Multi-junction surface emitting laser and light-emitting module

Abstract

A multi-junction surface emitting laser and a light-emitting module. The multi-junction surface emitting laser comprises: a substrate (110); and a first reflective layer (120), an active area (130), and a second reflective layer (150) which are sequentially stacked on the substrate (110). The active area (130) comprises at least two quantum well active areas (131), each quantum well active area (131) forms a PN junction or a P-I-N junction, and adjacent quantum well active areas (131) are connected by means of a tunnel junction (140). The substrate (110) is made of gallium arsenide or indium phosphide, and the substrate (110) has a crystal plane belonging to the {n11} family of crystal planes, wherein n is 0 or an integer greater than 1.

Description

Multijunction surface-emitting laser and light-emitting module

[0001] This application claims priority to Chinese Patent Application No. 202411567085.1, filed on November 5, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of semiconductor technology, for example to a multi-junction surface-emitting laser and a light-emitting module. Background Technology

[0003] Vertical-cavity surface-emitting lasers (VCSELs) have broad application prospects in optical communication, optical interconnects, and optical parallel processing. Compared with traditional edge-emitting lasers, VCSELs have advantages such as low threshold current, small size, circular symmetry for easy fiber coupling, high beam quality, single longitudinal mode, and easy integration due to their surface emission. These advantages have led to their rapid development in recent years, and they are widely used in 3D sensing (such as facial recognition), optical communication, lidar, and autonomous driving.

[0004] However, compared to edge-emitting lasers, VCSELs have two linearly orthogonal polarization states sharing the same output power. When the polarization direction changes with increasing injection current, significant distribution noise is generated. Therefore, high-power VCSELs with a single stable polarization are crucial for applications such as high-speed data transmission systems and high-power lidar systems. Current technologies for polarization control of VCSELs still have shortcomings. Summary of the Invention

[0005] This application provides a multi-junction surface-emitting laser and a light-emitting module, which improves laser gain, eliminates the need for additional grating structures, simplifies the fabrication process, and reduces fabrication costs.

[0006] In a first aspect, embodiments of this application provide a multi-junction surface-emitting laser, comprising: a substrate; a first reflective layer, an active region, and a second reflective layer sequentially stacked on the substrate; the active region includes at least two quantum well active regions, each of the quantum well active regions being formed by a P-type semiconductor and an N-type semiconductor junction, or by a P-type semiconductor, an intrinsic semiconductor, and an N-type semiconductor sequentially forming a P-type semiconductor-intrinsic semiconductor-N-type semiconductor junction, and adjacent quantum well active regions being connected by a tunnel junction; wherein the substrate is made of gallium arsenide or indium phosphide, and the crystal plane of the substrate is a {n11} family of crystal planes, where n is 0 or an integer greater than 1.

[0007] In some embodiments, the crystal planes of the substrate are a family of {nn1} crystal planes, where n is an integer greater than 1.

[0008] In some embodiments, the laser emission wavelength of the multijunction laser is in the range of 650 nm to 1600 nm.

[0009] In some embodiments, the output laser of the multi-junction surface-emitting laser is linearly polarized and has a polarization degree greater than 85%.

[0010] In some embodiments, the multijunction surface-emitting laser further includes a grating layer disposed on the surface of the second reflective layer.

[0011] In some embodiments, the grating period of the grating layer is between 0.01 micrometers and 1 micrometer, and the depth is between 10 nanometers and 200 nanometers.

[0012] In some embodiments, the grating layer material is gallium arsenide.

[0013] In some embodiments, the multijunction emitting laser further includes a metasurface structure disposed on the surface of the second reflective layer.

[0014] In some embodiments, the first reflective layer and the second reflective layer are one or any combination of distributed Bragg reflective structures, metal film reflective structures and dielectric film reflective structures.

[0015] Secondly, embodiments of this application also provide a light-emitting module, including an array of multi-junction surface-emitting lasers as described in any embodiment of this application; the light-emitting module further includes an optical element layer covering the light-emitting side of the array, the optical element layer being configured to control the direction of the light beam emitted by the multi-junction surface-emitting laser. Attached Figure Description

[0016] Figure 1 is a schematic diagram of a multi-junction surface-emitting laser provided in an embodiment of this application;

[0017] Figure 2 is a schematic diagram of another multi-junction surface-emitting laser provided in an embodiment of this application;

[0018] Figure 3 is a schematic diagram of another multi-junction surface-emitting laser provided in an embodiment of this application;

[0019] Figure 4 is a schematic diagram of the structure of a light-emitting module provided in an embodiment of this application. Detailed Implementation

[0020] The embodiments of this application will now be described with reference to the accompanying drawings. These described embodiments are some related to this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0021] Compared to edge-emitting lasers, VCSELs have two linearly orthogonal polarization states that share the same output power. When the polarization direction changes with increasing injection current, significant distribution noise is generated. Therefore, controlling the polarization of VCSELs is crucial in polarization-sensitive systems, high-speed data transmission systems with low bit error rates, and high-power lidar systems. Using a single-polarization VCSEL source can improve the signal-to-noise ratio and detection range. Related technologies introduce anisotropy in losses through the use of asymmetric device structures, such as surface grating structures. This anisotropy affects the difference in threshold carrier density between the two polarization directions of the VCSEL. Therefore, a grating structure needs to be placed on the output side of the device structure, which obviously increases the complexity of device fabrication and affects the fabrication cost.

[0022] Figure 1 is a schematic diagram of a multi-junction surface-emitting laser provided in an embodiment of this application. Referring to Figure 1, the multi-junction surface-emitting laser includes: a substrate 110; a first reflective layer 120, an active region 130, and a second reflective layer 150 sequentially stacked on the substrate 110; the active region 130 includes at least two quantum well active regions 131, each quantum well active region 131 is formed by P-type semiconductor and N-type semiconductor to form a P-type semiconductor-N-type semiconductor junction (PN junction), or is formed by P-type semiconductor, intrinsic semiconductor and N-type semiconductor sequentially to form a P-type semiconductor-intrinsic semiconductor-N-type semiconductor junction (PIN junction), and adjacent quantum well active regions 131 are connected by a tunnel junction 140; wherein, the material of the substrate 110 is gallium arsenide or indium phosphide, and the crystal plane of the substrate 110 is a {n11} crystal plane family, where n is 0 or an integer greater than 1.

[0023] For example, the VCSEL epitaxial structure from bottom to top consists of 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. The quantum well active regions 131 form a PN junction or PIN junction. A tunnel junction 140 is disposed between the PN junctions or PIN junctions, allowing charge carriers within one junction to continue flowing into the adjacent quantum well active region 131 through the tunnel junction 140, thereby continuing to generate gain. Therefore, by increasing the number of active regions 130, the luminous intensity of the laser is improved. One or more oxide confinement layers can be disposed on the surface of the quantum well active region 131 near at least one of the upper and lower structures. The unoxidized middle region of the oxide confinement layer forms an oxide hole, which serves as a channel for current and photons. The structure of the oxide hole can effectively reduce the threshold current of the VCSEL laser. The oxide confinement layer can be formed using an oxide layer containing aluminum and arsenic, such as aluminum gallium arsenic or aluminum arsenic, thereby enabling the semiconductor laser to have a good current confinement effect.

[0024] For example, in this embodiment of the application, a tunnel junction 140 is provided between two adjacent quantum well active regions 131. In some embodiments, multiple cascaded active regions 130 can be provided, with tunnel junctions 140 provided between adjacent quantum well active regions 131. Therefore, charge carriers can flow into adjacent quantum well active regions 131 through the tunnel junctions 140, thereby increasing the active gain. For example, there can be three, four, or more quantum well active regions 131, and two, three, or more corresponding tunnel junctions 140.

[0025] To reduce optical losses, the first reflective layer 120 on both sides of the active region 130 typically has a reflectivity close to 100%, making it suitable as a total internal reflection mirror for the resonant cavity. The second reflective layer 150, with relatively low reflectivity, can serve as an exit mirror for the resonant cavity. Exemplarily, the first reflective layer 120 and the second reflective layer 150 can be one or any combination of a distributed Bragg reflection structure, a metal film reflection structure, and a dielectric film reflection structure. In this embodiment, for example, the first reflective layer 120 and the second reflective layer 150 employ a distributed Bragg reflection structure. A distributed Bragg reflection structure is generally formed by alternating growth of two materials with different refractive indices and a thickness equal to one-quarter of the wavelength of light, such as alternating layers of gallium arsenide and aluminum gallium arsenide.

[0026] The overall structure of a vertical-cavity surface-emitting laser (VCSEL) is grown on a substrate 110 structure on a {n11} crystal plane family, where n is an integer of 0 or greater than 1. The substrate 110 material can be gallium arsenide or indium phosphide. The gain cavity of the VCSEL is cylindrically symmetric, and each lasing transverse mode has orthogonal double degenerate polarization modes. When these two orthogonally polarized beams are lased simultaneously, they can have the same mode gain and the same transverse distribution. In a VCSEL, due to the influence of crystal electro-optic and elasto-optic effects, when the current of the VCSEL is increased or stress is introduced, the polarization will randomly jump between 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 lased first to achieve linear polarization output, thereby controlling the polarization. Crystal orientation is usually represented by [hkl], where hkl is the Miller index, for example,

[0113] , representing the crystal orientation direction pointing to

[0113] . Crystal orientation families are usually represented by... <hkl>Indicate, for example <113> The directions represent crystal orientations pointing to

[0113] ,

[0131] , or

[0311] . Considering crystal symmetry, these crystal orientations are equivalent. Crystal planes are usually denoted by (hkl), for example, (113) represents a crystal plane with a normal to

[0113] . Crystal plane families are usually denoted by {hkl}, for example, {113} represents crystal planes with a normal to

[0113] ,

[0131] , or

[0311] . Considering crystal symmetry, these crystal planes are equivalent. For example, in the embodiments of this application, the crystal plane of the substrate 110 may include (311), (511), (011) or equivalent crystal planes, such as (113), (131), (151), (115), (101) or (110). By using a non-(001) oriented substrate 110, 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.

[0027] This application embodiment uses a first reflective layer, an active region consisting of at least two PN junctions or PIN junctions, and a second reflective layer sequentially stacked on a substrate, with the PN junctions or PIN junctions connected by a tunnel junction; wherein the substrate material is gallium arsenide or indium phosphide, the substrate crystal plane is a {n11} crystal plane family, where 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 a 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 fabrication process and reducing the fabrication cost.

[0028] In some embodiments, the crystal planes of the substrate 110 may also be a family of {nn1} crystal planes, where n is an integer greater than 1. For example, the crystal planes of the substrate 110 include (221) or equivalent crystal planes, 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 planes of the substrate 110 are a family of {n11} crystal planes, where n is 0 or an integer greater than 1, or the crystal planes of the substrate 110 are a family of {nn1} crystal planes, where n is an integer greater than 1. The slope efficiency of the multi-junction surface-emitting laser can be greater than 1.5 watts per ampere (W / A). Here, slope efficiency refers to the ratio of the laser output optical power to the pump optical power, that is, the laser gain. Slope efficiency 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 4 W / A, the emitted laser light is linearly polarized, and the degree of polarization is greater than 85%. The emitted laser 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 the emitted wavelength. Therefore, considering the resonant cavity structure and epitaxial material of the VCSEL, the emitted wavelength can be in the range of 650 nm to 1600 nm.

[0029] Figure 2 is a schematic diagram of another multi-junction surface-emitting laser provided in an embodiment of this application. Referring to Figure 2, in some embodiments, the multi-junction surface-emitting laser further includes a grating layer 210. The grating layer 210 is disposed on the surface of the second reflective layer 150. The grating layer 210 has different refractive indices for the two orthogonal polarization modes, resulting in different threshold gains for the two polarization modes, thereby achieving polarization control. The anisotropy of loss is introduced by the grating layer 210. The grating layer 210 is made of gallium arsenide and can be fabricated using techniques such as electron beam lithography, nanoimprint lithography, and holographic lithography. The grating period is between 0.01 micrometers and 1 micrometer. Different grating etching depths result in different positions of the grating in the standing wave waveform of the axial longitudinal wave. Depending on the design requirements, the etching depth can be between 10 nanometers and 200 nanometers. For example, a dielectric layer 170 may 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.

[0030] Figure 3 is a schematic diagram of another multi-junction surface-emitting laser provided in an embodiment of this application. Referring to Figure 3, in some embodiments, the multi-junction surface-emitting laser further includes a metasurface structure 310, which is disposed on the surface of the second reflective layer 150. The metasurface structure 310 is an artificially designed layered material with a thickness smaller than the wavelength of electromagnetic waves. This structure can be divided into two categories according to different in-plane forms: one type has a transverse subwavelength microstructure, and the other type is a uniform film layer. The metasurface structure 310 can effectively control the phase, polarization, and propagation mode of electromagnetic waves.

[0031] In some embodiments, referring to Figures 1 to 3, the multijunction surface-emitting laser further includes a metal contact layer 160, which may be disposed on the surface of the second reflective layer 150, the grating layer 210, or the metasurface structure 310.

[0032] This application also provides a light-emitting module, which can emit light from a point light source or an array of light sources. It is applied in fields such as display, communication and sensing. Since it includes the multi-junction surface-emitting laser of any embodiment of this application, it has the same beneficial effects.

[0033] In other embodiments, Figure 4 is a schematic diagram of a light-emitting module provided in an embodiment of this application. Referring to Figure 4, the light-emitting module 200 includes an array of multi-junction surface-emitting lasers 111 and an optical element layer 222 covering the light-emitting side of the array. The optical element layer 222 is configured to control the direction of the light beam emitted by the multi-junction surface-emitting lasers 111. For example, the optical element layer 222 may be a collimating lens array.< / hkl>

Claims

1. A multi-junction emitting laser, comprising: A substrate; a first reflective layer, an active region, and a second reflective layer are sequentially stacked on the substrate; the active region includes at least two quantum well active regions, each of the quantum well active regions being formed by a P-type semiconductor and an N-type semiconductor junction, or by a P-type semiconductor, an intrinsic semiconductor, and an N-type semiconductor sequentially forming a P-type semiconductor-intrinsic semiconductor-N-type semiconductor junction, and adjacent quantum well active regions being connected by a tunnel junction; wherein the substrate is made of gallium arsenide or indium phosphide, and the crystal plane of the substrate is a {n11} family of crystal planes, where n is 0 or an integer greater than 1.

2. The multi-junction surface-emitting laser according to claim 1, wherein, The substrate has a family of {nn1} crystal planes, where n is an integer greater than 1.

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

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

5. The multijunction surface-emitting laser according to any one of claims 1 to 2 further includes a grating layer disposed on the surface of the second reflective layer.

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

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

8. The multi-junction surface-emitting laser according to any one of claims 1 to 2 further includes a metasurface structure disposed on the surface of the second reflective layer.

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

10. A light-emitting module comprising an array of multi-junction surface-emitting lasers as described in any one of claims 1 to 9, wherein the light-emitting module further comprises an optical element layer covering the light-emitting side of the array, the optical element layer being configured to directionally control the light beam emitted by the multi-junction surface-emitting laser.

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