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

Abstract

The application discloses a kind of to be related to the field of semiconductor laser, specifically discloses a kind of grating structure for DFB laser and its preparation method, DFB laser.The preparation method of grating structure includes: S1, grating layer is grown on initial epitaxial wafer;S2, grating layer is etched;S3, load into MOCVD reaction chamber, warm up to T1, keep warm first preset time;PH3 is continuously imported during the process of warming up;PH3 is imported flow rate F1 when keeping warm ends;S4, warm up to T2, PH3 and TMIn are continuously imported during the process of warming up;T2-T1>10 ℃, and PH3 import flow rate is increasing during the process of warming up;S5, cool down to T1, PH3 and TMIn are continuously imported during the process of cooling down;PH3 import flow rate is decreasing during the process of cooling down;S6, periodically repeat steps S4 and S5, until buried layer is obtained, grating structure is obtained.The application can reduce grating remelting, improve the crystal quality of grating structure, reduce interface roughness, so as to improve the side mode suppression ratio, slope efficiency of 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 a type of high-performance semiconductor laser, have become a core light source in modern optical communication, gas sensing, and medical devices due to their superior single-mode characteristics, narrow linewidth, and high side-mode suppression ratio. Their performance is highly dependent on the quality of the internally integrated Bragg grating, which achieves precise wavelength selection and stable single-mode output by forming a distributed feedback mechanism within the resonant cavity. However, traditional processes typically require fabricating nanoscale gratings on a structure formed through primary epitaxy (e.g., an InGaAsP grating layer), followed by secondary epitaxial growth to cover the grating and complete the device structure. In the high-temperature environment of secondary epitaxy (typically above 650°C), phosphorus (P) in the grating layer material (such as InGaAsP) is prone to volatilization due to its high equilibrium vapor pressure, leading to grating morphology collapse, compositional changes, and even structural failure. This not only disrupts the grating's periodicity and coupling coefficient, resulting in a decrease in the side-mode suppression ratio, but also introduces defects, significantly degrading the laser's output power, wavelength stability, and lifetime.

[0003] To suppress grating remelting, existing technologies often employ low-temperature epitaxy (growth temperature ≤550℃) for secondary epitaxial growth. While low temperatures reduce phosphorus volatilization, they also introduce new problems: the migration ability of surface atoms is severely insufficient at low temperatures, leading to poor crystal quality in the epitaxial layer. This manifests as increased point defects and decreased carrier mobility, thus limiting the efficiency and high-frequency response characteristics of the laser. Therefore, traditional single low-temperature processes face a dilemma of simultaneously failing to suppress remelting and ensuring crystal quality. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a grating structure for DFB lasers and a method for fabricating the same, which can suppress grating remelting and improve its crystal quality.

[0005] Another technical problem that this invention aims to solve is to provide a DFB laser epitaxial wafer.

[0006] Another technical problem that the present invention needs to solve is to provide a DFB laser.

[0007] 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. Etch the grating layer to form periodically distributed grating ridges to obtain the first intermediate; S3. The first intermediate is loaded into the MOCVD reaction chamber, and the MOCVD reaction chamber is heated to T1 and held at that temperature for a first preset time; wherein, 300℃≤T1≤600℃; PH3 is continuously introduced during the heating process; and the flow rate of PH3 at the end of the holding period is F1. S4. Heat the MOCVD reaction chamber to T2, continuously introducing TMI and PH3 during the heating process; wherein, T2-T1>10℃, and the flow rate of PH3 increases during the heating process. S5. Cool the MOCVD reaction chamber to T1, continuously introducing TMI and PH3 during the cooling process; the flow rate of PH3 decreases during the cooling process. S6. Repeat steps S4 and S5 periodically until a buried layer covering the grating ridge is obtained, thus obtaining the grating structure.

[0008] As an improvement to the above technical solution, in step S4, the heating time is t. r In step S5, the cooling time is t. P -t r ;t r :(t P -t r = 1:2~2:1 and / or In step S6, the duration of a single repetition cycle is t. P , t P ≥50s; Number of cycles ≥5; and / or The thickness of the buried layer is 2nm to 6nm greater than the height of the grating ridge.

[0009] As an improvement to the above technical solution, in step S4, the flow rate of PH3 is calculated according to the following set of formulas:

[0010]

[0011] In the formula, Let F1 be the flow rate of PH3 at time i, and F1 be the flow rate of PH3 at the end of the heat preservation in step S3. T is a constant, and its value ranges from 5 to 15; i Let T1 be the temperature of the MOCVD reaction chamber at time i, T2 be the temperature of the MOCVD reaction chamber after the temperature rise in step S3, and T3 be the temperature of the MOCVD reaction chamber after the temperature rise in step S4. For the heating time in a single step S4, t iLet t be the time interval between time i and time k, where time k is the end time of step S3, n is the number of repetition cycles in step S6, and t is the time interval between time i and time k. p The duration of a single repetition cycle in step S6.

[0012] As an improvement to the above technical solution, in step S5, the flow rate of PH3 is calculated according to the following set of formulas:

[0013]

[0014] In the formula, Let F1 be the flow rate of PH3 at time j, and F1 be the flow rate of PH3 at the end of the heat preservation process in step S3. T is a constant, and its value ranges from 5 to 15; j Let T1 be the temperature of the MOCVD reaction chamber at time j, T2 be the temperature of the MOCVD reaction chamber after the temperature rise in step S3, and T2 be the temperature of the MOCVD reaction chamber after the temperature rise in step S4. For the heating time in a single step S4, t j Let t be the time interval between time j and time k, where time k is the end time of step S3, n is the number of repetition cycles in step S6, and t is the time interval between time j and time k. p The duration of a single repetition cycle in step S6.

[0015] As an improvement to the above technical solution, the value range of F1 is 500 sccm to 650 sccm; The value of T1 ranges from 500℃ to 560℃; The value of T2 ranges from 580℃ to 620℃; In step S6, the duration of a single repetition cycle is t. p , t p The value range is 50s~150s, and the number of cycles is 8~20.

[0016] As an improvement to the above technical solution, in steps S4 and S5, the TMI flow rate is the same, and TMI is carried into the MOCVD reaction chamber by H2 as a carrier gas, with an H2 flow rate of 200 sccm to 500 sccm; and / or In step S4, the heating rate is 0.1℃ / s to 3℃ / s; and / or In step S5, the cooling rate is 0.1℃ / s to 3℃ / s.

[0017] As an improvement to the above technical solution, step S3 includes: S31: The first intermediate is loaded into the MOCVD reaction chamber and heated to 400℃~500℃ at a heating rate of 5℃ / min~15℃ / min, and held at that temperature for 10min~20min. S32: Introduce H2 and PH3 into the MOCVD reaction chamber and heat to T1 at a heating rate of 3℃ / min~10℃ / min, and hold for 10min~30min; wherein, the flow rate of H2 is 800sccm~1200sccm and the flow rate of PH3 is 800sccm~1000sccm. S33: After the insulation is completed, adjust the flow rate of PH3 to F1.

[0018] 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.

[0019] Accordingly, the present invention also discloses a DFB laser epitaxial wafer, which includes the above-described grating structure.

[0020] Accordingly, the present invention also discloses a DFB laser, which includes the above-mentioned DFB laser epitaxial wafer.

[0021] 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 employs a periodic, repeating growth mode of gradient heating and gradient cooling during the growth of the buried layer. The heating process provides migration energy to surface atoms, promoting defect repair; the gradient cooling enables relaxation freezing of the crystal structure, reducing dislocation density. Furthermore, the increasing flow rate of PH3 during gradient heating suppresses the volatilization of P in the grating layer at high temperatures, significantly reducing the remelting rate and lowering the interface roughness at the contact between the grating layer and the buried layer. Conversely, the decreasing flow rate of PH3 during gradient cooling improves the crystal quality of the buried layer itself, further reducing interface roughness. Specifically, the grating structure obtained by the above fabrication method has an interface roughness ≤0.8 nm. This grating structure exhibits high coupling efficiency, improving the side-mode suppression ratio and slope efficiency of the DFB laser based on this grating structure. Attached Figure Description

[0022] 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; Figure 2 This is a transmission electron microscope image of the grating structure obtained in Embodiment 1 of the present invention; Figure 3 This is a transmission electron microscope image of the grating structure obtained in Comparative Example 1. Detailed Implementation

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Please see Figure 1 As 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, heat the MOCVD reaction chamber to T1, and keep it at that temperature for a first preset time. S4. Heat the MOCVD reaction chamber to T2, continuously introducing TMI and PH3 during the heating process; S5. Cool the MOCVD reaction chamber to T1, continuously introducing TMI and PH3 during the cooling process; S6. Repeat steps S4 and S5 periodically until a buried layer covering the grating ridge is obtained, thus obtaining the grating structure.

[0028] In step S3, 300℃≤T1≤600℃; PH3 is continuously introduced during the heating process; the PH3 flow rate at the end of the holding period is F1; in step S4, T2-T1>10℃, and the PH3 flow rate increases during the heating process; in step S5, the PH3 flow rate decreases during the cooling process. Based on the above preparation method, a periodic repetitive growth mode of gradient heating-gradient cooling is adopted during the growth of the buried layer. The heating process can provide migration energy for surface atoms, promoting defect repair; the gradient cooling can achieve relaxation freezing of the crystal structure, reducing dislocation density. In addition, the increasing PH3 flow rate during the gradient heating process can suppress the volatilization of P in the grating layer at high temperatures, significantly reducing the remelting rate and reducing the interface roughness at the contact between the grating layer and the buried layer. The decreasing PH3 flow rate during the gradient cooling process is beneficial to improving the crystal quality of the buried layer itself and further reducing the interface roughness. Specifically, the grating structure obtained based on the above preparation method has an interface roughness ≤0.8nm. This grating structure has high coupling efficiency, improving the side-mode suppression ratio and slope efficiency of the DFB laser based on this grating structure.

[0029] 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.

[0030] 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.

[0031] 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 -3The 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 -3 The 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 18–22 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 .

[0032] 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 50 nm.

[0033] 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~30nm.

[0034] Specifically, in step S3, by continuously introducing PH3 during the heating process, a protective atmosphere can be formed to prevent P from overflowing from the grating layer. Specifically, the PH3 flow rate F1 at the end of the heat preservation period ranges from 500 sccm to 700 sccm; exemplary values ​​are 520 sccm, 550 sccm, 580 sccm, 610 sccm, 640 sccm, or 670 sccm, but are not limited thereto. Preferably, the value of F1 ranges from 500 sccm to 650 sccm.

[0035] Preferably, in some embodiments, step S3 includes: S31: The first intermediate is loaded into the MOCVD reaction chamber and heated to 400℃~500℃ at a heating rate of 5℃ / min~15℃ / min, and held at that temperature for 10min~20min. Using a higher heating rate at low temperatures can improve preparation efficiency, and holding at 400℃~500℃ can better remove surface contaminants.

[0036] S32: Introduce H2 and PH3 into the MOCVD reaction chamber, and heat to T1 at a heating rate of 3℃ / min~10℃ / min, and hold for 10min~30min; Specifically, using a lower heating rate at this stage reduces the accumulation of thermal stress in the grating, providing a foundation for the subsequent formation of a smooth interface; the heat preservation at this stage ensures uniform sample temperature. Simultaneously, the protective atmosphere formed by H2 and PH3 is beneficial for sample surface reconstruction. Specifically, the H2 inlet flow rate is 800 sccm~1200 sccm, and the PH3 inlet flow rate is 800 sccm~1000 sccm. S33: After the insulation is completed, adjust the flow rate of PH3 to F1.

[0037] Specifically, in step S4, 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. Preferably, in some embodiments, the heating rate is constant, more specifically, the heating rate is 0.1℃ / s to 3.5℃ / s, exemplary values ​​are 0.5℃ / s, 1.0℃ / s, 1.5℃ / s, 2.0℃ / s, or 2.5℃ / s, but it is not limited to these; preferably it is 0.1℃ / s to 3℃ / s. This rate takes into account both crystal growth quality and process stability.

[0038] Specifically, in step S4, after the temperature rise is completed, the difference between T2 and T1 (i.e., T2-T1) is greater than 10℃ to improve the crystal quality of the buried layer. Specifically, the value of T2 ranges from 580℃ to 640℃, exemplarily 600℃, 610℃, 620℃, or 630℃, but is not limited to these. Preferably, the value of T2 ranges from 580℃ to 620℃.

[0039] Specifically, in step S4, the flow rate of PH3 increases gradually during the heating process; this increase can be linear or non-linear to match the enhanced reactivity resulting from the increased temperature. Preferably, in some embodiments, the flow rate of PH3 is calculated according to the following set of formulas:

[0040]

[0041] In the formula, Let F1 be the flow rate of PH3 at time i, and F1 be the flow rate of PH3 at the end of the heat preservation in step S3. T is a constant, and its value ranges from 5 to 15; i Let T1 be the temperature of the MOCVD reaction chamber at time i, T2 be the temperature of the MOCVD reaction chamber after the temperature rise in step S3, and T3 be the temperature of the MOCVD reaction chamber after the temperature rise in step S4. For the heating time in a single step S4, t i Let t be the time interval between time i and time k, where time k is the end time of step S3, n is the number of repetition cycles in step S6, and t is the time interval between time i and time k. p The duration of a single repetition cycle in step S6.

[0042] Specifically, in step S4, the flow rate of TMI is constant, and it is carried into the MOCVD reaction chamber by a carrier gas. The carrier gas can be N2 and / or H2, preferably H2. More specifically, the flow rate of the carrier gas (H2) used to carry TMI is 200 sccm to 500 sccm, exemplary values ​​are 240 sccm, 280 sccm, 320 sccm, 360 sccm, 400 sccm, 440 sccm or 480 sccm, but is not limited thereto.

[0043] Specifically, in step S5, the cooling process can be carried out at a constant rate or at a non-constant rate. For example, step-wise cooling or cooling that starts fast and then slows down can be used, but these methods are not limited to these. Preferably, in some embodiments, the cooling is carried out at a constant rate, more specifically, the cooling rate is 0.1℃ / s to 3.5℃ / s, exemplary values ​​are 0.5℃ / s, 1.0℃ / s, 1.5℃ / s, 2.0℃ / s, or 2.5℃ / s, but these are not limited to these; preferably, it is 0.1℃ / s to 3℃ / s. This cooling rate takes into account both crystal growth quality and process stability.

[0044] Specifically, in step S5, the flow rate of PH3 decreases during the cooling process; this decrease can be linear or non-linear. Preferably, in some embodiments, the flow rate of PH3 is calculated according to the following set of formulas:

[0045]

[0046] In the formula, Let F1 be the flow rate of PH3 at time j, and F1 be the flow rate of PH3 at the end of the heat preservation process in step S3. T is a constant, and its value ranges from 5 to 15; j Let T1 be the temperature of the MOCVD reaction chamber at time j, T2 be the temperature of the MOCVD reaction chamber after the temperature rise in step S3, and T2 be the temperature of the MOCVD reaction chamber after the temperature rise in step S4. For the heating time in a single step S4, t j Let t be the time interval between time j and time k, where time k is the end time of step S3, n is the number of repetition cycles in step S6, and t is the time interval between time j and time k. p The duration of a single repetition cycle in step S6.

[0047] Specifically, in step S5, the flow rate of TMI is constant, and it is carried into the MOCVD reaction chamber by a carrier gas. The carrier gas can be N2 and / or H2, preferably H2. More specifically, the flow rate of the carrier gas (H2) used to carry TMI is 200 sccm to 500 sccm, exemplary values ​​are 240 sccm, 280 sccm, 320 sccm, 360 sccm, 400 sccm, 440 sccm or 480 sccm, but is not limited thereto.

[0048] Specifically, in step S6, the duration of a single repetition cycle (i.e., repeating step S4 and step S5 once) is t. p The time consumed in a single step S4 (i.e., the heating time) is t. r The time consumed in a single step S5 (i.e., the cooling time) is t. p -tr ;t r :(t p -t r ) = 1:2 ~ 2:1, and t p ≥50s; number of cycles ≥5. More preferably, t p The value range is 50s~150s, and the number of cycles is 8~20.

[0049] Specifically, in step S6, the thickness of the buried layer at the end of growth is 2nm~6nm greater than the height of the grating ridge, thus achieving complete burial of the grating ridge.

[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, an interface roughness ≤0.8 nm, and a complete grating ridge structure with 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 contact 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 -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 -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 is loaded into the MOCVD reaction chamber and heated to 450°C at a heating rate of 10°C / min, and held at that temperature for 10 min; (4) Introduce 850 sccm of H2 and 900 sccm of PH3 into the MOCVD reaction chamber, and heat it to 550℃ (T1) at a heating rate of 5℃ / min, and hold it for 20 min; after holding, adjust the flow rate of PH3 to 550 sccm (F1).

[0058] (5) The MOCVD reaction chamber is heated to 590℃ (T2) at a heating rate of 0.8℃ / s, and TMI and PH3 are continuously introduced during the heating process; TMI is carried in by H2 as a carrier gas, and the flow rate of H2 is 300 sccm; the flow rate of PH3 is calculated according to the following set of formulas:

[0059]

[0060] In the formula, Let F1 be the flow rate of PH3 at time i, and F1 be the flow rate of PH3 at the end of the heat preservation in step S3, which is 550 sccm. T is a constant whose value ranges from 8; i Let T1 be the temperature of the MOCVD reaction chamber at time i, and T2 be the temperature of the MOCVD reaction chamber after heating in step (4), which is 550℃; T3 be the temperature of the MOCVD reaction chamber after heating in step (5), which is 590℃. The heating time in a single step S4 is 50 seconds; t i Let be the time interval between time i and time k, where time k is the end time of step S3, n is the number of repetition cycles in step (7), and t is the time interval between time i and time k. p The duration of a single repetition cycle in step S6 is 100s.

[0061] (6) The MOCVD reaction chamber is cooled to 550℃ (T1) at a cooling rate of 0.8℃ / s, during which TMI and PH3 are continuously introduced; TMI is carried in by H2 as a carrier gas, and the flow rate of H2 is 300 sccm; the flow rate of PH3 is calculated according to the following set of formulas:

[0062]

[0063] In the formula, F1 is the flow rate of PH3 at time j, and F1 is the flow rate of PH3 at the end of the heat preservation in step S3, which is 550 sccm. T is a constant with a value of 8. j Let T1 be the temperature of the MOCVD reaction chamber at time j, and T2 be the temperature of the MOCVD reaction chamber after heating in step (4), which is 550℃; T3 be the temperature of the MOCVD reaction chamber after heating in step (5), which is 590℃. The heating time in a single step S4 is 50 seconds; t j Let be the time interval between time j and time k, where time k is the end time of step S3, n is the number of repetition cycles in step (7), and t is the time interval between time j and time k. p The duration of a single repetition cycle in step S6 is 100s.

[0064] (7) Repeat steps (5) and (6) periodically until a buried layer covering the grating ridge is obtained, thus obtaining the grating structure.

[0065] The number of repetition cycles is 15, and the thickness of the buried layer is 30nm.

[0066] 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.

[0067] 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.

[0068] (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°.

[0069] (3) The first intermediate is loaded into the MOCVD reaction chamber and heated to 450°C at a heating rate of 10°C / min, and held at that temperature for 10 min; (4) Introduce 850 sccm of H2 and 900 sccm of PH3 into the MOCVD reaction chamber, and heat it to 560℃ (T1) at a heating rate of 5℃ / min, and hold it for 20 min; after holding, adjust the flow rate of PH3 to 600 sccm (F1).

[0070] (5) The MOCVD reaction chamber is heated to 590℃ (T2) at a heating rate of 1.67℃ / s, and TMI and PH3 are continuously introduced during the heating process; TMI is carried in by H2 as a carrier gas, and the flow rate of H2 is 300 sccm; the flow rate of PH3 is calculated according to the following set of formulas:

[0071]

[0072] In the formula, Let F1 be the PH3 flow rate at time i, and F1 be the PH3 flow rate at the end of the heat preservation in step S3, which is 600 sccm. T is a constant whose value ranges from 10; i Let T1 be the temperature of the MOCVD reaction chamber at time i, and T2 be the temperature of the MOCVD reaction chamber after heating in step (4), which is 560℃; T3 be the temperature of the MOCVD reaction chamber after heating in step (5), which is 590℃. The heating time in a single step S4 is 30 seconds; t i Let be the time interval between time i and time k, where time k is the end time of step S3, n is the number of repetition cycles in step (7), and t is the time interval between time i and time k. p The duration of a single repetition cycle in step S6 is 60 seconds.

[0073] (6) The MOCVD reaction chamber is cooled to 560℃ (T1) at a cooling rate of 1.67℃ / s, during which TMI and PH3 are continuously introduced; TMI is carried in by H2 as a carrier gas, and the flow rate of H2 is 300 sccm; the flow rate of PH3 is calculated according to the following set of formulas:

[0074]

[0075] In the formula, F1 is the flow rate of PH3 at time j, and F1 is the flow rate of PH3 at the end of the heat preservation in step S3, which is 600 sccm. T is a constant with a value of 10; j Let T1 be the temperature of the MOCVD reaction chamber at time j, and T2 be the temperature of the MOCVD reaction chamber after heating in step (4), which is 560℃; T3 be the temperature of the MOCVD reaction chamber after heating in step (5), which is 590℃. The heating time in a single step S4 is 30 seconds; t j Let be the time interval between time j and time k, where time k is the end time of step S3, n is the number of repetition cycles in step (7), and t is the time interval between time j and time k. p The duration of a single repetition cycle in step S6 is 60 seconds.

[0076] (7) Repeat steps (5) and (6) periodically until a buried layer covering the grating ridge is obtained, thus obtaining the grating structure.

[0077] The number of repetition cycles is 18, and the thickness of the buried layer is 28.8 nm.

[0078] Comparative Example 1 This comparative example provides a method for fabricating a grating structure for a DFB laser, which differs from Example 1 in that the method for fabricating the buried layer is as follows: (1) The first intermediate was loaded into the MOCVD reaction chamber, H2 was introduced at 850 sccm, and the temperature was increased to 650℃ at a heating rate of 10℃ / min and held for 10 min. (2) Maintain the temperature in the MOCVD reaction chamber at 650℃ and introduce TMI and PH3; TMI is carried in by H2 as carrier gas with a flow rate of 300 sccm; the flow rate of PH3 is 800 sccm; and a buried layer with a thickness of 30 nm is grown.

[0079] Everything else is the same as in Example 1.

[0080] Comparative Example 2 This comparative example provides a method for fabricating a grating structure for a DFB laser, which differs from Example 1 in that the method for fabricating the buried layer is as follows: (1) The first intermediate was loaded into the MOCVD reaction chamber, H2 was introduced at 850 sccm, and the temperature was increased to 550℃ at a heating rate of 10℃ / min and held for 10 min. (2) Maintain the temperature in the MOCVD reaction chamber at 550℃ and introduce TMI and PH3; TMI is carried in by H2 as carrier gas with a flow rate of 300 sccm; the flow rate of PH3 is 600 sccm; and a buried layer with a thickness of 30 nm is grown.

[0081] Everything else is the same as in Example 1.

[0082] The grating structures obtained in Examples 1, 2, 1, and 2 were used to fabricate DFB lasers, and their performance was tested. The specific results are shown in the table below:

[0083] Note: W / A in the table is watts per ampere.

[0084] As can be seen from the table, the fabrication method of the grating structure in this invention can effectively reduce interface roughness and improve the performance of the DFB laser. A comparison between Example 1 and Comparative Example 1 shows that when using the technical solution of Example 1, the grating structure is intact and there is no obvious remelting (see Example 1). Figure 2 However, when using the technical solution of Comparative Example 1 (which uses a higher temperature to grow the buried layer), the grating undergoes remelting (see Comparative Example 1). Figure 3The sidewalls of the grating ridge showed significant collapse and rounding, and the trench depth was reduced, resulting in a decrease in the performance of the fabricated DFB laser. Furthermore, high-temperature testing showed that the characteristic temperature of the DFB laser in Comparative Example 1 was only around 60K, indicating that the device is highly sensitive to temperature and struggles to maintain single-mode characteristics at high temperatures. This demonstrates that a constant high-temperature environment exacerbates the volatilization of phosphorus in the grating layer, leading to irreversible grating morphology damage, which in turn reduces device yield and weakens performance. A comparison of Comparative Example 1 and Comparative Example 2 shows that although low-temperature growth can reduce remelting, it results in poor crystal quality, leading to low slope efficiency and low side-mode suppression ratio in the DFB laser chip based on Comparative Example 2.

[0085] 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. Etch the grating layer to form periodically distributed grating ridges to obtain the first intermediate; S3. The first intermediate is loaded into the MOCVD reaction chamber, and the MOCVD reaction chamber is heated to T1 and held at that temperature for a first preset time; wherein, 300℃≤T1≤600℃; PH3 is continuously introduced during the heating process; and the flow rate of PH3 at the end of the holding period is F1. S4. Heat the MOCVD reaction chamber to T2, continuously introducing TMI and PH3 during the heating process; wherein, T2-T1>10℃, and the flow rate of PH3 increases during the heating process. S5. Cool the MOCVD reaction chamber to T1, continuously introducing TMI and PH3 during the cooling process; the flow rate of PH3 decreases during the cooling process. S6. Repeat steps S4 and S5 periodically until a buried layer covering the grating ridge is obtained, thus obtaining the grating structure.

2. The method for fabricating a grating structure for a DFB laser as described in claim 1, characterized in that, In step S4, the temperature increase time is t r ; in step S5, the temperature decrease time is t P -t r ; t r : (t P -t r ) = 1:2 ~ 2:1 and / or In step S6, the duration of a single repetition cycle is t. P , t P ≥50s; Number of cycles ≥5; and / or The thickness of the buried layer is 2nm to 6nm greater than the height of the grating ridge.

3. The method for fabricating a grating structure for a DFB laser as described in claim 1, characterized in that, In step S4, the flow rate of PH3 is calculated according to the following set of formulas: In the formula, Let F1 be the flow rate of PH3 at time i, and F1 be the flow rate of PH3 at the end of the heat preservation in step S3. T is a constant, and its value ranges from 5 to 15; i Let T1 be the temperature of the MOCVD reaction chamber at time i, T2 be the temperature of the MOCVD reaction chamber after the temperature rise in step S3, and T3 be the temperature of the MOCVD reaction chamber after the temperature rise in step S4. For the heating time in a single step S4, t i Let t be the time interval between time i and time k, where time k is the end time of step S3, n is the number of repetition cycles in step S6, and t is the time interval between time i and time k. p The duration of a single repetition cycle in step S6.

4. The method for fabricating a grating structure for a DFB laser as described in claim 1, characterized in that, In step S5, the flow rate of PH3 is calculated according to the following set of formulas: In the formula, Let F1 be the flow rate of PH3 at time j, and F1 be the flow rate of PH3 at the end of the heat preservation process in step S3. T is a constant, and its value ranges from 5 to 15; j Let T1 be the temperature of the MOCVD reaction chamber at time j, T2 be the temperature of the MOCVD reaction chamber after the temperature rise in step S3, and T2 be the temperature of the MOCVD reaction chamber after the temperature rise in step S4. For the heating time in a single step S4, t j Let t be the time interval between time j and time k, where time k is the end time of step S3, n is the number of repetition cycles in step S6, and t is the time interval between time j and time k. p The duration of a single repetition cycle in step S6.

5. The method for fabricating a grating structure for a DFB laser as described in claim 1, characterized in that, The value of F1 ranges from 500 sccm to 650 sccm; The value of T1 ranges from 500℃ to 560℃; The value of T2 ranges from 580℃ to 620℃; In step S6, the duration of a single repetition cycle is t. p , t p The value range is 50s~150s, and the number of cycles is 8~20.

6. The method for fabricating a grating structure for a DFB laser as described in claim 1, characterized in that, In steps S4 and S5, the TMI flow rate is the same. TMI is carried into the MOCVD reaction chamber by H2 as a carrier gas, and the H2 flow rate is 200 sccm to 500 sccm; and / or In step S4, the heating rate is 0.1℃ / s to 3℃ / s; and / or In step S5, the cooling rate is 0.1℃ / s to 3℃ / s.

7. The method for fabricating a grating structure for a DFB laser as described in claim 1, characterized in that, Step S3 includes: S31: The first intermediate is loaded into the MOCVD reaction chamber and heated to 400℃~500℃ at a heating rate of 5℃ / min~15℃ / min, and held at that temperature for 10min~20min. S32: Introduce H2 and PH3 into the MOCVD reaction chamber and heat to T1 at a heating rate of 3℃ / min~10℃ / min, and hold for 10min~30min; wherein, the flow rate of H2 is 800sccm~1200sccm and the flow rate of PH3 is 800sccm~1000sccm. S33: After the insulation is completed, adjust the flow rate of PH3 to F1.

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 as described in claim 8.

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

Images