Wide-ridge single-mode semiconductor laser and manufacturing method thereof

Abstract

The invention provides a wide-ridge single-mode semiconductor laser and a manufacturing method thereof.The laser comprises an N electrode, a substrate layer, an epitaxial structure and a P electrode which are stacked in sequence, a grating layer is arranged in the epitaxial structure, and a grating is etched in the portion, close to the center, of the grating layer; the epitaxial structure is partially etched with the area where the grating is located as the center, a ridge-shaped structure is obtained, and the width of the ridge-shaped structure is larger than that of the grating. The grating is arranged in the epitaxial structure, and the high-order mode lasing of the wide-ridge semiconductor laser can be inhibited by regulating and controlling the feedback effect of the grating on different modes of the semiconductor laser, so that the quality of a fundamental mode beam is improved.

Description

Technical Field

[0001] The present invention relates to the field of laser design, and in particular to a wide-ridge single-mode semiconductor laser and a manufacturing method thereof. Background Art

[0002] Wide-ridge semiconductor lasers are a key technology for achieving high-power output. Currently, the maximum continuous output power of 930nm wide-stripe semiconductor lasers has reached 132W, showing great potential for applications in additive manufacturing, medical aesthetics, and other fields. However, due to the large number of lasing modes permitted by wide-ridge lasers, their beam quality has long been a key bottleneck that has plagued laser equipment and laser system developers. Summary of the Invention

[0003] In view of the above problems existing in the prior art, the present invention proposes a wide-ridge single-mode semiconductor laser and a manufacturing method thereof, which mainly solves the problems of poor beam quality and limited output power of the existing wide-ridge laser.

[0004] In order to achieve the above-mentioned and other purposes, the technical solutions adopted by the present invention are as follows.

[0005] The present application provides a wide-ridge single-mode semiconductor laser, which includes an N-electrode, a base layer, an epitaxial structure, and a P-electrode stacked in sequence. A grating layer is provided in the epitaxial structure, and a grating is etched near the center of the grating layer. The epitaxial structure is partially etched with the area where the grating is located as the center to obtain a ridge structure, wherein the width of the ridge structure is greater than the width of the grating.

[0006] In one embodiment of the present application, the epitaxial structure includes an N-type cladding, a waveguide layer, a P-type cladding and a contact layer stacked in sequence, the grating layer is arranged in the P-type cladding, and the ridge structure extends from the contact layer to the P-type cladding, and the sides of the ridge structure are covered with a passivation layer for electrical isolation.

[0007] In one embodiment of the present application, the epitaxial structure includes an N-type cladding, a waveguide layer, a P-type cladding and the grating layer stacked in sequence, and the ridge structure extends from the grating layer to the N-type cladding, and the sides of the ridge structure are covered with a passivation layer for electrical isolation.

[0008] In one embodiment of the present application, an oxide layer is further provided in the P-type cladding layer, and a light-emitting hole is provided in a region of the oxide layer facing the grating, wherein the aperture of the light-emitting hole is larger than the width of the grating.

[0009] In one embodiment of the present application, the width of the ridge structure is greater than or equal to 5 microns, or the aperture of the light-emitting hole is greater than 5 microns.

[0010] In one embodiment of the present application, the coupling coefficients of the grating to different order modes of the laser have the following relationship:

[0011] k1≥0.2;

[0012] k1≥k2+0.1;

[0013] k1≥k3+0.1;

[0014] Among them, k1 is the coupling coefficient of the grating to the first-order mode of the laser, k2 is the coupling coefficient of the grating to the second-order mode of the laser, and k3 is the coupling coefficient of the grating to the third-order mode of the laser.

[0015] In one embodiment of the present application, the front cavity of the laser is provided with an anti-reflection film, and the rear cavity is provided with a high-reflection film; or, the front cavity of the laser is provided with a high-reflection film, and the rear cavity is provided with an anti-reflection film.

[0016] In one embodiment of the present application, the product of the front cavity reflectivity and the back cavity reflectivity of the laser is less than or equal to 0.001.

[0017] The present application also provides a method for manufacturing a wide-ridge single-mode semiconductor laser, the method comprising: providing a base layer; manufacturing an epitaxial structure on the base layer, wherein a grating layer is provided in the epitaxial structure, and a grating is etched near the center of the grating layer; partially etching the epitaxial structure with the area where the grating is located as the center to obtain a ridge structure, wherein the width of the ridge structure is greater than the width of the grating; manufacturing a P electrode on the side of the ridge structure away from the base layer; and forming an N electrode on the side of the base layer away from the epitaxial structure.

[0018] As described above, the wide-ridge single-mode semiconductor laser and the manufacturing method thereof of the present invention have the following beneficial effects.

[0019] The present application sets a grating in the epitaxial structure and regulates the feedback effect of the grating on different modes of the semiconductor laser, thereby suppressing the high-order mode lasing of the wide-ridge semiconductor laser and improving the quality of the fundamental mode beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the front structure of a wide-ridge single-mode semiconductor laser in one embodiment of the present application.

[0021] Figure 2 for Figure 1 Side view of the structure shown.

[0022] Figure 3 Schematic diagram comparing the first-order mode light field distribution and the grating active area in one embodiment of the present application.

[0023] Figure 4Schematic diagram comparing the second-order mode light field distribution and the grating active area in one embodiment of the present application.

[0024] Figure 5 Schematic diagram comparing the third-order mode light field distribution and the grating active area in one embodiment of the present application.

[0025] Figure 6 This is a schematic diagram of the front structure of a wide-ridge single-mode semiconductor laser in another embodiment of the present application.

[0026] Figure 7 This is a schematic diagram of the front structure of a wide-ridge single-mode semiconductor laser in another embodiment of the present application.

[0027] Figure 8 This is a schematic diagram of the front structure of a wide-ridge single-mode laser in another embodiment of the present application.

[0028] Figure 9 Schematic diagram of the process of manufacturing a broad-ridge single-mode laser in one embodiment of the present application.

[0029] Figure 10 This is a schematic structural diagram of a broad-ridge single-mode laser in another embodiment of the present application.

[0030] Figure 11 Schematic diagram of the first-order mode spot distribution in one embodiment of the present application.

[0031] Figure 12 Schematic diagram of the second-order mode spot distribution in one embodiment of the present application.

[0032] Figure 13 Schematic diagram of the third-order mode spot distribution in one embodiment of the present application.

[0033] Figure 14 Schematic diagram of the power-current curve of the first-order mode of the gratingless laser.

[0034] Figure 15 Schematic diagram of the power-current curve of the second-order mode of the gratingless laser.

[0035] Figure 16 Schematic diagram of the power-current curve of the third-order mode of the gratingless laser.

[0036] Figure 17 FIG. 1 is a schematic diagram of a power-current curve of a first-order mode of a grating laser in an embodiment of the present application.

[0037] Figure 18 FIG. 1 is a schematic diagram of a power-current curve of a second-order mode of a grating laser in an embodiment of the present application.

[0038] Figure 19FIG. 1 is a schematic diagram of a power-current curve of a third-order mode of a grating laser in an embodiment of the present application.

[0039] Figure 20 Schematic diagram of the spectral characteristics of a broad-ridge single-mode laser with a grating introduced in one embodiment of the present application. DETAILED DESCRIPTION

[0040] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0041] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0042] The inventors have found that:

[0043] To achieve high beam quality, single-mode semiconductor lasers are the best choice. However, single-mode semiconductor lasers have a narrow ridge and high carrier and photon density, making them susceptible to power saturation or catastrophic damage to the cavity surface due to factors such as thermal effects and spatial hole burning. Their output power is generally below 1W. Resolving the relationship between semiconductor laser ridge width and mode control is a key issue in the development of high-power lasers.

[0044] Based on the problems existing in the prior art, the embodiments of the present application propose a wide-ridge single-mode semiconductor laser and a manufacturing method thereof. The technical solution of the present application is described in detail below in conjunction with specific embodiments.

[0045] See also Figure 1 , Figure 1 This is a schematic diagram of the front structure of a wide-ridge single-mode semiconductor laser in one embodiment of the present application. The wide-ridge single-mode semiconductor laser in this embodiment of the present application comprises: an N-electrode, a base layer, an epitaxial structure, and a P-electrode stacked in sequence; a grating layer is provided within the epitaxial structure; a grating is etched near the center of the epitaxial structure; the epitaxial structure is partially etched around the area where the grating is located to obtain a ridge structure, wherein the width of the ridge structure is greater than the width of the grating.

[0046] In one embodiment, the base layer may include a substrate and a buffer layer. The N-electrode is disposed on one side of the substrate, and the buffer layer is disposed on a side of the substrate facing away from the N-electrode. The epitaxial structure is disposed on a side of the buffer layer facing away from the substrate. The substrate may be made of materials such as gallium arsenide (GaAs) or indium phosphide (InP), and the specific material can be adjusted based on actual production requirements.

[0047] In one embodiment, the epitaxial structure may include an N-type cladding, a waveguide layer, a P-type cladding and a contact layer stacked in sequence. A grating layer is provided in the P-type cladding, and the grating layer is etched near the center region by electron beam direct writing, nanoimprinting or holographic interference exposure lamp to form a grating. The ridge structure is also obtained by etching, which etches the contact layer and the P-type cladding. The ridge structure consists of a contact layer, a grating layer and part of the P-type cladding. The width of the ridge structure is greater than the width of the grating. Here, the width of the ridge structure can be set to be greater than 5 microns. A P electrode is provided on the top of the ridge structure, and passivation layers are provided on both sides. Charges are injected through the P electrode and the N electrode to excite the waveguide layer to generate laser. The waveguide layer contains active materials. For example, the active material can form quantum wells or quantum dots.

[0048] See also Figure 2 , Figure 2 for Figure 1 The left and right sides of the side view correspond to the front cavity and the back cavity of the laser, respectively. An anti-reflection film can be set in the front cavity and a high-reflection film can be set in the back cavity, or a high-reflection film can be set in the front cavity and an anti-reflection film can be set in the back cavity, so that the front cavity reflectivity R0 and the back cavity reflectivity R L The product R0R L Always less than or equal to 0.001. L The smaller it is, the greater the cavity loss of the laser mode, the greater the threshold gain of the laser mode, and the easier it is to suppress the high-order modes of the laser. Among them, the laser mode can include the first-order mode, the second-order mode and the third-order mode. The first-order mode is also called the fundamental mode. The first-order mode is the simplest mode in the transverse light field distribution formed in the laser resonant cavity, which appears as a single circular or elliptical light spot on the cross section of the beam; the first-order mode has only a single light spot, while the higher-order modes (such as the second and third orders) will present multiple separated light spots or complex patterns on the cross section. Please refer to Figure 3-5 , Figure 3 Schematic diagram comparing the first-order mode light field distribution and the grating active area in one embodiment of the present application. Figure 4 Schematic diagram comparing the second-order mode light field distribution and the grating active area in one embodiment of the present application. Figure 5This is a schematic diagram comparing the third-order mode light field distribution and the grating active area in one embodiment of the present application. A buried grating structure is used, and the grating layer is located inside the FP laser epitaxial layer. The epitaxial layer is composed of an N cladding layer (also called an N-type cladding), a waveguide layer containing active material, a P cladding layer containing a grating layer (also called a P-type cladding), and a contact layer from bottom to top. The ridge is formed by etching and has a width of W. r The grating is obtained by selective etching of the grating layer, and the width of the grating etching area is W g , where W g <W r .W r Affects the distribution of the light field mode in the laser. When W r When W is ≥5μm, there may be more modes in the ridge region. g <W r When the grating actually acts on only part of the light field, the feedback effect of the grating on each mode is the same as the light field in the grating action area W. g The light confinement factor of the first-order mode (fundamental mode) is positively correlated with the light confinement factor of the grating. From the figure, it can be seen that the light confinement factor of the first-order mode (fundamental mode) is the largest in the grating action area, and the grating has the strongest feedback effect on the first-order mode (fundamental mode). The feedback effect of the grating on each mode can be expressed by the coupling coefficient k i Characterize, where i is the order of the mode, unit is cm -1 When the laser k i The larger the value, the stronger the feedback effect of the grating, the smaller the threshold gain of the laser, the easier it is for the laser in this mode to be emitted, and the easier it is for the laser in other modes to be suppressed. However, the above theory is only applicable to the analysis of the distributed feedback grating (DFB) mode, not the Fabry-Perot (FP) mode. The threshold gain of the FP mode is not related to the grating feedback effect, and high-order mode lasing may still occur. In order to suppress the FP mode lasing, in the present invention, the front cavity surface reflectivity R0 and the back cavity surface R L The product of reflectivity R0R L ≤0.001, R0R L The smaller it is, the greater the cavity surface loss of the FP mode, the greater the threshold gain of the FP mode, and the easier it is to suppress the FP mode.

[0049] See also Figure 6 , Figure 6This is a schematic diagram of the front structure of a wide-ridge single-mode semiconductor laser in another embodiment of the present application. The semiconductor laser may also adopt a non-oxidized surface grating wide-ridge single-mode laser, the epitaxial structure of which includes an N-type cladding, a waveguide layer, a P-type cladding and the grating layer stacked in sequence, and the ridge structure extends from the grating layer to the N-type cladding, and the ridge structure is covered on the side with a passivation layer for electrical isolation. The laser is composed of an N-electrode, a substrate, a buffer layer, an N-type cladding, a waveguide layer containing active material, a P-type cladding, a contact layer, a passivation layer and a P-electrode from top to bottom. The ridge is formed by etching, and the etching position is above the active material, with a width of W. r (W r ≥5um). The grating is formed by etching the contact layer and the P cladding layer by electron beam direct writing, nanoimprinting or holographic interference exposure. The grating is only written in the center with a width of W. g (W g <W r The coupling coefficient of the grating satisfies the following relationship: k1≥0.2, k1≥k2+0.1, and k1≥k3+0.1.

[0050] See also Figure 7 , Figure 7 This is a schematic diagram of the front structure of a wide ridge single-mode semiconductor laser in another embodiment of the present application. The semiconductor laser can also use a non-oxidized surface grating wide ridge single-mode laser. Figure 6 The P-type cladding of the structure shown is also provided with an oxide layer, and a light-emitting hole is provided in the area of ​​the oxide layer facing the grating, wherein the aperture of the light-emitting hole is larger than the width of the grating. Specifically, the oxide surface grating wide ridge single-mode laser is composed of an N electrode, a substrate, a buffer layer, an N-type cladding, a waveguide layer containing an active material, a P-type cladding containing an oxide layer, a grating layer, a passivation layer and a P electrode from top to bottom. The ridge is formed by etching, and the etching position is below the oxide layer. The oxide layer is formed into a light-emitting aperture by a wet oxidation process, and the aperture width is W. r (W r ≥5um). The grating is formed by etching the grating layer by electron beam direct writing, nanoimprinting or holographic interference exposure. The grating is only written in the center with a width of W. g (W g <W r The coupling coefficient of the grating satisfies the following relationship: k1≥0.2, k1≥k2+0.1, and k1≥k3+0.1.

[0051] See also Figure 8 , Figure 8 This is a schematic diagram of the front structure of a wide ridge single-mode laser in another embodiment of the present application. The etching depth of the ridge structure can be set and adjusted according to the actual application requirements. For example, the etching depth of the ridge structure can be adjusted to the N-type cladding layer to obtain the following: Figure 8The structure shown.

[0052] The solution of the embodiment of the present application can enable a wide-ridge semiconductor laser with a ridge width or oxidation aperture of more than 5 μm to still operate in the fundamental mode, which is of great significance for optimizing the beam quality of high-power lasers and improving the output power bottleneck of single-mode lasers.

[0053] See also Figure 9 , Figure 9 This is a flow chart of a method for manufacturing a broad-ridge single-mode laser according to an embodiment of the present application. The method comprises the following steps:

[0054] Step S900, providing a base layer;

[0055] Step S910, fabricating an epitaxial structure on the base layer, wherein a grating layer is provided in the epitaxial structure, and a grating is etched near the center of the grating layer;

[0056] Step S920, partially etching the epitaxial structure with the area where the grating is located as the center to obtain a ridge structure, wherein the width of the ridge structure is greater than the width of the grating;

[0057] Step S930, forming a P electrode on a side of the ridge structure away from the base layer;

[0058] Step S940 , forming an N electrode on a side of the base layer away from the epitaxial structure.

[0059] See also Figure 10 , Figure 10 This is a schematic diagram of the structure of a wide ridge single-mode laser in another embodiment of the present application. The laser consists of a GaAs substrate, a GaAs buffer layer, an Al 0.25 Ga 0.75 As cladding (N-type cladding), including GaAs / In 0.34 Ga 0.66 Al in As / GaAs (active material) strained quantum wells 0.05 Ga 0.95 As waveguide layer, including GaAs / Ga 0.5 In 0.5 Al in the P / GaAs suspended grating layer 0.25 Ga 0.75 As cladding (P-type cladding) and contact layer, while SiO2 is used for surface passivation and electrical isolation, and the upper and lower electrodes are used to inject current into the laser.

[0060] The fabrication method for this example is as follows: A GaAs buffer layer is grown from bottom to top on a GaAs substrate using MBE, MOCVD, or LPCVD. A grating is etched from a central 1.4μm area on the suspended grating layer to a depth of 40-60nm, a grating period of 149nm, and a grating duty cycle of 50%. GaAs is then grown from bottom to top using MBE, MOCVD, or LPCVD to a contact layer. This concludes the semiconductor epitaxial growth process and enters the chip fabrication process. First, a SiO2 passivation film is deposited using equipment such as PECVD. A ridge with a width of 7μm is etched to a depth of 1.43μm centered on the grating center. Another SiO2 passivation film is deposited. The passivation film at the top of the ridge is removed to form an electrical injection window. A P-side electrode is sputtered and alloyed using methods such as magnetron sputtering. The wafer is thinned and polished. Finally, an N-side electrode is sputtered using methods such as magnetron sputtering. This completes the fabrication process.

[0061] By performing simulation analysis on this example, we can obtain the following: (1) The first-order, second-order, and third-order mode distributions of the structure are as follows: Figure 11-13 As shown, it can be seen that both the first-order mode and the second-order mode are likely to be lased; (2) In the case of no grating etching, the power-current curves of the three modes of the laser are as follows Figure 14-16 As shown in the figure, it can be seen that the output power ratio of the first-order mode and the second-order mode is approximately 1:1, and the total output mode has significant multi-mode; (3) When the grating etching is introduced, the coupling coefficients k1, k2, and k3 of the grating to the three modes are 0.601 cm -1 , 0.044cm -1 、0.146cm -1 , k1 is significantly greater than k2 and k3; (4) When grating etching is introduced, the power-current curves of the three laser modes are as follows Figure 17-19 As shown, it can be seen that the first-order mode power is more than 10 times that of the second-order mode power and is much larger than the third-order mode power. In actual situations, due to the existence of mode competition, the advantage of the first-order mode will be stronger; (5) When grating etching is introduced, the spectral characteristics of the laser are as follows Figure 20 As shown, it has good single-wavelength characteristics and a side mode suppression ratio of more than 50dB.

[0062] In summary, this structure significantly improves the single-mode characteristics of the laser with a ridge width of 7μm, achieves full suppression of high-order modes, and proves the effectiveness of the invention.

[0063] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A broad-ridge single-mode semiconductor laser, characterized in that: The laser includes an N-electrode, a base layer, an epitaxial structure and a P-electrode stacked in sequence, a grating layer is provided in the epitaxial structure, a grating is etched near the center of the grating layer, and the epitaxial structure is partially etched with the area where the grating is located as the center to obtain a ridge structure, wherein the width of the ridge structure is greater than the width of the grating.

2. The broad ridge single-mode semiconductor laser according to claim 1, characterized in that: The epitaxial structure includes an N-type cladding, a waveguide layer, a P-type cladding and a contact layer stacked in sequence. The grating layer is arranged in the P-type cladding, and the ridge structure extends from the contact layer to the P-type cladding. The sides of the ridge structure are covered with a passivation layer for electrical isolation.

3. The broad-ridge single-mode semiconductor laser according to claim 1, wherein: The epitaxial structure includes an N-type cladding layer, a waveguide layer, a P-type cladding layer and the grating layer stacked in sequence, and the ridge structure extends from the grating layer to the N-type cladding layer. The sides of the ridge structure are covered with a passivation layer for electrical isolation.

4. The broad-ridge single-mode semiconductor laser according to claim 3, characterized in that: An oxide layer is further provided in the P-type cladding layer, and a light-emitting hole is provided in a region of the oxide layer facing the grating, wherein the aperture of the light-emitting hole is larger than the width of the grating.

5. The broad-ridge single-mode semiconductor laser according to claim 4, characterized in that: The width of the ridge structure is greater than or equal to 5 micrometers, or the aperture of the light-emitting hole is greater than 5 micrometers.

6. The broad-ridge single-mode semiconductor laser according to claim 1, characterized in that: The coupling coefficients of the grating to different order modes of the laser have the following relationship: k1≥0.2； k1≥k2+0.1; k1≥k3+0.1; Among them, k1 is the coupling coefficient of the grating to the first-order mode of the laser, k2 is the coupling coefficient of the grating to the second-order mode of the laser, and k3 is the coupling coefficient of the grating to the third-order mode of the laser.

7. The broad-ridge single-mode semiconductor laser according to claim 1, characterized in that: The front cavity of the laser is provided with an anti-reflection film, and the rear cavity is provided with a high-reflection film; or the front cavity of the laser is provided with a high-reflection film, and the rear cavity is provided with an anti-reflection film.

8. The broad-ridge single-mode semiconductor laser according to claim 7, characterized in that: The product of the front cavity reflectivity and the back cavity reflectivity of the laser is less than or equal to 0.

001.

9. A method for manufacturing a broad-ridge single-mode semiconductor laser, characterized in that: The method comprises: Provides a base layer; Fabricating an epitaxial structure on the substrate layer, wherein a grating layer is provided in the epitaxial structure, and a grating is etched near the center of the grating layer; Partially etching the epitaxial structure with the grating area as the center to obtain a ridge structure, wherein the width of the ridge structure is greater than the width of the grating; Fabricate a P electrode on a side of the ridge structure away from the base layer; An N electrode is formed on a side of the base layer away from the epitaxial structure.

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