 9.

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