Multi-junction surface emitting laser and light emitting module

Abstract

The invention provides a multi-junction surface-emitting laser and a light-emitting module. A first reflecting layer, an active region and a second reflecting layer are sequentially stacked on a substrate, the active region is composed of at least two PN junctions or P-I-N junctions, and the PN junctions or the P-I-N junctions are connected through tunnel junctions; wherein the material of the substrate is gallium arsenide or indium phosphide, the crystal face of the substrate is {n11} crystal face family, n is 0 or an integer greater than 1, and anisotropic gain can be obtained in the VCSEL by using the non-(001)-oriented substrate and the quantum well, so that polarization in a quantum well plane (active region) is controlled to obtain higher gain, a grating structure does not need to be additionally arranged, the preparation process is simplified, and the preparation cost is reduced.

Description

[0001] Cross-references and priority claims

[0002] This patent application claims priority to U.S. provisional application “A multi-junction polarized VCSEL based on special substrate orientations” with provisional patent application serial number 63 / 549,933 filed on February 5, 2024, and the entire contents of the above U.S. provisional application are incorporated herein by reference. Technical Field

[0003] The embodiments of the present invention relate to the field of semiconductor technology, and in particular to a multi-junction surface emitting laser and a light-emitting module. Background Art

[0004] Vertical Cavity Surface Emitting Laser (VCSEL) has broad application prospects in the fields of optical communication, optical interconnection, optical parallel processing, etc. Compared with traditional edge-emitting lasers, VCSELs have developed rapidly in recent years due to their advantages such as low threshold current, small size, circularly symmetrical spot for easy fiber coupling, high beam quality, single longitudinal mode, and easy integration of surface emission. They are widely used in three-dimensional sensing such as face recognition, optical communication, laser radar, and unmanned driving.

[0005] However, compared with edge-emitting lasers, VCSELs have two linear orthogonal polarization states that output power together. When the polarization direction changes with the increase of the injected current, a large distribution noise will be generated. Therefore, for application scenarios such as high-speed data transmission systems and high-power lidar systems, high-power VCSELs with a single stable polarization are very important. There are still deficiencies in the polarization control of 0VCSEL in the prior art. Summary of the invention

[0006] The present invention provides a multi-junction surface emitting laser and a light-emitting module, which improve the laser gain without adding a grating structure, simplify the preparation process and reduce the preparation cost.

[0007] In a first aspect, an embodiment of the present invention provides a multi-junction surface emitting laser, comprising: a substrate; a first reflective layer, an active region consisting of at least two PN junctions or PIN junctions, and a second reflective layer stacked in sequence on the substrate; the PN junctions or PIN junctions are connected by tunnel junctions; wherein the material of the substrate is gallium arsenide or indium phosphide, the crystal plane of the substrate is the {n11} crystal plane family, and n is 0 or an integer greater than 1.

[0008] Optionally, the crystal plane of the substrate is of the {nn1} crystal plane family, where n is an integer greater than 1.

[0009] Optionally, the laser emission wavelength is in the range of 650nm to 1600nm.

[0010] Optionally, the output polarization of the laser is linearly polarized, and the polarization degree is greater than 85%.

[0011] Optionally, the multi-junction surface emitting laser further includes a grating layer, and the grating layer is arranged on the surface of the second reflective layer.

[0012] Optionally, the grating period of the grating layer is between 0.01 micrometer and 1 micrometer, and the depth is between 10 nm and 200 nm.

[0013] Optionally, the grating layer material is gallium arsenide.

[0014] Optionally, the multi-junction surface emitting laser further includes a supersurface structure, and the supersurface structure is arranged on the surface of the second reflective layer.

[0015] Optionally, the first reflection layer and the second reflection layer are one structure or any combination of a distributed Bragg reflection structure, a metal film reflection structure and a dielectric film reflection structure.

[0016] In a second aspect, an embodiment of the present invention further provides a light-emitting module, comprising the multi-junction surface emitting lasers described in any embodiment of the present invention arranged in an array.

[0017] The technical solution provided by the embodiment of the present invention comprises a first reflective layer, an active region composed of at least two PN junctions or PIN junctions, and a second reflective layer stacked in sequence on a substrate, wherein the PN junctions or the PIN junctions are connected by tunnel junctions; wherein the material of the substrate is gallium arsenide or indium phosphide, the crystal plane is of the {n11} crystal plane family, n is 0 or an integer greater than 1, and by using a non-(001) oriented substrate, the quantum well can obtain anisotropic gain in the VCSEL, thereby controlling the polarization in the quantum well plane (active region) to obtain higher gain, without the need to add a grating structure, simplifying the preparation process, and reducing the preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic structural diagram of a multi-junction surface emitting laser is provided for an embodiment of the present invention;

[0019] Figure 2 A schematic structural diagram of another multi-junction surface emitting laser is provided for an embodiment of the present invention;

[0020] Figure 3 A structural schematic diagram of another multi-junction surface emitting laser is provided for an embodiment of the present invention. DETAILED DESCRIPTION

[0021] 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Compared with edge-emitting lasers, VCSELs have two linear orthogonal polarization states that output power together. When the polarization direction changes with the increase of injected current, a large distribution noise will be generated. Therefore, it plays an important role in controlling the polarization of VCSEL in polarization-sensitive systems, high-speed data transmission systems with low bit error rates, and high-power lidar systems. The use of a single-polarization VCSEL light source can improve the signal-to-noise ratio and detection distance. In the existing technology, loss anisotropy is introduced by using an asymmetric device structure, such as a surface grating structure, and the loss anisotropy will affect the difference in threshold carrier density in the two polarization directions of the VCSEL. Therefore, a grating structure needs to be set on the output side of the device structure, which will obviously increase the complexity of device preparation and affect the device preparation cost.

[0023] In view of this, Figure 1 A schematic diagram of the structure of a multi-junction surface emitting laser is provided in an embodiment of the present invention. Figure 1 , including: a substrate 110; a first reflective layer 120, an active area 130 consisting of at least two PN junctions or PIN junctions, and a second reflective layer 150 stacked in sequence on the substrate 110; the PN junctions or PIN junctions are connected by a tunnel junction 140; wherein the material of the substrate 110 is gallium arsenide or indium phosphide, the crystal plane of the substrate 110 is {n11} crystal plane family, and n is 0 or an integer greater than 1.

[0024] Specifically, the epitaxial structure of the VCSEL from bottom to top is a substrate 110, a first reflective layer 120, an active region 130 composed of at least two PN junctions or PIN junctions, and a second reflective layer 150. The active region 130 includes at least two quantum well active regions 131 and at least one tunnel junction 140, and the quantum well active region 131 forms a PN junction or a PIN junction. A tunnel junction 140 is arranged between the PN junctions or the PIN junctions, so that the carriers in one junction continue to flow into the adjacent quantum well active region 131 through the tunnel junction 140, thereby continuing to generate gain, and thus by adding more active regions 130, the luminous intensity of the laser is increased. Among them, one or more layers of oxidation restriction layers (not shown in the figure) can be arranged at the surface position of the quantum well active region 131 close to the upper structure and / or the lower structure, and oxidation holes are formed in the unoxidized middle region of the oxidation restriction layer. The oxidation holes serve as channels for current and photons, and the structure of the oxidation holes can effectively reduce the threshold current of the VCSEL laser. The oxide limiting layer can be formed by an oxide layer containing aluminum and arsenic materials, such as aluminum gallium arsenic, aluminum cadmium arsenic, and aluminum arsenic, so that the semiconductor laser has a good current limiting effect.

[0025] Exemplarily, in the embodiment of the present invention, a tunnel junction 140 is provided between two adjacent quantum well active regions 131. In some embodiments, multiple cascaded active regions 130 may be provided, and tunnel junctions 140 are provided between adjacent quantum well active regions 131, so that carriers can flow into the adjacent quantum well active regions 131 through the tunnel junctions 140, thereby increasing more active gain. For example, the quantum well active regions 131 may be three, four or more, and the corresponding tunnel junctions 140 may be two, three or more.

[0026] Usually, in order to reduce optical loss, the reflectivity of the first reflective layer 120 of the first reflective layer 120 and the second reflective layer 150 on both sides of the active region 130 is close to 100%, and can be used as a total reflector of the resonant cavity, while the reflectivity of the second reflective layer 150 is relatively low, and can be used as an exit mirror of the resonant cavity. Exemplarily, the first reflective layer 120 and the second reflective layer 150 are one of a distributed Bragg reflection structure, a metal film reflection structure, and a dielectric film reflection structure, or any combination of structures. In the embodiment of the present invention, exemplarily, the first reflective layer 120 and the second reflective layer 150 adopt a distributed Bragg reflection structure, and the distributed Bragg reflection structure is generally formed by alternating the growth of two materials with different refractive indices and a thickness of one quarter of the wavelength of light, for example, by alternating gallium arsenide material layers and gallium aluminum arsenide material layers.

[0027] The overall structure of the vertical cavity surface emitting laser is grown on a substrate 110 structure on the {n11} crystal plane family, where n is 0 or an integer greater than 1, and the substrate 110 material can be gallium arsenide or indium phosphide. The gain cavity of the vertical cavity surface emitting laser is cylindrically symmetric, and each lasing transverse mode has an orthogonal dual degenerate polarization mode. When these two orthogonal polarized lights are simultaneously lased, they can have the same mode gain and the same lateral distribution. In VCSEL, due to the influence of the crystal electro-optic effect and the elasto-optic effect, when the VCSEL increases the current or introduces stress, the polarization will randomly jump between the two polarization directions. When the threshold gain of one polarization is lower than that of the other polarization in its orthogonal direction, the polarization in this direction is first lased to achieve linear deflection, thereby playing a role in controlling the polarization. Among them, the crystal direction is usually represented by [hkl], where hkl is the Miller index, for example

[113] , which represents the crystal direction pointing to

[113] . The crystal direction family is usually represented by <hkl>Indicates, for example <113> Represents a crystal direction pointing to

[113] or

[131] or

[311] . Considering the crystal symmetry, these crystal directions are equivalent. A crystal plane is usually represented by (hkl), for example, (113) represents a crystal plane with a normal direction of

[113] . A crystal plane family is usually represented by {hkl}, for example, {113} represents a crystal plane with a normal direction of

[113] or

[131] or

[311] . Considering the crystal symmetry, these crystal planes are equivalent. Exemplarily, the crystal planes of the substrate 110 in the embodiment of the present invention may include (311), (511), (011) or equivalent crystal planes, such as (113), (131), (151), (115), (101) or (110). By using a substrate 110 that is not (001) oriented, the quantum well can obtain anisotropic gain in the VCSEL, thereby controlling the polarization in the quantum well plane (active region) and obtaining high gain.

[0028] The technical solution provided by the embodiment of the present invention comprises a first reflective layer, an active region composed of at least two PN junctions or PIN junctions, and a second reflective layer stacked in sequence on a substrate, wherein the PN junctions or the PIN junctions are connected by tunnel junctions; wherein the material of the substrate is gallium arsenide or indium phosphide, the crystal plane is of the {n11} crystal plane family, n is 0 or an integer greater than 1, and by using a non-(001) oriented substrate, the quantum well can obtain anisotropic gain in the VCSEL, thereby controlling the polarization in the quantum well plane (active region) to obtain higher gain, without the need to add a grating structure, simplifying the preparation process, and reducing the preparation cost.

[0029] In some embodiments, the crystal plane of the substrate 110 can also be a {nn1} crystal plane family, where n is an integer greater than 1. For example, the crystal plane of the substrate 110 includes (221) or an equivalent crystal plane, such as (122) or (212). Based on the above embodiments, the multi-junction surface emitting laser includes an active region 130 composed of at least two PN junctions or PIN junctions, and the junctions are connected by a tunnel junction 140. The crystal plane of the substrate 110 is a {n11} crystal plane family, where n is 0 or an integer greater than 1, or the crystal plane of the substrate 110 is a {nn1} crystal plane family, where n is an integer greater than 1. The slope efficiency of the multi-junction surface emitting laser can be greater than 1.5W / A. Among them, the slope efficiency refers to the ratio of the laser output optical power to the pump optical power, that is, the gain of the laser. It can reflect the electro-optical conversion efficiency and optical performance of the laser. When the number of PN junctions or PIN junctions in the active region 130 is at least 5 and the total number of tunnel junctions 140 is at least 4, the slope efficiency of the multi-junction surface emitting laser can be greater than 4W / A, the output polarization of the laser is linearly polarized, and the polarization degree is greater than 85%. The laser emission wavelength of the multi-junction surface emitting laser is usually related to the optical thickness of the resonant cavity formed by the first reflective layer 120 and the second reflective layer 150, and the optical thickness of the resonant cavity is usually an integer multiple of half of the emission wavelength. Therefore, considering the resonant cavity structure and epitaxial material of the VCSEL, the emission wavelength can be in the range of 650nm-1600nm.

[0030] Figure 2 A schematic diagram of a multi-junction surface emitting laser is provided for an embodiment of the present invention. Figure 2 In some embodiments, the multi-junction surface emitting laser further includes a grating layer 210, which is disposed on the surface of the second reflective layer 150. The grating layer 210 has different refractive indices for two orthogonal polarization modes, thereby causing different threshold gains for the two polarization modes, thereby further realizing polarization control, and introducing loss anisotropy using the grating layer 210. The grating layer 210 is made of gallium arsenide, and the grating layer 210 can be prepared by techniques such as electron beam exposure, nanoimprinting, and holographic lithography. The grating period is between 0.01 microns and 1 micron. Different grating etching depths will also cause different positions of the grating in the standing wave waveform of the axial longitudinal wave. According to design requirements, the etching depth can be between 10nm and 200nm. Exemplarily, a dielectric layer 170 can be disposed between the grating layer 210 and the metal contact layer 160. The dielectric layer 170 can protect the grating layer 210 and provide electrical connection between the metal contact layer 160 and the underlying structure.

[0031] Figure 3 A schematic diagram of a multi-junction surface emitting laser is provided for an embodiment of the present invention. Figure 3 In some embodiments, the multi-junction surface emitting laser further includes a metasurface structure 310, and the metasurface structure 310 is disposed on the surface of the second reflective layer 150. The metasurface structure 310 is an artificially designed layered material, the thickness of which is less than the wavelength of the electromagnetic wave. This structure can be divided into two categories according to different forms within the plane: one has a lateral subwavelength microstructure, and the other is a uniform film layer. The metasurface structure 310 can effectively regulate the phase, polarization mode, propagation mode and other characteristics of the electromagnetic wave.

[0032] An embodiment of the present invention further provides a light-emitting module, wherein the light-emitting module can emit a point light source or an array light source, and is applied to fields such as display, communication, and sensing. Since it includes the multi-junction surface emitting laser of any embodiment of the present invention, it has the same beneficial effects and will not be repeated here.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.< / hkl>

Claims

1. A multi-junction surface emitting laser, characterized in that: include: A substrate; a first reflective layer, an active region consisting of at least two PN junctions or PIN junctions, and a second reflective layer stacked in sequence on the substrate; the PN junctions or PIN junctions are connected by tunnel junctions; wherein the material of the substrate is gallium arsenide or indium phosphide, the crystal plane of the substrate is {n11} crystal plane family, and n is 0 or an integer greater than 1.

2. The multi-junction surface emitting laser according to claim 1, characterized in that The crystal plane of the substrate belongs to the {nn1} crystal plane family, where n is an integer greater than 1.

3. The multi-junction surface emitting laser according to any one of claims 1 to 2, characterized in that: The laser emission wavelength is in the range of 650nm to 1600nm.

4. The multi-junction surface emitting laser according to any one of claims 1 to 2, characterized in that: The output polarization of the laser is linearly polarized, and the polarization degree is greater than 85%.

5. The multi-junction surface emitting laser according to any one of claims 1 to 2, characterized in that: It also includes a grating layer, which is arranged on the surface of the second reflective layer.

6. The multi-junction surface emitting laser according to claim 5, characterized in that The grating period of the grating layer is between 0.01 micrometer and 1 micrometer, and the depth is between 10nm and 200nm.

7. The multi-junction surface emitting laser according to claim 6, characterized in that The grating layer material is gallium arsenide.

8. The multi-junction surface emitting laser according to any one of claims 1 to 2, characterized in that: It also includes a super surface structure, and the super surface structure is arranged on the surface of the second reflective layer.

9. The multi-junction surface emitting laser according to any one of claims 1 to 2, characterized in that: The first reflection layer and the second reflection layer are one structure or any combination of distributed Bragg reflection structures, metal film reflection structures and dielectric film reflection structures.

10. A light emitting module, characterized in that: A multi-junction surface emitting laser according to any one of claims 1 to 9 arranged in an array.

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