Dual-ridge waveguide semiconductor laser and method of making same

Abstract

This invention discloses a double-ridged waveguide semiconductor laser and its fabrication method. A first mask layer is formed on an n-type electrode, and a first strip-shaped window is formed within the first mask layer. An n-type ridged waveguide is formed within the first strip-shaped window. An epitaxial structure is formed on the surface of the n-type ridged waveguide. A second mask layer is formed on the surface of the epitaxial structure, and a second strip-shaped window is formed within the second mask layer. A p-type ridged waveguide is formed within the second strip-shaped window. A current spreading layer is formed on the surface of the p-type ridged waveguide. A p-type electrode is formed on the surface of the current spreading layer. The double-ridged waveguide semiconductor laser and its fabrication method of this invention yield a semiconductor laser with ridged waveguides at both ends, which can further enhance lateral optical field confinement and current confinement, and facilitates the fabrication of ridged waveguides with complex shapes, greatly simplifying the process and reducing costs.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a double-ridged waveguide semiconductor laser and its fabrication method. Background Technology

[0002] Semiconductor laser diodes (LDs) have the best energy conversion efficiency among various lasers. With continuous breakthroughs in power, efficiency, brightness, lifespan, multi-wavelength, and modulation rate, they are widely used in materials processing, medical, optical communication, sensing, and defense fields.

[0003] To enhance the lateral optical field confinement and current confinement of semiconductor lasers, traditional semiconductor lasers, both domestically and internationally, typically incorporate ridge waveguides in the p-type confinement layer and p-type contact layer. Furthermore, the primary technique for fabricating ridge waveguides in traditional semiconductor lasers currently employs dry etching. However, this method causes sidewall damage that is difficult to repair, damages the p-type contact layer surface, reduces the p-type ohmic contact area and the conductive channel on the p-side, thereby increasing optical absorption loss, creating leakage current channels, hindering heat dissipation, and potentially increasing the laser's operating voltage.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a double-ridged waveguide semiconductor laser and its fabrication method. This method fabricates both the p-type region (p-type capping layer and p-type confinement layer) and the n-type region (n-type capping layer and n-type confinement layer) of the semiconductor laser into ridges, resulting in a semiconductor laser with ridged waveguides at both ends. This further enhances lateral optical field confinement and current confinement. Furthermore, the fabrication of the n-type and p-type ridged waveguides can be completed without photolithography and etching of the p-type and n-type regions. It also facilitates the fabrication of ridged waveguides with complex shapes, greatly simplifying the process and reducing costs.

[0006] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0007] A double-ridged waveguide semiconductor laser, comprising:

[0008] An n-type electrode has a first surface;

[0009] A first mask layer is formed on the first surface, and a first strip window is formed within the first mask layer, the first strip window exposing a portion of the first surface;

[0010] An n-type ridge waveguide is formed within the first strip window. The n-type ridge waveguide includes an n-type capping layer formed on the first surface and an n-type confinement layer formed on the surface of the n-type capping layer opposite to the n-type electrode.

[0011] An epitaxial structure is formed on the surface of the n-type confinement layer opposite to the n-type electrode;

[0012] A second mask layer is formed on the surface of the epitaxial structure opposite to the n-type electrode. A second strip window is formed in the second mask layer, and the second strip window exposes a portion of the surface of the epitaxial structure.

[0013] A p-type ridge waveguide is formed within the second strip window. The p-type ridge waveguide includes a p-type confinement layer formed on the surface of the epitaxial structure and a p-type capping layer formed on the surface of the p-type confinement layer facing away from the n-type electrode.

[0014] A current spreading layer is formed on the surface of the p-type ridge waveguide opposite to the n-type electrode; and

[0015] The p-type electrode is formed on the surface of the current spreading layer opposite to the n-type electrode.

[0016] In one or more embodiments of the present invention, the width of the first strip window at the end near the n-type electrode is greater than or equal to the width at the end near the epitaxial structure.

[0017] In one or more embodiments of the present invention, the width of the second strip window at the end near the epitaxial structure is less than or equal to the width at the end near the p-type confinement layer.

[0018] In one or more embodiments of the present invention, the n-type ridge waveguide is formed by the following steps:

[0019] The first mask layer is etched to form the first strip window;

[0020] An n-type cladding layer and an n-type confinement layer are sequentially grown within the first strip window to form an n-type ridge waveguide.

[0021] In one or more embodiments of the present invention, the p-type ridge waveguide is formed by the following steps:

[0022] The second mask layer is etched to form the second strip window;

[0023] A p-type confinement layer and a p-type capping layer are grown sequentially within the second strip window to form a p-type ridge waveguide.

[0024] A specific embodiment of the present invention also provides a method for fabricating a double-ridged waveguide semiconductor laser, comprising:

[0025] A substrate is provided, and a first mask layer is formed on the surface of the substrate;

[0026] The first mask layer is etched to create a first strip window on the first mask layer;

[0027] An n-type capping layer and an n-type confinement layer are sequentially grown within the first strip window to form an n-type ridge waveguide;

[0028] An epitaxial structure is grown on the surface of the n-type confinement layer;

[0029] A second mask layer is formed on the surface of the epitaxial structure;

[0030] The second mask layer is etched to prepare a second strip window on the second mask layer;

[0031] A p-type confinement layer and a p-type capping layer are grown sequentially within the second strip window to form a p-type ridge waveguide;

[0032] A current spreading layer is formed on the surface of the p-type ridge waveguide, and a p-type electrode is formed on the surface of the current spreading layer;

[0033] The substrate is removed, and an n-type electrode is formed on the surface of the n-type capping layer to obtain a semiconductor laser epitaxial wafer.

[0034] In one or more embodiments of the present invention, the n-type capping layer and the n-type confinement layer are epitaxially grown within the first strip window using a lateral epitaxial overgrowth technique.

[0035] In one or more embodiments of the present invention, the thickness of the n-type cover layer is less than the thickness of the first mask layer, and the sum of the thicknesses of the n-type cover layer and the n-type confinement layer is greater than or equal to the thickness of the first mask layer.

[0036] In one or more embodiments of the present invention, the p-type confinement layer and the p-type cover layer are epitaxially grown within the second strip window using a lateral epitaxial overgrowth technique.

[0037] In one or more embodiments of the present invention, a first strip window arranged in parallel is prepared on the first mask layer by photolithography, wet etching, and dry etching processes, wherein the first strip window exposes a portion of the substrate.

[0038] In one or more embodiments of the present invention, the thickness of the first mask layer is 1 μm to 2 μm.

[0039] In one or more embodiments of the present invention, the spacing between adjacent first strip windows is 1.5 μm to 3 μm.

[0040] In one or more embodiments of the present invention, the material of the first mask layer includes SiO2 or SiN. x .

[0041] In one or more embodiments of the present invention, second strip windows arranged side by side are prepared on the second mask layer by photolithography, wet etching, and dry etching processes, and the second strip windows expose part of the epitaxial structure.

[0042] In one or more embodiments of the present invention, the thickness of the second mask layer is 1 μm to 2 μm.

[0043] In one or more embodiments of the present invention, the spacing between adjacent second strip windows is 1.5 μm to 3 μm.

[0044] In one or more embodiments of the present invention, the material of the second mask layer includes SiO2 or SiN. x .

[0045] In one or more embodiments of the present invention, the width of the first strip window at the end near the substrate is greater than or equal to the width at the end near the epitaxial structure.

[0046] In one or more embodiments of the present invention, the width of the second strip window at the end near the epitaxial structure is less than or equal to the width at the end near the p-type confinement layer.

[0047] In one or more embodiments of the present invention, the shape of the n-type ridge waveguide is changed by adjusting the shape of the first strip window.

[0048] In one or more embodiments of the present invention, the shape of the p-shaped ridge waveguide is changed by adjusting the shape of the second strip window.

[0049] In one or more embodiments of the present invention, after the step of sequentially growing a p-type confinement layer and a p-type cover layer within the second strip window, the method further includes:

[0050] The step of growing a p-type contact layer on the surface of the p-type cover layer;

[0051] The current spreading layer is grown on the surface of the p-type contact layer.

[0052] In one or more embodiments of the present invention, the epitaxial structure includes a lower waveguide layer, an active layer, and an upper waveguide layer sequentially grown on the surface of the n-type confinement layer.

[0053] In one or more embodiments of the present invention, removing the substrate includes: removing the substrate by grinding, thinning, or polishing; or removing the substrate by laser stripping.

[0054] In one or more embodiments of the present invention, the method for fabricating a double-ridged waveguide semiconductor laser further includes: dicing, cleaving, and cavity surface coating of the semiconductor laser epitaxial wafer to obtain a double-ridged waveguide semiconductor laser.

[0055] Compared with the prior art, the double-ridged waveguide semiconductor laser of the present invention makes both the p-type region (p-type capping layer and p-type confinement layer) and the n-type region (n-type capping layer and n-type confinement layer) of the semiconductor laser into ridges, resulting in a semiconductor laser with ridged waveguides at both ends, which can further enhance the transverse optical field confinement and current confinement.

[0056] The dual-ridge waveguide semiconductor laser of the present invention employs an inverted trapezoidal ridge waveguide semiconductor laser, which allows for a much larger electrode contact area than that of a traditional ridge semiconductor laser with the same emitting area. This reduces energy loss, results in lower series resistance and thermal resistance, and improves the performance of the semiconductor laser.

[0057] The fabrication method of the dual-ridge waveguide semiconductor laser of the present invention bypasses the photolithography and etching processes of the p-type and n-type regions, and directly completes the fabrication of the n-type and p-type ridge waveguides. It is also easy to fabricate ridge waveguides with complex shapes, which greatly simplifies the process and reduces costs.

[0058] The method for fabricating a double-ridged waveguide semiconductor laser of the present invention involves preparing a first strip-shaped window on a substrate and using lateral epitaxial overgrowth (ELOG) technology to directly form a ridge along the first strip-shaped window during epitaxial growth of the n-type capping layer and the n-type confinement layer. Simultaneously, by preparing a second strip-shaped window on the epitaxial structure, and using lateral epitaxial overgrowth (ELOG) technology, directly form a ridge along the second strip-shaped window during epitaxial growth of the p-type capping layer and the p-type confinement layer, thus forming a double-ridged waveguide. This effectively avoids sidewall damage caused by etching processes in the prior art, thereby reducing the threshold current of the semiconductor laser and improving the reliability of the device.

[0059] The method for fabricating a dual-ridge waveguide semiconductor laser of the present invention can easily obtain the desired but complex ridge waveguide shape by changing the shape of the first strip window on the first mask layer and the shape of the second strip window on the second mask layer, thereby improving the performance of the semiconductor laser.

[0060] The method for fabricating a dual-ridged waveguide semiconductor laser of the present invention uses dry etching or wet etching to process the mask layers (first mask layer and second mask layer) into special shapes. The shape and angle are easier to control, and the required special ridge structure can be more easily formed through subsequent epitaxial growth. The process is convenient to control and greatly saves costs, thus improving the feasibility of fabricating special ridged waveguides. Attached Figure Description

[0061] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0062] Figure 1 This is a schematic diagram of a double-ridged waveguide semiconductor laser in one embodiment of the present invention;

[0063] Figure 2 This is a process flow diagram of a method for fabricating a double-ridged waveguide semiconductor laser according to an embodiment of the present invention;

[0064] Figures 3a-3g This is a schematic diagram illustrating the process steps of fabricating a double-ridged waveguide semiconductor laser according to an embodiment of the present invention. Detailed Implementation

[0065] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0066] As mentioned in the background section, current domestic and international conventional semiconductor lasers typically incorporate ridge waveguides in the p-type confinement layer and p-type contact layer to enhance lateral optical field confinement and current confinement. Furthermore, the main technical approach for fabricating ridge waveguides in conventional semiconductor lasers currently employs dry etching processes. However, this traditional method has the following drawbacks:

[0067] The etching process can cause sidewall damage, which damages the surface of the p-type contact layer, reduces the p-type ohmic contact area and the conductive channel on the p side, thereby increasing light absorption loss, forming a leakage channel, which is not conducive to heat dissipation and can easily increase the operating voltage of the laser.

[0068] Lasers with ridge waveguides at both ends are difficult to fabricate and have a complex manufacturing process.

[0069] Understandably, dry etching of ridge waveguides reduces the ohmic contact area of ​​the p-type electrode, hindering heat dissipation and potentially increasing the laser's operating voltage. Therefore, specially shaped ridges, such as inverted structures, are typically used to increase the contact area with the electrode. However, these specially shaped ridges are complex and difficult to obtain through simple etching processes. This is especially true for GaN materials commonly used in semiconductor lasers, which, due to their high hardness, can only be etched using dry etching. However, dry etching of specially shaped ridges is challenging, with difficulty in controlling directionality and a tendency for over-etching or under-etching. It often requires multiple photolithography steps, which undoubtedly increases process complexity and further exacerbates damage to the semiconductor laser.

[0070] Based on this, the present invention provides a double-ridged waveguide semiconductor laser and its fabrication method. By fabricating ridges in both the p-type region (p-type capping layer and p-type confinement layer) and the n-type region (n-type capping layer and n-type confinement layer) of the semiconductor laser, a semiconductor laser with ridged waveguides at both ends is obtained, which can further enhance lateral optical field confinement and current confinement. Simultaneously, a first strip-shaped window is fabricated on the substrate, and lateral epitaxial overgrowth (ELOG) technology is used to directly form ridges along the first strip-shaped window during epitaxial growth of the n-type capping layer and n-type confinement layer. Simultaneously, a second strip-shaped window is fabricated on the epitaxial structure, and lateral epitaxial overgrowth (ELOG) technology is used to directly form ridges along the second strip-shaped window during epitaxial growth of the p-type capping layer and p-type confinement layer, forming a double-ridged waveguide. This method eliminates the need for etching the n-type and p-type regions to fabricate the ridged waveguides, effectively avoiding sidewall damage caused by etching processes in existing technologies. This reduces the threshold current of the semiconductor laser and improves device reliability.

[0071] like Figure 1 As shown, a dual-ridge waveguide semiconductor laser in one embodiment of the present invention includes: a first mask layer 20, an n-type ridge waveguide, an epitaxial structure, a second mask layer 50, a p-type ridge waveguide, a current spreading layer 71, a p-type electrode 72, and an n-type electrode 80.

[0072] The n-type electrode 80 has a first surface, and the n-type electrode 80 is preferably made of Ti / Al / Ti / Au with a wavelength of 50nm / 100nm / 50nm / 100nm.

[0073] A first mask layer 20 is formed on the first surface. A first strip-shaped window 21 is formed within the first mask layer 20, exposing a portion of the first surface. The material of the first mask layer 20 can be SiO2 / SiN. xThe mask material is used, and the thickness of the first mask layer 20 is 1μm to 2μm. The cross-sectional shape of the first strip window 21 can be designed according to the desired ridge shape, and can be any shape such as triangle, square, trapezoid, etc. Preferably, the width of the end of the first strip window 21 near the n-type electrode 80 is greater than or equal to the width of the end near the epitaxial structure. This design ensures that the n-type ridge waveguide grown in the first strip window 21 has at least a square structure or a truncated pyramidal structure that is narrower at the top and wider at the bottom, which can increase the contact area with the n-type electrode 80 and facilitate heat dissipation.

[0074] An n-type ridge waveguide is formed within the first strip window 21. The n-type ridge waveguide includes an n-type capping layer 31 formed on the first surface and an n-type confinement layer 32 formed on the surface of the n-type capping layer 31 facing away from the n-type electrode 80. The thickness of the n-type capping layer 31 is less than the thickness of the first mask layer 20, and the sum of the thicknesses of the n-type capping layer 31 and the n-type confinement layer 32 is greater than or equal to the thickness of the first mask layer 20.

[0075] For example, the n-type capping layer 31 can be an n-type GaN capping layer with a thickness of 2 μm and a doping concentration of 5 × 10⁻⁶. 18 cm -3 ~6×10 18 cm -3 The n-type confinement layer 32 can be an n-type AlGaN confinement layer with a thickness of 1.2 μm and a doping concentration of 3 × 10⁻⁶. 17 cm -3 .

[0076] The epitaxial structure is formed on the surface of the n-type confinement layer 32 facing away from the n-type electrode 80. The epitaxial structure may include a lower waveguide layer 41, an active layer 42, and an upper waveguide layer 43 sequentially grown on the surface of the n-type confinement layer 32.

[0077] For example, the lower waveguide layer 41 can be undoped In. 0.07 Ga 0.93 The lower waveguide layer is 160 nm thick. The active layer 42 can be undoped In. 0.25 Ga 0.75 The N / GaN active layer has two periods of multiple quantum wells, with the InGaN well width ranging from 3 nm to 5 nm and the GaN barrier width ranging from 8 nm to 10 nm. The upper waveguide layer 43 can be undoped In. 0.07 Ga 0.93 The waveguide layer on N has a thickness of 120nm.

[0078] The second mask layer 50 is formed on the upper waveguide layer 43 of the epitaxial structure. A second strip-shaped window 51 is formed within the second mask layer 50, exposing a portion of the upper waveguide layer 43. The material of the second mask layer 50 can be SiO2 / SiN.x The mask material is similar, and the thickness of the second mask layer 50 is 1μm to 2μm. The cross-sectional shape of the second strip window 51 can be designed according to the desired ridge shape, and can be any shape such as triangle, square, trapezoid, etc. Preferably, the width of the end of the second strip window 51 near the upper waveguide layer 43 is less than or equal to the width of the end away from the upper waveguide layer 43. This design ensures that the p-type ridge waveguide grown in the second strip window 51 has at least a square structure or an inverted frustum structure that is wider at the top and narrower at the bottom, which can increase the contact area with the current spreading layer 71 and the p-type electrode 72, and facilitate heat dissipation.

[0079] A p-type ridge waveguide is formed within the second strip window 51. The p-type ridge waveguide includes a p-type confinement layer 61 formed on the upper waveguide layer 43 of the epitaxial structure and a p-type capping layer 62 formed on the surface of the p-type confinement layer 61 facing away from the n-type electrode 80. The p-type ridge waveguide may also include a p-type contact layer 63 formed on the surface of the p-type capping layer 62 facing away from the n-type electrode 80.

[0080] For example, the p-type confinement layer 61 can be a p-type Al 0.08 Ga 0.92 The N-confinement layer has a thickness of 0.4 μm and a doping concentration of 8 × 10⁻⁶. 18 cm -3 The p-type capping layer 62 can be a p-type GaN capping layer with a thickness of 60 nm and a doping concentration of 1 × 10⁻⁶. 20 cm -3 The p-type contact layer 63 can be a p-type InGaN contact layer with a thickness of 5nm to 20nm and a doping concentration of 1×10⁻⁶. 20 cm -3 .

[0081] A current spreading layer 71 is formed on the surface of the p-type ridge waveguide facing away from the n-type electrode 80. A p-type electrode 72 is formed on the surface of the current spreading layer 71 facing away from the n-type electrode 80. For example, the current spreading layer 71 is preferably an ITO layer with a thickness of 200 nm. The p-type electrode 72 consists of two layers: the first layer is a contact metal, commonly one or more of Pd, Ni, Pt, Al, and Ti, with a common thickness of 1 nm to 300 nm. The second layer is a contact electrode, commonly made of Au, with a thickness generally greater than or equal to 30 nm. When the p-type electrode 72 is used in a laser, the electrode material is preferably Ti / Au (100 nm / 500 nm).

[0082] Compared with the prior art, the double-ridged waveguide semiconductor laser of the present invention makes both the p-type region (p-type capping layer and p-type confinement layer) and the n-type region (n-type capping layer and n-type confinement layer) of the semiconductor laser into ridges, resulting in a semiconductor laser with ridged waveguides at both ends, which can further enhance the transverse optical field confinement and current confinement.

[0083] The dual-ridge waveguide semiconductor laser of the present invention employs an inverted trapezoidal ridge waveguide semiconductor laser, which allows for a much larger electrode contact area than that of a traditional ridge semiconductor laser with the same emitting area. This reduces energy loss, results in lower series resistance and thermal resistance, and improves the performance of the semiconductor laser.

[0084] refer to Figure 2 As shown, a method for fabricating a double-ridged waveguide semiconductor laser according to an embodiment of the present invention includes the following steps:

[0085] S1, providing a substrate, and forming a first mask layer on the surface of the substrate;

[0086] S2, Etch the first mask layer to prepare a first strip window on the first mask layer;

[0087] S3, an n-type cladding layer and an n-type confinement layer are grown sequentially within the first strip window to form an n-type ridge waveguide;

[0088] S4, growing an epitaxial structure on the surface of an n-type confinement layer;

[0089] S5, a second mask layer is formed on the surface of the epitaxial structure;

[0090] S6, etch the second mask layer to prepare a second strip window on the second mask layer;

[0091] S7, a p-type confinement layer and a p-type capping layer are grown sequentially within the second strip window to form a p-type ridge waveguide;

[0092] S8, a current spreading layer is formed on the surface of the p-type ridge waveguide, and a p-type electrode is formed on the surface of the current spreading layer;

[0093] S9, remove the substrate and form an n-type electrode on the surface of the n-type capping layer to obtain a semiconductor laser epitaxial wafer;

[0094] S10 involves dicing, cleaving, and cavity surface coating of the semiconductor laser epitaxial wafer to obtain a double-ridged waveguide semiconductor laser.

[0095] In step S1, plasma-enhanced chemical vapor deposition (PECVD) is used to grow the first mask layer, and the growth thickness of the first mask layer is 1μm-2μm.

[0096] In step S2, first strip windows arranged side-by-side are formed using photolithography, wet etching, and dry etching processes, with a spacing of 1.5 μm to 3 μm between adjacent first strip windows. The cross-section of each first strip window is triangular, square, or trapezoidal, etc. Preferably, the width of the end of the first strip window closest to the substrate is greater than or equal to the width of the end closest to the epitaxial structure. The first strip windows expose a portion of the substrate.

[0097] It is understandable that the shape of the n-type ridge waveguide grown within the first strip window can be changed by adjusting its shape. Moreover, compared to the existing technology of directly etching the n-type region using dry etching, directly etching the first mask layer is simpler, easier to control the shape and angle of the first strip window, and easier to obtain the desired shape of the n-type ridge waveguide.

[0098] In step S3, the n-type capping layer and the n-type confinement layer are epitaxially grown using the lateral epitaxial overgrowth (ELOG) technique. Due to the difference in bond energy, the n-type capping layer is deposited much faster on the sidewalls within the first strip window than on the surface of the first mask layer. This causes the n-type capping layer to preferentially grow on the sidewalls within the first strip window, suppressing its nucleation on the surface of the first mask layer. Lateral epitaxy is performed with a sufficiently large lateral-to-longitudinal growth rate ratio, thus enabling selective growth of the n-type capping layer. Consequently, the n-type capping layer and the n-type confinement layer directly form a ridge waveguide during the growth process, avoiding the sidewall damage caused by relying on dry etching to form the ridge waveguide in traditional methods.

[0099] In step S3, the thickness of the n-type capping layer is less than the thickness of the first mask layer, and the sum of the thicknesses of the n-type capping layer and the n-type confinement layer is greater than or equal to the thickness of the first mask layer. That is, the n-type confinement layer is grown to cover the first mask layer; or the n-type confinement layer is grown to the point where its surface away from the n-type capping layer is flush with the surface of the first mask layer away from the substrate.

[0100] In step S4, after the n-type confinement layer has grown to cover the first mask layer or grown to the point where its surface away from the n-type cover layer is flush with the surface of the first mask layer away from the substrate, an epitaxial structure is then grown on the n-type confinement layer. The epitaxial structure may include a lower waveguide layer, an active layer, and an upper waveguide layer sequentially grown on the surface of the n-type confinement layer.

[0101] In step S5, plasma-enhanced chemical vapor deposition (PECVD) is also used to grow the second mask layer, and the growth thickness of the second mask layer is 1μm-2μm.

[0102] In step S6, second strip-shaped windows arranged side-by-side are formed using photolithography, wet etching, and dry etching processes. The spacing between adjacent second strip-shaped windows is 1.5 μm to 3 μm. The cross-section of each second strip-shaped window is triangular, square, or trapezoidal, etc. Preferably, the width of the end of the second strip-shaped window closest to the epitaxial structure is less than or equal to the width of the end furthest from the epitaxial structure. The second strip-shaped windows expose a portion of the epitaxial structure. The shape of the second strip-shaped windows can be the same as or different from that of the first strip-shaped windows.

[0103] In step S7, the p-type confinement layer and p-type capping layer are epitaxially grown using the lateral epitaxial overgrowth (ELOG) technique. Due to the difference in bond energy, the p-type confinement layer deposits much faster on the sidewalls within the second strip window than on the surface of the second mask layer. This allows the p-type confinement layer to preferentially grow on the sidewalls within the second strip window, suppressing its nucleation on the surface of the second mask layer. This enables lateral epitaxy with a sufficiently large lateral-to-longitudinal growth rate ratio, allowing for selective growth of the p-type confinement layer. Consequently, the p-type confinement layer and p-type capping layer directly form a ridge waveguide during the growth process, avoiding the sidewall damage caused by relying on dry etching to form the ridge waveguide in traditional methods. A p-type contact layer can also be grown on the side of the p-type capping layer facing away from the substrate.

[0104] It is understandable that the shape of the p-type ridge waveguide grown within the second strip window can be changed by adjusting its shape. Moreover, compared to the existing technology of directly etching the p-type region using dry etching, directly etching the second mask layer is simpler, easier to control the shape and angle of the second strip window, and easier to obtain the desired p-type ridge waveguide shape.

[0105] In step S8, a current spreading layer and a p-type electrode are fabricated through photolithography, deposition, and other steps. Since etching is not involved, damage to the p-type confinement layer, p-type capping layer, and p-type contact layer is avoided, as is the reduction of the ohmic contact area of ​​the p-type contact layer, which helps to solve the heat dissipation problem.

[0106] In step S9, the substrate is removed by thinning and polishing. Alternatively, the substrate can be removed by laser lift-off. After substrate removal, an n-type electrode is fabricated on the surface of the n-type capping layer.

[0107] In step S10, the semiconductor laser epitaxial wafer is diced and cleaved, and the resulting bar strips (laser strips formed by multiple semiconductor single tubes arranged side by side) are subjected to cavity surface coating. At this point, the fabrication of the double-ridged waveguide semiconductor laser is complete. The mask layers (first mask layer and second mask layer) between each double-ridged waveguide semiconductor laser naturally form a passivation layer, completing the isolation between the lasers.

[0108] The following detailed description of the fabrication method of the double-ridged waveguide semiconductor laser of this application is provided through a specific embodiment to facilitate a further understanding of the technical solution of this application.

[0109] Please refer to Figure 3a As shown, SiO2 / SiN is first deposited on substrate 10. x The first mask layer 20 is formed by using mask materials such as photolithography and wet etching. The mask pattern of the first strip window 21 is then prepared on the first mask layer 20 through processes such as photolithography and wet etching. The purpose is to provide a model for subsequent epitaxial growth.

[0110] The substrate 10 is preferably a self-supporting GaN substrate. (SiO2 / SiN) x The mask material is grown using plasma-enhanced chemical vapor deposition (PECVD) to a thickness of 1 μm to 2 μm. Multiple first strip windows 21 arranged side-by-side are fabricated using photolithography, wet etching, and dry etching processes for subsequent epitaxial growth. The spacing between adjacent first strip windows 21 is 1.5 μm to 3 μm. The cross-sectional shape of the first strip window 21 can be designed according to the desired ridge shape, and can be any shape such as triangle, square, or trapezoid. Preferably, in this embodiment, the width of the first strip window 21 at the end closest to the substrate 10 is greater than the width at the end furthest from the substrate 10. This design results in the n-type ridge waveguide grown within the first strip window 21 having a truncated pyramidal structure that is narrower at the top and wider at the bottom, increasing the contact area with the subsequently fabricated n-type electrode 80 and facilitating heat dissipation.

[0111] Please refer to Figure 3b As shown, Figure 3a The substrate 10 with a special shaped mask pattern is placed in the epitaxial equipment chamber, and the n-type capping layer 31 and the n-type confinement layer 32 are epitaxially grown in the first strip window 21 using the lateral epitaxial overgrowth (ELOG) technique.

[0112] For example, the n-type capping layer 31 is an n-type GaN capping layer with a thickness of 2 μm and a doping concentration of 5 × 10⁻⁶. 18 cm -3 ~6×10 18 cm -3 The n-type confinement layer 32 is an n-type Al. 0.1 Ga 0.9 The N-confinement layer has a thickness of 1.2 μm and a doping concentration of 3 × 10⁻⁶. 17 cm -3 Epitaxial equipment includes, but is not limited to, metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE).

[0113] Due to the difference in bond energy, the GaN capping layer is deposited much faster on the first strip window than on the surface of the first mask layer. This causes the GaN capping layer to preferentially grow on the first strip window and suppress its nucleation on the surface of the first mask layer. Lateral epitaxy is performed with a sufficiently large lateral-to-longitudinal growth rate ratio, thus enabling selective growth of the GaN capping layer. Consequently, the n-type GaN capping layer and the n-type AlGaN confinement layer directly form a ridge waveguide during the growth process, avoiding the sidewall damage caused by relying on dry etching to form the ridge waveguide in traditional methods.

[0114] Please refer to Figure 3c As shown, after the n-type AlGaN confinement layer covers the first mask layer 20, or the surface of the n-type AlGaN confinement layer away from the n-type GaN cover layer is flush with the surface of the first mask layer 20 away from the substrate 10 so that the first strip window 21 is completely filled, the epitaxial structure of the double-ridged waveguide semiconductor laser continues to be grown. The epitaxial structure includes a lower waveguide layer 41, an active layer 42, and an upper waveguide layer 43 sequentially grown on the surface of the n-type AlGaN confinement layer.

[0115] For example, undoped In is grown sequentially. 0.07 Ga 0.93 The lower waveguide layer is N-type, with a thickness of 160 nm; undoped In... 0.25 Ga 0.75 The N / GaN active layer has two periods of multiple quantum wells, with the InGaN well width being 3nm–5nm and the GaN barrier width being 8nm–10nm; the undoped In... 0.07 Ga 0.93 The waveguide layer on N has a thickness of 120nm;

[0116] Please refer to Figure 3d As shown, SiO2 / SiN is deposited on the upper waveguide layer 43 of the epitaxial structure. x The mask material is used to form a second mask layer 50. The mask pattern of the second strip window 51 is prepared on the second mask layer 50 through photolithography, wet etching and other processes. The purpose is to provide a model for the epitaxial growth of the p-type ridge waveguide.

[0117] Among them, SiO2 / SiN xThe mask material is grown using plasma-enhanced chemical vapor deposition (PECVD) to a thickness of 1 μm to 2 μm. Multiple parallel second strip-shaped windows 51 are fabricated using photolithography, wet etching, and dry etching processes for subsequent epitaxial growth. The spacing between adjacent second strip-shaped windows 51 is 1.5 μm to 3 μm. The cross-sectional shape of the second strip-shaped window 51 can be designed according to the desired ridge shape, and can be any shape such as triangle, square, or trapezoid. Preferably, in this embodiment, the width of the second strip-shaped window 51 at the end closest to the epitaxial structure is smaller than the width at the end furthest from the epitaxial structure. This design results in the p-type ridge waveguide grown within the second strip-shaped window 51 having an inverted frustum-shaped structure that is wider at the top and narrower at the bottom, which increases the contact area with the subsequently fabricated current spreading layer 71 and p-type electrode 72, facilitating heat dissipation.

[0118] Please refer to Figure 3e As shown, Figure 3d The resulting epitaxial wafer with a special shaped mask pattern is placed in the epitaxial equipment chamber, and the p-type confinement layer 61, p-type capping layer 62 and p-type contact layer 63 are epitaxially grown in the second strip window 51 using the transverse epitaxial overgrowth (ELOG) technique.

[0119] For example, the p-type confinement layer 61 can be a p-type Al 0.08 Ga 0.92 The N-confinement layer has a thickness of 0.4 μm and a doping concentration of 8 × 10⁻⁶. 18 cm -3 The p-type capping layer 62 can be a p-type GaN capping layer with a thickness of 60 nm and a doping concentration of 1 × 10⁻⁶. 20 cm -3 The p-type contact layer 63 can be a p-type InGaN contact layer with a thickness of 5nm to 20nm and a doping concentration of 1×10⁻⁶. 20 cm -3 Epitaxial equipment includes, but is not limited to, metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE).

[0120] Due to the difference in bond energy, the AlGaN confinement layer is deposited much faster on the second strip window than on the surface of the second mask layer. This causes the AlGaN confinement layer to preferentially grow on the second strip window while suppressing its nucleation on the surface of the second mask layer. Lateral epitaxy is then performed with a sufficiently large lateral-to-longitudinal growth rate ratio, allowing for selective growth of the AlGaN confinement layer. Consequently, the p-type AlGaN confinement layer and the p-type GaN capping layer directly form a ridge waveguide during the growth process, avoiding the sidewall damage caused by relying on dry etching to form the ridge waveguide in traditional methods.

[0121] Please refer to Figure 3fAs shown, the current spreading layer 71 and the p-type electrode 72 are fabricated through photolithography, deposition, and other steps. Since etching is not involved, damage to the p-type confinement layer and the p-type contact layer is avoided, as is the reduction of the ohmic contact area of ​​the p-type contact layer, which helps to solve the heat dissipation problem.

[0122] For example, the current spreading layer 71 is preferably an ITO layer. The deposition equipment used to deposit the ITO layer and the p-type electrode 72 can be a coating equipment such as electron beam evaporation or magnetron sputtering. An ITO layer of 200 nm is deposited as a partial optical confinement layer using an electron beam evaporation device at a deposition temperature of 300 °C.

[0123] The deposited p-type electrode 72 consists of two layers. The first layer is a contact metal, commonly one or more of Pd, Ni, Pt, Al, and Ti, with a typical thickness of 1 nm to 300 nm. The second layer is the contact electrode, commonly made of Au, with a thickness generally greater than or equal to 30 nm. When the p-type electrode 72 is used in a laser, the preferred electrode material is Ti / Au (100 nm / 500 nm).

[0124] Please refer to Figure 3g As shown, the substrate 10 is ground, thinned and polished to remove the substrate 10, and an n-type electrode is prepared on the n-type capping layer 31.

[0125] For example, the substrate 10 is thinned, ground, and polished using a thinning machine, a grinding machine, and a polishing machine to remove the substrate 10, or the substrate 10 is directly removed using laser lift-off. After removing the substrate 10, an n-type electrode 80 is finally deposited on the n-type capping layer 31 using magnetron sputtering. The n-type electrode 80 is preferably a 50nm / 100nm / 50nm / 100nm Ti / Al / Ti / Au electrode.

[0126] The semiconductor laser epitaxial wafer is diced and cleaved, and the resulting strips (laser strips formed by multiple semiconductor single tubes arranged side by side) are subjected to cavity surface coating. At this point, the fabrication of the double-ridged waveguide semiconductor laser is complete. The mask layer between each double-ridged waveguide semiconductor laser naturally forms a passivation layer, achieving isolation between the lasers. The structure of a single laser chip is referenced. Figure 1 As shown.

[0127] For example, a laser dicing machine is used to cut the semiconductor laser epitaxial wafer into suitable sizes for cleaving, facilitating subsequent cleaving into strips. The cleaving process uses a Loomis cleaving machine to cut the semiconductor laser epitaxial wafer into single strips, each strip potentially containing multiple semiconductor laser chips. Cavity surface coating is performed using an optical coating machine. The cleaved strips are placed in a fixture, and nine pairs of SiO2 / Ta2O5 are deposited as the back cavity film of the laser, while a single layer of SiO2 is used as the front cavity film. The front cavity surface is coated with a 17% reflective film, and the back cavity surface with a 93% reflective film.

[0128] Compared with the prior art, the fabrication method of the dual-ridge waveguide semiconductor laser of the present invention bypasses the photolithography and etching processes of the p-type and n-type regions, and directly completes the fabrication of the n-type and p-type ridge waveguides. It is also easy to fabricate ridge waveguides with complex shapes, which greatly simplifies the process and reduces costs.

[0129] The present invention discloses a method for fabricating a double-ridged waveguide semiconductor laser. A first strip-shaped window is fabricated on a substrate, and an n-type capping layer and an n-type confinement layer are directly formed into a ridge along the first strip-shaped window during epitaxial growth using lateral epitaxial overgrowth (ELOG) technology. Simultaneously, a second strip-shaped window is fabricated on the epitaxial structure, and a p-type capping layer and a p-type confinement layer are directly formed into a ridge along the second strip-shaped window during epitaxial growth using ELOG technology, thus forming a double-ridged waveguide. Compared to a traditional single-ridged waveguide, the double-ridged waveguide can further enhance the confinement of the optical field. Furthermore, the fabrication of the ridges effectively avoids sidewall damage caused by etching processes in existing technologies, thereby improving the current injection efficiency, reducing the threshold current, and enhancing the reliability of the device.

[0130] The method for fabricating a dual-ridge waveguide semiconductor laser of the present invention can easily obtain the desired but complex ridge waveguide shape by changing the shape of the first strip window on the first mask layer and the shape of the second strip window on the second mask layer, thereby improving the performance of the semiconductor laser.

[0131] The method for fabricating a dual-ridged waveguide semiconductor laser of the present invention uses dry etching or wet etching to process the mask layers (first mask layer and second mask layer) into special shapes. The shape and angle are easier to control, and the required special ridge structure can be more easily formed through subsequent epitaxial growth. The process is convenient to control and greatly saves costs, thus improving the feasibility of fabricating special ridged waveguides.

[0132] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0133] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A double-ridged waveguide semiconductor laser, characterized in that, include: An n-type electrode has a first surface; A first mask layer is formed on the first surface, and a first strip window is formed within the first mask layer, the first strip window exposing a portion of the first surface; An n-type ridge waveguide is formed within the first strip window. The n-type ridge waveguide includes an n-type capping layer formed on the first surface and an n-type confinement layer formed on the surface of the n-type capping layer opposite to the n-type electrode. An epitaxial structure is formed on the surface of the n-type confinement layer opposite to the n-type electrode; A second mask layer is formed on the surface of the epitaxial structure opposite to the n-type electrode. A second strip window is formed in the second mask layer, and the second strip window exposes a portion of the surface of the epitaxial structure. A p-type ridge waveguide is formed within the second strip window. The p-type ridge waveguide includes a p-type confinement layer formed on the surface of the epitaxial structure and a p-type capping layer formed on the surface of the p-type confinement layer facing away from the n-type electrode. A current spreading layer is formed on the surface of the p-type ridge waveguide away from the n-type electrode; as well as The p-type electrode is formed on the surface of the current spreading layer opposite to the n-type electrode.

2. The double-ridged waveguide semiconductor laser according to claim 1, characterized in that, The width of the first strip window at the end near the n-type electrode is greater than or equal to the width at the end near the epitaxial structure; and / or, The width of the second strip window at the end near the epitaxial structure is less than or equal to the width at the end near the p-type confinement layer.

3. The double-ridged waveguide semiconductor laser according to claim 1, characterized in that, The n-type ridge waveguide is formed through the following steps: The first mask layer is etched to form the first strip window; An n-type capping layer and an n-type confinement layer are sequentially grown within the first strip window to form an n-type ridge waveguide; And / or, The p-type ridge waveguide is formed through the following steps: The second mask layer is etched to form the second strip window; A p-type confinement layer and a p-type capping layer are grown sequentially within the second strip window to form a p-type ridge waveguide.

4. A method for fabricating a double-ridged waveguide semiconductor laser, characterized in that, include: A substrate is provided, and a first mask layer is formed on the surface of the substrate; The first mask layer is etched to create a first strip window on the first mask layer; An n-type capping layer and an n-type confinement layer are sequentially grown within the first strip window to form an n-type ridge waveguide; An epitaxial structure is grown on the surface of the n-type confinement layer; A second mask layer is formed on the surface of the epitaxial structure; The second mask layer is etched to prepare a second strip window on the second mask layer; A p-type confinement layer and a p-type capping layer are grown sequentially within the second strip window to form a p-type ridge waveguide; A current spreading layer is formed on the surface of the p-type ridge waveguide, and a p-type electrode is formed on the surface of the current spreading layer; The substrate is removed, and an n-type electrode is formed on the surface of the n-type capping layer to obtain a semiconductor laser epitaxial wafer.

5. The method for fabricating a double-ridged waveguide semiconductor laser according to claim 4, characterized in that, Within the first strip window, the n-type capping layer and the n-type confinement layer are epitaxially grown using a lateral epitaxial overgrowth technique; and / or, The thickness of the n-type capping layer is less than the thickness of the first mask layer, and the sum of the thicknesses of the n-type capping layer and the n-type confinement layer is greater than or equal to the thickness of the first mask layer; and / or, The p-type confinement layer and the p-type capping layer are epitaxially grown within the second strip window using a lateral epitaxial overgrowth technique.

6. The method for fabricating a double-ridged waveguide semiconductor laser according to claim 4, characterized in that, A first strip-shaped window arranged in parallel is fabricated on the first mask layer using photolithography, wet etching, and dry etching processes, the first strip-shaped window exposing a portion of the substrate; and / or, The thickness of the first mask layer is 1 μm to 2 μm; and / or, The spacing between adjacent first strip windows is 1.5 μm to 3 μm; and / or, The material of the first mask layer comprises SiO2 or SiN x .

7. The method for fabricating a double-ridged waveguide semiconductor laser according to claim 4, characterized in that, A second strip-shaped window, arranged in parallel, is fabricated on the second mask layer using photolithography, wet etching, and dry etching processes. The second strip-shaped window exposes a portion of the epitaxial structure; and / or, The thickness of the second mask layer is 1 μm to 2 μm; and / or, The spacing between adjacent second strip windows is 1.5 μm to 3 μm; and / or The material of the second mask layer includes SiO2 or SiN. x .

8. The method for fabricating a double-ridged waveguide semiconductor laser according to claim 4, characterized in that, The width of the first strip window at its end near the substrate is less than or equal to the width at its end near the epitaxial structure; and / or, The width of the second strip window at the end near the epitaxial structure is greater than or equal to the width at the end near the p-type confinement layer.

9. The method for fabricating a double-ridged waveguide semiconductor laser according to claim 4, characterized in that, The shape of the n-type ridge waveguide can be changed by adjusting the shape of the first strip window; and / or, The shape of the p-type ridge waveguide can be changed by adjusting the shape of the second strip window.

10. The method for fabricating a double-ridged waveguide semiconductor laser according to claim 4, characterized in that, After the step of sequentially growing the p-type confinement layer and the p-type capping layer within the second strip window, the method further includes: The step of growing a p-type contact layer on the surface of the p-type cover layer; The current spreading layer is grown on the surface of the p-type contact layer.

Images