Semiconductor laser and preparation method thereof

Abstract

The invention relates to the technical field of semiconductor lasers, and discloses a semiconductor laser and a preparation method thereof, the semiconductor laser comprises a substrate layer and an epitaxial structure, the epitaxial structure comprises a plurality of light emitting structures, a tunnel junction and an ohmic contact layer; the light-emitting structure comprises a lower limiting layer, an active region and an upper limiting layer which are arranged from bottom to top, and further comprises a first oxide layer; the multiple light-emitting structures are arranged in a stacked mode, every two adjacent light-emitting structures are connected through a tunnel junction, the light-emitting structure on the lowest layer is arranged on the surface of one side of the substrate layer, and the ohmic contact layer is arranged on the surface of the side, away from the substrate layer, of the epitaxial structure on the uppermost layer; a ridge-shaped waveguide structure or a columnar hole array structure is formed in the epitaxial structure in the direction perpendicular to the epitaxial growth direction and the light emitting direction, and the side wall, close to the ridge-shaped waveguide structure or the columnar hole, of the first oxide layer is an insulating layer. According to the invention, power doubling is realized under the same electric injection, Joule heat is reduced, and power density is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor lasers, and in particular to a semiconductor laser and a method for preparing the semiconductor laser. Background Art

[0002] 980 nanometer (nm) single-mode semiconductor laser refers to a semiconductor laser with an emission wavelength of 980nm and laser output in a single transverse mode (such as fundamental mode) during operation. 980nm single-mode semiconductor laser has the advantages of good monochromaticity, single transverse mode lasing, low threshold current, easy coupling with optical fiber and high stability. It is widely used in laser printing, 3D sensing, optical communication and optical storage.

[0003] Traditional 980nm single-mode semiconductor lasers use a single quantum well epitaxial structure to achieve high-order mode confinement and suppression through a ridge waveguide with a width of 2 microns (μm) to 10μm. Due to the narrow width of the light-emitting area, the optical power density at the cavity surface of the single-mode semiconductor laser is extremely high, and cavity surface ablation failure is prone to occur. In addition, due to reasons such as the thermal lens effect, it is difficult for the laser to maintain single-mode lasing at high currents, and the electro-optical efficiency is low. Summary of the invention

[0004] In view of this, the present invention provides a semiconductor laser and a method for preparing the semiconductor laser to solve the problem that the output power of the semiconductor laser is limited due to factors such as low efficiency, high power density and thermal effect.

[0005] In a first aspect, the present invention provides a semiconductor laser, which includes a substrate layer and an epitaxial structure, wherein the epitaxial structure includes a plurality of light-emitting structures, a tunnel junction and an ohmic contact layer; the light-emitting structure includes a lower confinement layer, an active region and an upper confinement layer arranged in sequence from bottom to top, and the light-emitting structure also includes a first oxide layer, wherein the first oxide layer is arranged on a surface of a side of the upper confinement layer away from the active region, or the first oxide layer is arranged in the upper confinement layer; the plurality of light-emitting structures are arranged in a stacked manner, wherein two adjacent light-emitting structures are connected by a tunnel junction, the light-emitting structure of the lowest layer is arranged on a surface of a side of the substrate layer, and the ohmic contact layer is arranged on a surface of a side of the epitaxial structure of the highest layer away from the substrate layer; the epitaxial structure is arranged perpendicular to the epitaxial growth direction A ridge waveguide structure or a columnar hole array structure is formed in the light-emitting direction and the light-emitting direction, the sidewall of the first oxide layer close to the ridge waveguide structure or the columnar hole is an insulating layer, and the area of ​​the first oxide layer close to the lateral center of the ridge waveguide structure or the center of the columnar holes on both sides is a conductive layer; after the ridge waveguide structure is formed, the first oxide layer is oxidized inward from the etching interface of the ridge waveguide structure to form a second oxide layer; or after the columnar hole array structure is formed, the first oxide layer is oxidized from the sidewall of each columnar hole of the epitaxial structure to form a second oxide layer, and the oxidation areas corresponding to the two adjacent columnar holes on the same side overlap, and the depth of the columnar hole is greater than or equal to the distance from the ohmic contact layer to the first oxide layer in the light-emitting structure closest to the substrate layer.

[0006] Optionally, a lateral waveguide is formed by forming a ridge waveguide structure or a columnar hole array structure of a special shape in the lateral direction, and the high-order mode is suppressed by the refractive index difference in the lateral direction to achieve fundamental mode lasing.

[0007] Optionally, the epitaxial structure is provided with an electrical isolation region formed by ion implantation in a region outside the light emitting region, wherein the ion implantation depth is greater than the distance from the surface of the ohmic contact layer away from the substrate layer to the lower confinement layer of the light emitting structure closest to the substrate layer.

[0008] Optionally, the width of the ridge waveguide structure is less than 15 μm.

[0009] Optionally, limiting the width of the ridge waveguide structure to 3 μm to 7 μm helps achieve single-mode lasing, reduce high-order mode gain, and improve beam quality.

[0010] Optionally, the etching depth of the ridge waveguide structure is greater than the thickness of the lower confinement layer from the surface of the ohmic contact layer away from the substrate to the light emitting structure closest to the substrate, and the bottom of the pattern is generally within the lower confinement layer.

[0011] Optionally, the columnar hole array structure is located on both sides of the light-emitting area, the shape of the columnar holes in the columnar hole array structure is triangular, circular or polygonal, the etching depth is from the surface of the ohmic contact layer away from the substrate to below the first oxide layer of the light-emitting structure closest to the substrate layer, the etched holes can be multiple rows or a single row, and can be evenly distributed or discretely distributed.

[0012] Optionally, under high temperature and high humidity conditions, the first oxide layer is oxidized inward from the etched interface of the lateral waveguide, and the oxidized portion forms electrical insulation, limiting the current injection area from the direction away from the substrate to the direction close to the substrate, thereby making the current injection area of ​​the quantum well in each light-emitting junction the same, increasing the output light mode coupling efficiency, and achieving light confinement.

[0013] Optionally, the first oxide layer material is an aluminum-containing semiconductor compound, and the aluminum component can be rapidly oxidized in a high temperature and high humidity environment.

[0014] Optionally, the first oxide layer material may be AlAs, Al x Ga 1-x As material.

[0015] Optionally, the aluminum components of the first oxide layers of the multiple light-emitting structures may be different. The depth of oxidation is related to the aluminum component of the first oxide layer and the oxidation conditions. Generally, the higher the aluminum component, the faster the oxidation rate under the same oxidation conditions. By adjusting the aluminum component of each first oxide layer, the width of the oxidation region of the oxide layer above each quantum well (active area) can be adjusted, thereby balancing the injection width of the quantum wells between the multiple light-emitting structures, improving the coupling efficiency between the epitaxial structures, and improving the problem of reduced efficiency due to lateral diffusion of carriers.

[0016] Optionally, an electrical isolation region can be formed outside the current injection region by ion implantation. The high-energy ion implantation destroys the lattice arrangement of the region, and annealing is performed to form an electrical isolation region with stable performance, thereby limiting the lateral diffusion of carriers and improving efficiency.

[0017] In a second aspect, the present invention provides a method for preparing a semiconductor laser, the method comprising: providing a substrate layer; sequentially growing a lower confinement layer, an active region and an upper confinement layer on a side surface of the substrate layer to form a light-emitting structure; wherein the light-emitting structure further comprises a first oxide layer, the first oxide layer being formed on a side surface of the upper confinement layer away from the active region, or the first oxide layer being formed in the upper confinement layer; forming a tunnel junction on a side surface of the upper confinement layer away from the substrate layer; forming at least one light-emitting structure again on a side surface of the tunnel junction away from the substrate layer, wherein two adjacent light-emitting structures are connected via a tunnel junction; forming an ohmic contact layer on a side surface of the uppermost light-emitting structure away from the substrate layer to obtain an epitaxial structure; forming a ridge waveguide structure or a columnar hole array structure on the epitaxial structure perpendicular to the epitaxial growth direction and the light emitting direction to obtain the semiconductor laser of the first aspect or any corresponding embodiment thereof, wherein the sidewall of the first oxide layer close to the ridge waveguide structure or the columnar hole is an insulating layer, and the area of ​​the first oxide layer close to the lateral center of the ridge waveguide structure or the center of the columnar holes on both sides is a conductive layer.

[0018] Optionally, a ridge waveguide structure is formed on the epitaxial structure perpendicular to the epitaxial growth direction and the light emitting direction, including: etching the epitaxial structure so that the epitaxial structure is ridge-shaped in the direction perpendicular to the epitaxial growth direction and the light emitting direction; oxidizing the ridge structure so that the first oxide layer is oxidized inwardly from the area close to the side wall of the ridge structure to form a second oxide layer.

[0019] Optionally, a columnar hole array structure is formed in the epitaxial structure perpendicular to the epitaxial growth direction and the light emitting direction, including: etching the epitaxial structure to form a columnar hole array structure on both sides of the light emitting area; using the columnar holes as oxidation windows for oxidation treatment, so that the first oxide layer of the epitaxial structure is oxidized inward from the area close to the side wall of the columnar hole to form a second oxide layer, and the second oxide layers corresponding to two adjacent columnar holes on the same side overlap.

[0020] Optionally, a method for forming a ridge waveguide or a columnar hole array structure on the side of the epitaxial structure includes: growing a layer of hard mask material, including but not limited to SiO2, Si x N y Materials. Spin-coat photoresist and develop it by photolithography to form a photolithographic pattern on the surface of the epitaxial wafer away from the substrate. Etch the hard mask to make the hard mask replicate the photolithographic pattern and then remove the resist. Etch the lateral waveguide using dry etching or wet etching or a combination of the two to accurately control the etching depth.

[0021] Optionally, the mask may be a photoresist mask, or a hard mask and a photoresist mask.

[0022] Optionally, the epitaxial wafer etched with the lateral waveguide structure is placed in a high temperature and high humidity environment, the first oxide layer is oxidized to form a second oxide layer, and the oxidized portion forms an electrical insulating material, thereby achieving light confinement.

[0023] Optionally, after forming an ohmic contact layer on a surface of the uppermost light-emitting structure away from the substrate layer, the method further comprises: injecting ions into a region of the epitaxial structure other than the light-emitting region to form an electrical isolation region.

[0024] Optionally, ion implantation can form a current injection area and an electrical isolation area before etching a ridge waveguide structure or a columnar hole array structure. Spin-coat the photoresist and form a photoresist pattern in the epitaxial wafer away from the light-emitting area of ​​the substrate surface through photolithography development. Adjust the implantation energy and implantation angle, and perform high-energy ion implantation in the ion implantation equipment to allow the implanted ions to penetrate into the N confinement layer of the light-emitting junction of the epitaxial wafer closest to the substrate. Annealing is performed to form electrical insulation in the ion implantation area.

[0025] Optionally, ion implantation can be performed after etching the ridge waveguide structure or the columnar hole array structure. Spin-coat the photoresist, align the photolithography, set a mask layer above the current injection area in the direction away from the substrate on the ohmic contact layer, and then perform ion implantation to form an electrical isolation area (taking the ridge waveguide structure as an example).

[0026] The technical solution of the present invention has at least the following beneficial effects: The technical solution of the present invention adopts a double-junction or multi-junction epitaxial structure, and by setting a ridge waveguide structure or a columnar hole array structure downward on the surface of the epitaxial structure away from the substrate layer, a weak refractive index waveguide is formed in the vertical epitaxial growth direction and the lateral direction of the light-emitting direction, thereby realizing the restriction of high-order modes and fundamental mode lasing. The multi-junction epitaxial structure doubles the power under the same current injection, and the efficiency is improved. Each light-emitting structure sets a high-aluminum material layer in the P-type doped region, and oxidizes inward along the contact interface between the high-aluminum material and the air. By adjusting the aluminum component of the high-aluminum material of each junction, the oxidation rate is controlled to achieve the adjustment of the width of the active area of ​​the multi-junction epitaxial structure, reduce the overlap of light with the ridge waveguide structure or the side wall of the columnar hole, reduce the surface scattering loss of light, and increase the power. High-energy ion implantation is performed downward from the epitaxial layer away from the substrate to the outside of the light-emitting area, and the implanted area forms electrical insulation, which hinders the lateral diffusion of current, improves the electro-optical conversion efficiency, and realizes multi-junction electrical limitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the related technologies, the drawings required for use in the specific embodiments or the related technical descriptions will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 is a schematic structural diagram of a first semiconductor laser epitaxy according to an embodiment of the present invention; Figure 2 is a schematic structural diagram of a second semiconductor laser epitaxy according to an embodiment of the present invention; Figure 3 is a schematic structural diagram of a third semiconductor laser epitaxy according to an embodiment of the present invention; Figure 4 is a schematic diagram of a ridge waveguide structure according to an embodiment of the present invention; Figure 5 is an etching morphology diagram of a ridge waveguide structure according to an embodiment of the present invention; Figure 6 is a schematic diagram of the structure of the ridge waveguide structure after oxidation according to an embodiment of the present invention; Figure 7 is a schematic structural diagram of a columnar hole array according to an embodiment of the present invention; Figure 8 is a schematic diagram of the structure of the columnar hole array after oxidation according to an embodiment of the present invention; Fig. 9 is a schematic diagram of ion implantation according to an embodiment of the present invention; Fig.10 is a schematic diagram of a ridge waveguide structure and ion implantation according to an embodiment of the present invention; Fig.11 is a schematic diagram of a process for preparing a semiconductor laser according to an embodiment of the present invention.

[0029] Figure numerals: 110, substrate layer; 120, light-emitting structure; 121, lower confinement layer; 122, active area; 123, upper confinement layer; 124, first oxide layer; 125, columnar hole array; 126, second oxide layer; 130, tunnel junction; 140, ohmic contact layer; 150, current injection region; 160, electrical isolation region. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0031] Semiconductor lasers are widely used in fields such as optical communications, material processing, pump light sources, military and medical applications due to their outstanding advantages such as small size, light weight, low cost, high efficiency, long life, easy modulation and wide wavelength coverage.

[0032] The traditional 980nm single-mode semiconductor laser has a narrow light-emitting area, which leads to extremely high optical power density at the cavity surface, and is prone to cavity surface ablation failure. In addition, due to thermal lens effects and other reasons, it is difficult for 980nm single-mode semiconductor lasers to maintain single-mode lasing at high currents. In other words, due to factors such as low efficiency, high power density and thermal effects, the output power of 980nm single-mode semiconductor lasers is greatly limited.

[0033] In view of this, the present invention provides a semiconductor laser, which can double the power under the same electrical injection by connecting multiple groups of light-emitting structures with tunnel junctions and utilizing the tunneling effect, thereby reducing Joule heat generation and lowering power density, thereby improving the output power of the semiconductor laser.

[0034] The structure of the semiconductor laser provided by the present invention is described in detail below with reference to the accompanying drawings.

[0035] For example, Figure 1 and Figure 2 As shown, the semiconductor laser provided by the present invention includes a substrate layer 110 and an epitaxial structure, and the epitaxial structure includes a plurality of light-emitting structures 120 , a tunnel junction 130 and an ohmic contact layer 140 .

[0036] in, Figure 1 and Figure 2 Taking a semiconductor laser including two light emitting structures 120 as an example, but not limited to this, for example, the number of light emitting structures 120 included in the semiconductor laser can be 3 or 4, etc. The number of light emitting structures 120 in the semiconductor laser can be determined by the designer based on the application scenario.

[0037] like Figure 1 As shown, a plurality of light-emitting structures 120 are stacked, and two adjacent light-emitting structures 120 are connected via a tunnel junction 130. The bottom light-emitting structure 120 is disposed on a side surface of a substrate layer 110, and an ohmic contact layer 140 is disposed on a side surface of the top light-emitting structure 120 away from the substrate layer 110.

[0038] That is, one light emitting structure 120 is located above another light emitting structure 120, and the light emitting structures are connected to each other through a tunnel junction 130. Figure 1 In the direction indicated by the Y axis, the lower surface of the first light emitting structure is disposed on the upper surface of the substrate layer 110, and the ohmic contact layer 140 is disposed on the upper surface of the last light emitting structure.

[0039] Specifically, the substrate layer 110 provides mechanical support for the entire semiconductor laser structure to ensure the stability and reliability of the device during manufacturing and use, wherein the lattice constant of the substrate layer 110 should match the epitaxial structure as much as possible to reduce crystal defects and improve the crystal quality of the epitaxial layer. The present invention does not specifically limit the material of the substrate layer 110, such as gallium arsenide (GaAs), indium phosphide (InP) or sapphire (Al2O3).

[0040] The light emitting structure 120 is used to generate laser light of a specific wavelength (eg, 980 nm). By controlling parameters such as the thickness, doping concentration, and material composition of the light emitting structure 120 , performance indicators such as the wavelength, threshold current, and output power of the semiconductor laser can be adjusted.

[0041] like Figure 2 As shown, the light emitting structure 120 includes a lower confinement layer 121, an active region 122, and an upper confinement layer 123 stacked from bottom to top. That is, the active region 122 is disposed on the upper surface of the lower confinement layer 121, and the upper confinement layer 123 is disposed on the upper surface of the active region 122. Exemplarily, the lower confinement layer 121 may be an N-type confinement layer, the active region 122 may be a quantum well region, and the upper confinement layer 123 may be a P-type confinement layer.

[0042] Specifically, the lower confinement layer 121 is used to confine the injected electrons, prevent the electrons from diffusing to unnecessary areas and concentrate the electrons near the active area 122, which can improve the recombination efficiency of electrons and holes in the active area 122, thereby enhancing the light-emitting effect of the semiconductor laser. The lower confinement layer 121 can be composed of an N-type semiconductor material with a relatively high electron concentration, such as silicon (Si)-doped gallium arsenide (GaAs) or Si-doped indium phosphide (InP).

[0043] The active region 122 is the core part of the semiconductor laser, and is used to make carriers (electrons and holes) recombine and emit light at a specific quantum energy level through the quantum confinement effect. The upper confinement layer 123 is used to limit the diffusion of holes, ensuring that the holes are concentrated in the active region 122 and recombine with electrons efficiently, thereby improving the luminous efficiency.

[0044] In one example, the light emitting structure 120 further includes a lower waveguide layer and an upper waveguide layer, that is, the light emitting structure 120 includes a lower confinement layer 121, a lower waveguide layer, an active region 122, an upper waveguide layer, and an upper confinement layer 123 stacked from bottom to top. Specifically, the lower waveguide layer may be an N-type waveguide layer, and the upper waveguide layer may be a P-type waveguide layer.

[0045] Specifically, the lower waveguide layer is used to provide a transmission channel for electrons and guide the electrons to enter the active region 122 more efficiently. The lower waveguide layer is also used to limit the light field and limit the light as much as possible in the active region 122 to improve the light gain and the performance of the semiconductor laser. The upper waveguide layer is similar to the lower waveguide layer. On the one hand, it is used to provide a transmission path for the injected holes and guide the holes to reach the active region 122 smoothly. On the other hand, it is used to limit and guide the light field to ensure the effective propagation and enhancement of light in the active region 122.

[0046] The tunnel junction 130 is used to realize efficient carrier transmission between adjacent epitaxial structures by using the quantum tunnel effect, and can quickly inject electrons from one epitaxial structure to another epitaxial structure without increasing additional voltage drop, thereby improving the injection efficiency of carriers. The tunnel junction 130 helps to realize the series connection of multiple light-emitting structures, thereby increasing the volume of the active region and improving the output power of the semiconductor laser.

[0047] The tunnel junction 130 may be composed of a heavily doped semiconductor material. In one example, the tunnel junction 130 may be composed of heavily doped N-type and P-type gallium arsenide (GaAs) or gallium nitride (GaN).

[0048] The ohmic contact layer 140 is used to provide low-resistance electrode contact to ensure that current can be smoothly injected into the semiconductor laser. Good ohmic contact can reduce the series resistance of the semiconductor laser and improve the current injection efficiency, thereby reducing the threshold current of the semiconductor laser and increasing the output power.

[0049] In this embodiment, a plurality of active regions can be formed through a double-junction epitaxial structure or a multi-junction epitaxial structure, thereby increasing the area for generating light, doubling the power under the same electrical injection, reducing Joule heat generation and lowering the power density, thereby increasing the output power of the semiconductor laser.

[0050] Furthermore, if Figure 3 As shown, the light emitting structure 120 further includes a first oxide layer 124. The present invention does not specifically limit the material of the first oxide layer 124, and can be aluminum gallium arsenide (Al x Ga 1-x As) or aluminum arsenide (AlAs), etc.

[0051] Specifically, the first oxide layer 124 can be disposed on the surface of the upper limiting layer 123 away from the active region 122, or in the upper limiting layer 123, or on the surface of the upper waveguide layer away from the active region 122, or in the upper waveguide layer. Figure 3Taking the example that the first oxide layer 124 is disposed on a surface of the upper limiting layer 123 away from the active area 122 , but not limited thereto, the position of the first oxide layer 124 in the light emitting structure 120 can be determined by designers based on design requirements.

[0052] Below Figure 3 Based on the Figures 4 to 6 Three methods for achieving high-order mode suppression (high aspect ratio ridge waveguide structure + oxidation, oxidation-etched holes, and ion implantation isolation) are described in detail.

[0053] In some optional embodiments, such as Figure 4 As shown, by forming a vertical cross section in the epitaxial structure perpendicular to the epitaxial growth direction ( Figure 1 A ridge waveguide structure with a high aspect ratio is etched in the direction of the light output (in the direction shown by the X-axis) and the light output direction (which can be the direction of the Z-axis), forming a weak refractive index difference on the lateral structure to limit the light field, thereby achieving suppression of high-order modes and lasing of the fundamental mode.

[0054] Specifically, the width of the ridge waveguide structure is less than 15 μm. Preferably, the width of the ridge waveguide structure ( Figure 1 The value range of the ridge waveguide structure (in the direction indicated by the X-axis) is 3 μm to 7 μm. That is, the width of the ridge waveguide structure can be any value between 3 μm and 7 μm, for example, the width of the ridge waveguide structure can be 3 μm, 4 μm, 5 μm or 7 μm.

[0055] The narrower ridge waveguide structure can better limit the distribution of the light field in the lateral direction, help form single-mode laser output, and improve the quality of the light beam.

[0056] Specifically, the depth of the ridge waveguide structure can be greater than the distance between the ohmic contact layer 140 and the lower waveguide layer in the lowest light-emitting structure 120, and less than the distance between the ohmic contact layer 140 and the lower confinement layer 121 in the lowest light-emitting structure 120, and the aspect ratio (ratio of depth to width) of the ridge waveguide structure is greater than or equal to 2:1.

[0057] Furthermore, in this embodiment, the material of the first oxide layer is a high aluminum component material (such as an aluminum component ratio greater than or equal to 0.6), and the high aluminum component material is oxidized to generate an aluminum oxide material, which plays a lateral electrical insulation role for the current injected from top to bottom. Under the same conditions, the oxidation speed of the first oxide layer 124 is positively correlated with the aluminum component content in the first oxide layer.

[0058] For the epitaxial structure composed of multiple light-emitting structures 120, the ridge waveguide structure has a large depth-width ratio, and it is difficult to form an absolutely vertical etching morphology, resulting in different widths of multiple quantum wells (active regions) from top to bottom, thereby affecting the coupling of light fields between multiple quantum wells. Therefore, the aluminum content of the first oxide layer in each layer of the light-emitting structure 120 can take different values ​​according to design requirements. In other words, in the bottom-up direction, the aluminum content of the first oxide layer in multiple epitaxial structures can be different.

[0059] Specifically, since the semiconductor laser provided by the present invention is provided with a plurality of light emitting structures 120, during the process of etching to form a ridge waveguide structure, due to the generation of etching byproducts and the loss of the mask, the formed ridge waveguide structure may present a trapezoidal shape with a narrow top and a wide bottom. Figure 5 As shown, the inclination angle of the side wall of the ridge waveguide structure is about 87°. When the distance between the active regions 122 in the two light emitting structures 120 is 4 μm, the width difference between the two adjacent active regions 122 is 0.21 μm. Figure 4 Dashed line), the current injection areas of the upper and lower active regions 122 are different, resulting in a mismatch in the size of the lateral light field, which in turn affects the coupling of the modes between the light-emitting structures 120.

[0060] In this embodiment, the aluminum content of the first oxide layer in the multiple light-emitting structures 120 is gradually reduced in a bottom-up direction. The difference in oxidation speed of the first oxide layer is used to balance the injection width of the quantum wells between the multiple light-emitting structures 120, thereby improving the coupling efficiency between the light-emitting structures and improving the problem of reduced efficiency due to lateral diffusion of carriers.

[0061] For example, Figure 6 As shown, for the upper and lower active areas 122, the width of the second oxide layer 126 formed by oxidation of the first oxide layer 124 is different, so that the remaining unoxidized parts of the upper and lower first oxide layers 124 are the same. When the current flows through this area and reaches the active area 122, it has the same coverage area, thereby achieving the purpose of the same effective injection area area. The upper and lower active areas 122 have the same light field size and can be coupled more efficiently.

[0062] Optionally, the thickness of the first oxide layer 124 can range from 5nm to 50nm, that is, the thickness of the first oxide layer 124 can be any value between 5nm and 50nm, for example, the thickness of the first oxide layer 124 can be 5nm, 15nm, 20nm, 25nm, 40nm, 48nm or 50nm, etc.

[0063] Specifically, when the thickness of the first oxide layer is relatively small, the current injection limiting effect is relatively small; when the thickness of the first oxide layer is relatively large, problems such as stress mismatch between the first oxide layer and the materials on both sides and lateral carrier limitation may occur. Limiting the thickness of the first oxide layer 124 to 5nm to 50nm can ensure the current injection limiting effect while avoiding problems such as stress mismatch and carrier limitation as much as possible.

[0064] In other optional embodiments, such as Figure 7 As shown, the epitaxial structure is provided with a current injection region 150, and a columnar hole array 125 formed by etching is provided on both sides of the current injection region 150. The columnar hole array 125 is etched into the lower confinement layer 121 of the lowermost light-emitting structure and penetrates each first oxide layer 124 from top to bottom. Figure 8 As shown, the first oxide layer 124 begins to oxidize from the portion of the sidewall of each columnar hole exposed to the air to form a second oxide layer 126 , and the second oxide layers 126 corresponding to two adjacent columnar holes on the same side may have an overlapping area.

[0065] In this embodiment, by providing a plurality of columnar holes and oxidizing to form the second oxide layer 126, the lateral refractive index of the epitaxial structure can be made to be a low refractive index-high refractive index-low refractive index distribution, thereby achieving light restriction and electrical restriction. Compared with the setting method of the ridge waveguide structure, the lateral waveguide is formed in the form of oxidation etching holes, which can avoid the risk of collapse caused by the high aspect ratio.

[0066] In this embodiment, the lateral waveguide is composed of an array of columnar holes of a special shape. The etched hole interface can be triangular, circular, polygonal, etc. The etching depth is from the surface of the ohmic contact layer away from the substrate to below the first oxide layer 124 of the light-emitting junction closest to the substrate. The etched holes can be multiple rows or a single row, and can be evenly distributed or discretely distributed.

[0067] As with the ridge waveguide structure in the previous embodiment, the etching of the columnar holes in this embodiment may also result in inconsistent etching cross sections, resulting in different widths of the upper and lower quantum wells, resulting in lateral optical size mismatch. The arrangement of the oxide layer material components and the oxidation process in this embodiment are the same as those in the previous embodiment, and will not be repeated here.

[0068] In some other optional embodiments, an electrical isolation region 160 ( Fig. 9 The shaded area is the area where high-energy ion injection destroys the lattice arrangement. Through annealing, it forms an electrically isolated area with stable performance, thereby limiting the lateral diffusion of carriers and improving efficiency.

[0069] In this embodiment, ion implantation can be performed before etching the ridge waveguide structure or the columnar hole array structure to form Fig. 9 The current injection region 150 and the electrical isolation region 160 are then aligned by photolithography and waveguide etching is performed to form a ridge waveguide structure or a columnar hole array structure, and the etching region should be outside the current injection region 150 .

[0070] In this embodiment, ion implantation can be performed after etching the ridge waveguide structure or the columnar hole array structure. Fig.10 Taking the ridge waveguide structure as an example, through photolithography alignment, a mask layer is set above the current injection region 150 in a direction away from the substrate of the ohmic contact layer, and then ion implantation is performed to form the electrical isolation region 160 .

[0071] In this embodiment, the electrical isolation region 160 formed by ion implantation and the second oxide layer formed by oxidation both produce current insulation effects, and the two can be implemented alone or simultaneously.

[0072] In this embodiment, an electrical isolation region 160 is formed outside the current injection region 150, which can not only limit the lateral diffusion of carriers in the epitaxial structure, but also inhibit the diffusion of carriers toward the bottom of the channel, thereby reducing the loss of carriers and improving the electro-optical conversion efficiency of the semiconductor laser.

[0073] This embodiment also provides a method for preparing a semiconductor laser. Fig.11 FIG. 1 is a flow chart of a method for preparing a semiconductor laser according to an embodiment of the present invention. Fig.11 As shown, the method comprises the following steps: Step S1101, providing a substrate layer.

[0074] Specifically, a suitable substrate layer may be selected based on the design requirements of the semiconductor laser. For example, the substrate layer may be gallium arsenide (GaAs), indium phosphide (InP), or sapphire (Al2O3).

[0075] Step S1102, a lower confinement layer, an active region and an upper confinement layer are sequentially grown on a surface of one side of the substrate layer to form a light emitting structure.

[0076] Specifically, a metal-organic chemical vapor deposition (MOCVD) process or a molecular beam epitaxy (MBE) process can be used to sequentially grow a lower confinement layer, an active region and an upper confinement layer on one surface of the substrate layer to obtain a light-emitting structure.

[0077] MOCVD uses organic compounds of group III and group II elements and hydrides of group V and group VI elements as crystal growth source materials, and performs vapor phase epitaxial growth on the substrate layer through thermal decomposition reaction of the source materials. MBE is to spray the molecular beam or atomic beam of each element that makes up the thin film onto the heated substrate surface in a certain way under high vacuum conditions, and a physical or chemical process occurs on the substrate surface to form a thin film.

[0078] In some optional embodiments, the method for preparing a semiconductor laser further includes forming a first oxide layer in the light emitting structure, and the forming of the first oxide layer in the light emitting structure is specifically: forming the first oxide layer on a surface of the upper limiting layer away from the active region; or, forming the first oxide layer in the upper limiting layer; or, forming the first oxide layer between the upper waveguide layer and the upper limiting layer; or, forming the first oxide layer in the upper waveguide layer.

[0079] Step S1103, forming a tunnel junction on a surface of the upper confinement layer away from the substrate layer.

[0080] Specifically, after forming the upper confinement layer, the upper surface of the upper confinement layer is doped with high concentration through ion implantation or diffusion process to form a heavily doped region; and an N-type semiconductor material is grown or deposited on the upper surface of the upper confinement layer to form a tunnel junction.

[0081] Step S1104, forming at least one light-emitting structure again on the surface of the tunnel junction away from the substrate layer.

[0082] Among them, two adjacent epitaxial structures are connected through a tunnel junction.

[0083] Specifically, the light emitting structure is formed in the same manner as step S1102 , and the tunnel junction between two adjacent epitaxial structures is formed in the same manner as step S1103 .

[0084] Step S1105 , forming an ohmic contact layer on a surface of the uppermost light emitting structure away from the substrate layer to obtain an epitaxial structure.

[0085] For example, an ohmic contact layer may be formed on a surface of the uppermost light emitting structure that is away from the substrate layer through a deposition process.

[0086] Step S1106, forming a ridge waveguide structure or a columnar hole array structure on the epitaxial structure perpendicular to the epitaxial growth direction and the light emitting direction to obtain a semiconductor laser.

[0087] Specifically, in order to suppress the high-order mode, after the epitaxial structure is formed, a lateral waveguide is formed on the epitaxial structure perpendicular to the epitaxial growth direction and the light emitting direction, and the lateral waveguide can be a ridge waveguide structure or a columnar hole array structure. The sidewall of the first oxide layer close to the ridge waveguide structure or the columnar hole is an insulating layer, and the area of ​​the first oxide layer close to the lateral center of the ridge waveguide structure or the center of the columnar holes on both sides is a conductive layer.

[0088] In some optional embodiments, forming a lateral waveguide includes: etching the epitaxial structure so that the epitaxial structure is ridge-shaped in a direction perpendicular to the epitaxial growth direction and the light output direction; oxidizing the ridge structure so that the first oxide layer is oxidized inward from the area close to the side wall of the ridge structure to form a second oxide layer.

[0089] Specifically, after the epitaxial structure is formed, SiO2 or Si is formed on the upper surface of the uppermost epitaxial structure. x N y The dielectric film forms a hard mask; a photoresist layer is spin-coated; the photoresist layer is exposed; after the exposure, the photoresist layer is developed; then, the hard mask and the epitaxial structure are etched using the remaining photoresist of the photoresist layer as a mask, so that the epitaxial structure is ridge-shaped; then, the photoresist layer is removed.

[0090] Specifically, the photoresist layer may be removed after etching the hard mask or after etching the epitaxial structure.

[0091] In this embodiment, forming the first oxide layer in the light emitting structure includes: pre-growing a high-aluminum material layer at a preset position; and after forming the lateral waveguide, oxidizing the high-aluminum material layer to form the first oxide layer.

[0092] The preset position may be the upper surface of the upper confinement layer, the interior of the upper confinement layer, the upper surface of the upper waveguide layer, or the interior of the upper waveguide layer. The high aluminum material layer may be an aluminum arsenide (AlAs) material layer, an aluminum gallium arsenide (Al x Ga 1-x As) material layer, the temperature range of the oxidation treatment process can be 400°C to 430°C, and the humidity of the oxidation treatment process is related to the flow rate of the nitrogen (N2) introduced.

[0093] Specifically, the aluminum material layer exposed at the etched cross section will oxidize rapidly in a high temperature and high humidity environment to form electrical insulation. By controlling the aluminum component of the aluminum material layer in different epitaxial structures and the oxidation process, the depth of aluminum material oxidation can be controlled, so that the electrical injection width of the quantum wells of the upper and lower epitaxial structures is equal.

[0094] Since the ridge waveguide structure may be narrow at the top and wide at the bottom during etching, by making the aluminum component of the lower first oxide layer slightly higher than that of the upper first oxide layer, the oxidation rate (i.e., width) of the lower oxide layer can be greater than that of the upper layer, thereby making the width of the unoxidized area in the middle consistent.

[0095] In other optional embodiments, forming a lateral waveguide includes etching an epitaxial structure to form a columnar hole array structure on both sides of the light-emitting area; the columnar holes are used as oxidation windows for oxidation treatment, so that the first oxide layer is oxidized near the side wall of the columnar hole to form a second oxide layer, and the second oxide layers corresponding to two adjacent columnar holes on the same side overlap.

[0096] Specifically, etching the epitaxial structure to form a columnar hole array structure on both sides of the light-emitting region may include: after forming the epitaxial structure, forming SiO2 or Si on the upper surface of the uppermost epitaxial structure; x N y The dielectric film forms a hard mask; a photoresist layer is spin-coated; the photoresist layer is exposed; after the exposure, the photoresist layer is developed; after the development, the hard mask and the epitaxial structure are etched using the remaining photoresist of the photoresist layer as a mask to form a plurality of columnar holes; and then, the photoresist layer is removed.

[0097] Specifically, the photoresist layer may be removed after etching the hard mask or after etching the epitaxial structure.

[0098] The arrangement of the plurality of columnar holes can be as follows: Figure 7 As shown, the holes can be arranged in a single row, a double row, or an irregular row, which is not specifically limited in this application. The hole shape can be any shape such as a circle or a polygon.

[0099] Specifically, the columnar hole is used as an oxidation window for oxidation treatment, so that the epitaxial structure forms a second oxide layer near the side wall of the columnar hole, and the second oxide layers corresponding to two adjacent columnar holes on the same side have an overlapping area. Specifically, a high-temperature and high-humidity oxidation process is performed to make each columnar hole serve as an oxidation window and diffuse to the surroundings until the designed oxidation depth is reached.

[0100] In order to further limit the current and improve the electro-optical conversion efficiency, the method for preparing the semiconductor laser also includes: injecting ions into the area of ​​the epitaxial structure except the light-emitting area to form an electrical isolation area.

[0101] Alternatively, the step of ion implantation to form the electrical isolation region may be performed after forming the epitaxial structure or after forming the lateral waveguide.

[0102] Specifically, Fig. 9As shown, an ion implantation method is used to implant ions into an area outside the light-emitting area to destroy the lattice arrangement of the area; then, an annealing treatment is performed to form an electrically isolated area with stable performance in the area outside the light-emitting area of ​​the epitaxial structure.

[0103] The implanted ions include but are not limited to hydrogen ions, silicon ions and oxygen ions. The depth of the ion implantation can be adjusted according to the design requirements of the epitaxial structure. The depth of the ion implantation can reach the lower confinement layer closest to the substrate layer.

[0104] In some embodiments, after forming the lateral waveguide, a dielectric film layer and a metal layer are sequentially grown on the upper surface of the ohmic contact layer, wherein the metal layer is used as an electrode to inject current into the semiconductor laser.

[0105] Specifically, the thickness of the dielectric film layer may be in the range of 100 nm to 500 nm, for example, the thickness of the dielectric film layer may be 100 nm, 200 nm, 300 nm, 400 nm or 500 nm, etc. The thickness of the metal layer may be in the range of 0.8 μm to 2.5 μm, for example, the thickness of the metal layer may be 0.8 μm, 0.9 μm, 1 μm, 1.5 μm, 2 μm or 2.5 μm, etc.

[0106] The material of the dielectric film layer includes but is not limited to silicon dioxide (SiO2) or silicon nitride (Si x N y ), the material of the metal layer can be titanium (Ti) / platinum (Pt) / gold (Au), etc., and the growth method includes but is not limited to evaporation, sputtering or electroplating, etc.

[0107] The method for preparing a semiconductor laser provided in this embodiment can double the output power of the semiconductor laser and improve its efficiency through multiple epitaxial structures. By applying ion implantation or oxidation insulation process, it can suppress lateral diffusion of current, suppress high-order mode output, and improve electro-optical conversion efficiency.

[0108] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0109] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0110] In the description of this specification, the description with reference to the terms "this embodiment", "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0111] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0112] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the present invention.

Claims

1. A semiconductor laser, characterized in that: The semiconductor laser comprises a substrate layer and an epitaxial structure, wherein the epitaxial structure comprises a plurality of light emitting structures, a tunnel junction and an ohmic contact layer; The light emitting structure comprises a lower limiting layer, an active region and an upper limiting layer which are sequentially arranged from bottom to top, and the light emitting structure further comprises a first oxide layer, wherein the first oxide layer is arranged on a surface of the upper limiting layer away from the active region, or the first oxide layer is arranged in the upper limiting layer; A plurality of the light-emitting structures are stacked, two adjacent light-emitting structures are connected by the tunnel junction, the light-emitting structure of the bottom layer is arranged on a side surface of the substrate layer, and the ohmic contact layer is arranged on a side surface of the light-emitting structure of the top layer away from the substrate layer; The epitaxial structure is formed with a ridge waveguide structure or a columnar hole array structure in a lateral direction perpendicular to the epitaxial growth direction and the light emitting direction, the first oxide layer is an insulating layer near the sidewall of the ridge waveguide structure or the columnar hole, and the first oxide layer is a conductive layer near the lateral center of the ridge waveguide structure or the center of the columnar holes on both sides; After the ridge waveguide structure is formed, the first oxide layer is oxidized inward from the etching interface of the ridge waveguide structure to form a second oxide layer; or after the columnar hole array structure is formed, the first oxide layer is oxidized from the side wall of the epitaxial structure close to each columnar hole to form a second oxide layer, and the oxidation areas corresponding to two adjacent columnar holes on the same side overlap, and the depth of the columnar hole is greater than or equal to the distance from the ohmic contact layer to the first oxide layer in the light-emitting structure closest to the substrate layer.

2. The semiconductor laser according to claim 1, characterized in that The epitaxial structure is provided with an electrical isolation region formed by ion implantation in a region outside the light emitting region, wherein the ion implantation depth is greater than the distance from the surface of the ohmic contact layer away from the substrate layer to the lower confinement layer in the light emitting structure closest to the substrate layer.

3. The semiconductor laser according to claim 1, characterized in that The width of the ridge waveguide structure is less than 15 μm.

4. The semiconductor laser according to claim 3, characterized in that The width of the ridge waveguide structure ranges from 3 μm to 7 μm.

5. The semiconductor laser according to claim 1, characterized in that The columnar hole array structure is located at two sides of the light emitting area, and the columnar holes in the columnar hole array structure are in the shape of a triangle, a circle or a polygon.

6. The semiconductor laser according to any one of claims 1 to 5, characterized in that The aluminum components of the first oxide layers of the plurality of light emitting structures are different.

7. A method for preparing a semiconductor laser, characterized in that: The method comprises: providing a substrate layer; A lower confinement layer, an active region, and an upper confinement layer are sequentially grown on a surface of one side of the substrate layer to form a light-emitting structure; wherein the light-emitting structure further comprises a first oxide layer, the first oxide layer being formed on a surface of a side of the upper confinement layer away from the active region, or the first oxide layer being formed in the upper confinement layer; forming a tunnel junction on a surface of the upper confinement layer away from the substrate layer; At least one of the light-emitting structures is formed again on a surface of the tunnel junction away from the substrate layer, wherein two adjacent light-emitting structures are connected through the tunnel junction; forming an ohmic contact layer on a surface of the uppermost light emitting structure away from the substrate layer to obtain an epitaxial structure; A ridge waveguide structure or a columnar hole array structure is formed on the epitaxial structure perpendicular to the epitaxial growth direction and the light emitting direction to obtain a semiconductor laser as described in any one of claims 1 to 6, wherein the first oxide layer is an insulating layer near the sidewall of the ridge waveguide structure or the columnar hole, and the first oxide layer is a conductive layer near the lateral center of the ridge waveguide structure or the center of the columnar holes on both sides.

8. The method according to claim 7, characterized in that A ridge waveguide structure is formed on the epitaxial structure perpendicular to the epitaxial growth direction and the light output direction, including: Etching the epitaxial structure so that the epitaxial structure is ridge-shaped in a direction perpendicular to the epitaxial growth direction and the light emitting direction; The ridge structure is oxidized so that the first oxide layer is oxidized inwards from a region close to a side wall of the ridge structure to form a second oxide layer.

9. The method according to claim 7, characterized in that: A columnar hole array structure is formed on the epitaxial structure perpendicular to the epitaxial growth direction and the light emitting direction, comprising: Etching the epitaxial structure to form a columnar hole array structure on both sides of the light-emitting region; The columnar holes are used as oxidation windows for oxidation treatment, so that the first oxide layer of the epitaxial structure is oxidized inward from the area close to the side wall of the columnar holes to form a second oxide layer, and the second oxide layers corresponding to two adjacent columnar holes on the same side overlap.

10. The method according to any one of claims 7 to 9, characterized in that After forming an ohmic contact layer on a surface of the uppermost light emitting structure away from the substrate layer, the method further comprises: Ions are implanted into the region of the epitaxial structure except the light emitting region to form an electrical isolation region.

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