Semiconductor light-emitting structure and preparation method thereof

Abstract

The invention discloses a semiconductor light-emitting structure and a preparation method thereof. The semiconductor light-emitting structure comprises a substrate layer; the active layer is arranged on one side of the substrate layer; the refractive index modulation layer is arranged on one side, away from the substrate layer, of the active layer; the refractive index modulation layer is a sub-wavelength grating, the period of the sub-wavelength grating is the same, the duty ratio of the sub-wavelength grating is not completely the same, the height of the sub-wavelength grating is equal to the thickness of the refractive index modulation layer, a groove of the sub-wavelength grating is filled with a first material, and the refractive index of the first material is different from the refractive index of the material of the sub-wavelength grating. According to the semiconductor light-emitting structure and the preparation method thereof disclosed by the invention, the refractive index modulation layer of the sub-wavelength grating structure is arranged, and the duty ratio of the sub-wavelength grating in the refractive index modulation layer is adjusted, so that the refractive index can be adjusted at will, the change of the refractive index caused by temperature and carriers is reduced, the thermal lens effect is effectively reduced, and the light-emitting efficiency is improved. Performance of the semiconductor light-emitting structure is improved, and light beam quality is optimized.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and particularly to a semiconductor light-emitting structure and a method for manufacturing the same. Background Art

[0002] The development direction of high-power semiconductor laser chips includes higher power conversion efficiency, higher output optical power, and higher brightness. Generally, by increasing the width of the light-emitting region of the laser chip, a wide-waveguide semiconductor laser chip is fabricated to improve the optical power. The physical size of a high-power wide-region semiconductor laser in the slow axis (lateral) direction is much larger than its typical operating wavelength (0.8 to 2.0 μm), and it tends to emit multimodes laterally, thus significantly reducing its lateral beam quality and restricting the further application of high-power wide-region semiconductor lasers.

[0003] The far-field in the lateral direction of a high-power wide-region semiconductor laser usually becomes wider as the current increases. The lateral refractive index gradient caused by the non-uniform temperature distribution inside the waveguide enhances the refractive index guiding of the laser mode, and this effect is also known as the thermal lens. The thermal lens effect is the main reason for the deterioration of the lateral beam quality of high-power wide-region semiconductor lasers.

[0004] Currently, the common method to improve the thermal lens effect is to set an external thermal compensation layer on the side of the P-type confinement layer away from the substrate layer to adjust the thermal conductivity, reduce the thermal gradient, and relieve the refractive index change caused by temperature non-uniformity. However, the addition of the external thermal compensation layer will cause a change in the stress distribution inside the device, produce an undesired modulation of the refractive index, affect the polarization performance, optical field distribution, and long-term use stability of the laser, and reduce the reliability and lifespan of the laser. In addition, self-focusing caused by the refractive index change due to carrier accumulation and depletion is also a reason for the deterioration of the lateral beam quality of high-power wide-region semiconductor lasers. Summary of the Invention

[0005] To solve one or more of the above problems, this application proposes a semiconductor light-emitting structure and a method for manufacturing the same.

[0006] According to one aspect of this application, there is provided a semiconductor light-emitting structure, including: A substrate layer; An active layer disposed on one side of the substrate layer; A refractive index modulation layer disposed on the side of the active layer away from the substrate layer; The refractive index modulation layer is a sub-wavelength grating. The periods of the sub-wavelength gratings are the same, the duty cycles of the sub-wavelength gratings are not completely the same, the height of the sub-wavelength grating is equal to the thickness of the refractive index modulation layer, the grooves of the sub-wavelength grating are filled with a first material, and the refractive index of the first material is different from the refractive index of the material of the sub-wavelength grating.

[0007] According to another aspect of the present application, there is provided a method for preparing a semiconductor light-emitting structure for preparing any of the above semiconductor light-emitting structures, including the following steps: Prepare a substrate; Perform a first epitaxial growth on the substrate; Fabricate a refractive index modulation layer on the grown epitaxial wafer; Use the regrowth technique to complete the fabrication of other epitaxial structures; Wherein, the refractive index modulation layer is a sub-wavelength grating, the periods of the sub-wavelength gratings are the same, the duty cycles of the sub-wavelength gratings are not completely the same, the height of the sub-wavelength grating is equal to the thickness of the refractive index modulation layer, the grooves of the sub-wavelength grating are filled with a first material, and the refractive index of the first material is different from the refractive index of the material of the sub-wavelength grating.

[0008] The semiconductor light-emitting structure and its preparation method disclosed in the present application, by arranging a refractive index modulation layer with a sub-wavelength grating structure inside the semiconductor light-emitting structure, and by setting the duty cycles of the gratings in the refractive index modulation layer, realize the pre-compensation of the effective refractive index in the lateral direction of the semiconductor light-emitting structure, and at the same time will not cause temperature and stress changes inside the semiconductor light-emitting structure, realize arbitrary adjustment and precise regulation of the refractive index, reduce the refractive index changes caused by temperature and carriers, effectively reduce the thermal lens effect and carrier effect, improve the lateral performance of the semiconductor light-emitting structure, optimize the beam quality, significantly improve the lateral beam quality, and ensure the long-term stability of the semiconductor light-emitting structure under high-power operation. Description of the Drawings

[0009] Figure 1 It is a schematic cross-sectional view perpendicular to the light-emitting direction of the semiconductor light-emitting structure provided by an embodiment of the present application.

[0010] Figure 2 It is a schematic diagram of the effective refractive index change caused by heat when a 40W thermal power is applied to the semiconductor light-emitting structure without a refractive index modulation layer in an embodiment of the present application.

[0011] Figure 3 It is a schematic diagram of the adjustment ability of the effective refractive index of the refractive index modulation layer located in the P-side confinement layer and 20nm away from the interface between the P-side waveguide layer and the P-side confinement layer under different grating thicknesses and duty cycles. Detailed Embodiments

[0012] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are part of the embodiments of the present invention, rather than all of the embodiments, and are only used to explain the present invention, not to limit the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work belong to the scope of protection of the present invention.

[0013] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "inner", "outer", "both ends", "both sides", "bottom", "top", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the element to which it refers must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "superior", "inferior", "main", "secondary", etc. are only used for descriptive purposes and can be simply used to more clearly distinguish different components, and should not be construed as indicating or implying relative importance.

[0014] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", and "connected" 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 directly connected or indirectly connected through an intermediate medium. It can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0015] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0016] Embodiment 1: The embodiment of the present invention provides a semiconductor light-emitting structure, which at least includes: a substrate layer 1; an active layer 4 disposed on one side of the substrate layer 1; and a refractive index modulation layer 6 disposed on the side of the active layer 4 away from the substrate layer 1.

[0017] The semiconductor light-emitting structure may include a substrate layer 1, an N-type confinement layer 2, an N-type waveguide layer 3, an active layer 4, a P-type waveguide layer 5, and a P-type confinement layer 7 arranged in sequence from bottom to top.

[0018] The refractive index modulation layer 6 can be disposed within the P-type waveguide layer 5, or the refractive index modulation layer 6 can be disposed within the P-type confinement layer 7, or the refractive index modulation layer 6 can be disposed between the P-type waveguide layer 5 and the P-type confinement layer 7.

[0019] Refer to the attached specification Figure 1 , which shows a schematic cross-sectional view of the semiconductor light-emitting structure perpendicular to the light-emitting direction when the refractive index modulation layer 6 is disposed between the P-type waveguide layer 5 and the P-type confinement layer 7.

[0020] The refractive index modulation layer 6 can be a sub-wavelength grating with the same period, that is, the period of the grating in the refractive index modulation layer 6 is much lower than the laser effective wavelength of the semiconductor light-emitting structure, and the periods of the gratings in the refractive index modulation layer 6 are the same.

[0021] The duty ratios of the sub-wavelength gratings in the refractive index modulation layer 6 are not exactly the same. Thus, by setting the duty ratios within each period of the sub-wavelength gratings in the refractive index modulation layer 6, arbitrary modification of the refractive index can be achieved.

[0022] The refractive index modulation layer 6 includes alternately arranged gratings 61 and grooves 62. The gratings 61 are arranged along the light-emitting direction of the semiconductor light-emitting structure. The gratings 61 can be strip gratings, and the lengths of the gratings 61 along the light-emitting direction of the semiconductor light-emitting structure can be equal. The grooves 62 are filled with a first material, and the refractive index of the first material is different from that of the material of the gratings 61.

[0023] Refer to the attached specification Figure 1 As shown, where h represents the height of the gratings 61, a represents the width of the gratings 61, b represents the width of the grooves 62, and the duty ratio f = a / (a + b). Thus, the gratings 61 and the grooves 62 are made of two materials with different refractive indices, and different settings of the duty ratio can be achieved by adjusting the volumes of the gratings 61 and the grooves 62, thereby realizing the modification of the refractive index.

[0024] In an alternative embodiment, the material of the gratings 61 in the refractive index modulation layer 6 can be GaAs, and the first material filled in the grooves 62 can be Al 70 GaAs.

[0025] In an alternative embodiment, when the refractive index modulation layer 6 is disposed within the P-type waveguide layer 5, the first material may be the same as the material of the P-type waveguide layer 5. When the refractive index modulation layer 6 is disposed within the P-type confinement layer 7, the first material may be the same as the material of the P-type confinement layer 7. Thus, only one layer of material needs to be introduced inside the semiconductor light-emitting structure to form the grating 61, which can be combined with the original materials in the epitaxial layer of the semiconductor light-emitting structure to form the refractive index modulation layer 6. This can effectively reduce the refractive index change caused by heat and carriers without causing temperature and stress changes inside the semiconductor light-emitting structure. At the same time, the refractive index can be precisely adjusted by setting the duty cycle of the sub-wavelength grating, fundamentally suppressing the refractive index change caused by uneven temperature and carrier change.

[0026] In an alternative embodiment, when the refractive index modulation layer 6 is disposed between the P-type waveguide layer 5 and the P-type confinement layer 7, the material of the grating 61 is the same as the material of the P-type waveguide layer 5, and the first material filled in the groove 62 is the same as the material of the P-type confinement layer 7. Thus, by disposing the refractive index modulation layer 6 at the interface between the P-type waveguide layer 5 and the P-type confinement layer 7, without introducing any materials, the original materials in the epitaxial layer of the semiconductor light-emitting structure can be directly used to form the refractive index modulation layer 6. While further simplifying the preparation steps and reducing the preparation difficulty, it reduces the thermal lens effect caused by temperature gradient and carrier change, and at the same time can avoid affecting the temperature distribution and stress distribution of the semiconductor light-emitting structure, improving the semiconductor performance and optimizing the beam quality. Since there is no need to consider problems such as lattice matching, thermal conductivity change, and energy band change that may be caused by the introduction of new materials, reducing the impact on the semiconductor light-emitting structure, it is not only applicable to GaAs-based semiconductor light-emitting structures, but also can be used in GaN, QCL, and silicon photonic devices, expanding the application range, reducing the preparation difficulty, and improving the production efficiency.

[0027] In an alternative embodiment, the thickness of the refractive index modulation layer 6 is less than 100 nm. Thus, the thickness and material of the refractive index modulation layer 6 will not have an obvious impact on the temperature distribution.

[0028] In an alternative embodiment, the sub-wavelength grating is disposed along a first direction, and the first direction is perpendicular to the epitaxial direction and the light-emitting direction of the semiconductor light-emitting structure respectively. Refer to the attached Figure 1 description. In the figure, the x direction shown is the first direction, and the z direction is the epitaxial direction.

[0029] The attached description Figure 2The figure shows a schematic diagram of the thermally induced effective refractive index change value of a semiconductor light-emitting structure without a refractive index modulation layer when loaded with 40 W of thermal power. Specifically, the semiconductor light-emitting structure without a refractive index modulation layer may include a substrate layer, an N-type confinement layer, an N-type waveguide layer, an active layer, a P-type waveguide layer, and a P-type confinement layer arranged in sequence from bottom to top. The parameters of the semiconductor light-emitting structure without a refractive index modulation layer are a lasing wavelength of 980 nm, a cavity length of 4.5 mm, and a stripe width of 230 microns. Under these parameters, 40 W of thermal power far exceeds the typical value of the thermal power of a semiconductor light-emitting structure of this specification. In the attached Figure 2 to the specification, the horizontal axis represents the position in the first direction, with the unit of μm, and the vertical axis represents the effective refractive index change.

[0030] The attached Figure 3 to the specification shows a schematic diagram of the refractive index adjustment ability of a refractive index modulation layer located within the P-side confinement layer and 20 nm away from the interface between the P-side waveguide layer and the P-side confinement layer under different grating thicknesses and duty cycles. Among them, the horizontal axis represents the refractive index modulation layer thickness, with the unit of nm, and the vertical axis represents the effective refractive index change amount.

[0031] Taking the semiconductor light-emitting structure and the refractive index modulation layer shown in the attached Figure 2 and the attached Figure 3 to the specification as an example, an explanation is given on how to determine the parameters of the sub-wavelength grating in the refractive index modulation layer 6.

[0032] It can be seen from the attached Figure 2 to the specification that when loaded with 40 W of thermal power, the thermally induced refractive index change range is 0 - 0.003. In order to balance this effect, as long as the refractive index adjustment ability of the refractive index modulation layer 6 is within ±0.0015, the maximum refractive index change of 0.003 can be completely eliminated. For example, if the compensated target effective refractive index is denoted as n, then the refractive index n(x) after loading 40 W of thermal power at each position is read in the attached Figure 2 to the specification. After calculating the value of n - n(x), the corresponding data points are found in the attached Figure 3 to the specification according to the calculated refractive index difference, and then the thickness and duty cycle of the refractive index modulation layer at this position are determined.

[0033] When there is no refractive index modulation layer in the semiconductor light-emitting structure, the refractive index changes caused by temperature and carriers can both be detected. Therefore, as long as the refractive index change value is determined, precise refractive index pre-compensation can be performed for each position point through the setting of the duty cycle of the sub-wavelength grating in the refractive index modulation layer, thereby enabling arbitrary adjustment of the refractive index.

[0034] It should be noted that depending on the material of the grating 61 and the first material filled in the groove 62, the refractive index adjustment ability of the refractive index modulation layer 6 varies.

[0035] The closer the refractive index modulation layer 6 is to the P-type waveguide layer 5, the weaker the modulation ability required for the refractive index modulation layer 6. The farther the refractive index modulation layer 6 is from the P-type waveguide layer 5, the stronger the modulation ability required for the refractive index modulation layer 6. The modulation ability is the amount of change in the effective refractive index.

[0036] At the position where the change value of the effective refractive index is larger, the geometric size ratio of the groove 62 is larger, that is, the duty cycle is smaller. At the position where the effective refractive index change caused by heat is smaller, the geometric size ratio of the grating 61 is larger, that is, the duty cycle is larger. Thus, by adjusting the duty cycle of the sub-wavelength gratings at different positions in the refractive index modulation layer 6, arbitrary adjustment of the refractive index can be achieved, fundamentally solving the influence caused by the thermal lens effect or carriers, and improving the lifetime and light-emitting quality of the semiconductor light-emitting structure.

[0037] In an alternative embodiment, the refractive index modulation layer 6 is a sub-wavelength grating with a gradually changing duty cycle. The duty cycle of the grating located at the center of the refractive index modulation layer 6 is the smallest, and the duty cycle of the sub-wavelength grating increases as the distance from the center of the refractive index modulation layer increases. The sub-wavelength gratings are symmetrically arranged on both sides of the grating with the smallest duty cycle.

[0038] In an alternative embodiment, the duty cycle of the sub-wavelength grating can be changed at the center or edge of the refractive index modulation layer 6, which can compensate for the refractive index change caused by carrier accumulation or depletion. The higher the carriers, the lower the refractive index. Therefore, at the place where the carrier accumulation is too high, the refractive index is increased, or at the place where the carriers are depleted, the refractive index is decreased.

[0039] The semiconductor light-emitting structure disclosed in this application realizes pre-compensation of the lateral effective refractive index of the semiconductor light-emitting structure by setting a refractive index modulation layer with a sub-wavelength grating structure inside the semiconductor light-emitting structure, and by adjusting the duty cycle of the sub-wavelength gratings in the refractive index modulation layer. At the same time, it will not cause temperature and stress changes inside the semiconductor light-emitting structure, realizes arbitrary adjustment and precise regulation of the effective refractive index, reduces the refractive index change caused by temperature and carriers, effectively reduces the thermal lens effect and carrier effect, improves the lateral performance of the semiconductor light-emitting structure, optimizes the beam quality, significantly improves the lateral beam quality, and ensures the long-term stability of the semiconductor light-emitting structure under high-power operation.

[0040] Embodiment 2: The embodiment of the present invention also provides a method for manufacturing a semiconductor light-emitting structure, which is used to manufacture any semiconductor light-emitting structure in the above embodiments, and includes the following steps: Prepare a substrate; Perform primary epitaxial growth on the substrate; Prepare a refractive index modulation layer on the grown epitaxial wafer; Use the regrowth technology to complete the preparation of other epitaxial structures; Among them, the refractive index modulation layer is a sub-wavelength grating. The periods of the sub-wavelength gratings are the same, the duty cycles of the sub-wavelength gratings are not completely the same, the height of the sub-wavelength grating is equal to the thickness of the refractive index modulation layer, the grooves of the sub-wavelength grating are filled with a first material, and the refractive index of the first material is different from that of the material of the sub-wavelength grating.

[0041] When the material of the grating is GaAs and the refractive index modulation layer is located in the P-type waveguide layer, the epitaxial growth includes sequentially growing an N-type confinement layer, an N-type waveguide layer, an active layer, and a P-type waveguide layer that are stacked. The preparation of the refractive index modulation layer on the grown epitaxial wafer includes growing a GaAs layer on the side of the P-type waveguide layer away from the active layer, etching gratings with different duty cycles on the GaAs layer, and using the regrowth technology to complete the preparation of other epitaxial structures, including using the regrowth technology to fill the grooves in the refractive index modulation layer, and then continuing to grow the P-type waveguide layer, the P-type confinement layer, and other epitaxial structures, finally realizing the preparation of a complete epitaxial structure. At this time, the first material filled in the grooves is the same as the material of the P-type waveguide layer.

[0042] When the material of the grating is the same as that of the P-type waveguide layer and the first material filled in the grooves is the same as that of the P-type confinement layer, during one epitaxial growth, an N-type confinement layer, an N-type waveguide layer, an active layer, and a P-type waveguide layer that are stacked are sequentially grown. Among them, the thickness of the P-type waveguide layer is the sum of the preset thickness of the P-type waveguide layer and the preset thickness of the refractive index modulation layer; the preparation of the refractive index modulation layer on the grown epitaxial wafer includes etching sub-wavelength gratings on the grown P-type waveguide layer using etching technology, where the height of the sub-wavelength grating is equal to the preset thickness of the refractive index modulation layer; during the regrowth process, the material of the P-type confinement layer can fill the grooves in the refractive index modulation layer to form a complete refractive index modulation layer.

[0043] The features of this embodiment that are the same as those of Embodiment 1 will not be elaborated here.

[0044] In the preparation method of the semiconductor light-emitting structure disclosed in this application, by arranging a refractive index modulation layer with a sub-wavelength grating structure inside the semiconductor light-emitting structure, through adjusting the duty cycle of the sub-wavelength grating in the refractive index modulation layer, the lateral effective refractive index pre-compensation of the semiconductor light-emitting structure is realized. At the same time, it will not cause temperature and stress changes inside the semiconductor light-emitting structure, realizing arbitrary adjustment and precise regulation of the effective refractive index, reducing the refractive index changes caused by temperature and carriers, effectively reducing the thermal lens effect and carrier effect, improving the lateral performance of the semiconductor light-emitting structure, optimizing the beam quality, significantly improving the lateral beam quality, and ensuring the long-term stability of the semiconductor light-emitting structure under high-power operation.

[0045] The above are only alternative embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A semiconductor light emitting structure, characterized in that: include: substrate layer; An active layer disposed on one side of the substrate layer; A refractive index modulation layer disposed on a side of the active layer away from the substrate layer; The refractive index modulation layer is a sub-wavelength grating, the periods of the sub-wavelength gratings are the same, the duty cycles of the sub-wavelength gratings are not completely the same, the height of the sub-wavelength gratings is equal to the thickness of the refractive index modulation layer, and the grooves of the sub-wavelength gratings are filled with a first material, and the refractive index of the first material is different from the refractive index of the material of the sub-wavelength grating.

2. The semiconductor light emitting structure according to claim 1, characterized in that: The refractive index modulation layer is disposed in the P-type waveguide layer, or the refractive index modulation layer is disposed between the P-type waveguide layer and the P-type confinement layer, or the refractive index modulation layer is disposed in the P-type confinement layer.

3. The semiconductor light emitting structure according to claim 2, characterized in that: When the refractive index modulation layer is disposed between a P-type waveguide layer and a P-type confinement layer, the material of the sub-wavelength grating is the same as that of the P-type waveguide layer, and the first material is the same as that of the P-type confinement layer.

4. The semiconductor light emitting structure according to claim 1, characterized in that: The sub-wavelength grating is arranged along a first direction, and the first direction is perpendicular to the epitaxial direction and the light emitting direction of the semiconductor light emitting structure.

5. The semiconductor light emitting structure according to claim 1, characterized in that: The thickness of the refractive index modulation layer is less than 100 nm.

6. The semiconductor light emitting structure according to claim 1, characterized in that: The sub-wavelength gratings have the same length along the light emitting direction of the semiconductor light emitting structure.

7. A method for preparing a semiconductor light-emitting structure, for preparing the semiconductor light-emitting structure according to any one of claims 1 to 6, characterized in that: The following steps are involved: preparing a substrate; Performing epitaxial growth on the substrate; preparing a refractive index modulation layer on the grown epitaxial wafer; Use regrowth technology to complete the preparation of other epitaxial structures; Among them, the refractive index modulation layer is a sub-wavelength grating, the period of the sub-wavelength grating is the same, the duty cycle of the sub-wavelength grating is not completely the same, the height of the sub-wavelength grating is equal to the thickness of the refractive index modulation layer, and the groove of the sub-wavelength grating is filled with a first material, and the refractive index of the first material is different from the refractive index of the material of the sub-wavelength grating.

8. The method for preparing a semiconductor light emitting structure according to claim 7, characterized in that: During a primary epitaxial growth, a stacked N-type confinement layer, an N-type waveguide layer, an active layer, and a P-type waveguide layer are grown in sequence, wherein the thickness of the P-type waveguide layer is the sum of a preset thickness of the P-type waveguide layer and a preset thickness of the refractive index modulation layer; A sub-wavelength grating is etched on the grown P-type waveguide layer using an etching technique, wherein the height of the sub-wavelength grating is equal to the thickness of a preset refractive index modulation layer.

9. The method for preparing a semiconductor light emitting structure according to claim 8, characterized in that: During the regrowth process, the material of the P-type confinement layer can fill the grooves in the refractive index modulation layer to form a complete refractive index modulation layer.

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