CW-DFB laser epitaxial structure, preparation method thereof and CW-DFB laser

Abstract

The application relates to the field of semiconductor lasers, and particularly discloses a CW-DFB laser epitaxial structure, a preparation method thereof and a CW-DFB laser. The CW-DFB laser epitaxial structure comprises a substrate with oppositely arranged first and second surfaces; a buffer layer arranged on the first surface; a ridge structure arranged above the buffer layer, the ridge structure comprising a first waveguide layer, an active layer, a second waveguide layer, a grating layer, a cladding layer and a contact layer which are sequentially stacked; and a buried layer arranged on both sides of the ridge structure and burying the ridge structure; the buried layer comprises an intrinsic InP layer, a ZnCdSe layer, an N-type InP layer and a Fe-doped InP layer which are sequentially stacked. The application can improve the electro-optical conversion efficiency and reliability of the CW-DFB laser.

Description

Technical Field

[0001] This invention relates to the field of lasers, and more particularly to a CW-DFB laser epitaxial structure and its fabrication method, and a CW-DFB laser. Background Technology

[0002] Mainstream CW-DFB lasers typically employ InP-based lateral current blocking layers with PN junctions or PNP structures. When this approach operates under high temperature and high current conditions, its reverse leakage current increases significantly, leading to a decrease in current limiting capability, an increase in threshold current, and a reduction in efficiency. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an epitaxial structure for a CW-DFB laser and its fabrication method, which can reduce the threshold current and improve the electro-optical conversion efficiency.

[0004] Another technical problem to be solved by the present invention is to provide a CW-DFB laser with high electro-optical conversion efficiency.

[0005] To address the aforementioned technical problems, this invention provides a CW-DFB laser epitaxial structure, comprising: A substrate having a first surface and a second surface disposed opposite to each other; A buffer layer is disposed on the first surface; A ridge structure, disposed above the buffer layer, comprises a first waveguide layer, an active layer, a second waveguide layer, a grating layer, a cladding layer, and a contact layer stacked sequentially; and A buried layer is disposed on both sides of the ridge structure and buries the ridge structure; the buried layer includes an intrinsic InP layer, a ZnCdSe layer, an N-type InP layer and an Fe-doped InP layer stacked sequentially.

[0006] As an improvement to the above technical solution, the thickness of the intrinsic InP layer is 150nm~300nm; The thickness of the ZnCdSe layer is 10nm~50nm, and the proportion of Zn component is 0.4~0.8%. The thickness of the N-type InP layer is 100 nm to 300 nm, and its S doping concentration is 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 ; The thickness of the Fe-doped InP layer is 2 μm to 5 μm, and its Fe doping concentration is 2 × 10⁻⁶. 16 cm -3 ~1×10 17 cm -3 .

[0007] As an improvement to the above technical solution, the substrate is an N-InP substrate; The buffer layer is an N-type InP layer with a thickness of 500 nm to 1500 nm and an S doping concentration of 1 × 10⁻⁶. 18 cm -3 ~1×10 19 cm -3 ; The first waveguide layer is an undoped InGaAsP layer with a thickness of 50nm~300nm; The active layer comprises alternating layers of InGaAsP well layers and InGaAsP barrier layers, the thickness of the InGaAsP well layers is 5nm~10nm, the thickness of the InGaAsP barrier layers is 8nm~15nm, and the number of periods of the active layer is 3~15. The second waveguide layer is an undoped InGaAsP layer with a thickness of 50nm~200nm; The grating layer is a P-type InGaAsP layer with a thickness of 15nm~50nm and a Zn doping concentration of 1×10⁻⁶. 17 cm -3 ~1×10 18 cm -3 ; The cladding layer is a P-type InP layer with a thickness of 1 μm to 4 μm and a Zn doping concentration of 1 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 ; The contact layer is a p-type InGaAs layer with a thickness of 200 nm to 500 nm and a Zn doping concentration of 5 × 10⁻⁶. 18 cm -3 ~5×10 19 cm -3 .

[0008] As an improvement to the above technical solution, it also includes a first waveguide extension layer, a first spacer layer and a second waveguide extension layer, which are stacked sequentially between the buffer layer and the ridge structure; The first waveguide extension layer is an InGaAsP layer with a thickness of 30nm~100nm; The first spacer layer is an InP layer with a thickness of 100nm~300nm; The second waveguide extension layer is an InGaAsP layer with a thickness of 50nm~200nm.

[0009] As an improvement to the above technical solution, the ridge structure includes a second spacer layer, a first waveguide layer, an active layer, a second waveguide layer, an electron blocking layer, a third spacer layer, a grating layer, a grating buried layer, a cladding layer, and a contact layer, which are sequentially stacked on the second waveguide extension layer. The second spacer layer is an InP layer with a thickness of 200nm~500nm; The first waveguide layer is an undoped InGaAsP layer with a thickness of 50nm~300nm; The active layer comprises alternating layers of InGaAsP well layers and InGaAsP barrier layers, the thickness of the InGaAsP well layers is 5nm~10nm, the thickness of the InGaAsP barrier layers is 8nm~15nm, and the number of periods of the active layer is 3~15. The second waveguide layer is an undoped InGaAsP layer with a thickness of 50nm~200nm; The electron blocking layer is an AlInAs layer with a thickness of 5nm~50nm; The third spacer layer is an InP layer with a thickness of 100nm~300nm; The grating layer is a P-type InGaAsP layer with a thickness of 15nm~50nm and a Zn doping concentration of 1×10⁻⁶. 17 cm -3 ~1×10 18 cm -3 ; The grating buried layer is an InP layer with a thickness of 20nm~100nm; The cladding layer is a P-type InP layer with a thickness of 1 μm to 4 μm and a Zn doping concentration of 1 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 ; The contact layer is a p-type InGaAs layer with a thickness of 200 nm to 500 nm and a Zn doping concentration of 5 × 10⁻⁶. 18 cm -3 ~5×10 19 cm -3 .

[0010] As an improvement to the above technical solution, multiple alternating non-grating regions and grating regions are formed on the grating layer. The grating layer in the grating region is etched to form a grating structure, while the grating layer in the non-grating region is not etched. The non-grating region and the grating region are alternately distributed along the direction from the reflecting surface to the light-emitting surface, with the non-grating region being closest to the reflecting surface and the grating region being closest to the light-emitting surface.

[0011] Accordingly, the present invention also discloses a method for fabricating a CW-DFB laser epitaxial structure, which is used to fabricate the aforementioned CW-DFB laser epitaxial structure, comprising: Provide substrate; An initial epitaxial layer is formed on the substrate; wherein the initial epitaxial layer includes a buffer layer, a first waveguide layer, an active layer, a second waveguide layer, a grating layer, a cladding layer and a contact layer sequentially stacked on a first surface of the substrate; The initial epitaxial layer is etched to form a ridge structure and steps; wherein the steps are located on both sides of the ridge structure; A burial layer is formed on the steps; The buried layer comprises an intrinsic InP layer, a ZnCdSe layer, an N-type InP layer, and an Fe-doped InP layer stacked sequentially.

[0012] As an improvement to the above technical solution, the buried layer is grown by MOCVD; The growth temperature of the intrinsic InP layer is 620℃~660℃, and the growth pressure is 10 torr~200 torr. The growth temperature of the ZnCdSe layer is 350℃~550℃, and the growth pressure is 10 torr~150 torr. The growth temperature of the N-type InP layer is 620℃~660℃, and the growth pressure is 10 torr~200 torr. The growth temperature of the Fe-doped InP layer is 600℃~630℃, and the growth pressure is 10 torr~100 torr.

[0013] As an improvement to the above technical solution, the step of etching the initial epitaxial layer to form the ridge structure and steps includes: The initial epitaxial layer is etched using an ICP etching process; The initial epitaxial layer is etched using a wet process to form a ridge structure and steps.

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

[0015] Implementing this invention has the following beneficial effects: An embodiment of the present invention provides an epitaxial structure for a CW-DFB laser, comprising a substrate, a buffer layer, a ridge structure, and a buried layer. The substrate has a first surface and a second surface disposed opposite to each other. The buffer layer is disposed on the first surface, and the ridge structure is disposed above the buffer layer. The ridge structure comprises a first waveguide layer, an active layer, a second waveguide layer, a grating layer, a cladding layer, and a contact layer, sequentially stacked above the buffer layer. The buried layer is disposed on both sides of the ridge structure and buries it. Specifically, the buried layer comprises an intrinsic InP layer, a ZnCdSe layer, an N-type InP layer, and an Fe-doped InP layer, sequentially stacked above the buffer layer. The buried layer provides excellent blocking properties at high temperatures and high current densities, reducing leakage current, improving carrier confinement capability, lowering the threshold current of the CW-DFB laser based on this epitaxial structure, and improving its electro-optical conversion efficiency and reliability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the epitaxial structure of a CW-DFB laser in one embodiment of the present invention; Figure 2 This is a schematic diagram of the epitaxial structure of a CW-DFB laser in another embodiment of the present invention; In the figure: 100 is the substrate, 200 is the buffer layer, 300 is the first waveguide extension layer, 400 is the first spacer layer, 500 is the second waveguide extension layer, 600 is the ridge structure, 610 is the second spacer layer, 620 is the first waveguide layer, 630 is the active layer, 640 is the second waveguide layer, 650 is the electron blocking layer, 660 is the third spacer layer, 670 is the grating layer, 680 is the grating buried layer, 690 is the cladding layer, 710 is the contact layer, 800 is the buried layer, 810 is the intrinsic InP layer, 820 is the ZnCdSe layer, 830 is the N-type InP layer, and 840 is the Fe-doped InP layer. 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] 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.

[0020] 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.

[0021] Please see Figure 1 As a first aspect of the present invention, the present invention provides an epitaxial structure for a CW-DFB laser, comprising a substrate 100, a buffer layer 200, a ridge structure 600, and a buried layer 800. The substrate 100 has a first surface and a second surface disposed opposite to each other. The buffer layer 200 is disposed on the first surface, and the ridge structure 600 is disposed above the buffer layer 200. The ridge structure 600 includes a first waveguide layer 620, an active layer 630, a second waveguide layer 640, a grating layer 670, a cladding layer 690, and a contact layer 710 sequentially stacked above the buffer layer 200. The buried layer 800 is disposed on both sides of the ridge structure 600 and buries the ridge structure 600. Specifically, the buried layer 800 includes an intrinsic InP layer 810, a ZnCdSe layer 820, an N-type InP layer 830, and an Fe-doped InP layer 840 sequentially stacked above the buffer layer 200. The aforementioned buried layer 800 has a good blocking effect at high temperatures and high current densities, reducing leakage current, improving carrier confinement capability, reducing the threshold current of CW-DFB lasers based on this epitaxial structure, and improving their electro-optical conversion efficiency and reliability.

[0022] Specifically, the intrinsic InP layer 810 is an unintentionally doped InP layer with high resistivity and low refractive index, which effectively confines photons and charge carriers; it also effectively prevents other doped materials from diffusing into the active layer 630. Specifically, the thickness of the intrinsic InP layer 810 is 120nm to 350nm, exemplary values ​​are 140nm, 180nm, 200nm, 220nm, 240nm, 260nm, 280nm, 320nm, or 340nm, preferably 150nm to 350nm. More preferably, it is 200nm to 300nm.

[0023] Specifically, the ZnCdSe layer 820 has a large band gap (Eg > 2.0 eV), which effectively blocks electron overflow, and its low refractive index helps to enhance optical field confinement. The ZnCdSe layer 820 can also further block dopants in the N-type InP layer 830 and the Fe-doped InP layer 840, preventing them from entering the active layer 630. Furthermore, the ZnCdSe layer 820 has a high lattice matching degree with InP and similar coefficients of thermal expansion, significantly reducing interfacial stress and suppressing defect formation. The thickness of the ZnCdSe layer 820 is 5 nm to 50 nm, exemplary values ​​are 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, or 45 nm, but is not limited thereto. Preferably, the thickness of the ZnCdSe layer 820 is 10 nm to 50 nm. More preferably, it is 15 nm to 40 nm.

[0024] Specifically, the proportion of Zn component in the ZnCdSe layer 820 is 0.4~0.9, exemplaryly 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8 or 0.85, but not limited thereto. Preferably, the proportion of Zn component in the ZnCdSe layer 820 is 0.4~0.8. More preferably, it is 0.4~0.7.

[0025] Specifically, the N-type InP layer 830 can form a high-barrier heterojunction with the ZnCdSe layer 820, further suppressing electron reverse injection and reducing carrier leakage. The N-type InP layer 830 can suppress the double injection phenomenon of the Fe-doped InP layer 840, reducing lateral leakage current. Moreover, it will not adversely react with the Fe-doped InP layer 840, ensuring structural stability. The thickness of the N-type InP layer 830 is 100nm~500nm, exemplary of 120nm, 160nm, 200nm, 240nm, 280nm, 320nm, 360nm, 400nm or 450nm, but is not limited thereto. Preferably, the thickness of the N-type InP layer 830 is 100nm~300nm. More preferably, it is 150nm~250nm.

[0026] Specifically, the doping element of the N-type InP layer 830 is Si or S, but is not limited to these. Preferably, it is S. The S doping concentration of the N-type InP layer 830 is 1 × 10⁻⁶. 17 cm -3 ~8×10 18 cm -3 For example, 3×10 17 cm -3 5×10 17 cm -3 7×10 17 cm -3 1×10 18 cm -3 3×10 18 cm -3 5×10 18 cm -3 Or 7×10 18 cm -3 However, it is not limited to this. Preferably, the S doping concentration of the N-type InP layer 830 is 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 More preferably 8×10 17 cm -3 ~3×10 18 cm -3 .

[0027] Specifically, the Fe-doped InP layer 840 exhibits semi-insulating properties, which can significantly reduce leakage current and improve the electro-optical conversion efficiency and reliability of the device. The thickness of the Fe-doped InP layer 840 is 1.5 μm to 6 μm, exemplarily 1.8 μm, 2.2 μm, 2.6 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.2 μm, or 5.8 μm, but is not limited thereto. Preferably, the thickness of the Fe-doped InP layer 840 is 2 μm to 5 μm; more preferably, it is 3 μm to 4.5 μm.

[0028] Specifically, the Fe doping concentration in the Fe-doped InP layer 840 is 1×10⁻⁶. 16 cm -3 ~5×10 17 cm -3 For example, 3 × 10 16 cm -3 5×10 16 cm -3 7×10 16 cm -3 9×10 16 cm -3 1.5×10 17 cm-3 2.5×10 17 cm -3 Or 4×10 17 cm -3 However, it is not limited to this. Preferably, the Fe doping concentration in the Fe-doped InP layer 840 is 2 × 10⁻⁶. 16 cm -3 ~1×10 17 cm -3 More preferably 6×10 16 cm -3 ~1×10 17 cm -3 .

[0029] Specifically, the substrate 100 may be an InP substrate or a GaAs substrate, but is not limited thereto. Preferably, in some embodiments, the substrate 100 is an InP substrate, and more preferably an N-type InP substrate.

[0030] Specifically, the buffer layer 200 is an N-type InP layer or a P-type InP layer, but is not limited thereto. Preferably, in some embodiments, the buffer layer 200 is an N-type InP layer with a thickness of 500 nm to 1500 nm and an S doping concentration of 1 × 10⁻⁶. 18 cm -3 ~1×10 19 cm -3 .

[0031] Specifically, the ridge structure 600 is an etched strip-shaped mesa structure that has a trapezoidal cross-section that is narrower at the top and wider at the bottom or an arc-shaped cross-section that is wider at the top and narrower at the bottom in the substrate thickness direction, but is not limited to these.

[0032] Specifically, the first waveguide layer 620 is an undoped AlGaInAs layer, an undoped AlInAs layer, or an undoped InGaAsP layer, but is not limited to these. Preferably, in some embodiments, the first waveguide layer 620 is an undoped InGaAsP layer with a thickness of 50 nm to 300 nm. By controlling the proportions of Al, Ga, In, and As elements in this layer, the refractive index and bandgap of the first waveguide layer 620 can be made to increase progressively, effectively reducing carrier leakage and increasing internal quantum efficiency. More specifically, from the active layer 630 to the buffer layer 200, the bandgap and refractive index of the first waveguide layer 620 increase progressively.

[0033] Specifically, the active layer 630 is composed of alternating layers of AlGaInAs well layers and AlGaInAs barrier layers, or alternating layers of InGaAsP well layers and InGaAsP barrier layers, but is not limited thereto. Preferably, in some embodiments, the active layer 630 includes alternating layers of InGaAsP well layers and InGaAsP barrier layers. The thickness of the InGaAsP well layers is 5 nm to 10 nm, the thickness of the InGaAsP barrier layers is 8 nm to 15 nm, and the number of periods in the active layer 630 is 3 to 15.

[0034] Specifically, the second waveguide layer 640 is an undoped AlGaInAs layer, an undoped AlInAs layer, or an undoped InGaAsP layer, but is not limited to these. Preferably, in some embodiments, the second waveguide layer 640 is an undoped InGaAsP layer with a thickness of 50 nm to 200 nm. By controlling the proportions of Al, Ga, In, and As elements in this layer, the refractive index and bandgap of the second waveguide layer 640 can be made to decrease progressively, effectively reducing carrier leakage and increasing internal quantum efficiency. More specifically, from the active layer 630 to the grating layer 670, the bandgap of the second waveguide layer 640 decreases progressively, and the refractive index decreases progressively.

[0035] Specifically, the grating layer 670 is an InGaAsP layer or an AlGaAs layer, but is not limited thereto. Preferably, in some embodiments, the grating layer 670 is a p-type InGaAsP layer with a thickness of 15 nm to 50 nm and a Zn doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 18 cm -3 The grating layer 670 is etched to form a grating structure through an etching process. The grating can be a local grating, a uniform grating, or a phase-shifting grating, but is not limited to these.

[0036] Specifically, the cladding layer 690 is a P-type InP layer, a P-type InGaAsP layer, or a P-type AlGaInAs layer, but is not limited to these. Preferably, in some embodiments, the cladding layer 690 is a P-type InP layer with a thickness of 1 μm to 4 μm and a Zn doping concentration of 1 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 .

[0037] Specifically, the contact layer 710 is a P-type InGaAs layer or a P-type InGaAsP layer, but is not limited thereto. Preferably, in some embodiments, the contact layer 710 is a P-type InGaAs layer with a thickness of 200 nm to 500 nm and a Zn doping concentration of 5 × 10⁻⁶. 18 cm -3~5×10 19 cm -3 .

[0038] Preferably, in some embodiments, the CW-DFB laser epitaxial structure further includes a first waveguide extension layer 300, a first spacer layer 400, and a second waveguide extension layer 500, which are sequentially stacked between the buffer layer 200 and the ridge structure 600. Specifically, the first waveguide extension layer 300 is an InGaAsP layer with a thickness of 30nm~100nm; the first spacer layer 400 is an InP layer with a thickness of 100nm~300nm; and the second waveguide extension layer 500 is an InGaAsP layer with a thickness of 50nm~200nm. Based on this structure, the optical field can be more uniformly confined near the active region, significantly reducing transverse mode noise and improving single-mode stability and output power consistency.

[0039] Preferably, see Figure 2 In some embodiments, the ridge structure 600 includes a second spacer layer 610, a first waveguide layer 620, an active layer 630, a second waveguide layer 640, an electron blocking layer 650, a third spacer layer 660, a grating layer 670, a grating buried layer 680, a cladding layer 690, and a contact layer 710, which are sequentially stacked on the second waveguide extension layer 500. The second spacer layer 610 is an InP layer with a thickness of 200 nm to 500 nm; the first waveguide layer 620 is an undoped InGaAsP layer with a thickness of 50 nm to 300 nm; and the active layer 630 includes alternately stacked InGaAsP well layers. The active layer 630 consists of an InGaAsP barrier layer, an InGaAsP well layer with a thickness of 5 nm to 10 nm, an InGaAsP barrier layer with a thickness of 8 nm to 15 nm, and an active layer with a period number of 3 to 15. The second waveguide layer 640 is an undoped InGaAsP layer with a thickness of 50 nm to 200 nm. The electron blocking layer 650 is an AlInAs layer with a thickness of 5 nm to 50 nm. The third spacer layer 660 is an InP layer with a thickness of 100 nm to 300 nm. The grating layer 670 is a P-type InGaAsP layer with a thickness of 15 nm to 50 nm and a Zn doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 18 cm -3 The grating buried layer 680 is an InP layer with a thickness of 20nm~100nm; the cladding layer 690 is a P-type InP layer with a thickness of 1μm~4μm and a Zn doping concentration of 1×10⁻⁶. 17 cm -3 ~5×10 18 cm -3 The contact layer 710 is a p-type InGaAs layer with a thickness of 200 nm to 500 nm and a Zn doping concentration of 5 × 10⁻⁶.18 cm -3 ~5×10 19 cm -3 The 600 ridge structure further enhances its adaptability to operating conditions under high temperature and high current density, improving electro-optical conversion efficiency and reliability.

[0040] Preferably, in some embodiments, a plurality of alternating non-grating regions and grating regions are formed on the grating layer 670. The grating layer 670 in the grating regions is etched to form a grating structure, while the grating layer 670 in the non-grating regions is not etched. The non-grating regions and grating regions are alternately distributed along the direction from the reflecting surface to the emitting surface, with the non-grating region being closest to the reflecting surface and the grating region being closest to the emitting surface. Based on this, the output power can be further improved while maintaining single-mode stability.

[0041] Accordingly, as a second aspect of the present invention, the present invention provides a method for fabricating a CW-DFB laser epitaxial structure, which includes the following steps: S1: Provides a substrate; S2: An initial epitaxial layer is formed on a substrate; wherein the initial epitaxial layer includes a buffer layer, a first waveguide layer, an active layer, a second waveguide layer, a grating layer, a cladding layer and a contact layer sequentially stacked on a first surface of the substrate; S3: Etch the initial epitaxial layer to form ridge structures and steps; S4: A burial layer is formed on the steps; The steps are located on both sides of the ridge structure; the buried layer includes an intrinsic InP layer, a ZnCdSe layer, an N-type InP layer, and an Fe-doped InP layer stacked sequentially on the steps. These buried layers exhibit excellent blocking properties at high temperatures and high current densities, reducing leakage current, improving carrier confinement capability, lowering the threshold current of the CW-DFB laser based on this epitaxial structure, and enhancing electro-optical conversion efficiency and reliability.

[0042] Specifically, in some implementations, in steps S2 and S4, various layer structures are grown by MOCVD. More specifically, the growth temperature of the intrinsic InP layer is 620℃~660℃, and the growth pressure is 10 torr~200 torr; the growth temperature of the ZnCdSe layer is 350℃~550℃, and the growth pressure is 10 torr~150 torr; the growth temperature of the N-type InP layer is 620℃~660℃, and the growth pressure is 10 torr~200 torr; the growth temperature of the Fe-doped InP layer is 600℃~630℃, and the growth pressure is 10 torr~100 torr.

[0043] Specifically, in step S3, the initial epitaxial layer can be etched using wet etching or dry etching processes to form ridge structures and steps, but is not limited thereto. Preferably, in some embodiments, step S3 includes: S31: The initial epitaxial layer is etched using ICP etching process; S32: The initial epitaxial layer is etched using a wet process to form a ridge structure and steps.

[0044] Based on the above etching method, a ridge structure with arc-shaped sidewalls can be formed, which can effectively reduce end-face reflection loss and light field scattering, and improve electro-optical conversion efficiency.

[0045] Accordingly, as a third aspect of the present invention, a CW-DFB laser is also disclosed, which includes the aforementioned CW-DFB laser epitaxial structure. It also includes a passivation layer, an upper electrode, a lower electrode, and other structures.

[0046] The present invention will be further described below with reference to specific embodiments: Example 1 This embodiment provides an epitaxial structure for a CW-DFB laser, comprising: a substrate, a buffer layer, a ridge structure, and a buried layer. The substrate is an N-type InP substrate having a first surface and a second surface disposed opposite to each other; the buffer layer is an N-type InP layer with a thickness of 1 μm and an S doping concentration of 1 × 10⁻⁶. 18 cm -3 The ridge structure is located above the buffer layer. The ridge structure comprises a first waveguide layer, an active layer, a second waveguide layer, a grating layer, a grating buried layer, a cladding layer, and a contact layer, stacked sequentially. The first waveguide layer is an undoped InGaAsP layer with a thickness of 70 nm. The active layer comprises alternating layers of InGaAsP well layers and InGaAsP barrier layers, with the InGaAsP well layers having a thickness of 5 nm and the InGaAsP barrier layers having a thickness of 8 nm. The active layer has 6 periods. The second waveguide layer is an undoped InGaAsP layer with a thickness of 60 nm. The grating layer is a P-type InGaAsP layer with a thickness of 17 nm and a Zn doping concentration of 8 × 10⁻⁶. 17 cm -3 The grating buried layer is an InP layer with a thickness of 70 nm; the cladding layer is a P-type InP layer with a thickness of 2.5 μm. In the direction from the grating buried layer to the contact layer, the Zn doping concentration of the cladding layer ranges from 5 × 10⁻⁶. 17 cm -3 Increase to 2×10 18 cm -3 The contact layer is a p-type InGaAs layer with a thickness of 300 nm and a Zn doping concentration of 4.6 × 10⁻⁶. 19 cm -3 .

[0047] The buried layers are located on both sides of the ridge structure and bury the ridge structure. The buried layers consist of sequentially stacked intrinsic InP, ZnCdSe, N-type InP, and Fe-doped InP layers. The intrinsic InP layer has a thickness of 180 nm, the ZnCdSe layer has a thickness of 15 nm with a Zn content of 0.48%, and the N-type InP layer has a thickness of 150 nm with an S doping concentration of 1 × 10⁻⁶. 18 cm -3 The thickness of the Fe-doped InP layer is 2.77 μm, and its Fe doping concentration is 8 × 10⁻⁶. 16 cm -3 .

[0048] Example 2 This embodiment provides an epitaxial structure for a CW-DFB laser, comprising: a substrate, a buffer layer, a first waveguide extension layer, a first spacer layer, a second waveguide extension layer, a ridge structure, and a buried layer. The substrate is an N-type InP substrate with a first surface and a second surface disposed opposite to each other. The buffer layer, the first waveguide extension layer, the first spacer layer, the second waveguide extension layer, and the ridge structure are sequentially stacked on the first surface. The buffer layer is an N-type InP layer with a thickness of 1 μm and an S doping concentration of 1 × 10⁻⁶. 18 cm -3 The first waveguide extension layer is an InGaAsP layer with a thickness of 50 nm; the first spacer layer is an InP layer with a thickness of 200 nm; and the second waveguide extension layer is an InGaAsP layer with a thickness of 90 nm. The ridge structure comprises a second spacer layer, a first waveguide layer, an active layer, another second waveguide layer, an electron blocking layer, a third spacer layer, a grating layer, a grating buried layer, a cladding layer, and a contact layer, sequentially stacked on a second waveguide extension layer. The second spacer layer is an InP layer with a thickness of 400 nm. The first waveguide layer is an undoped InGaAsP layer with a thickness of 70 nm. The active layer comprises alternating InGaAsP well layers and InGaAsP barrier layers, with the InGaAsP well layers having a thickness of 5 nm and the InGaAsP barrier layers having a thickness of 8 nm. The active layer has 6 periods. The second waveguide layer is an undoped InGaAsP layer with a thickness of 60 nm. The electron blocking layer is an AlInAs layer with a thickness of 10 nm. The third spacer layer is an InP layer with a thickness of 200 nm. The grating layer is a P-type InGaAsP layer with a thickness of 17 nm and a Zn doping concentration of 8 × 10⁻⁶. 17 cm -3 The grating buried layer is an InP layer with a thickness of 70 nm; the cladding layer is a P-type InP layer with a thickness of 2.5 μm. In the direction from the grating buried layer to the contact layer, the Zn doping concentration of the cladding layer ranges from 5 × 10⁻⁶. 17 cm -3 Increase to 2×1018 cm -3 The contact layer is a p-type InGaAs layer with a thickness of 300 nm and a Zn doping concentration of 4.6 × 10⁻⁶. 19 cm -3 .

[0049] The buried layers are located on both sides of the ridge structure and bury the ridge structure. The buried layers consist of sequentially stacked intrinsic InP, ZnCdSe, N-type InP, and Fe-doped InP layers. The intrinsic InP layer is 200 nm thick, the ZnCdSe layer is 25 nm thick with a Zn content of 0.48%, and the N-type InP layer is 200 nm thick with an S doping concentration of 1 × 10⁻⁶. 18 cm -3 The thickness of the Fe-doped InP layer is 2.77 μm, and its Fe doping concentration is 8 × 10⁻⁶. 16 cm -3 .

[0050] Comparative Example 1 This comparative example provides a CW-DFB laser epitaxial structure, which differs from Example 1 in that: The buried layer does not include the N-type InP layer, and the thickness of the remaining layers is enlarged proportionally to the original thickness, resulting in a total buried layer thickness of 3115 nm.

[0051] Everything else is the same as in Example 1.

[0052] Comparative Example 2 This comparative example provides a CW-DFB laser epitaxial structure, which differs from Example 1 in that: The buried layer does not include the ZnCdSe layer, and the thickness of the remaining layers is enlarged proportionally to the original thickness, resulting in a total buried layer thickness of 3115 nm.

[0053] Everything else is the same as in Example 1.

[0054] Comparative Example 3 This comparative example provides a CW-DFB laser epitaxial structure, which differs from Example 1 in that: The buried layer does not include the intrinsic InP layer, and the thickness of the remaining layers is enlarged proportionally to the original thickness, resulting in a total buried layer thickness of 3115 nm.

[0055] Everything else is the same as in Example 1.

[0056] Comparative Example 4 This comparative example provides a CW-DFB laser epitaxial structure, which differs from Example 1 in that: The buried layer does not include the intrinsic InP layer and ZnCdSe layer. The thickness of the remaining layers is enlarged proportionally to the original thickness, resulting in a total buried layer thickness of 3115 nm.

[0057] Everything else is the same as in Example 1.

[0058] The CW-DFB laser epitaxial structures obtained in Examples 1-2 and Comparative Examples 1-4 were fabricated into CW-DFB laser chips and tested. The specific performance parameters are as follows:

[0059] 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. An epitaxial structure for a CW-DFB laser, characterized in that, include: A substrate having a first surface and a second surface disposed opposite to each other; A buffer layer is disposed on the first surface; A ridge structure, disposed above the buffer layer, comprises a first waveguide layer, an active layer, a second waveguide layer, a grating layer, a cladding layer, and a contact layer stacked sequentially; and A buried layer is disposed on both sides of the ridge structure and buries the ridge structure; the buried layer includes an intrinsic InP layer, a ZnCdSe layer, an N-type InP layer and an Fe-doped InP layer stacked sequentially; The first waveguide layer is an undoped AlGaInAs layer, an undoped AlInAs layer, or an undoped InGaAsP layer, with a thickness of 50nm~300nm. The active layer comprises alternating layers of InGaAsP well layers and InGaAsP barrier layers, the thickness of the InGaAsP well layers is 5nm~10nm, the thickness of the InGaAsP barrier layers is 8nm~15nm, and the number of periods of the active layer is 3~15. The second waveguide layer is an undoped AlGaInAs layer, an undoped AlInAs layer, or an undoped InGaAsP layer, with a thickness of 50nm~200nm. The grating layer is an InGaAsP layer or an AlGaAs layer, with a thickness of 15nm~50nm; The cladding layer is a P-type InP layer, a P-type InGaAsP layer, or a P-type AlGaInAs layer, with a thickness of 1 μm to 4 μm and a Zn doping concentration of 1 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 ; The contact layer is a P-type InGaAs layer or a P-type InGaAsP layer with a thickness of 200 nm to 500 nm and a Zn doping concentration of 5 × 10⁻⁶. 18 cm -3 ~5×10 19 cm -3 ; The thickness of the intrinsic InP layer is 120nm~350nm; The thickness of the ZnCdSe layer is 5nm~50nm, and the proportion of Zn component is 0.4~0.

9. The thickness of the N-type InP layer is 100 nm to 500 nm, and its S doping concentration is 1 × 10⁻⁶. 17 cm -3 ~8×10 18 cm -3 ; The thickness of the Fe-doped InP layer is 1.5 μm to 6 μm, and its Fe doping concentration is 1 × 10⁻⁶. 16 cm -3 ~5×10 17 cm -3 .

2. The CW-DFB laser epitaxial structure as described in claim 1, characterized in that, The thickness of the intrinsic InP layer is 150 nm to 300 nm; The thickness of the ZnCdSe layer is 10nm~50nm, and the proportion of Zn component is 0.4~0.8%. The thickness of the N-type InP layer is 100 nm to 300 nm, and its S doping concentration is 5 × 10⁻⁶. 17 cm -3 ~5×10 18 cm -3 ; The thickness of the Fe-doped InP layer is 2 μm to 5 μm, and its Fe doping concentration is 2 × 10⁻⁶. 16 cm -3 ~1×10 17 cm -3 .

3. The CW-DFB laser epitaxial structure as described in claim 1, characterized in that, The substrate is an N-InP substrate; The buffer layer is an N-type InP layer with a thickness of 500 nm to 1500 nm and an S doping concentration of 1 × 10⁻⁶. 18 cm -3 ~1×10 19 cm -3 ; The first waveguide layer is an undoped InGaAsP layer; The second waveguide layer is an undoped InGaAsP layer; The grating layer is a P-type InGaAsP layer with a Zn doping concentration of 1×10⁻⁶. 17 cm -3 ~1×10 18 cm -3 ; The coating layer is a P-type InP layer; The contact layer is a P-type InGaAs layer.

4. The CW-DFB laser epitaxial structure as described in any one of claims 1 to 3, characterized in that, It also includes a first waveguide extension layer, a first spacer layer and a second waveguide extension layer, which are stacked sequentially between the buffer layer and the ridge structure; The first waveguide extension layer is an InGaAsP layer with a thickness of 30nm~100nm; The first spacer layer is an InP layer with a thickness of 100nm~300nm; The second waveguide extension layer is an InGaAsP layer with a thickness of 50nm~200nm.

5. The CW-DFB laser epitaxial structure as described in claim 4, characterized in that, The ridge structure includes a second spacer layer, a first waveguide layer, an active layer, a second waveguide layer, an electron blocking layer, a third spacer layer, a grating layer, a grating buried layer, a cladding layer, and a contact layer, which are sequentially stacked on the second waveguide extension layer. The second spacer layer is an InP layer with a thickness of 200nm~500nm; The first waveguide layer is an undoped InGaAsP layer; The second waveguide layer is an undoped InGaAsP layer; The electron blocking layer is an AlInAs layer with a thickness of 5nm~50nm; The third spacer layer is an InP layer with a thickness of 100nm~300nm; The grating layer is a P-type InGaAsP layer with a Zn doping concentration of 1×10⁻⁶. 17 cm -3 ~1×10 18 cm -3 ; The grating buried layer is an InP layer with a thickness of 20nm~100nm; The coating layer is a P-type InP layer; The contact layer is a P-type InGaAs layer.

6. The CW-DFB laser epitaxial structure as described in claim 1, characterized in that, The grating layer has multiple alternating non-grating regions and grating regions. The grating layer in the grating region is etched to form a grating structure, while the grating layer in the non-grating region is not etched. The non-grating region and the grating region are alternately distributed along the direction from the reflecting surface to the light-emitting surface, with the non-grating region being closest to the reflecting surface and the grating region being closest to the light-emitting surface.

7. A method for fabricating a CW-DFB laser epitaxial structure, used to fabricate the CW-DFB laser epitaxial structure as described in any one of claims 1 to 6, characterized in that, include: Provide substrate; An initial epitaxial layer is formed on the substrate; wherein the initial epitaxial layer includes a buffer layer, a first waveguide layer, an active layer, a second waveguide layer, a grating layer, a cladding layer and a contact layer sequentially stacked on a first surface of the substrate; The initial epitaxial layer is etched to form a ridge structure and steps; wherein the steps are located on both sides of the ridge structure; A burial layer is formed on the steps; The buried layer comprises an intrinsic InP layer, a ZnCdSe layer, an N-type InP layer, and an Fe-doped InP layer stacked sequentially.

8. The method for fabricating the CW-DFB laser epitaxial structure as described in claim 7, characterized in that, The buried layer is grown by MOCVD; The growth temperature of the intrinsic InP layer is 620℃~660℃, and the growth pressure is 10 torr~200 torr. The growth temperature of the ZnCdSe layer is 350℃~550℃, and the growth pressure is 10 torr~150 torr. The growth temperature of the N-type InP layer is 620℃~660℃, and the growth pressure is 10 torr~200 torr. The growth temperature of the Fe-doped InP layer is 600℃~630℃, and the growth pressure is 10 torr~100 torr.

9. The method for fabricating the CW-DFB laser epitaxial structure as described in claim 7, characterized in that, The step of etching the initial epitaxial layer to form the ridge structure and steps includes: The initial epitaxial layer is etched using an ICP etching process; The initial epitaxial layer is etched using a wet process to form a ridge structure and steps.

10. A CW-DFB laser, characterized in that, Includes the CW-DFB laser epitaxial structure as described in any one of claims 1 to 6.

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