Epitaxial structure of dfb laser and preparation method thereof, and dfb laser
By using ICP etching and plasma ashing processes to form a grating structure with high verticality and low roughness, the problem of large sidewall tilt and roughness of the grating structure in traditional DFB lasers is solved, thus improving the performance of DFB lasers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGXI ZHAO CHI SEMICON CO LTD
- Filing Date
- 2026-03-31
- Publication Date
- 2026-06-19
AI Technical Summary
Traditional DFB lasers have grating structures with large sidewall inclinations and rough surfaces, which cannot meet the requirements for high performance.
The grating layer is etched using a mixed gas of Cl2, BCl3, SO2, CH3F and Ar through ICP etching process, and an SOCF composite passivation layer is formed on the sidewall. The composite passivation layer is then removed by plasma ashing process to form a grating structure with high verticality and low roughness.
The verticality of the grating structure was improved and the roughness was reduced, thus optimizing the performance of the DFB laser, reducing the threshold current, and improving the slope efficiency.
Smart Images
Figure CN122246567A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lasers, and more particularly to an epitaxial structure for a DFB laser, its fabrication method, and a DFB laser. Background Technology
[0002] In DFB lasers, the quality of the grating structure directly determines the device's wavelength, single-mode characteristics, and reliability. Traditional grating structures are formed through wet etching or using Cl2 as the primary etching gas. The resulting grating structures often have large sidewall inclinations and rough surfaces, which cannot meet the requirements for high performance. Summary of the Invention
[0003] The technical problem to be solved by the present invention is to provide an epitaxial structure for a DFB laser and a method for fabricating the same, wherein the grating structure has high perpendicularity and low surface roughness, which can optimize the performance of the DFB laser.
[0004] Another technical problem that the present invention needs to solve is to provide a DFB laser.
[0005] To address the aforementioned technical problems, this invention provides a method for fabricating an epitaxial structure of a DFB laser, comprising: A substrate is provided, on which a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer, and a grating layer are sequentially formed; A mask layer is formed on the grating layer, exposing a predetermined area of the grating layer; The exposed grating layer is etched using an ICP etching process, and a composite passivation layer is formed on the etched sidewalls. The etching gases used in the ICP etching process are Cl2, BCl3, SO2, CH3F, and Ar. The composite passivation layer is removed by plasma ashing process; Remove the mask layer to form a grating structure and obtain the first intermediate product; A grating buried layer is formed on the first intermediate to cover the grating structure; A cladding layer and a contact layer are formed on the grating buried layer to obtain the epitaxial structure of the DFB laser.
[0006] As an improvement to the above technical solution, in the step of etching the exposed grating layer by ICP etching and forming a composite passivation layer on the sidewalls formed by etching: The flow rate of Cl2 is 10 sccm to 50 sccm, the flow rate of BCl3 is 5 sccm to 20 sccm, the flow rate of HBr is 5 sccm to 45 sccm, the flow rate of CH3F is 10 sccm to 40 sccm, the flow rate of SO2 is 5 sccm to 20 sccm, and the flow rate of Ar is 50 sccm to 150 sccm. The ICP chamber pressure is 3 mtorr~8 mtorr.
[0007] As an improvement to the above technical solution, in the step of etching the exposed grating layer by ICP etching and forming a composite passivation layer on the sidewalls formed by etching: ICP power is 500W~800W, and RF power is 80W~150W.
[0008] As an improvement to the above technical solution, the ratio of SO2 flow rate to CH3F flow rate is 1:1.5 to 1:2.5.
[0009] As an improvement to the above technical solution, in the step of removing the composite passivation layer by plasma ashing process: The plasma power is 200W~500W, the chamber pressure is 50mtorr~500mtorr, the O2 flow rate is 50sccm~200sccm, and the processing time is 30s~120s.
[0010] As an improvement to the above technical solution, the mask layer is a SiO2 layer.
[0011] As an improvement to the above technical solution, the grating layer is an undoped InGaAsP layer with a thickness of 20nm~60nm.
[0012] As an improvement to the above technical solution, the verticality of the sidewall of the grating structure is ≥88° and the roughness is ≤1.5nm.
[0013] Accordingly, the present invention also discloses a DFB laser epitaxial structure, which is prepared by the above-described method for preparing a DFB laser epitaxial structure.
[0014] Accordingly, the present invention also discloses a DFB laser, which includes the above-described DFB laser epitaxial structure.
[0015] Implementing this invention has the following beneficial effects: In one embodiment of the present invention, the fabrication method of the epitaxial structure of a DFB laser involves ICP etching using a mixed gas of Cl2, BCl3, SO2, CH3F, and Ar as the etching gas during the formation of the grating structure. This gas forms an SOCF composite passivation layer during etching, providing excellent sidewall protection and resulting in high perpendicularity and low roughness of the grating structure's sidewalls. Furthermore, the composite passivation layer is subsequently removed using a plasma drawing process, ensuring the growth quality of subsequent structural layers such as the grating buried layer. This reduces internal optical losses and interface defect density, thereby lowering the threshold current and improving the slope efficiency of the DFB laser, thus optimizing the overall performance of the DFB laser. Attached Figure Description
[0016] Figure 1 This is a flowchart of a method for fabricating a DFB laser epitaxial structure according to an embodiment of the present invention. Detailed Implementation
[0017] 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.
[0018] 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.
[0019] The following embodiments are provided for the purpose of illustrating various embodiments of the present invention and are not intended to limit the invention in any way. Those skilled in the art will understand that variations and other uses as defined in the claims are included within the spirit and scope of the invention. Unless otherwise specified, the materials, reagents, etc., used in the following embodiments are commercially available.
[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] Unless otherwise specified, the temperature parameters in this invention can be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument.
[0022] Please see Figure 1 As a first aspect of the present invention, the present invention provides a method for fabricating an epitaxial structure of a DFB laser, which includes the following steps: S1: Provide a substrate, on which a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer, and a grating layer are sequentially formed; S2: Form a mask layer on the grating layer and expose the grating layer of the preset area; S3: The exposed grating layer is etched by ICP etching, and a composite passivation layer is formed on the sidewalls formed by the etching. S4: The composite passivation layer is removed by plasma ashing process; S5: Remove the mask layer to form a grating structure and obtain the first intermediate product; S6: Form a grating buried layer on the first intermediate to cover the grating structure; S7: A cladding and contact layer are formed on the grating buried layer to obtain the epitaxial structure of the DFB laser.
[0023] The etching gases used in the ICP etching process are Cl2, BCl3, SO2, CH3F, and Ar. Based on this combination of etching gases, an SOCF composite passivation layer can be formed during etching, providing excellent sidewall protection. This results in high perpendicularity and low roughness of the grating structure's sidewalls, significantly improving the laser's single-mode stability and output power consistency. This composite passivation layer can be completely and uniformly removed during plasma ashing, leaving no carbide or oxide impurities. This ensures the growth quality of subsequent grating buried layers, reduces internal optical losses and interface defect density, and consequently lowers the threshold current and improves the slope efficiency of the DFB laser.
[0024] Specifically, in step S1, the substrate is an InP substrate, more specifically an N-type InP semiconductor doped with Si, with a doping concentration of 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 .
[0025] Specifically, in step S1, the lower confinement layer is a Si-doped N-type AlInAs layer with a thickness of 30 nm to 300 nm and a doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 18 cm -3 The lower confinement layer can confine charge carriers and light within the waveguide layer and the active layer, preventing them from diffusing into the substrate.
[0026] Specifically, in some implementations, the lower confinement layer can be prepared by MOCVD. More specifically, an N-type AlInAs layer is grown using H2 as the carrier gas, trimethylindium (TMIn) as the In source, trimethylaluminum (TMAl) as the Al source, arsine (AsH3) as the As source, and silane (SiH4) as the Si source, as the N-type AlInAs layer.
[0027] Specifically, in step S1, the lower waveguide layer is an undoped AlGaInAs layer with a thickness of 30nm~240nm. The lower waveguide layer serves as both an optical waveguide and a confinement layer for charge carriers.
[0028] Specifically, in some implementations, the lower waveguide layer can be fabricated by MOCVD. More specifically, an undoped AlGaInAs layer is grown using H2 and N2 as carrier gases, trimethylindium (TMIn) as the In source, trimethylaluminum (TMAl) as the Al source, trimethylgallium (TMGa) or triethylgallium (TeGa) as the Ga source, and arsine (AsH3) as the As source, as the lower waveguide layer.
[0029] Specifically, in step S1, the active layer is a periodic structure formed by alternating AlGaInAs well layers and AlGaInAs barrier layers, with a period number of 3 to 12. The thickness of the AlGaInAs well layer is 4 nm to 12 nm, and the thickness of the AlGaInAs barrier layer is 8 nm to 20 nm.
[0030] Specifically, in some implementations, the active layer can be fabricated by MOCVD. More specifically, using H2 and N2 as carrier gases, trimethylindium (TMIn) as the In source, trimethylaluminum (TMAl) as the Al source, trimethylgallium (TMGa) or triethylgallium (TeGa) as the Ga source, and arsine (AsH3) as the As source, AlGaInAs well layers and AlGaInAs barrier layers are alternately grown until the active layer is obtained.
[0031] Specifically, in step S1, the upper waveguide layer is an undoped AlGaInAs layer, which is symmetrical with the lower waveguide layer and also serves as an optical waveguide and carrier confinement layer. The thickness of the upper waveguide layer is 30nm~240nm.
[0032] Specifically, in some implementations, the upper waveguide layer is fabricated by MOCVD. More specifically, an undoped AlGaInAs layer is grown using H2 and N2 as carrier gases, trimethylindium (TMIn) as the In source, trimethylaluminum (TMAl) as the Al source, trimethylgallium (TMGa) or triethylgallium (TeGa) as the Ga source, and arsine (AsH3) as the As source, as the As source, to serve as the upper waveguide layer.
[0033] Specifically, in step S1, the upper confinement layer is a Zn-doped P-type AlInAs layer with a thickness of 30 nm to 300 nm and a doping concentration of 5 × 10⁻⁶. 17 cm -3 ~1×10 18 cm -3 The upper confinement layer can enhance the band matching between the upper waveguide layer and subsequent layers, thereby improving the confinement of light and charge carriers.
[0034] Specifically, in some embodiments, the upper confinement layer is prepared by MOCVD. More specifically, a p-type AlInAs layer is grown using H2 as the carrier gas, trimethylindium (TMIn) as the In source, trimethylaluminum (TMAl) as the Al source, arsine (AsH3) as the As source, and diethylzinc (Et2Zn) as the Zn source, as the P-type AlInAs layer, serving as the upper confinement layer.
[0035] Specifically, in step S1, the grating layer is an InGaAsP layer, an InGaP / InGaAsP / InGaP stacked structure, or an InP / InGaAsP / InP stacked structure. Preferably, in some embodiments, the grating layer is an undoped InGaAsP layer with a thickness of 20 nm to 60 nm.
[0036] Specifically, in some implementations, the grating layer is fabricated by MOCVD. More specifically, an undoped InGaAsP layer is grown using H2 as the carrier gas, trimethylindium (TMIn) as the In source, trimethylgallium (TMGa) as the Ga source, arsine (AsH3) as the As source, and phosphine (PH3) as the P source, to serve as the grating layer.
[0037] Specifically, in step S2, the mask layer can be a photoresist layer or a SiO2 layer, but is not limited to these. Preferably, in some embodiments, the mask layer is a SiO2 layer, which has stronger resistance to etching ions during the ICP etching process, and can further optimize the perpendicularity and roughness of the grating structure sidewalls, thereby improving the diffraction efficiency of the grating and the photoelectric conversion performance of the device. Specifically, the thickness of the mask layer is 80nm~120nm.
[0038] Specifically, in some implementations, a SiO2 layer is deposited by PECVD as a mask layer, but this is not limited to this. After forming the mask layer, the SiO2 layer is patterned using BOE etchant to form a periodic mask structure.
[0039] Specifically, in step S3, inductively coupled plasma (ICP) etching is performed using etching gases Cl2, BCl3, SO2, CH3F, and Ar. Cl2 is the primary etching gas, reacting with In and Ga to generate volatile chlorides; Cl2 also participates in forming a highly active plasma, increasing the etching rate. BCl3 provides boron atoms to enhance sidewall passivation and suppress lateral etching; it also removes the natural oxide layer on the surface, improving etching uniformity. HBr further modulates the etching selectivity and anisotropy, controlling the morphology and improving the sidewall profile. CH3F provides a carbon source, forming a CH-rich polymer, which not only suppresses sidewall etching and improves grating morphology fidelity but also facilitates subsequent removal. SiO2 primarily suppresses sidewall etching and enhances sidewall stability by forming a sulfide passivation layer. Ar is used to dilute the etching gas, enhance ion bombardment, and promote anisotropy. Based on the above-mentioned etching gas combination, an easily removable SOCF composite passivation layer can be formed, optimizing the sidewall morphology and reducing roughness, thereby significantly improving the diffraction efficiency of the grating.
[0040] The flow rate of Cl2 is 10 sccm to 50 sccm, exemplarily 12 sccm, 18 sccm, 24 sccm, 30 sccm, 36 sccm or 42 sccm, but is not limited thereto. Preferably, it is 20 sccm to 40 sccm.
[0041] The flow rate of BCl3 is 5 sccm to 20 sccm, exemplarily 8 sccm, 12 sccm, 16 sccm or 20 sccm, but not limited thereto. Preferably it is 10 sccm to 15 sccm.
[0042] The HBr flow rate is 5 sccm to 45 sccm, exemplarily 10 sccm, 15 sccm, 20 sccm, 25 sccm, 30 sccm or 35 sccm, but not limited thereto. Preferably it is 10 sccm to 20 sccm.
[0043] The flow rate of CH3F is 10 sccm to 40 sccm, exemplarily 14 sccm, 18 sccm, 22 sccm, 26 sccm, 30 sccm, 34 sccm or 38 sccm, but is not limited thereto. Preferably, it is 15 sccm to 25 sccm.
[0044] The SO2 flow rate is 5 sccm to 20 sccm, exemplarily 8 sccm, 11 sccm, 14 sccm or 17 sccm, but not limited thereto. Preferably it is 8 sccm to 15 sccm.
[0045] The flow rate of Ar is 50 sccm to 150 sccm, exemplarily 65 sccm, 80 sccm, 95 sccm, 110 sccm, 125 sccm or 140 sccm, but not limited thereto. Preferably it is 80 sccm to 120 sccm.
[0046] Preferably, in some embodiments, the ratio of SO2 flow rate to CH3F flow rate is 1:1.5 to 1:2.5. Based on this ratio, the thickness of the composite passivation layer can be optimized, making it easier to remove in the future.
[0047] Specifically, in step S3, the ICP power is 500W to 800W, exemplarily 550W, 600W, 650W, 700W, or 750W, but not limited to these. Preferably, it is 700W to 800W. By using a higher ICP power, the plasma density can be enhanced, improving the etching rate and uniformity.
[0048] Specifically, in step S3, the RF power is 80W~150W, exemplarily 90W, 100W, 110W, 120W, 130W or 140W, but not limited to these. Preferably, it is 100W~130W, which can balance ion bombardment energy and surface damage, further improve sidewall verticality and reduce its roughness.
[0049] Specifically, in step S3, the ICP chamber pressure is 3 mtorr to 8 mtorr, exemplarily 3.5 mtorr, 4 mtorr, 4.5 mtorr, 5 mtorr, 5.5 mtorr, 6 mtorr, 6.5 mtorr, 7 mtorr, or 7.5 mtorr, but not limited thereto. Preferably, it is 4.5 mtorr to 6.5 mtorr.
[0050] Specifically, in step S3, the etching temperature is 20°C to 40°C, exemplarily 25°C, 30°C or 35°C, but not limited to this.
[0051] Specifically, in step S4, the composite passivation layer can be removed by a plasma ashing process. O2, a mixture of O2 and N2, or other gases can be used, but are not limited to these. Preferably, in some embodiments, O2 is used for plasma ashing, with a flow rate of 50 sccm to 200 sccm, exemplarily 70 sccm, 90 sccm, 110 sccm, 130 sccm, 150 sccm, 170 sccm, or 190 sccm, but not limited to these. Preferably, it is 80 sccm to 150 sccm.
[0052] Specifically, in step S4, the plasma power is 200W to 500W, exemplarily 250W, 300W, 350W, 400W, or 450W, but not limited thereto. Preferably, it is 200W to 400W.
[0053] Specifically, in step S4, the ashing treatment time is 30s to 120s, exemplarily 45s, 60s, 75s, 90s or 105s, but not limited to these. Preferably, it is 40s to 80s.
[0054] Specifically, in step S4, the chamber pressure is 50 mtorr to 500 mtorr, exemplarily 100 mtorr, 150 mtorr, 200 mtorr, 250 mtorr, 300 mtorr, 350 mtorr, 400 mtorr or 450 mtorr, but not limited thereto; preferably 50 mtorr to 200 mtorr.
[0055] Specifically, in step S5, the remaining mask layer can be removed by wet cleaning, for example, by using BOE etching solution, but is not limited to this. Preferably, in some embodiments, after removing the remaining mask layer, cleaning and drying are performed.
[0056] Specifically, in step S6, the grating buried layer is an undoped InP layer with a thickness of 50nm~200nm.
[0057] Specifically, in some implementations, the grating buried layer is fabricated by MOCVD. More specifically, an undoped InP layer is grown using H2 as the carrier gas, trimethylindium (TMIn) as the In source, and phosphine (PH3) as the P source, to serve as the grating buried layer.
[0058] Specifically, in step S7, the cladding is a Zn-doped P-type InP layer with a thickness of 1.2 μm to 2.2 μm and a doping concentration of 1 × 10⁻⁶. 16 cm -3 ~1×10 18 cm -3 The cladding can further restrict the lateral diffusion of charge carriers and also reduce leakage current.
[0059] Specifically, in some implementations, the cladding is prepared by MOCVD. More specifically, a p-type InP layer is grown as the cladding using H2 as the carrier gas, trimethylindium (TMIn) as the In source, phosphine (PH3) as the P source, and diethylzinc (Et2Zn) as the Zn source.
[0060] Specifically, in step S7, the contact layer is a Zn-doped P-type InGaAs layer with a thickness of 50 nm to 350 nm and a doping concentration of 1 × 10⁻⁶.19 cm -3 ~1×10 20 cm -3 The contact layer can reduce electrode contact resistance and optimize photoelectric conversion efficiency.
[0061] Specifically, in some implementations, the contact layer is grown via MOCVD. More specifically, a p-type InGaAs layer is grown as the contact layer using H2 and N2 as carrier gases, trimethylindium (TMIn) as the In source, trimethylgallium (TMGa) or triethylgallium (TeGa) as the Ga source, arsine (AsH3) as the As source, and diethylzinc (Et2Zn) as the Zn source.
[0062] Preferably, in some embodiments, an etch stop layer (P-type InGaAsP layer), a barrier gradient layer (P-type InGaAsP layer), etc., may also be formed on the grating buried layer. However, this is not the only option.
[0063] Specifically, based on the fabrication method of the DFB laser epitaxial structure described above in this technical solution, the perpendicularity of the sidewalls of the grating structure (i.e., the tilt angle of the sidewalls) can be ≥88°, and the roughness ≤1.5nm. This significantly improves the grating diffraction efficiency and mode selectivity, greatly reduces optical scattering loss, lowers the threshold current of the DFB laser, and improves its slope efficiency.
[0064] Accordingly, as a second aspect of the present invention, the present invention also provides a DFB laser epitaxial structure, which is prepared by the above-described method for preparing a DFB laser epitaxial structure. The preparation method of this technical solution improves the sidewall perpendicularity of the grating structure, reduces its surface roughness, reduces the threshold current of the DFB laser, and improves its slope efficiency.
[0065] Accordingly, as a third aspect of the present invention, the present invention also provides a DFB laser comprising the above-described DFB laser epitaxial structure. Preferably, it further comprises an upper electrode and a lower electrode, and is etched to form a ridge waveguide structure.
[0066] The present invention will be further described below with reference to specific embodiments: Example 1 This embodiment provides a method for fabricating an epitaxial structure of a DFB laser, which includes the following steps: (1) Provide a substrate, and form a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer and a grating layer sequentially on the substrate; The substrate is an N-type InP semiconductor doped with Si, with a doping concentration of 7.5 × 10⁻⁶. 17 cm -3The lower confinement layer is a Si-doped N-type AlInAs layer with a thickness of 150 nm and a doping concentration of 5.5 × 10⁻⁶. 17 cm -3 The lower waveguide layer is an undoped AlGaInAs layer with a thickness of 120 nm. The active layer is a periodic structure formed by alternating AlGaInAs well and AlGaInAs barrier layers, with a period number of 10. The AlGaInAs well layer has a thickness of 8 nm, and the AlGaInAs barrier layer has a thickness of 15 nm. The upper waveguide layer is an undoped AlGaInAs layer with a thickness of 120 nm. The upper confinement layer is a Zn-doped p-type AlInAs layer with a thickness of 150 nm and a doping concentration of 5.5 × 10⁻⁶. 17 cm -3 The grating layer is an undoped InGaAsP layer with a thickness of 50 nm.
[0067] The lower confinement layer, lower waveguide layer, active layer, upper waveguide layer, upper confinement layer, and grating layer are all grown by MOCVD.
[0068] (2) A mask layer is formed on the grating layer, and the grating layer of the preset area is exposed; The mask layer is a SiO2 layer with a thickness of 100nm, which is formed by PECVD and patterned by BOE etching solution.
[0069] (3) The exposed grating layer is etched by ICP etching process, and a composite passivation layer is formed on the sidewall formed by etching; The etching gases were Cl2, BCl3, SO2, CH3F, and Ar. The flow rates were as follows: Cl2 30 sccm, BCl3 10 sccm, HBr 15 sccm, CH3F 15 sccm, SO2 15 sccm, and Ar 100 sccm.
[0070] The ICP power is 750W, the RF power is 120W, and the ICP chamber pressure is 5.5 mtorr. The etching temperature is 25℃.
[0071] (4) The composite passivation layer is removed by plasma ashing process; The plasma ashing process uses O2 with a flow rate of 100 sccm, a plasma power of 300 W, an ashing time of 60 s, and a chamber pressure of 100 mtorr.
[0072] (5) Remove the mask layer to form a grating structure and obtain the first intermediate product; The remaining mask layer was removed using BOE etching solution, followed by RCA cleaning.
[0073] (6) A grating buried layer is formed on the first intermediate to cover the grating structure; The grating buried layer is an undoped InP layer with a thickness of 80 nm. The grating buried layer is fabricated using MOCVD.
[0074] (7) A cladding and contact layer are formed on the grating buried layer to obtain the epitaxial structure of the DFB laser.
[0075] The cladding layer is a Zn-doped P-type InP layer with a thickness of 1.5 μm and a doping concentration of 3.5 × 10⁻⁶. 17 cm -3 The contact layer is a Zn-doped p-type InGaAs layer with a thickness of 220 nm and a doping concentration of 6.5 × 10⁻⁶. 19 cm -3 .
[0076] The cladding and contact layers are both formed by MOCVD.
[0077] Example 2 This embodiment provides a method for fabricating an epitaxial structure of a DFB laser, which includes the following steps: (1) Provide a substrate, and form a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer and a grating layer sequentially on the substrate; The substrate is an N-type InP semiconductor doped with Si, with a doping concentration of 7.5 × 10⁻⁶. 17 cm -3 The lower confinement layer is a Si-doped N-type AlInAs layer with a thickness of 150 nm and a doping concentration of 5.5 × 10⁻⁶. 17 cm -3 The lower waveguide layer is an undoped AlGaInAs layer with a thickness of 120 nm. The active layer is a periodic structure formed by alternating AlGaInAs well and AlGaInAs barrier layers, with a period number of 10. The AlGaInAs well layer has a thickness of 8 nm, and the AlGaInAs barrier layer has a thickness of 15 nm. The upper waveguide layer is an undoped AlGaInAs layer with a thickness of 120 nm. The upper confinement layer is a Zn-doped p-type AlInAs layer with a thickness of 150 nm and a doping concentration of 5.5 × 10⁻⁶. 17 cm -3 The grating layer is an undoped InGaAsP layer with a thickness of 50 nm.
[0078] The lower confinement layer, lower waveguide layer, active layer, upper waveguide layer, upper confinement layer, and grating layer are all grown by MOCVD.
[0079] (2) A mask layer is formed on the grating layer, and the grating layer of the preset area is exposed; The mask layer is a SiO2 layer with a thickness of 80 nm, which is formed by PECVD and patterned by BOE etching solution.
[0080] (3) The exposed grating layer is etched by ICP etching process, and a composite passivation layer is formed on the sidewall formed by etching; The etching gases were Cl2, BCl3, SO2, CH3F, and Ar. The flow rates were: Cl2 40 sccm, BCl3 14 sccm, HBr 30 sccm, CH3F 15 sccm, SO2 18 sccm, and Ar 120 sccm.
[0081] The ICP power is 750W, the RF power is 120W, and the ICP chamber pressure is 6.5 mtorr. The etching temperature is 25℃.
[0082] (4) The composite passivation layer is removed by plasma ashing process; The plasma ashing process uses O2 with a flow rate of 90 sccm, a plasma power of 250 W, an ashing time of 40 s, and a chamber pressure of 80 mtorr.
[0083] (5) Remove the mask layer to form a grating structure and obtain the first intermediate product; The remaining mask layer was removed using BOE etching solution, followed by RCA cleaning.
[0084] (6) A grating buried layer is formed on the first intermediate to cover the grating structure; The grating buried layer is an undoped InP layer with a thickness of 80 nm. The grating buried layer is fabricated using MOCVD.
[0085] (7) A cladding and contact layer are formed on the grating buried layer to obtain the epitaxial structure of the DFB laser.
[0086] The cladding layer is a Zn-doped P-type InP layer with a thickness of 1.5 μm and a doping concentration of 3.5 × 10⁻⁶. 17 cm -3 The contact layer is a Zn-doped p-type InGaAs layer with a thickness of 220 nm and a doping concentration of 6.5 × 10⁻⁶. 19 cm -3 .
[0087] The cladding and contact layers are both formed by MOCVD.
[0088] Example 3 This embodiment provides a method for fabricating an epitaxial structure of a DFB laser, which includes the following steps: (1) Provide a substrate, and form a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer and a grating layer sequentially on the substrate; The substrate is an N-type InP semiconductor doped with Si, with a doping concentration of 7.5 × 10⁻⁶. 17 cm -3 The lower confinement layer is a Si-doped N-type AlInAs layer with a thickness of 150 nm and a doping concentration of 5.5 × 10⁻⁶. 17 cm -3 The lower waveguide layer is an undoped AlGaInAs layer with a thickness of 120 nm. The active layer is a periodic structure formed by alternating AlGaInAs well and AlGaInAs barrier layers, with a period number of 10. The AlGaInAs well layer has a thickness of 8 nm, and the AlGaInAs barrier layer has a thickness of 15 nm. The upper waveguide layer is an undoped AlGaInAs layer with a thickness of 120 nm. The upper confinement layer is a Zn-doped p-type AlInAs layer with a thickness of 150 nm and a doping concentration of 5.5 × 10⁻⁶. 17 cm -3 The grating layer is an undoped InGaAsP layer with a thickness of 50 nm.
[0089] The lower confinement layer, lower waveguide layer, active layer, upper waveguide layer, upper confinement layer, and grating layer are all grown by MOCVD.
[0090] (2) A mask layer is formed on the grating layer, and the grating layer of the preset area is exposed; The mask layer is a SiO2 layer with a thickness of 100nm, which is formed by PECVD and patterned by BOE etching solution.
[0091] (3) The exposed grating layer is etched by ICP etching process, and a composite passivation layer is formed on the sidewall formed by etching; The etching gases were Cl2, BCl3, SO2, CH3F, and Ar. The flow rates were as follows: Cl2 30 sccm, BCl3 10 sccm, HBr 15 sccm, CH3F 25 sccm, SO2 15 sccm, and Ar 100 sccm.
[0092] The ICP power is 700W, the RF power is 120W, and the ICP chamber pressure is 6.0 mtorr. The etching temperature is 25℃.
[0093] (4) The composite passivation layer is removed by plasma ashing process; The plasma ashing process uses O2 with a flow rate of 100 sccm, a plasma power of 300 W, an ashing time of 60 s, and a chamber pressure of 100 mtorr.
[0094] (5) Remove the mask layer to form a grating structure and obtain the first intermediate product; The remaining mask layer was removed using BOE etching solution, followed by RCA cleaning.
[0095] (6) A grating buried layer is formed on the first intermediate to cover the grating structure; The grating buried layer is an undoped InP layer with a thickness of 80 nm. The grating buried layer is fabricated using MOCVD.
[0096] (7) A cladding and contact layer are formed on the grating buried layer to obtain the epitaxial structure of the DFB laser.
[0097] The cladding layer is a Zn-doped P-type InP layer with a thickness of 1.5 μm and a doping concentration of 3.5 × 10⁻⁶. 17 cm -3 The contact layer is a Zn-doped p-type InGaAs layer with a thickness of 220 nm and a doping concentration of 6.5 × 10⁻⁶. 19 cm -3 .
[0098] The cladding and contact layers are both formed by MOCVD.
[0099] Comparative Example 1 This comparative example provides a DFB laser epitaxial structure, which differs from Example 1 in that: In step (3), a mixture of Cl2 and H2 gas is used as the etching gas. The flow rate of Cl2 is 10 sccm, the flow rate of H2 is 20 sccm, the ICP power is 350W, the RF power is 180W, and the ICP chamber pressure is 6.0 mtorr. The etching temperature is 25℃.
[0100] The epitaxial structures of the DFB lasers in Examples 1-3 and Comparative Example 1 were tested, and DFB lasers were fabricated and tested. The specific results are shown in the table below:
[0101] As can be seen from the table, the fabrication method of the DFB laser epitaxial structure in this technical solution can improve the sidewall perpendicularity, reduce its sidewall roughness, thereby reducing the threshold current of the DFB laser and improving its slope efficiency.
[0102] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of the present invention to facilitate a specific and detailed understanding of the technical solution of the present invention, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.
[0103] It should be understood that any technical solutions obtained by those skilled in the art based on the technical solutions provided in this invention through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.
Claims
1. A method for fabricating an epitaxial structure of a DFB laser, characterized in that, include: A substrate is provided, on which a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer, and a grating layer are sequentially formed; A mask layer is formed on the grating layer, exposing a predetermined area of the grating layer; The exposed grating layer is etched using an ICP etching process, and a composite passivation layer is formed on the etched sidewalls. The etching gases used in the ICP etching process are Cl2, BCl3, SO2, CH3F, and Ar. The composite passivation layer is removed by plasma ashing process; Remove the mask layer to form a grating structure and obtain the first intermediate product; A grating buried layer is formed on the first intermediate to cover the grating structure; A cladding layer and a contact layer are formed on the grating buried layer to obtain the epitaxial structure of the DFB laser.
2. The method for fabricating the epitaxial structure of a DFB laser as described in claim 1, characterized in that, In the step of etching the exposed grating layer by ICP etching and forming a composite passivation layer on the sidewalls formed by the etching: The flow rate of Cl2 is 10 sccm to 50 sccm, the flow rate of BCl3 is 5 sccm to 20 sccm, the flow rate of HBr is 5 sccm to 45 sccm, the flow rate of CH3F is 10 sccm to 40 sccm, the flow rate of SO2 is 5 sccm to 20 sccm, and the flow rate of Ar is 50 sccm to 150 sccm. The ICP chamber pressure is 3 mtorr~8 mtorr.
3. The method for fabricating the epitaxial structure of a DFB laser as described in claim 1, characterized in that, In the step of etching the exposed grating layer by ICP etching and forming a composite passivation layer on the sidewalls formed by the etching: ICP power is 500W~800W, and RF power is 80W~150W.
4. The method for fabricating the epitaxial structure of a DFB laser as described in claim 1, characterized in that, The ratio of SO2 flow rate to CH3F flow rate is 1:1.5 to 1:2.
5.
5. The method for fabricating the epitaxial structure of a DFB laser as described in claim 1, characterized in that, In the step of removing the composite passivation layer by plasma ashing process: The plasma power is 200W~500W, the chamber pressure is 50mtorr~500mtorr, the O2 flow rate is 50sccm~200sccm, and the processing time is 30s~120s.
6. The method for fabricating the epitaxial structure of a DFB laser as described in any one of claims 1 to 5, characterized in that, The mask layer is a SiO2 layer.
7. The method for fabricating the epitaxial structure of a DFB laser as described in any one of claims 1 to 5, characterized in that, The grating layer is an undoped InGaAsP layer with a thickness of 20nm~60nm.
8. The method for fabricating the epitaxial structure of a DFB laser as described in any one of claims 1 to 5, characterized in that, The verticality of the sidewalls of the grating structure is ≥88° and the roughness is ≤1.5nm.
9. An epitaxial structure for a DFB laser, characterized in that, It is prepared by the method for preparing the epitaxial structure of a DFB laser as described in any one of claims 1 to 8.
10. A DFB laser, characterized in that, Includes the DFB laser epitaxial structure as described in claim 9.