Semiconductor laser structure and preparation method thereof

Abstract

The invention relates to the technical field of lasers, in particular to a semiconductor laser structure and a preparation method thereof, and the semiconductor laser structure comprises a substrate and an N-type DBR layer which are stacked in sequence; the step structure is located on the surface, away from the substrate, of the N-type DBR layer, and the step structure comprises an active layer, an oxide layer, a P-type DBR layer and a P-type electrode which are sequentially stacked in the direction away from the N-type DBR layer; and the N-type electrode is located on the surface, away from the substrate, of the N-type DBR layer, the N-type electrode comprises a first N-type electrode part and a second N-type electrode part which are independent from each other, and the first N-type electrode part and the second N-type electrode part are located on the two opposite sides of the step structure respectively. The invention is at least beneficial to enabling the semiconductor laser to output single-line polarized light.

Description

Technical Field

[0001] The present invention belongs to the technical field of lasers, and particularly relates to a semiconductor laser structure and a preparation method thereof. Background Art

[0002] With the development of the information society, higher requirements are put forward for the mode characteristics and polarization of the laser output by VCSELs (Vertical Cavity Surface Emitting Lasers) in fields such as micro quantum sensing systems, optical communications, and even artificial intelligence. Since the traditional VCSEL structure is mainly a columnar symmetric waveguide structure, its linearly polarized direction often jumps between two perpendicular directions, which hinders the application of VCSEL devices in micro quantum sensing systems; the aperture size required for the single-mode output of traditional VCSELs needs to be controlled within 3 μm, which is difficult in the process and limits the laser power level of VCSELs. For VCSELs, how to achieve high power and single-mode single-polarization output under a large light-emitting aperture has become an urgent problem to be solved. Summary of the Invention

[0003] In view of this, the present invention aims to provide a semiconductor laser structure and a preparation method thereof.

[0004] To achieve the above object, the technical solution of the present invention is realized as follows:

[0005] On the one hand, the present invention provides a semiconductor laser structure, including: a substrate and an N-type DBR layer stacked in sequence; a step structure located on the surface of the N-type DBR layer away from the substrate, the step structure including an active layer, an oxide layer, a P-type DBR layer, and a P-type electrode stacked in sequence along the direction away from the N-type DBR layer; an N-type electrode located on the surface of the N-type DBR layer away from the substrate, the N-type electrode including independent first and second N-type electrode portions, and the first and second N-type electrode portions are respectively located on opposite sides of the step structure.

[0006] Further, there is a spacing distance between the N-type electrode and the step structure.

[0007] Further, the orthographic projection of the step structure on the surface of the N-type DBR layer is elliptical, and the first and second N-type electrode portions are arranged on opposite sides of the step structure along the extension direction of the long axis of the ellipse; or, the orthographic projection of the step structure on the surface of the N-type DBR layer is rhombic, and the first and second N-type electrode portions are arranged on opposite sides of the step structure along the extension direction of the long diagonal of the rhombus.

[0008] Further, the shape of the first N-type electrode portion is the same as that of the second N-type electrode portion, and the first N-type electrode portion and the second N-type electrode portion are symmetrically distributed on opposite sides of the step structure.

[0009] Further, the orthographic projection of the first N-type electrode portion or the second N-type electrode portion on the surface of the N-type DBR layer is rectangular, trapezoidal or triangular.

[0010] Further, the oxide layer has oxidation holes, the surface of the P-type DBR layer away from the oxide layer has an annular groove, the center of the annular groove is directly opposite to the center of the oxidation hole, and the P-type electrode is located in the annular groove.

[0011] Further, the orthographic projection of the inner circle of the annular groove on the substrate surface is located within the orthographic projection of the oxidation hole on the substrate surface.

[0012] Further, it further includes: a photonic crystal structure, and the photonic crystal structure extends from the P-type electrode in the annular groove to the P-type DBR layer.

[0013] On the other hand, the present invention provides a method for manufacturing a semiconductor laser structure, including: forming a substrate and an N-type DBR layer stacked in sequence; forming a step structure, the step structure is located on the surface of the N-type DBR layer away from the substrate, and the step structure includes an active layer, an oxide layer, a P-type DBR layer and a P-type electrode stacked in sequence along the direction away from the N-type DBR layer; forming an N-type electrode, the N-type electrode is located on the surface of the N-type DBR layer away from the substrate, and the N-type electrode includes independent first and second N-type electrode portions, and the first and second N-type electrode portions are respectively located on opposite sides of the step structure.

[0014] Compared with the prior art, the present invention can achieve the following beneficial effects: The semiconductor laser structure provided by the present invention can achieve stable single-mode and single-polarization operation. In the semiconductor laser structure, there are a structure with mode filtering and a structure with polarization selection, which are used to regulate the beam quality of the semiconductor laser structure. For mode filtering, it is mainly achieved through the photonic crystal structure and the P-type electrode arranged in the annular groove. For polarization selection, it is mainly achieved by designing the N-type electrode, and the first and second N-type electrode portions are respectively arranged on both sides of the step structure to guide asymmetric gain, thereby realizing polarization selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0016] Figure 1 is a schematic structural diagram of a semiconductor laser structure according to an embodiment of the present invention;

[0017] Figure 2 A cross-sectional view of a semiconductor laser structure according to an embodiment of the present invention;

[0018] Figure 3 A top view of a semiconductor laser structure according to an embodiment of the present invention;

[0019] Figure 4 Another top view of a semiconductor laser structure according to an embodiment of the present invention;

[0020] Figure 5 Another top view of a semiconductor laser structure according to an embodiment of the present invention;

[0021] Figure 6 Another top view of a semiconductor laser structure according to an embodiment of the present invention. Detailed implementation manners

[0022] Through analysis, it is found that currently, in order to solve the polarization selection problem, generally, it is considered to form an asymmetric intracavity reflectivity or gain through an asymmetric oxidation hole to achieve polarization selection in a certain direction. However, the controllability of the etching process and oxidation process for forming the oxidation hole is poor. Therefore, it is very easy to affect the effect of polarization selection, and the process repeatability is poor; another method is to introduce a stress layer in the active region and use the birefringence effect to achieve polarization control. However, the design and process implementation of the stress layer are relatively difficult, and its effect will also change with temperature, and the stability is poor.

[0023] To solve the above problems, the present invention provides a semiconductor laser structure. By providing a first N-type electrode portion and a second N-type electrode portion on the N-type DBR (distributed Bragg reflector) layer to generate asymmetric gain, the polarization control of the VCSEL is realized. Moreover, the first N-type electrode portion and the second N-type electrode portion can be easily realized by using the Lift-off process. At the same time, a higher polarization selection ratio can also be achieved. Combining with the photonic crystal structure and the P-type electrode arranged in the annular groove can realize single-mode output under a large oxidation aperture, which greatly optimizes the beam quality.

[0024] In order to make the purpose, technical solution and advantages of the present invention clearer, the following further details the present invention in combination with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention.

[0025] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0026] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying 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 construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0027] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may 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 through specific circumstances.

[0028] The present invention will be described in detail below with reference to the drawings and in conjunction with embodiments.

[0029] Reference Figures 1 to 6 , on the one hand, the present invention provides a semiconductor laser structure, including: a substrate 10 and an N-type DBR layer 11 stacked in sequence; a step structure, the step structure is located on the surface of the N-type DBR layer 11 away from the substrate 10, and the step structure includes an active layer 12, an oxide layer 13, a P-type DBR layer 14, and a P-type electrode 16 stacked in sequence along the direction away from the N-type DBR layer 11. The orthographic projection of the step structure on the surface of the substrate 10 is located within the orthographic projection of the N-type DBR layer 11 on the surface of the substrate 10; an N-type electrode, the N-type electrode is located on the surface of the N-type DBR layer 11 away from the substrate 10, and the N-type electrode includes independent first N-type electrode portions 18 and second N-type electrode portions 19, and the first N-type electrode portions 18 and the second N-type electrode portions 19 are respectively located on opposite sides of the step structure.

[0030] It should be noted that the semiconductor laser structure provided by the present invention is a VCSEL.

[0031] The present invention realizes gain selection in a certain direction and further controls the polarization direction by combining the first N-type electrode part 18 and the second N-type electrode part 19 provided on the N-type DBR layer 11 with the P-type electrode 16 closer to the center of the top surface of the step structure.

[0032] For the selection of the polarization direction, in some embodiments, taking the active layer 12 using a GaAs and AlGaAs material system or an InGaAs material system as an example, since the crystal structure of the active region material is anisotropic and the polarization direction is related to the crystal orientation of the material, if a symmetric cavity structure is adopted and no polarization control is designed, the polarization direction may randomly distribute along the

[011] crystal orientation,

[110] crystal orientation or other crystal orientations of the crystal. The present invention designs the N-type electrode as the first N-type electrode part 18 and the second N-type electrode part 19 that are not completely opposite to the P-type electrode 16, so as to generate non-directional symmetric gain, and guide the polarization direction to exist alone in the

[011] crystal orientation,

[110] crystal orientation or other certain crystal orientations of the material, thereby realizing the selection of the polarization direction. Specifically, any crystal orientation among the multiple crystal orientations of the active region material can be selected as the polarization direction, and then the arrangement directions of the first N-type electrode part 18 and the second N-type electrode part 19 are determined according to the selected crystal orientation. Through the guiding effect of the electrode on the current, the current flows along the selected crystal orientation, and gain is achieved in the selected crystal orientation, thereby realizing the control of the polarization direction.

[0033] That is to say, the arrangement directions of the first N-type electrode part 18 and the second N-type electrode part 19 correspond to: any crystal orientation selected as the polarization direction among the multiple crystal orientations of the active layer 12 material. It should be noted that in some other embodiments, it is not limited to selecting the polarization direction based on the crystal orientation, and any direction can also be selected as the polarization direction, and then the first N-type electrode part 18 and the second N-type electrode part 19 are arranged based on the selected polarization direction.

[0034] In addition, the N-type electrode in the present invention is located on the surface of the N-type DBR layer 11 away from the substrate 10, which is beneficial to shortening the current flow path, thereby reducing the series resistance of the device, and further facilitating the realization of higher-efficiency lasing.

[0035] In some embodiments, the semiconductor laser structure further includes an insulating layer 15. The insulating layer 15 is located on the side surface of the step structure, the top surface of the step structure outside the P-type electrode 16, and the top surface of the N-type DBR layer 11 away from the substrate 10 outside the N-type electrode. The inner circle of the annular groove serves as the light output hole 17. Therefore, the top surface of the P-type DBR layer 14 exposed by the light output hole 17 also does not have the insulating layer 15.

[0036] In some embodiments, there is a spacing distance between the N-type electrode and the step structure.

[0037] In some embodiments, the orthographic projection of the stepped structure on the surface of the N-type DBR layer 11 is circular, elliptical, rectangular, rhombic or other shapes.

[0038] In some embodiments, the orthographic projection of the stepped structure on the surface of the N-type DBR layer 11 is elliptical, and the first N-type electrode portion 18 and the second N-type electrode portion 19 are arranged on opposite sides of the stepped structure along the extending direction of the major axis of the ellipse; alternatively, the orthographic projection of the stepped structure on the surface of the N-type DBR layer 11 is rhombic, and the first N-type electrode portion 18 and the second N-type electrode portion 19 are arranged on opposite sides of the stepped structure along the extending direction of the long diagonal of the rhombus. The advantage of such an arrangement is that: for the elliptical stepped structure, its shape itself has a certain gain for the polarization direction. Generally, the extending direction of the major axis of the ellipse has a gain. On this basis, arranging the first N-type electrode portion 18 and the second N-type electrode portion 19 along the extending direction of the major axis is beneficial to further increasing the gain in the polarization direction. For the rhombic stepped structure, similarly, the extending direction of its long diagonal has a gain. On this basis, arranging the first N-type electrode portion 18 and the second N-type electrode portion 19 along the extending direction of the long diagonal is beneficial to further increasing the gain in the polarization direction.

[0039] In some embodiments, the shape of the first N-type electrode portion 18 is the same as the shape of the second N-type electrode portion 19, and the first N-type electrode portion 18 and the second N-type electrode portion 19 are symmetrically distributed on opposite sides of the stepped structure.

[0040] In some embodiments, the orthographic projection of the first N-type electrode portion 18 or the second N-type electrode portion 19 on the surface of the N-type DBR layer 11 is rectangular, trapezoidal or triangular.

[0041] In some embodiments, the oxide layer 13 has oxide holes 21, the surface of the P-type DBR layer 14 away from the oxide layer 13 has an annular groove, and the center of the annular groove is aligned with the center of the oxide hole 21. The P-type electrode 16 is located in the annular groove. It should be noted that the shape of the annular groove provided by the present invention may include, but is not limited to, a circular ring shape. The shape of the annular groove may also be a square shape, or the annular groove may be a groove of other shapes surrounding the center of the top surface of the stepped structure.

[0042] In some embodiments, the orthographic projection of the inner circle of the annular groove on the surface of the substrate 10 is located within the orthographic projection of the oxide hole 21 on the surface of the substrate 10. That is to say, the size of the light-emitting hole is larger than the size of the oxide hole.

[0043] In some examples, the aperture diameter of the oxide hole is in the range of 4 μm to 8 μm.

[0044] In some embodiments, the semiconductor laser structure further includes: a photonic crystal structure 20 that extends from the P-type electrode 16 within the annular groove towards the P-type DBR layer 14.

[0045] In some embodiments, the material system of the semiconductor laser structure provided by the present invention includes, but is not limited to, GaAs, GaN, InP, etc.

[0046] On the other hand, the present invention provides a method for manufacturing a semiconductor laser structure for manufacturing the semiconductor laser structure provided in the above embodiments. The method for manufacturing the semiconductor laser structure includes: forming a substrate 10 and an N-type DBR layer 11 stacked in sequence; forming a step structure on the surface of the N-type DBR layer 11 away from the substrate 10. The step structure includes an active layer 12, an oxidation layer 13, a P-type DBR layer 14, and a P-type electrode 16 stacked in sequence along the direction away from the N-type DBR layer 11; forming an N-type electrode on the surface of the N-type DBR layer 11 away from the substrate 10. The N-type electrode includes independent first and second N-type electrode portions 18 and 19, and the first and second N-type electrode portions 18 and 19 are respectively located on opposite sides of the step structure.

[0047] In some embodiments, the method for manufacturing the semiconductor laser structure is specifically as follows: GaAs is used as the material of the substrate 10, and N-type doped AlGaAs with different compositions is alternately grown on the substrate 10 by plasma-enhanced chemical vapor deposition to form the N-type DBR layer 11. Then, an initial active layer and an initial oxidation layer are grown. The material of the initial oxidation layer can be AlAs. Then, P-type doped AlGaAs with different compositions is alternately grown on the initial oxidation layer as the initial P-type DBR layer. The initial active layer, the initial oxidation layer, and the initial P-type DBR layer are patterned by photolithography and etching processes to form a step structure. After forming the step structure, side oxidation is performed to form an oxidation layer 13 with oxidation holes 21; an annular groove is prepared on the top surface of the step structure by photolithography and etching processes. The inner ring of the annular groove corresponds to the light-emitting hole 17. A P-type electrode 16 is evaporated in the annular groove, and an N-type electrode is evaporated on the surface of the part of the N-type DBR layer 11 outside the step structure.

[0048] In some embodiments, the method for manufacturing the semiconductor laser structure further includes forming an insulating layer 15. The insulating layer 15 is located on the side surface of the step structure, the top surface of the step structure outside the P-type electrode 16, and the top surface of the N-type DBR layer 11 away from the substrate 10 outside the N-type electrode. The inner ring of the annular groove serves as the light-emitting hole 17. Therefore, the top surface of the exposed part of the P-type DBR layer 14 of the light-emitting hole 17 also does not have the insulating layer 15.

[0049] For the semiconductor laser structure provided by the present invention, since the fundamental mode is mainly distributed in the central region of the stepped structure, when the high-order mode laser around the central region reaches the annular groove, due to the reflectivity loss caused by the etching of the annular groove plus the absorption and scattering losses of the P-type electrode 16, the excitation threshold of the high-order mode will be greatly increased, achieving the mode filtering effect. Thus, while filtering out the high-order mode, it does not affect the stable output of the single-mode laser in the central region of the stepped structure. At the same time, the P-type electrode 16 is closer to the center of the stepped structure than the traditional structure. Therefore, the intracavity current path can greatly improve the carrier distribution in the active layer 12. Coupled with the guidance of the N-type electrode, the current only flows in a single direction. Figure 1 The green arrow in Figure 1 shows the current flow direction between the first N-type electrode portion 18 and the P-type electrode 16. The single flow direction of the current can obtain effective gain in this direction, realizing polarization direction control.

[0050] In some embodiments, in the manufacturing method of the semiconductor laser structure, after forming the annular groove and before forming the P-type electrode 16, it further includes: forming a plurality of pores by using a photolithography process and an etching process. The pores are arranged in an array, and each pore extends from the annular groove to the P-type DBR layer 14. During the subsequent formation of the P-type electrode 16, the material of the P-type electrode 16 is also formed in the pores to form a photonic crystal structure 20. The photonic crystal structure 20 can greatly increase the loss of the high-order mode and improve the single-mode performance. The P-type electrode 16 extends into the P-type DBR layer 14 through the photonic crystal structure 20, which can also reduce the series resistance of current transmission. The N-type electrode cooperates with the P-type electrode 16 closer to the light output hole 17, which can not only improve the carrier distribution in the active layer 12 but also guide the asymmetric gain to achieve free control of the linear polarization direction.

[0051] In the semiconductor laser structure provided by the above embodiments, forming the P-type electrode 16 in the annular groove and adopting the photonic crystal structure 20 can enhance the loss of the high-order mode, so that the high-order mode cannot be output together with the fundamental mode, which is conducive to enabling the VCSEL to output a single fundamental mode laser with high stability. In addition, the N-type electrode is located on the N-type DBR layer 11 and includes a first N-type electrode portion 18 and a second N-type electrode portion 19, which is conducive to promoting the current flow direction in the laser cavity to be a single direction, greatly reducing the gain in the vertical direction, thereby realizing single linear polarization output. In addition, the manufacturing process of the semiconductor laser structure is simple, the process stability is high, and the repeatability is strong.

[0052] It should be understood that various forms of the processes shown above can be used, reordering, adding or deleting steps. For example, the steps recorded in the disclosure of the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present invention can be achieved. This is not limited herein.

[0053] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A semiconductor laser structure, characterized in that: include: A substrate and an N-type DBR layer are stacked in sequence; A step structure, the step structure is located on a surface of the N-type DBR layer away from the substrate, the step structure comprising an active layer, an oxide layer, a P-type DBR layer and a P-type electrode stacked in sequence in a direction away from the N-type DBR layer; An N-type electrode is located on a surface of the N-type DBR layer away from the substrate, and includes a first N-type electrode portion and a second N-type electrode portion that are independent of each other, and the first N-type electrode portion and the second N-type electrode portion are respectively located on opposite sides of the step structure.

2. The semiconductor laser structure according to claim 1, characterized in that: There is a spacing distance between the N-type electrode and the step structure.

3. The semiconductor laser structure according to claim 1, characterized in that: The orthographic projection of the step structure on the surface of the N-type DBR layer is an ellipse, and the first N-type electrode portion and the second N-type electrode portion are arranged on opposite sides of the step structure along the extension direction of the major axis of the ellipse; Alternatively, the orthographic projection of the step structure on the surface of the N-type DBR layer is a rhombus, and the first N-type electrode portion and the second N-type electrode portion are arranged on opposite sides of the step structure along the extension direction of the long diagonal line of the rhombus.

4. The semiconductor laser structure according to claim 1, characterized in that: The first N-type electrode portion has the same shape as the second N-type electrode portion, and the first N-type electrode portion and the second N-type electrode portion are symmetrically distributed on opposite sides of the step structure.

5. The semiconductor laser structure according to claim 4, characterized in that: The orthographic projection of the first N-type electrode portion or the second N-type electrode portion on the surface of the N-type DBR layer is rectangular, trapezoidal or triangular.

6. The semiconductor laser structure according to claim 1, characterized in that: The oxide layer has an oxide hole, the surface of the P-type DBR layer away from the oxide layer has an annular groove, the center of the annular groove is opposite to the center of the oxide hole, and the P-type electrode is located in the annular groove.

7. The semiconductor laser structure according to claim 6, characterized in that: The orthographic projection of the inner circle of the annular groove on the substrate surface is located within the orthographic projection of the oxidation hole on the substrate surface.

8. The semiconductor laser structure according to claim 6, characterized in that: Also includes: A photonic crystal structure extends from the P-type electrode in the annular groove to the P-type DBR layer.

9. A method for preparing a semiconductor laser structure, characterized in that: include: forming a substrate and an N-type DBR layer stacked in sequence; Forming a step structure, the step structure is located on a surface of the N-type DBR layer away from the substrate, the step structure comprising an active layer, an oxide layer, a P-type DBR layer and a P-type electrode stacked in sequence in a direction away from the N-type DBR layer; An N-type electrode is formed, the N-type electrode is located on the surface of the N-type DBR layer away from the substrate, the N-type electrode includes a first N-type electrode portion and a second N-type electrode portion that are independent of each other, the first N-type electrode portion and the second N-type electrode portion are respectively located on opposite sides of the step structure.

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