Quantum dot DFB laser based on substrate buried grating and preparation method

Abstract

The invention provides a quantum dot DFB laser based on a substrate buried grating. The quantum dot DFB laser comprises a substrate; the buffer layer is formed on the substrate; the N-type doped lower coating layer is formed on the buffer layer; the quantum dot active region is formed on the N-type doped lower coating layer; the P-type doped upper coating layer is formed in the quantum dot active region; and the N-type doped lower coating layer comprises a buried grating structure layer. The invention further provides a preparation method of the quantum dot DFB laser based on the substrate buried grating, and the flow ratio and the growth rate of the five-family elements and the three-family elements are optimized when the grating layer grows and the grating layer is buried. Through the design that the grating is buried on the lower substrate, the problem of damage of high temperature to a quantum dot active region in a traditional process is reduced, meanwhile, the limiting layer epitaxial design is optimized, the vertical divergence angle of a light field is reduced, the optical fiber coupling loss is reduced, and multi-mode oscillation is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor lasers, and in particular to a quantum dot DFB laser and a preparation method. BACKGROUND

[0002] In the fields of optical communication, laser radar and artificial intelligence optical computing chips, distributed feedback (DFB) lasers as core light sources directly affect the running efficiency and stability of the entire system. Quantum dot distributed feedback (DFB) lasers, with the three-dimensional carrier confinement effect, combine the advantages of low threshold, high temperature stability of quantum dot materials and single mode characteristics of DFB structure, and should be the ideal choice for the above-mentioned fields. However, the process architecture of traditional quantum dot DFB lasers has many significant defects, which seriously restricts the performance improvement and large-scale production.

[0003] Firstly, in terms of process, the quantum dot active region usually needs to be grown at low temperature (<520℃) by molecular beam epitaxy (MBE) to ensure the uniformity of the dot-like morphology, while the grating of quantum dot distributed feedback (DFB) relies on the high-temperature process of MOCVD. In the traditional scheme, the grating structure is usually grown above the quantum dot active region, which leads to serious damage to the quantum dot region during the preparation of the grating. Quantum dots are extremely sensitive to temperature, and high temperature can easily cause uncontrollable changes in the quantum dot structure, and also cause doping diffusion, thereby seriously affecting the performance parameters of the laser, such as wavelength drift, side mode suppression ratio (SMSR) drop, and more importantly, destroying the precision of the wavelength, making the laser unable to meet the needs of high-precision application scenarios.

[0004] The invention patent with publication number CN119050812A discloses an O-band silicon-based III-V quantum dot narrow linewidth laser and a preparation method thereof. The O-band silicon-based III-V quantum dot narrow linewidth laser includes a silicon substrate layer, and a buffer layer, a lower waveguide layer, a lower confinement layer, a quantum dot active layer, an upper confinement layer, an upper waveguide layer, an ohmic contact layer and an electrode layer are sequentially stacked on the silicon substrate layer; the upper waveguide layer and the ohmic contact layer form a ridge waveguide and a grating on at least one side of the ridge waveguide; and the quantum dot active layer includes an InAs quantum dot layer / InGaAs barrier layer. The O-band silicon-based III-V quantum dot narrow linewidth laser has the advantages of narrow linewidth, high reflection tolerance, high temperature stability and low threshold current density. However, it uses an upper surface grating, and in the process of preparing the grating, the high-temperature process will cause damage to the quantum dot region, affecting the performance parameters of the laser.

[0005] In addition, the quantum dot size is far smaller than the light wavelength, resulting in a weaker light field restriction ability than the quantum well structure, and a vertical divergence angle of 40°-60°. The large divergence angle leads to a mismatch between the light beam and the optical fiber mode field, increases the coupling loss, requires a complex lens system for compensation, increases the packaging cost, and causes low optical fiber coupling efficiency. The wide divergence angle is accompanied by excitation of high-order transverse modes, which easily causes multi-mode oscillation, especially under high temperature or high injection current, and destroys the single-mode characteristics of the DFB. SUMMARY

[0006] In view of the technical problems that the existing quantum dot distributed feedback (DFB) lasers mostly use upper surface gratings, which easily cause changes in the quantum dot structure during preparation and thus reduce the performance of the laser, and that a large vertical divergence angle leads to low optical fiber coupling efficiency and easy destruction of single-mode characteristics, the present application provides a quantum dot DFB laser based on a substrate buried grating and a preparation method thereof. The lower substrate buried grating design reduces the damage of the high temperature to the quantum dot active region in the traditional process, optimizes the design of the confinement layer epitaxy to reduce the vertical divergence angle of the light field, reduces the optical fiber coupling loss, and reduces the generation of multi-mode oscillation.

[0007] To achieve the above object, the technical scheme of the present application is as follows: A quantum dot DFB laser based on a substrate buried grating, comprising: a substrate; a buffer layer formed on the substrate; an N-doped lower cladding layer formed on the buffer layer; a quantum dot active region formed on the N-doped lower cladding layer; a P-doped upper cladding layer formed on the quantum dot active region; The N-doped lower cladding layer comprises a buried grating structure layer.

[0008] Specifically, the N-doped lower cladding layer comprises, from bottom to top, a first multilayer gradient confinement layer, a first non-gradient confinement layer, a grating layer, and a grating filling layer. The first multilayer gradient confinement layer is formed on the buffer layer, the first non-gradient confinement layer is formed on the first multilayer gradient confinement layer, the grating layer is formed on the first non-gradient confinement layer, and the grating filling layer is formed on the grating layer. The grating layer and the grating filling layer form the buried grating structure layer.

[0009] Specifically, the first multilayer gradient confinement layer is an n-type doped aluminum gallium arsenide n-Al x Ga (1-x) As with a thickness of 4000nm-5000nm. The component ratio x of aluminum Al gradually changes from x1 to x2 and then to x1, where 0.1 The first non-gradual restriction layer adopts undoped gallium arsenide GaAs, and the thickness is 30-50nm. The grating layer adopts but is not limited to indium gallium phosphorus and indium gallium arsenic phosphorus, the thickness is 10-20nm, the grating period is 100nm, and the duty cycle is 1:1. The grating filling layer adopts undoped gallium arsenide GaAs, and the thickness is 150-200nm.

[0010] Specifically, the quantum dot active region includes 6-10 quantum dot active region sublayers, each quantum dot active region sublayer from bottom to top includes a quantum dot layer and a strain relief layer in sequence, and a spacing layer is arranged between each quantum dot active region sublayer, and the quantum dot layer of the first layer of the quantum dot active region sublayer is formed on the grating filling layer.

[0011] Specifically, the P-type doped upper cladding layer includes a second non-gradual restriction layer, an etching stop layer, a second multilayer gradual restriction layer and a cap layer in sequence from bottom to top, the second non-gradual restriction layer is formed on the last spacing layer of the quantum dot active region, the etching stop layer is formed on the second non-gradual restriction layer, the second multilayer gradual restriction layer is formed on the etching stop layer, and the cap layer is formed on the second multilayer gradual restriction layer.

[0012] Specifically, the second non-gradual restriction layer adopts undoped gallium arsenide u-GaAs, and the thickness is 150-200nm. The etching stop layer is indium gallium phosphorus InGaP, and the thickness is 20nm. b Ga(1-b)P, and the thickness is 20nm. The second multilayer gradual restriction layer is a multilayer component gradually changed p-type doped aluminum gallium arsenide p-AlGaAs, and the thickness is 1200-2000nm. y Ga (1-y) As, and the thickness is 1200-2000nm, the component ratio y of aluminum Al gradually changes from y1 to y2 and then to y1, wherein 0.1

[0013] Specifically, the quantum dot layer is an indium arsenic quantum dot layer InAs QD, and the shape is spherical, hemispherical or equilateral triangular pyramid, the diameter of the spherical or hemispherical shape is 5-20nm, the edge length of the equilateral triangular pyramid is 5-20nm, and the center distance is 20-50nm, the strain relief layer is an indium gallium arsenic strain relief layer InGaAs SRL, and the thickness is 3-4nm, and the spacing layer adopts intrinsic gallium arsenide i-GaAs, and the thickness is 30-40nm. The buffer layer is an n-type doped arsenic layer n-GaAs, and the thickness is 300-500nm. The cap layer is a p-type doped gallium arsenide p-GaAs, and the thickness is 300nm-600nm.

[0014] A preparation method of a quantum dot DFB laser based on a substrate buried grating, steps are as follows: S1: growing a first epitaxial structure on a substrate by using MOCVD, a growth temperature is 600-750 DEG C, from bottom to top, there are a buffer layer, a N-doped lower cladding layer; S2: growing a quantum dot active region and a P-doped upper cladding layer on the N-doped lower cladding layer by using an MBE device, a growth temperature is 480 DEG C-520 DEG C.

[0015] The quantum dot DFB laser based on a substrate buried grating according to claim 8, a specific implementation method of step S1 is: Growing a first epitaxial structure on a substrate by using MOCVD, a growth temperature is 600-750 DEG C, from bottom to top, there are a buffer layer, a first multilayer gradually changing confinement layer, a first non-gradually changing confinement layer, and a non-etched grating layer; Preparing a periodic grating structure on the non-etched grating layer by using photoetching and plasma ICP etching, and obtaining a grating layer; Filling the grating layer by using MOCVD, and obtaining a grating filling layer; An implementation method of step S2 is: Growing a quantum dot active region, a second non-gradually changing confinement layer, an etching stop layer, a second multilayer gradually changing confinement layer and a cap layer on the grating filling layer by using MBE.

[0016] Specifically, when growing the non-etched grating layer, the flow ratio of the pentatomic element to the tritomic element and the growth rate are simultaneously optimized, the flow ratio of the pentatomic element to the tritomic element is 40-60, and the growth rate is 0.2-0.5 nm / s; When filling the grating layer, the flow ratio of the pentatomic element to the tritomic element and the growth rate are simultaneously optimized, the flow ratio of the pentatomic element to the tritomic element is 10-50, and the growth rate is 0.1-0.3 nm / s.

[0017] The present application has the following advantages: The present application avoids direct contact of quantum dots with high-temperature processes by designing a substrate buried grating, avoids damage to the morphology of quantum dots caused by high-temperature processes, avoids wavelength drift, and improves the side mode suppression ratio (SMSR) by improving the grating diffraction efficiency and reducing mode coupling in combination with the high refractive index difference between the InGaP / InGaAsP grating layer and the upper and lower GaAs layers.

[0018] The present application uses a lower / upper cladding layer bidirectional gradually changing design, compresses the vertical light field, reduces the vertical divergence angle, reduces the fiber coupling loss, and reduces the generation of multimode oscillation.

[0019] If the grating is placed below the quantum dot layer, although the high temperature damage can be avoided, the filling process after grating etching is easy to introduce high dislocation density on the material surface, the application selects the grating material matched with the lattice of the filling layer, optimizes the MOCVD filling parameter to inhibit the dislocation extension of the filling layer, and selects the grating filling to switch to the MBE low temperature growth quantum dot to further block the upward extension of the high dislocation area, so as to ensure the device reliability, combine the multi-layer quantum dot active region stack, enhance the carrier injection efficiency, reduce the non-radiative recombination, and then reduce the threshold current density and prolong the device life. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0021] Figure 1 The epitaxial structure diagram of the quantum dot DFB laser based on the substrate buried grating of the present application.

[0022] Figure 2 For Figure 1 The local enlarged view of the grating part in the middle; Figure 3 The simulation diagram of the divergence angle before using the structure optimization of the present application; Figure 4 The light field and divergence angle simulation diagram of embodiment 1; Figure 5 The spectrum test diagram of embodiment 1; Figure 6 The light field and divergence angle simulation diagram of embodiment 2; Figure 7 The spectrum test diagram of embodiment 2; Figure 8 The light field and divergence angle simulation diagram of embodiment 3; Figure 9 The spectrum test diagram of embodiment 3; Figure 10 The light field and divergence angle simulation diagram of embodiment 4; Figure 11 The spectrum test diagram of embodiment 4.

[0023] Figure 12 The laser epitaxial structure diagram after the ridge waveguide is made. DETAILED DESCRIPTION

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 like Figure 1 As shown, a quantum dot DFB laser based on a substrate buried grating is presented.

[0026] Including substrate; A buffer layer is formed on the substrate; An N-type doped undercoating layer is formed on the buffer layer; The quantum dot active region is formed on the N-type doped undercoating layer; A p-type doped overcoating layer is formed in the active region of the quantum dot; The N-type doped undercoating layer includes a buried grating structure layer.

[0027] Specifically, the substrate is made of GaAs with a thickness of 350 nm.

[0028] Specifically, the buffer layer is n-type doped gallium arsenide (n-GaAs), with a thickness of 300 nm and a doping concentration of 1.5 × 10⁻⁶. 18 / cm -3 The buffer layer is grown on the substrate using metal-organic chemical vapor deposition (MOCVD). This buffer can buffer dislocations during the growth of materials with different lattice constants, thereby improving growth quality.

[0029] Specifically, the N-type doped undercoating layer comprises, from bottom to top, a first multilayer graded confinement layer, a first non-graded confinement layer, a grating layer, and a grating buried layer, the grating layer and the grating buried layer forming the buried grating structure layer; the first multilayer graded confinement layer is grown on the buffer layer by metal-organic chemical vapor deposition (MOCVD); the first non-graded confinement layer is grown on the first multilayer graded confinement layer by metal-organic chemical vapor deposition (MOCVD); the grating layer is first grown on the first non-graded confinement layer by metal-organic chemical vapor deposition (MOCVD) to form an unetched grating layer, and then etched by photolithography and plasma-enhanced plasma (ICP) to obtain the grating layer; the grating buried layer is buried on the grating layer by metal-organic chemical vapor deposition (MOCVD) to obtain the N-type doped undercoating layer with a grating structure.

[0030] Specifically, the first multilayer graded confinement layer is an n-type doped aluminum gallium arsenide (n-Al) with multilayer graded composition.x Ga (1-x) As), thickness is 4000nm, doping concentration is 1.0x10 18 / cm -3 Wherein, the component ratio x of aluminum (Al) is gradually changed from x1 to x2 and then to x1, wherein 0.1 < x1 < 0.3 and 0.3 < x2 < 0.5, in the embodiment, wherein 0-2000nm, x is uniformly gradually changed from 0.11 to 0.31, 2000-4000nm x is uniformly gradually changed from 0.31 to 0.11, the design of the component gradually changing limit layer can effectively solve the problem of the large vertical divergence angle of the quantum dot laser, and significantly reduce the vertical divergence angle to 35° or less. The divergence angle simulation diagram before using the structure optimization of the application is shown in Figure 3 , the simulation results of the embodiment show that the vertical divergence angle is significantly reduced to 35°, and the simulation results are shown in Figure 4 . The multi-layer gradually changing limit layer can better limit the light field divergence.

[0031] Under the guidance of the gradually changing refractive index, the light field will expand more gently to the limit layer. The refractive index sudden interface is easy to produce additional reflection and mode distortion, which aggravates the non-uniformity of the light field, and the component gradual change eliminates the sudden interface, reduces such interference, and makes the light field distribution more symmetrical and gentle, thereby effectively reducing the vertical divergence angle.

[0032] Specifically, the first non-gradually changing limit layer is a gallium arsenide (GaAs) limit layer, and the thickness is 30nm. In addition to light field limitation, it can also be used for buffering between materials.

[0033] Specifically, as shown in Figure 2 , the grating layer uses but is not limited to indium gallium phosphide (InGaP) and indium gallium arsenide phosphide (InGaAsP), and the thickness is 12nm. The grating period is 100nm, and the duty cycle is 1:1. The grating layer InGaP / InGaAsP has a small refractive index, can form a high refractive index difference with the upper and lower layers of material, can improve the light field modulation capacity and efficient constraint, reduce the leakage loss, enhance the mode selection and wavelength locking capacity, and is beneficial to precise wavelength selection. And it is grown at a high temperature by using MOCVD equipment, and the growth temperature is 600-750℃. By optimizing the flow ratio of the five group elements to the three group elements and the growth rate, the flow ratio of the five group elements to the three group elements is 58, and the growth rate is 0.31nm / s. The thinner the grating layer, the smaller the growth rate. The epitaxial optimization improves the growth quality, and after the growth is completed, the dislocation density after the grating is filled can be obviously reduced to 70cm⁻². The grating layer can realize precise selection of wavelength by adjusting the grating period, and ensure the single mode characteristics of the light emission.

[0034] Specifically, the grating filling layer adopts undoped gallium arsenide GaAs material, the filling temperature is 600-750 DEG C, the GaAs filling thickness is 200 nm, and the flow ratio of the fifth element to the third element and the growth rate are optimized, the flow ratio of the fifth element to the third element is 35, and the growth rate is 0.21 nm / s, so that the dislocation density after grating filling can be reduced, and the dislocation density after filling is 340 cm-2. The grating filling layer and the grating layer form a high refractive index difference, which is beneficial to better wavelength control.

[0035] The high-quality grating layer needs high-temperature growth and filling of a metal organic chemical vapor deposition (MOCVD) equipment, and in order to avoid damage to the quantum dot region, the quantum dot active region is grown by using a molecular beam epitaxy (MBE) equipment with a lower growth temperature. In the existing quantum dot structure growth scheme, when the grating is grown above the active region, high temperature will cause quantum dot size and doping diffusion, and then affect the performance and wavelength accuracy of the laser. And the effective scheme for realizing the quantum dot DFB laser is to grow the grating by using the metal organic chemical vapor deposition (MOCVD) high-temperature growth and then grow the quantum dot structure by using the molecular beam epitaxy (MBE). And through the selection of the grating material and the optimization of the epitaxial growth conditions, high-quality and low-defect epitaxial growth can be realized, and through the high refractive index difference of the grating and the low-defect epitaxy of the grating filling layer, high-quality gratings can be obtained, which can match the specific wavelength mode of the grating period to obtain sufficient feedback, and other wavelength modes are suppressed due to insufficient feedback. This makes the device more easily realize single-mode output, realizes the effect of high side mode, and significantly improves the stability of the output wavelength (such as sensitivity to temperature and current). The side mode suppression ratio reaches 50.6 dB under the test conditions of 25 DEG C & 300 mA, as shown in the following figure. Figure 5

[0036] Specifically, the quantum dot active region includes 6 layers of quantum dot active region sublayers which are grown by overlapping and include indium arsenide quantum dot layers (InAs QD, small triangles) and indium gallium arsenide strain relief layers (InGaAs SRL). Each quantum dot active region sublayer is sequentially composed of a quantum dot layer and an indium gallium arsenide strain relief layer from bottom to top. The shape of the quantum dot in the quantum dot layer is spherical, hemispherical, the diameter is 3-5 nm, or the shape of the quantum dot is an equilateral triangular pyramid, the edge length is 5-20 nm, and the center distance is about 20-50 nm. In this embodiment, the shape of the quantum dot is an equilateral triangle, the edge length is 3 nm, and the center distance is 25 nm. A spacing layer is arranged between each quantum dot active region sublayer. The thickness of the indium gallium arsenide strain relief layer is 3 nm, the spacing layer adopts intrinsic gallium arsenide (i-GaAs), and the thickness of the spacing layer is 30 nm. The indium arsenide quantum dot, the indium gallium arsenide strain relief layer and the intrinsic gallium arsenide layer are grown by using the molecular beam epitaxy (MBE) method in sequence, and the growth temperature is kept at 480 DEG C-520 DEG C.

[0037] ​The quantum dot active region has unique structure and physical characteristics. The electrons and holes are strongly limited in three-dimensional space, narrow gain spectrum and low gain saturation threshold can be achieved. The strong quantum confinement effect of the quantum dot forms a potential well, which can bind the electrons and holes in the quantum dot and improve the energy conversion efficiency of the laser. The strain relief layer limits the distribution of carriers in the quantum dot region, reduces non-radiative recombination, and reduces the mode mismatch between the optical field and the active region, thereby improving the optical gain efficiency.

[0038] Specifically, the P-type doped upper cladding layer comprises, from bottom to top, a second non-gradual confining layer, an etching stop layer, a second multi-layer gradual confining layer, and a cap layer. The second non-gradual confining layer is grown on the last spacer layer of the quantum dot active region by a molecular beam epitaxy (MBE) method. The etching stop layer is grown on the second non-gradual confining layer by the MBE method. The second multi-layer gradual confining layer is grown on the etching stop layer by the MBE method. The cap layer is grown on the second multi-layer gradual confining layer by the MBE method.

[0039] Specifically, the second non-gradual confining layer is made of undoped gallium arsenide (ud GaAs) material with a thickness of 200 nm. The second non-gradual confining layer is used to limit the optical field and match the lattice constants of different materials as a buffer layer.

[0040] Specifically, the etching stop layer is indium gallium phosphide (In b Ga (1-b) P) with a thickness of 20 nm. The etching depth stopping effect is controlled by adjusting the indium ratio b and the gallium ratio (1-b). The etching stop layer is used for precise stopping of etching depth during ridge waveguide fabrication; b is 0.49.

[0041] Specifically, the second multi-layer gradual confining layer is a multi-layer component gradually changed p-type doped aluminum gallium arsenide (p-Al y Ga (1-y) As) with a thickness of 1200 nm and a doping concentration of 1.0×10 18 / cm -3 . y gradually changes from y1 (0.1<y1<0.3) to y2 (0.3<y2<0.6) and then to y1, where 0-1000 nm, the aluminum (Al) component ratio y uniformly changes from 0.11 to 0.31, 1000-1200 nm, y uniformly changes from 0.31 to 0.11.

[0042] Specifically, the cap layer is p-type doped gallium arsenide (p-GaAs) with a thickness of 300 nm and a doping concentration of 2.5×10 19 / cm -3 .

[0043] Example 2 A quantum dot DFB laser based on substrate buried grating In the embodiment of the application, the substrate is GaAs substrate with a thickness of 350 um; the buffer layer is n-type doped gallium arsenide (n-GaAs) with a thickness of 300 nm and a doping concentration of 2.5×10 18 / cm -3 .

[0044] Specifically, the first multi-layer gradient restriction layer is a multi-layer component gradient n-type doped aluminum gallium arsenide (n-Al x Ga (1-x) As) with a thickness of 5000 nm and a doping concentration of 1.5×10 18 / cm -3 The aluminum (Al) component ratio x is uniformly changed from x1 to x2 and then uniformly changed from x2 to x1, x1 is 0.29, and x2 is 0.49; wherein 0-2500 nm, x is uniformly changed from 0.29 to 0.49, and 2500-5000 nm, x is uniformly changed from 0.49 to 0.29. Simulation results show that the vertical divergence angle is significantly reduced to 34°, and the simulation results are shown in Figure 6 .

[0045] Specifically, the first non-gradient restriction layer is a gallium arsenide (GaAs) restriction layer with a thickness of 50 nm.

[0046] Specifically, the grating layer is not limited to indium gallium phosphide (InGaP) and indium gallium arsenide phosphide (InGaAsP) with a thickness of 20 nm, which is grown by metal organic chemical vapor deposition (MOCVD) at a high temperature of 600-750 ℃. By optimizing the flow ratio of group V elements to group III elements and the growth rate, the flow ratio of group V elements to group III elements is 53, and the growth rate is 0.4 nm / s. After growth, the defect density after grating filling can be significantly reduced to about 180 cm⁻².

[0047] Specifically, the grating filling layer is an undoped gallium arsenide (ud GaAs) material, the filling temperature is 600-750 ℃, the GaAs filling thickness is 150 nm; at the same time, the flow ratio of group V elements to group III elements and the growth rate are optimized, the flow ratio of group V elements to group III elements is 38, and the growth rate is 0.28 nm / s, and the dislocation density after filling is about 470 cm⁻². By selecting the grating material and optimizing the epitaxial growth conditions, high-quality and low-defect epitaxial growth can be achieved, and the side mode suppression ratio reaches 54.0 dB under the test conditions of 25 ℃ & 300 mA, as shown in Figure 7 .

[0048] Specifically, the quantum dot active region employs 10 overlapping quantum dot active region sub-layers, including indium arsenide quantum dot layers (InAs QD) and indium gallium arsenide strain relief layers (InGaAs SRL). The quantum dots in the quantum dot layers are spherical with a diameter of 3 nm and a center-to-center spacing of 20 nm. The indium gallium arsenide strain relief layer is 3.5 nm thick, and the spacer layer is made of intrinsic gallium arsenide (i-GaAs) with a thickness of 40 nm. The growth temperature is maintained at 480℃-520℃.

[0049] Specifically, the second non-gradient confinement layer is made of undoped gallium arsenide (GaAs) material with a thickness of 150 nm; the etch stop layer is indium gallium phosphide (In). b Ga (1-b) P has a thickness of 30 nm and b is 0.49.

[0050] Specifically, the second multilayer gradient confinement layer is a p-type doped aluminum gallium arsenide (p-Al) with multilayer gradient composition. y Ga (1-y) As), with a thickness of 2000 nm and a doping concentration of 1.5 × 10⁻⁶. 18 / cm -3 y1 is 0.29 and y2 is 0.49; where y gradually changes from 0.29 to 0.49 in the range of 0-1000nm, and from 0.49 to 0.29 in the range of 1000-2000nm.

[0051] Specifically, the capping layer is a p-type doped gallium arsenide (p-GaAs) with a thickness of 400 nm and a doping concentration of 3 × 10⁻⁶. 18 / cm -3 .

[0052] The other structures and principles are the same as in Example 2.

[0053] Example 3 A quantum dot DFB laser based on a substrate-buried grating is disclosed in this application. In this embodiment, the substrate is GaAs with a thickness of 350 μm; the buffer layer is n-type doped gallium arsenide (n-GaAs) with a thickness of 300 nm and a doping concentration of 3.0 × 10⁻⁶. 18 / cm -3 .

[0054] Specifically, the first multilayer gradient confinement layer is an n-type aluminum-doped gallium arsenide (n-Al) with multilayer gradient composition. x Ga (1-x) As), with a thickness of 4500 nm and a doping concentration of 1.3 × 10⁻⁶. 18 / cm -3, the component ratio x of aluminum (Al) is uniformly changed from x1 to x2 and then uniformly changed from x2 to x1, x1 is 0.11, x2 is 0.31, wherein 0-2000nm, x is uniformly changed from 0.15 to 0.35, 2000-4500nm x is uniformly changed from 0.35 to 0.15, the simulation results show that the vertical divergence angle is significantly reduced to about 32°, and the simulation results are as shown in Figure 8 .

[0055] Specifically, the first non-gradual restriction layer adopts gallium arsenide (GaAs) with a thickness of 40nm.

[0056] Specifically, the grating layer adopts indium gallium phosphide (InGaP) and indium gallium arsenide phosphide (InGaAsP) without limitation, with a thickness of 18nm, and a high-temperature growth temperature of 600-750℃ by metal organic chemical vapor deposition (MOCVD) method. By optimizing the flow ratio of group V elements to group III elements and the growth rate, the flow ratio of group V elements to group III elements is 55, and the growth rate is 0.37nm / s. After growth is completed, the defect density after grating filling can be obviously reduced by about 140cm⁻².

[0057] Specifically, the grating filling layer adopts undoped gallium arsenide (ud GaAs) material, with a filling temperature of 600-750℃ and a GaAs filling thickness of 180nm. At the same time, the flow ratio of group V elements to group III elements and the growth rate are optimized, the flow ratio of group V elements to group III elements is 34, and the growth rate is 0.23nm / s. After filling, the dislocation density is about 380cm⁻². By selecting the grating material and optimizing the epitaxial growth conditions, high-quality and low-defect epitaxial growth can be realized, and the side mode suppression ratio reaches 61.3dB under the test conditions of 25℃&300mA, as shown in Figure 9 .

[0058] Specifically, in the quantum dot active region, an 8-layer quantum dot active region sublayer including indium arsenide quantum dot layers (InAs QD) and indium gallium arsenide strain relief layers (InGaAs SRL) is used. The quantum dot layer has a hemispherical quantum dot shape with a diameter of 4nm and a center distance of 35nm. The indium gallium arsenide strain relief layer has a thickness of 4nm. The spacer layer adopts intrinsic gallium arsenide (i-GaAs) with a thickness of 35nm, and the growth temperature is maintained at 480-520℃.

[0059] Specifically, the second non-gradual restriction layer adopts undoped gallium arsenide (ud GaAs) material with a thickness of 180nm. The etching stop layer is indium gallium phosphide (InGaP) with a thickness of 20nm, and b is 0.49. b Ga (1-b) P, with a thickness of 20nm, and b is 0.49.

[0060] Specifically, the second multi-layer gradient confinement layer is a p-type doped aluminum gallium arsenide (p-Al y Ga (1-y) As) with a thickness of 1600 nm and a doping concentration of 1.3×10 18 / cm -3 , y1 is 0.15, y2 is 0.35, wherein 0-800 nm, y is uniformly graded from 0.15 to 0.35, 800-1600 nm, y is uniformly graded from 0.35 to 0.15.

[0061] Specifically, the cap layer is a p-type doped gallium arsenide (p-GaAs) with a thickness of 400 nm and a doping concentration of 2.8×10 19 / cm -3 .

[0062] The other structures and principles are the same as those of Embodiment 2.

[0063] Embodiment 4 A quantum dot DFB laser based on a substrate buried grating, in the embodiment of the application, the substrate is GaAs with a thickness of 350 um; the buffer layer is n-type doped gallium arsenide (n-GaAs) with a thickness of 450 nm and a doping concentration of 3.5×10 18 / cm -3 .

[0064] Specifically, the first multi-layer gradient confinement layer is an n-type doped aluminum gallium arsenide (n-Al x Ga (1-x) As) with a thickness of 4300 nm and a doping concentration of 1.6×10 18 / cm -3 , the aluminum (Al) component ratio x is uniformly graded from x1 to x2 and then graded to x1, x1 is 0.18, x2 is 0.42; wherein 0-2300 nm, x is uniformly graded from 0.18 to 0.42, 2300-4300 nm, x is graded from 0.42 to 0.18, simulation results show that the vertical divergence angle is significantly reduced to 33°, and the simulation results are shown in Figure 10 .

[0065] Specifically, the first non-gradient confinement layer is a gallium arsenide (GaAs) confinement layer with a thickness of 35 nm.

[0066] Specifically, the grating layer uses indium gallium phosphide (InGaP) and indium gallium arsenide phosphide (InGaAsP) without limitation, the thickness is 15 nm, the metal organic chemical vapor deposition (MOCVD) method is used for high-temperature growth, the growth temperature is 600-750℃, the flow ratio of the fifth element to the third element and the growth rate are optimized, the flow ratio of the fifth element to the third element is 58, the growth rate is 0.35 nm / s, and after the growth is completed, the defect density after grating filling can be obviously reduced by about 100 cm-2.

[0067] Specifically, the grating filling layer uses undoped gallium arsenide (ud GaAs) material, the filling temperature is 600-750℃, the GaAs filling thickness is 170 nm, the flow ratio of the fifth element to the third element and the growth rate are optimized, the flow ratio of the fifth element to the third element is 36, the growth rate is 0.24 nm / s, (the parameter value), and the dislocation density after filling is about 400 cm-2. Through the selection of the grating material and the optimization of the epitaxial growth conditions, high-quality and low-defect epitaxial growth can be realized, and the side mode suppression ratio reaches 60.7 dB under the test conditions of 25℃&300 mA, as shown in Figure 11 .

[0068] Specifically, in the quantum dot active region, an 8-layer quantum dot active region sublayer including indium arsenide quantum dot layers (InAs QD) and indium gallium arsenide strain relief layers (InGaAs SRL) is used for overlapping growth, the quantum dot layer has an equilateral triangle shape with a side length of 4 nm and a center distance of 50 nm, the indium gallium arsenide strain relief layer has a thickness of 3.5 nm, the spacer layer uses intrinsic gallium arsenide (i-GaAs) with a thickness of 35 nm, and the growth temperature is kept at 480℃-520℃.

[0069] Specifically, the second non-gradual restriction layer uses undoped gallium arsenide (ud GaAs) material with a thickness of 170 nm; and the etching stop layer is indium gallium phosphide (InGaP) with a thickness of 25 nm, b is 0.49. b Ga (1-b) P, the thickness is 25 nm, and b is 0.49.

[0070] Specifically, the second multi-layer gradual restriction layer is a multi-layer component gradually changed p-type doped aluminum gallium arsenide (p-Al y Ga (1-y) As) with a thickness of 1800 nm, a doping concentration of 1.6×10 18 / cm -3 , y1 is 0.18, and y2 is 0.42; wherein 0-900 nm, x gradually changes from 0.18 to 0.42, 900-1800 nm, x gradually changes from 0.42 to 0.18.

[0071] Specifically, the cover layer is p-type doped gallium arsenide (p-GaAs) with a thickness of 400 nm and a doping concentration of 3.6*10 18 / cm -3 .

[0072] Other structures and principles are the same as those of Embodiment 3.

[0073] Embodiment 5 A preparation method of a quantum dot DFB laser based on a substrate buried grating, comprising the following steps: S1, using a metal organic chemical vapor deposition (MOCVD) device to grow an epitaxial structure on a GaAs substrate, i.e., a buffer layer and an N-type doped lower cladding layer, a growth temperature is 600-750 ℃, from bottom to top, in order, are an n-GaAs buffer layer, an n-AlxGa(1-x)As first multilayer gradual change limiting layer, a GaAs first non-gradual change limiting layer, and an un-etched grating layer of InGaP or InGaAsP material.

[0074] S2, using photolithography and ion plasma (ICP) etching to prepare a periodic grating structure on the un-etched grating layer, to obtain a grating layer; S3, using a metal organic chemical vapor deposition (MOCVD) device to fill the grating layer, to grow a udGaAs grating filling layer; When growing the un-etched grating layer, simultaneously optimizing a flow ratio of a group V element to a group III element and a growth rate, the flow ratio of the group V element to the group III element is 40-60, and the growth rate is 0.2-0.5 nm / s; When filling the grating layer, simultaneously optimizing a flow ratio of a group V element to a group III element and a growth rate, the flow ratio of the group V element to the group III element is 10-50, and the growth rate is 0.1-0.3 nm / s.

[0075] S4, using a molecular beam epitaxy (MBE) device to grow a quantum dot active region and a P-type doped upper cladding layer, a growth temperature is 480-520 ℃, from top to bottom, in order, are 6-10 layers of quantum dot active region sub-layers (InAs QD, InGaAs SRL) and GaAs interval layers, after completing the growth of the quantum dot active region, in order, are a GaAs second non-gradual change limiting layer, an In b Ga (1-b) P etching stop layer, a p-Al x Ga (1-x) As second gradual change limiting layer, and a p-GaAs cover layer; to obtain a well-grown semiconductor material wafer.

[0076] S5, after completing the material growth, using photolithography and etching processes to prepare a ridge waveguide structure.

[0077] Specifically, first, photoresist is coated on the surface of the material, and the pattern of the ridge waveguide is defined through a photolithography process, so that the photoresist forms a required mask, dry etching (ICP) is used to etch the material to form a preliminary ridge structure, then wet etching is performed to a depth of the etching stop layer, and finally a complete ridge waveguide structure is formed, as shown in Figure 12 S6 The wafer with the ridge waveguide structure is cleaned, an insulating layer is grown, a window is opened through photolithography, metal film is plated and stripped, the back is ground and polished, the bar is cleaved, optical film is plated, and then the bar is cleaved again to obtain a DFB laser chip.

[0078] Specifically, after removing the mask on the surface of the ridge waveguide structure, the semiconductor material wafer is cleaned; a layer of insulating silicon oxide is grown on the surface of the semiconductor material wafer through MOCVD as an insulating layer; a window is opened as an electrode contact area through photolithography and etching process, and metal film is plated on the electrode contact area and stripped outside the electrode contact area; after the semiconductor material wafer is ground and polished, the wafer after grinding and polishing is cleaved along the preset cleaving surface to form a bar containing multiple chips, i.e. a bar, and finally the bar is optically plated, and then the bar is cleaved again along the interval between the chips to obtain a complete DFB laser chip.

[0079] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A quantum dot DFB laser based on substrate buried gratings, characterized in that, The substrate includes: a buffer layer formed on the substrate; an N-doped lower cladding layer formed on the buffer layer; a quantum dot active region formed on the N-doped lower cladding layer; a P-doped upper cladding layer formed on the quantum dot active region; The N-doped lower cladding layer includes a buried grating structure layer.

2. The substrate-based buried grating quantum dot DFB laser according to claim 1, wherein The N-doped lower cladding layer includes a first multilayer graded confinement layer, a first non-graded confinement layer, a grating layer, and a grating filling layer from bottom to top, the first multilayer graded confinement layer is formed on the buffer layer, the first non-graded confinement layer is formed on the first multilayer graded confinement layer, the grating layer is formed on the first non-graded confinement layer, and the grating filling layer is formed on the grating layer, and the grating layer and the grating filling layer form the buried grating structure layer. The first non-graded confinement layer is made of undoped gallium arsenide GaAs with a thickness of 30-50 nm; 3. The substrate buried grating based quantum dot DFB laser of claim 2, wherein, The first multilayer gradient confinement layer adopts a multilayer component gradient n-type doped aluminum gallium arsenide n-Al x Ga (1-x) As, with a thickness of 4000nm-5000nm; the component ratio x of aluminum Al is gradually changed from x1 to x2 and then gradually changed to x1, wherein 0.1 The grating layer is made of but not limited to indium gallium phosphide and indium gallium arsenide phosphide with a thickness of 10-20 nm, a grating period of 100 nm, and a duty cycle of 1:1; The grating filling layer is made of undoped gallium arsenide GaAs with a thickness of 150-200 nm. The quantum dot active region includes 6-10 layers of quantum dot active region sublayers, each layer of quantum dot active region sublayer includes a quantum dot layer and a strain relief layer from bottom to top, and a spacer layer is arranged between each layer of quantum dot active region sublayer, and the quantum dot layer of the first layer of quantum dot active region sublayer is formed on the grating filling layer.

4. A substrate buried grating based quantum dot DFB laser according to claim 2 or 3, wherein, The P-doped upper cladding layer includes a second non-graded confinement layer, an etching stop layer, a second multilayer graded confinement layer, and a cap layer from bottom to top, the second non-graded confinement layer is formed on the last spacer layer of the quantum dot active region, the etching stop layer is formed on the second non-graded confinement layer, the second multilayer graded confinement layer is formed on the etching stop layer, and the cap layer is formed on the second multilayer graded confinement layer.

5. The substrate buried grating based quantum dot DFB laser of claim 4, wherein, The second non-graded confinement layer is made of undoped gallium arsenide u-GaAs with a thickness of 150-200 nm; 6. The substrate buried grating based quantum dot DFB laser according to claim 5, wherein, 7. The substrate-based buried grating quantum dot DFB laser according to claim 6, wherein The corrosion stop layer is indium gallium phosphide In b Ga(1-b)P, 20 nm thick; The second multilayer gradually changing confinement layer is a p-type doped aluminum gallium arsenide p-Al y Ga (1-y) As, with a thickness of 1200-2000nm, and the aluminum Al component ratio y gradually changes from y1 to y2 and then from y2 to y1, wherein 0.1 The quantum dot layer is an indium arsenide quantum dot layer InAs QD, which is spherical, hemispherical, or equilateral triangular pyramid-shaped, the spherical or hemispherical diameter is 5-20 nm, the equilateral triangular pyramid edge length is 5-20 nm, and the center distance is 20-50 nm, the strain relief layer is an indium gallium arsenide strain relief layer InGaAs SRL with a thickness of 3-4 nm, and the spacer layer is made of intrinsic gallium arsenide i-GaAs with a thickness of 30-40 nm; The buffer layer is an n-doped gallium arsenide n-GaAs with a thickness of 300-500 nm; The cap layer is a p-doped gallium arsenide p-GaAs with a thickness of 300-600 nm. The steps are:

8. A method for fabricating a substrate buried grating based quantum dot DFB laser, characterized in that, ​ S1: growing a first epitaxial structure on a substrate by using MOCVD, the growth temperature is 600-750 DEG C, from bottom to top, sequentially, a buffer layer, an N-doped lower cladding layer; S2: growing a quantum dot active region and a P-doped upper cladding layer on the N-doped lower cladding layer by using an MBE device, the growth temperature is 480-520 DEG C.

9. The substrate buried grating based quantum dot DFB laser of claim 8, wherein, The specific implementation method of step S1 is: growing a first epitaxial structure on a substrate by using MOCVD, the growth temperature is 600-750 DEG C, from bottom to top, sequentially, a buffer layer, a first multilayer gradual confinement layer, a first non-gradual confinement layer, and a non-etched grating layer; preparing a periodic grating structure on the non-etched grating layer by using photoetching and plasma ICP etching, to obtain a grating layer; filling the grating layer by using MOCVD, to obtain a grating filling layer; The implementation method of step S2 is: growing a quantum dot active region, a second non-gradual confinement layer, an etching stop layer, a second multilayer gradual confinement layer, and a cap layer on the grating filling layer by using MBE.

10. The substrate buried grating based quantum dot DFB laser of claim 9, wherein, When growing the non-etched grating layer, the flow ratio of the group V element to the group III element and the growth rate are simultaneously optimized, the flow ratio of the group V element to the group III element is 40-60, and the growth rate is 0.2-0.5 nm / s; When filling the grating layer, the flow ratio of the group V element to the group III element and the growth rate are simultaneously optimized, the flow ratio of the group V element to the group III element is 10-50, and the growth rate is 0.1-0.3 nm / s.

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