Grating structure for dfb laser and preparation method thereof, and dfb laser

Abstract

This invention relates to the field of semiconductor lasers, specifically disclosing a grating structure for a DFB laser, its fabrication method, and the DFB laser itself. The fabrication method of the grating structure includes: S1, growing a grating layer on an initial epitaxial wafer; S2, etching the grating layer; S3, loading it into an MOCVD reaction chamber and heating it to T1; 300℃≤T1≤600℃; continuously introducing PH3 and H2 during the heating process, and setting the pressure to P0 after the heating is complete; S4, maintaining the temperature at T1 and introducing a flow rate of F. I1_H2 The H2 flow rate increases the pressure to P1 and is maintained for time t1; S5, the temperature is maintained at T1, and the H2 flow rate is reduced to F. I2_H2 The pressure is reduced to P2 and maintained for time t2; S6, steps S4 and S5 are repeated periodically; P1≥200 torr, P2≤60 torr, and P1-P2≥100 torr. Implementing this invention can remove contaminants from the surface of the grating structure, improve its crystal quality, and thereby improve the side-mode suppression ratio and slope efficiency of the DFB laser.

Description

Technical Field

[0001] This invention relates to the field of semiconductor lasers, and more particularly to a grating structure for a DFB laser, a method for fabricating the same, and a DFB laser. Background Technology

[0002] Distributed feedback (DFB) lasers, as core light sources in optical communication, sensing, and high-speed data transmission, rely heavily on the quality of their epitaxial growth interfaces for performance. The fabrication of DFB lasers typically involves multiple epitaxial growth stages: after the initial epitaxial growth forms the active region, waveguide layer, and other basic structures, a Bragg grating is fabricated using photolithography and etching processes. A second epitaxial growth stage is then performed to cover the grating and complete the device's vertical structure. However, the second epitaxial growth stage faces a critical challenge due to interface contamination: the etched grating surface is exposed to air, making it prone to the formation of native oxides (such as InO on the surface of InP-based materials). x GaO x The contaminants adsorb hydrocarbons. During the high-temperature secondary epitaxy process, these contaminants introduce high-density interface states, becoming non-radiative recombination centers, leading to increased threshold current, decreased slope efficiency, and deteriorated reliability. Traditional methods for removing contaminants involve continuous high-temperature hydrogen baking; however, prolonged high-temperature environments can cause thermal remelting of the grating sidewalls, resulting in grating morphology passivation, fluctuations in the coupling coefficient (κ), and ultimately affecting lasing wavelength stability and side-mode suppression ratio. Especially for buried heterojunction (BH) structures, the quality of the secondary epitaxy interface directly determines carrier confinement capability and device reliability. Defects at the interface can easily lead to carrier leakage, progressive performance degradation, and even catastrophic optical damage. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a grating structure for a DFB laser and a method for fabricating the same, which can remove contaminants from the surface of the grating structure and improve the photoelectric performance of the DFB laser.

[0004] Another technical problem that this invention aims to solve is to provide a DFB laser epitaxial wafer.

[0005] Another technical problem that the present invention needs to solve is to provide a DFB laser.

[0006] To address the aforementioned technical problems, this invention provides a method for fabricating a grating structure for a DFB laser, comprising the following steps: S1. Grate layer is grown on the initial epitaxial wafer; S2. The grating layer is etched to form periodically distributed grating ridges, resulting in a first intermediate body; wherein, grating grooves are formed between adjacent grating ridges. S3. The first intermediate is loaded into the MOCVD reaction chamber, and the MOCVD reaction chamber is heated to T1; wherein, 300℃≤T1≤600℃; PH3 and H2 are continuously introduced during the heating process, and the pressure in the MOCVD reaction chamber is P0 after the heating is completed. S4. Maintain the temperature of the MOCVD reaction chamber at T1 and introduce a flow rate of F. I1_H2 The H2 increases the pressure in the MOCVD reaction chamber to P1 and maintains it for time t1. S5. Maintain the temperature of the MOCVD reaction chamber at T1, and reduce the H2 flow rate to F. I2_H2 This is done to reduce the pressure in the MOCVD reaction chamber to P2 and maintain it for time t2. S6. Repeat steps S4 and S5 periodically for the first preset number of times to obtain the grating structure; Where P1≥200torr, P2≤60torr, and P1-P2≥100torr.

[0007] As an improvement to the above technical solution, t2≥t1≥3s, and t1+t2≥15s; The first preset number of times is ≥5 times.

[0008] As an improvement to the above technical solution, in step S4, F I1_H2 The value range of is 5slm~20slm, the value range of P1 is 220torr~350torr, and the value range of t1 is 5s~20s. In step S5, F I2_H2 The value range of P1 is 0slm~20slm, the value range of P2 is 35torr~60torr, and the value range of t2 is 6s~25s; The first preset number of times is 5 to 15 times.

[0009] As an improvement to the above technical solution, in step S4, F I1_H2 The value range of P1 is 15slm~20slm, the value range of P1 is 280torr~350torr, and the value range of t1 is 5s~10s. In step S5, F I2_H2 The value range of P1 is 0.5slm~3slm, the value range of P2 is 35torr~45torr, and the value range of t2 is 6s~12s. The first preset number of times is 10 to 15 times.

[0010] As an improvement to the above technical solution, in step S3, the value of T1 is in the range of 530℃~570℃, the flow rate of PH3 is in the range of 800sccm~1000sccm, the flow rate of H2 is in the range of 800sccm~1000sccm, and the value of P0 is in the range of 80torr~120torr. In steps S4 and S5, PH3 with a flow rate of 800 sccm to 1000 sccm is introduced into the MOCVD reaction chamber.

[0011] As an improvement to the above technical solution, step S6 includes: S61. Repeat steps S4 and S5 periodically for a second preset number of times until the partial pressures of H2O and CO2 in the exhaust gas at the outlet of the MOCVD reaction chamber are reduced to less than 10% of the partial pressures of H2O and CO2 in the exhaust gas at the outlet of the MOCVD reaction chamber in step S3. S62. Maintain the temperature of the MOCVD reaction chamber at T1, and introduce H2, a Group III MO source, a Group V reaction source, and / or PH3 to raise the pressure of the MOCVD reaction chamber to P1, and maintain this pressure for time t1; wherein the flow rate of H2 is F. I1_H2 ; S63. Maintain the temperature of the MOCVD reaction chamber at T1, and introduce H2, a Group III MO source, a Group V reaction source, and / or PH3 to reduce the pressure in the MOCVD reaction chamber to P2, and maintain this pressure for time t2; wherein the flow rate of H2 is F. I2_H2 ; S64. Repeat steps S62 and S63 a third preset number of times to form an in-situ covering layer on the grating ridge; wherein the thickness of the in-situ covering layer is less than the height of the grating ridge.

[0012] As an improvement to the above technical solution, the in-situ capping layer is an InP layer or an InGaAsP layer with a thickness of 2nm~6nm. The height of the grating ridge is 20nm~80nm.

[0013] Accordingly, the present invention also discloses a grating structure for a DFB laser, which is prepared by the above-described method for preparing a grating structure for a DFB laser.

[0014] Accordingly, the present invention also discloses a DFB laser epitaxial wafer, which includes the above-described grating structure.

[0015] Accordingly, the present invention also discloses a DFB laser, which includes the above-mentioned DFB laser epitaxial wafer.

[0016] Implementing this invention has the following beneficial effects: In one embodiment of the present invention, the fabrication method of the grating structure for a DFB laser involves first treating the grating ridge with high-flow-rate H2 and high-cavity pressure. This effectively promotes the decomposition of the oxide layer and carbon contaminants on the grating ridge surface. Then, a lower-flow-rate H2 and even lower-cavity pressure are used for further treatment, effectively promoting the discharge of the decomposed H2O and CO2. Through this cycle of steps, efficient and deep removal of the oxide layer and carbon contaminants from the grating ridge surface is achieved. The clean interface suppresses carrier leakage, improves the slope efficiency and reliability of the device, and reduces its threshold current. Furthermore, the fabrication method of the present invention effectively avoids prolonged high-temperature treatment of the grating structure, preventing grating ridge remelting. This improves the side-mode suppression ratio and slope efficiency of the DFB laser based on this grating structure. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for fabricating a grating structure for a DFB laser according to an embodiment of the present invention. Detailed Implementation

[0018] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional range of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0020] In this invention, terms such as "first aspect" and "second aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0021] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0022] Please see Figure 1As a first aspect of the present invention, the present invention provides a method for fabricating a grating structure for a DFB laser, comprising the following steps: S1. Grate layer is grown on the initial epitaxial wafer; S2. Etch the grating layer to form periodically distributed grating ridges to obtain the first intermediate; S3. Load the first intermediate into the MOCVD reaction chamber and heat the MOCVD reaction chamber to T1; S4. Maintain the temperature of the MOCVD reaction chamber at T1 and introduce a flow rate of F. I1_H2 The H2 increases the pressure in the MOCVD reaction chamber to P1 and maintains it for time t1. S5. Maintain the temperature of the MOCVD reaction chamber at T1 and reduce the H2 flow rate to F. I2_H2 This is done to reduce the pressure in the MOCVD reaction chamber to P2 and maintain it for time t2. S6. Repeat steps S4 and S5 periodically for the first preset number of times to obtain the grating structure; In step S2, 300℃≤T1≤600℃; PH3 and H2 are continuously introduced during the heating process, and the pressure in the MOCVD reaction chamber is P0 after the heating is completed; in step S4, P1≥200torr; in step S5, P2≤60torr, and P1-P2≥100torr.

[0023] Based on the above preparation method, high-flow-rate H2 and higher chamber pressure are used in step S4, which effectively promotes the decomposition of oxide layer and carbon contaminants on the grating ridge surface. In step S5, low-flow-rate H2 and lower chamber pressure are used, which effectively promotes the discharge of H2O and CO2 obtained from decomposition. Through the cycle of the above steps, efficient and deep removal of oxide layer and carbon contaminants on the grating ridge surface is achieved. The clean interface suppresses carrier leakage, improves the slope efficiency and reliability of the device, and reduces its threshold current. Moreover, the preparation method of the present invention can effectively avoid processing the grating structure at high temperature for a long time and avoid grating ridge remelting, which improves the side-mode suppression ratio and slope efficiency of the DFB laser based on the grating structure.

[0024] Specifically, in step S1, the initial epitaxial wafer includes a substrate, and a lower confinement layer, a multiple quantum well layer, and an upper confinement layer sequentially stacked on the substrate, but is not limited thereto. Specifically, the substrate can be an InP substrate, a Si substrate, or a GaAs substrate, but is not limited thereto. The lower confinement layer can be an N-type InGaAlAs layer, an N-type InAlAs layer, a P-type InGaAlAs layer, or a P-type InAlAs layer, but is not limited thereto. The multiple quantum well layer is a periodic structure formed by alternating stacks of InGaAlAs well layers and InGaAlAs barrier layers, or a periodic structure formed by alternating stacks of InGaAs P-well layers and InGaAs P-barrier layers, but is not limited thereto. The upper confinement layer can be an N-type InGaAlAs layer, an N-type InAlAs layer, a P-type InGaAlAs layer, or a P-type InAlAs layer, but is not limited thereto.

[0025] Preferably, in some embodiments, the initial epitaxial wafer includes a substrate, and a P-type InP lower cladding layer, a P-type InAlAs lower confinement layer, a P-type InGaAsP lower waveguide layer, an unintentionally doped InP spacer layer, an InGaAsP multiple quantum well active region, an N-type InAlAs upper confinement layer, an N-type InP etch stop layer, an N-type InGaAsP upper waveguide layer, and an N-type InP upper cladding layer are sequentially stacked on the substrate.

[0026] The substrate is an InP substrate. The thickness of the P-type InP underlayer is 280 nm to 320 nm, and the doping concentration is 1 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The thickness of the confinement layer in p-type InAlAs is 450 nm to 550 nm, and the doping concentration is 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The photoluminescence wavelength of the P-type InGaAsP waveguide layer is 1130 nm to 1140 nm, its thickness is 25 nm to 35 nm, and its doping concentration is 1 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The unintentionally doped InP spacer layer has a thickness of 550 nm to 650 nm and a background impurity concentration ≤ 5 × 10⁻⁶. 15 cm -3The InGaAsP multi-quantum-well active region comprises 3–7 cycles of InGaAsP well layers and InGaAsP barrier layers. The thickness of the InGaAsP well layers is 4 nm–6 nm, and the thickness of the InGaAsP barrier layers is 18 nm–22 nm. The emission wavelength of the InGaAsP multi-quantum-well active region is 1540 nm–1560 nm. The thickness of the N-type InAlAs confinement layer is 450 nm–550 nm, and the doping concentration is 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The thickness of the N-type InP etch stop layer is 1600 nm to 1700 nm, and the doping concentration is 1 × 10⁻⁶. 17 cm -3 ~3×10 18 cm -3 The photoluminescence wavelength of the waveguide layer on N-type InGaAsP is 1130 nm to 1140 nm, its thickness is 25 nm to 35 nm, and its doping concentration is 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The thickness of the cladding layer on N-type InP is 750 nm to 850 nm, and the doping concentration is 1 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 .

[0027] Specifically, in step S1, the grating layer is an InGaAsP layer, an AlGaAs layer, or an InP layer, but is not limited to these. Preferably, in some embodiments, the grating layer is an InGaAsP layer with a thickness of 30 nm to 100 nm.

[0028] Specifically, in step S2, the grating layer can be etched using ICP, RIE, or wet etching processes, but is not limited to these. The period of the grating ridge formed after etching is 240nm~245nm, and the height of the grating ridge (i.e., the etching depth) is 20nm~80nm.

[0029] Specifically, in step S3, by continuously introducing PH3 and H2 during the heating process, a protective atmosphere can be formed to prevent phosphorus from escaping from the grating layer and maintain the integrity of the grating structure. Specifically, the flow rate of PH3 is 800 sccm to 1000 sccm, exemplarily 825 sccm, 850 sccm, 875 sccm, 900 sccm, 925 sccm, 950 sccm, or 975 sccm, but not limited thereto. Preferably, the flow rate of PH3 is 850 sccm to 950 sccm. The flow rate of H2 is 800 sccm to 1000 sccm, exemplarily 825 sccm, 850 sccm, 875 sccm, 900 sccm, 925 sccm, 950 sccm, or 975 sccm, but not limited thereto. Preferably, the flow rate of H2 is 850 sccm to 950 sccm.

[0030] Specifically, in step S3, the heating process can be carried out at a constant rate or at a non-constant rate. For example, a stepped heating method or a rapid-then-slow heating method can be used, but it is not limited to these methods. Preferably, in some embodiments, the heating rate is constant. More specifically, the heating rate is 3℃ / min to 15℃ / min, exemplarily 4.5℃ / min, 6℃ / min, 7.5℃ / min, 9℃ / min, 10.5℃ / min, 12℃ / min or 13.5℃ / min, but it is not limited to these methods.

[0031] For example, in step S3, after the heating is completed, the temperature T1 inside the MOCVD reaction chamber is 350°C, 400°C, 450°C, 500°C, 550°C, or 580°C, but is not limited thereto. Preferably, in some embodiments, the value of T1 is in the range of 530°C to 570°C, more preferably 550°C to 570°C.

[0032] Specifically, in step S3, after the heating is completed, the pressure P0 in the MOCVD reaction chamber ranges from 80 torr to 120 torr, exemplarily 85 torr, 90 torr, 95 torr, 100 torr, 105 torr, 110 torr, or 115 torr, but is not limited thereto. Preferably, in some embodiments, the value of P0 ranges from 80 torr to 110 torr. More preferably, it ranges from 90 torr to 105 torr.

[0033] Specifically, in step S4, F I1_H2 The value range is 5 slm to 25 slm, exemplarily 7.5 slm, 10 slm, 12.5 slm, 15 slm, 17.5 slm, 20 slm, or 22.5 slm, but is not limited thereto. Preferably, in some embodiments, FI1_H2 The value range is 5slm to 20slm, and more preferably 15slm to 20slm.

[0034] Specifically, in step S4, the value of P1 ranges from 210 torr to 350 torr, exemplarily 220 torr, 240 torr, 260 torr, 280 torr, 300 torr, 320 torr, or 340 torr, but is not limited thereto. Preferably, in some embodiments, the value of P1 ranges from 220 torr to 350 torr, more preferably from 280 torr to 350 torr.

[0035] Specifically, in step S4, t1 ≥ 3s to ensure sufficient reaction with pollutants such as the oxide layer. Preferably, the value of t1 ranges from 5s to 25s, exemplarily 8s, 12s, 16s, 20s, or 24s, but is not limited thereto. More preferably, the value of t1 ranges from 5s to 20s; even more preferably, it ranges from 5s to 10s.

[0036] By controlling the flow rate of H2, the pressure in the MOCVD reaction chamber, and the holding time in step S4, it is possible to react with as many pollutants as possible with the oxide layer and reduce phosphorus overflow during this stage.

[0037] Specifically, in step S5, F I2_H2 The value range is 0 slm to 20 slm, exemplarily 1 slm, 4.5 slm, 8 slm, 12.5 slm, 15 slm, or 18.5 slm, but is not limited thereto. Preferably, in some embodiments, F I2_H2 The value range is 0slm to 20slm, and more preferably 0.5slm to 3slm.

[0038] Specifically, in step S5, the value of P2 ranges from 30 torr to 60 torr, exemplarily 35 torr, 40 torr, 45 torr, 50 torr, or 55 torr, but is not limited thereto. Preferably, in some embodiments, the value of P2 ranges from 35 torr to 60 torr, more preferably from 35 torr to 45 torr.

[0039] Specifically, in step S5, t2 ≥ 3s to better remove impurity gases (such as H2O, CO2, etc.) generated in step S4. Preferably, the value of t2 is in the range of 5s to 25s, exemplarily 8s, 12s, 16s, 20s, or 24s, but not limited thereto. More preferably, the value of t2 is in the range of 6s to 25s; even more preferably, it is in the range of 6s to 12s.

[0040] By controlling the H2 flow rate, the pressure inside the MOCVD reaction chamber, and the holding time in step S5, as many contaminants as possible can be removed during this stage.

[0041] Preferably, in some embodiments, t1+t2≥15s to ensure that contaminants are completely removed without damaging the epitaxial layer structure.

[0042] Specifically, in step S6, the first preset number of times is ≥5 times to better achieve deep removal of pollutants. More specifically, the first preset number of times is 5 to 20 times, exemplarily 6, 8, 10, 12, 14, 16, or 18 times, but not limited thereto. Preferably, in some embodiments, the first preset number of times is 5 to 15 times, more preferably 10 to 15 times.

[0043] Preferably, in some embodiments, in steps S4 and S5, PH3 with a flow rate of 800 sccm to 1000 sccm is introduced into the MOCVD reaction chamber. By continuously introducing PH3, the overflow of P in the grating structure can be effectively avoided, further ensuring the integrity of the grating structure and improving the various performance characteristics of the DFB laser.

[0044] Preferably, in some embodiments, step S6 includes: S61. Repeat steps S4 and S5 periodically for a second preset number of times until the partial pressures of H2O and CO2 in the exhaust gas at the outlet of the MOCVD reaction chamber are reduced to less than 10% of the partial pressures of H2O and CO2 in the exhaust gas at the outlet of the MOCVD reaction chamber in step S3. S62. Maintain the temperature of the MOCVD reaction chamber at T1, and introduce H2, a group III MO source, a group V reaction source and / or PH3 to increase the pressure of the MOCVD reaction chamber to P1 and maintain it for time t1. S63. Maintain the temperature of the MOCVD reaction chamber at T1, and introduce H2, a group III MO source and PH3 to reduce the pressure in the MOCVD reaction chamber to P2 and maintain it for time t2. S64. Repeat steps S62 and S63 a third preset number of times to form an in-situ covering layer on the grating ridge. In step S61, the partial pressure of H2O in the exhaust gas at the outlet of the MOCVD reaction chamber is P. O2_H2O The partial pressure of CO2 is P O2_CO2 In step S3, the partial pressure of H2O in the exhaust gas at the outlet of the MOCVD reaction chamber is P. O1_H2O The partial pressure of CO2 is P O1_CO2 That is, when P O2_H2O / P O1_H2O ≤10% and P O2_CO2 / P O1_CO2When the percentage is ≤10%, the number of cycles is the second preset number. After this cycle, the surface cleaning of the grating ridge is basically completed, so a group III MO source is subsequently introduced for in-situ growth of the capping layer.

[0045] In steps S62 and S63, the Group III MO source includes an In source and / or a Ga source, specifically TMI, TMG, TEGa, or TEIn, but is not limited thereto. The Group V reaction source is an As source, specifically AsH3, TBAs, or TMAs, but is not limited thereto. The Group III MO source can be introduced into the MOCVD reaction chamber via a carrier gas (H2 and / or N2), while the Group V reaction source can be directly introduced or introduced into the MOCVD reaction chamber via a carrier gas (H2 and / or N2). Preferably, in some embodiments, N2 is used as the carrier gas to carry TMI into the MOCVD reaction chamber, and the N2 flow rate is 40 sccm to 50 sccm.

[0046] In step S62, the inflow rate of H2 is F. I1_H2 The value of is in the range of 5slm to 25slm, preferably 5slm to 20slm, and more preferably 15slm to 20slm. The value of P1 is in the range of 210torr to 350torr, preferably 220torr to 350torr, and more preferably 280torr to 350torr. The value of t1 is in the range of 5s to 25s, preferably 5s to 20s; more preferably 5s to 10s.

[0047] In step S63, the inflow rate of H2 is F. I2_ The value of is 0 slm to 20 slm, preferably 0 slm to 20 slm, and more preferably 0.5 slm to 3 slm. The value of P2 is 30 torr to 60 torr, preferably 35 torr to 60 torr, and more preferably 35 torr to 45 torr. The value of t2 is 5 s to 25 s, preferably 6 s to 25 s; more preferably 6 s to 12 s.

[0048] In step S64, the third preset number of times can be determined based on the specific growth thickness of the in-situ capping layer. Specifically, the in-situ capping layer is an InP layer or an InGaAsP layer with a thickness of 2nm to 6nm. Further, the sum of the second and third preset number of times is 5 to 20 times, which is the first preset number of times.

[0049] By growing an in-situ capping layer on the cleaned grating ridge, interface defects can be further reduced, preventing the grating from being corroded or melted back, and improving the performance of the DFB laser.

[0050] Accordingly, as a second aspect of the present invention, the present invention also provides a grating structure for a DFB laser, which is prepared by the above-described method for preparing a grating structure for a DFB laser. This grating structure has high crystal quality, a complete grating ridge structure, and no obvious remelting.

[0051] Accordingly, as a third aspect of the present invention, the present invention also provides a DFB laser epitaxial wafer comprising the above-described grating structure for a DFB laser.

[0052] Furthermore, the DFB laser epitaxial wafer also includes a cladding layer, a barrier gradient layer, and a contact layer, but is not limited thereto. Preferably, in some embodiments, the DFB laser epitaxial wafer further includes a p-type InP cladding layer and a p-type InGaAs contact layer. The p-type InP cladding layer has a thickness of 1.7 μm to 2 μm and a doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 18 cm -3 The thickness of the p-type InGaAs layer is 180 nm to 220 nm, and the doping concentration is 1 × 10⁻⁶. 19 cm -3 ~1×10 20 cm -3 .

[0053] Accordingly, as a fourth aspect of the present invention, the present invention also provides a DFB laser comprising the above-described DFB laser epitaxial wafer.

[0054] The present invention is further illustrated below with specific embodiments: Example 1 This embodiment provides a method for fabricating a grating structure for a DFB laser, which includes the following steps: (1) A grating layer is grown on the initial epitaxial wafer; The initial epitaxial wafer includes a substrate, and P-type InP lower cladding, P-type InAlAs lower confinement layer, P-type InGaAsP lower waveguide layer, unintentionally doped InP spacer layer, InGaAsP multi-quantum well active region, N-type InAlAs upper confinement layer, N-type InP etch stop layer, N-type InGaAsP upper waveguide layer and N-type InP upper cladding are sequentially stacked on the substrate.

[0055] The substrate is an InP substrate. The thickness of the P-type InP cladding layer is 300 nm, and the doping concentration is 1 × 10⁻⁶. 18 cm -3 The thickness of the confinement layer in p-type InAlAs is 500 nm, and the doping concentration is 1 × 10⁻⁶. 18 cm -3The photoluminescence wavelength of the P-type InGaAsP waveguide layer is 1135 nm, its thickness is 30 nm, and its doping concentration is 1 × 10⁻⁶. 18 cm -3 The unintentionally doped InP spacer layer has a thickness of 600 nm and a background impurity concentration ≤ 5 × 10⁻⁶. 15 cm -3 The InGaAsP multiple quantum well active region comprises five periods of InGaAsP well layers and InGaAsP barrier layers. The InGaAsP well layers are 5 nm thick, and the InGaAsP barrier layers are 19 nm thick. The emission wavelength of the InGaAsP multiple quantum well active region is 1550 nm. The N-type InAlAs confinement layer is 500 nm thick and has a doping concentration of 5 × 10⁻⁶. 18 cm -3 The thickness of the N-type InP etch stop layer is 1650 nm, and the doping concentration is 1 × 10⁻⁶. 18 cm -3 The photoluminescence wavelength of the waveguide layer on N-type InGaAsP is 1135 nm, its thickness is 30 nm, and its doping concentration is 5 × 10⁻⁶. 18 cm -3 The thickness of the cladding layer on N-type InP is 800 nm, and the doping concentration is 1 × 10⁻⁶. 18 cm -3 The grating layer is an InGaAsP layer with a thickness of 45 nm.

[0056] (2) The grating layer is etched to form periodically distributed grating ridges, thus obtaining the first intermediate; Specifically, the grating layer is etched using an ICP etching process to form periodically distributed grating ridges with a period of 242 nm, a height of 25 nm, and a sidewall tilt angle of 88°.

[0057] (3) The first intermediate was loaded into the MOCVD reaction chamber and heated to 550℃ (T1) at a heating rate of 10℃ / min. During the heating process, PH3 with a flow rate of 900 sccm and H2 with a flow rate of 850 sccm were continuously introduced. After the heating was completed, the pressure in the MOCVD reaction chamber was 85 torr (P0).

[0058] (4) Maintain the temperature of the MOCVD reaction chamber at T1 and introduce a flow rate of 10 slm (F) I1_H2 The pressure in the MOCVD reaction chamber was increased to 250 torr (P1) by H2 and PH3 at a flow rate of 900 sccm and maintained for 15 s (t1). (5) Maintain the temperature of the MOCVD reaction chamber at T1 and reduce the H2 flow rate to 0 slm (F). I2_H2), and PH3 with a flow rate of 900 sccm is introduced to reduce the pressure in the MOCVD reaction chamber to 50 torr (P2) and maintain it for 15s (t2). (6) Repeat steps (4) and (5) periodically a total of 3 times; (7) Maintain the temperature of the MOCVD reaction chamber at T1 and introduce a flow rate of 10 slm (F). I1_H2 The pressure in the MOCVD reaction chamber was increased to 250 torr (P1) by using H2, PH3 at a flow rate of 900 sccm and TMIn (N2 as carrier gas at a flow rate of 40 sccm) and maintained for 15 s (t1). (8) Maintain the temperature of the MOCVD reaction chamber at T1, and introduce PH3 and TMIn at a flow rate of 900 sccm (N2 is used as the carrier gas, and the flow rate of the carrier gas is 40 sccm) to reduce the pressure in the MOCVD reaction chamber to 50 torr (P2) and maintain it for 15s (t2). (9) Repeat steps (7) and (8) a total of 7 times to form an in-situ capping layer on the grating ridge; wherein the in-situ capping layer is an InP layer with a thickness of 3nm.

[0059] Example 2 This embodiment provides a method for fabricating a grating structure for a DFB laser, which includes the following steps: (1) A grating layer is grown on the initial epitaxial wafer; The initial epitaxial wafer includes a substrate, and P-type InP lower cladding, P-type InAlAs lower confinement layer, P-type InGaAsP lower waveguide layer, unintentionally doped InP spacer layer, InGaAsP multi-quantum well active region, N-type InAlAs upper confinement layer, N-type InP etch stop layer, N-type InGaAsP upper waveguide layer and N-type InP upper cladding are sequentially stacked on the substrate.

[0060] The substrate is an InP substrate. The thickness of the P-type InP cladding layer is 300 nm, and the doping concentration is 1 × 10⁻⁶. 18 cm -3 The thickness of the confinement layer in p-type InAlAs is 500 nm, and the doping concentration is 1 × 10⁻⁶. 18 cm -3 The photoluminescence wavelength of the P-type InGaAsP waveguide layer is 1135 nm, its thickness is 30 nm, and its doping concentration is 1 × 10⁻⁶. 18 cm -3 The unintentionally doped InP spacer layer has a thickness of 600 nm and a background impurity concentration ≤ 5 × 10⁻⁶. 15 cm -3The InGaAsP multiple quantum well active region comprises five periods of InGaAsP well layers and InGaAsP barrier layers. The InGaAsP well layers are 5 nm thick, and the InGaAsP barrier layers are 19 nm thick. The emission wavelength of the InGaAsP multiple quantum well active region is 1550 nm. The N-type InAlAs confinement layer is 500 nm thick and has a doping concentration of 5 × 10⁻⁶. 18 cm -3 The thickness of the N-type InP etch stop layer is 1650 nm, and the doping concentration is 1 × 10⁻⁶. 18 cm -3 The photoluminescence wavelength of the waveguide layer on N-type InGaAsP is 1135 nm, its thickness is 30 nm, and its doping concentration is 5 × 10⁻⁶. 18 cm -3 The thickness of the cladding layer on N-type InP is 800 nm, and the doping concentration is 1 × 10⁻⁶. 18 cm -3 The grating layer is an InGaAsP layer with a thickness of 45 nm.

[0061] (2) The grating layer is etched to form periodically distributed grating ridges, thus obtaining the first intermediate; Specifically, the grating layer is etched using an ICP etching process to form periodically distributed grating ridges with a period of 242 nm, a height of 25 nm, and a sidewall tilt angle of 88°.

[0062] (3) The first intermediate was loaded into the MOCVD reaction chamber and heated to 570℃ (T1) at a heating rate of 10℃ / min. During the heating process, PH3 with a flow rate of 900 sccm and H2 with a flow rate of 850 sccm were continuously introduced. After the heating was completed, the pressure in the MOCVD reaction chamber was 85 torr (P0).

[0063] (4) Maintain the temperature of the MOCVD reaction chamber at T1 and introduce a flow rate of 18 slm (F). I1_H2 The pressure in the MOCVD reaction chamber was increased to 300 torr (P1) by H2 and PH3 at a flow rate of 900 sccm and maintained for 6 s (t1). (5) Maintain the temperature of the MOCVD reaction chamber at T1 and reduce the H2 flow rate to 1 slm (F I2_H2 Furthermore, PH3 with a flow rate of 900 sccm was introduced to reduce the pressure in the MOCVD reaction chamber to 40 torr (P2) and maintain it for 9s (t2). (6) Repeat steps (4) and (5) periodically a total of 3 times; (7) Maintain the temperature of the MOCVD reaction chamber at T1 and introduce a flow rate of 10 slm (F)I1_H2 The pressure in the MOCVD reaction chamber was increased to 300 torr (P1) by using H2, PH3 at a flow rate of 900 sccm and TMIn (N2 as carrier gas at a flow rate of 40 sccm) and maintained for 6 s (t1). (8) Maintain the temperature of the MOCVD reaction chamber at T1 and introduce a flow rate of 10 slm (F). I2_H2 The pressure in the MOCVD reaction chamber was reduced to 50 torr (P2) by H2, PH3 at a flow rate of 900 sccm and TMIn (N2 as carrier gas at a flow rate of 40 sccm) and maintained for 9 s (t2). (9) Repeat steps (7) and (8) a total of 9 times to form an in-situ capping layer on the grating ridge; wherein the in-situ capping layer is an InP layer with a thickness of 3.5 nm.

[0064] Comparative Example 1 This comparative example provides a method for fabricating a grating structure for a DFB laser. The difference between this method and Example 1 is that steps (3) to (9) are not included. After etching to form the grating ridge, the first intermediate is loaded into the MOCVD reaction chamber and heated to 670°C at a heating rate of 10°C / min. During the heating process, PH3 with a flow rate of 900 sccm and H2 with a flow rate of 2 slm are continuously introduced. After the heating is completed, the temperature is maintained for 300 s.

[0065] Everything else is the same as in Example 1.

[0066] Comparative Example 2 This comparative example provides a method for fabricating a grating structure for a DFB laser. The difference between this method and Example 1 is that steps (3) to (9) are not included. After etching to form the grating ridge, the first intermediate is loaded into the MOCVD reaction chamber and heated to 570°C at a heating rate of 10°C / min. During the heating process, PH3 with a flow rate of 900 sccm and H2 with a flow rate of 2 slm are continuously introduced. After the heating is completed, the temperature is maintained for 300 s.

[0067] Everything else is the same as in Example 1.

[0068] The grating structures obtained in Examples 1-2, Comparative Example 1, and Comparative Example 2 were fabricated into DFB laser chips, and their performance was tested. The specific results are as follows:

[0069] The above description is a preferred embodiment of the invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the invention, and these improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. A method for fabricating a grating structure for a DFB laser, characterized in that, Includes the following steps: S1. Grate layer is grown on the initial epitaxial wafer; S2. The grating layer is etched to form periodically distributed grating ridges, resulting in a first intermediate body; wherein, grating grooves are formed between adjacent grating ridges. S3. The first intermediate is loaded into the MOCVD reaction chamber, and the MOCVD reaction chamber is heated to T1; wherein, 300℃≤T1≤600℃; PH3 and H2 are continuously introduced during the heating process, and the pressure in the MOCVD reaction chamber is P0 after the heating is completed. S4. Maintain the temperature of the MOCVD reaction chamber at T1 and introduce a flow rate of F. I1_H2 The H2 increases the pressure in the MOCVD reaction chamber to P1 and maintains it for time t1. S5. Maintain the temperature of the MOCVD reaction chamber at T1, and reduce the H2 flow rate to F. I2_H2 This is done to reduce the pressure in the MOCVD reaction chamber to P2 and maintain it for time t2. S6. Repeat steps S4 and S5 periodically for the first preset number of times to obtain the grating structure; Where P1≥200torr, P2≤60torr, and P1-P2≥100torr.

2. The method for fabricating a grating structure for a DFB laser as described in claim 1, characterized in that, t2≥t1≥3s, and t1+t2≥15s; The first preset number of times is ≥5 times.

3. The method for fabricating a grating structure for a DFB laser as described in claim 1, characterized in that, In step S4, F I1_H2 The value range of is 5slm~20slm, the value range of P1 is 220torr~350torr, and the value range of t1 is 5s~20s. In step S5, F I2_H2 The value range of P1 is 0slm~20slm, the value range of P2 is 35torr~60torr, and the value range of t2 is 6s~25s; The first preset number of times is 5 to 15 times.

4. The method for fabricating a grating structure for a DFB laser as described in claim 1, characterized in that, In step S4, F I1_H2 The value range of P1 is 15slm~20slm, the value range of P1 is 280torr~350torr, and the value range of t1 is 5s~10s. In step S5, F I2_H2 The value range of P1 is 0.5slm~3slm, the value range of P2 is 35torr~45torr, and the value range of t2 is 6s~12s. The first preset number of times is 10 to 15 times.

5. The method for fabricating a grating structure for a DFB laser as described in claim 1, characterized in that, In step S3, the value of T1 ranges from 530℃ to 570℃, the flow rate of PH3 is 800 sccm to 1000 sccm, the flow rate of H2 is 800 sccm to 1000 sccm, and the value of P0 ranges from 80 torr to 120 torr. In steps S4 and S5, PH3 with a flow rate of 800 sccm to 1000 sccm is introduced into the MOCVD reaction chamber.

6. The method for fabricating a grating structure for a DFB laser as described in any one of claims 1 to 5, characterized in that, Step S6 includes: S61. Repeat steps S4 and S5 periodically for a second preset number of times until the partial pressures of H2O and CO2 in the exhaust gas at the outlet of the MOCVD reaction chamber are reduced to less than 10% of the partial pressures of H2O and CO2 in the exhaust gas at the outlet of the MOCVD reaction chamber in step S3. S62. Maintain the temperature of the MOCVD reaction chamber at T1, and introduce H2, a Group III MO source, a Group V reaction source, and / or PH3 to raise the pressure of the MOCVD reaction chamber to P1, and maintain this pressure for time t1; wherein the flow rate of H2 is F. I1_H2 ; S63. Maintain the temperature of the MOCVD reaction chamber at T1, and introduce H2, a Group III MO source, a Group V reaction source, and / or PH3 to reduce the pressure in the MOCVD reaction chamber to P2, and maintain this pressure for time t2; wherein the flow rate of H2 is F. I2_H2 ; S64. Repeat steps S62 and S63 a third preset number of times to form an in-situ covering layer on the grating ridge; wherein the thickness of the in-situ covering layer is less than the height of the grating ridge.

7. The method for fabricating a grating structure for a DFB laser as described in claim 6, characterized in that, The in-situ capping layer is an InP layer or an InGaAsP layer with a thickness of 2nm to 6nm; The height of the grating ridge is 20nm~80nm.

8. A grating structure for a DFB laser, characterized in that, It is prepared by the method for preparing a grating structure for a DFB laser as described in any one of claims 1 to 7.

9. A DFB laser epitaxial wafer, characterized in that, Includes the grating structure for a DFB laser as described in claim 8.

10. A DFB laser, characterized in that, Includes the DFB laser epitaxial wafer as described in claim 9.

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