Multi-junction VCSEL device, VCSEL chip, lidar system and its light source

Abstract

Embodiments of the present application relate to a multi-junction VCSEL device, a VCSEL chip, a lidar system and a light source thereof. The multi-junction VCSEL device includes: a substrate; a bottom mirror structure and a top mirror structure stacked on the substrate; the bottom mirror structure and the top mirror structure define a resonant cavity structure for generating a standing wave; the resonant cavity structure includes a plurality of active regions and a plurality of optical confinement layers, each optical confinement layer is respectively located on the side of the corresponding active region away from the substrate, and the optical confinement layer is located at the trough of the standing wave, and the optical confinement layer is used to define the light-emitting region of the multi-junction VCSEL device; a plurality of optical field modulation layers, the optical field modulation layers are arranged adjacent to the optical confinement layers, and the optical field modulation layers are configured to divide the optical field in the resonant cavity structure into at least three segments, and the intensity of each segment of the optical field is different.

Description

Technical Field

[0001] The present application relates to the field of laser technology, and particularly to a multi-junction VCSEL device, a VCSEL chip, a lidar system, and a light source thereof. Background Art

[0002] With the continuous development of semiconductor technology, vertical-cavity surface-emitting lasers (VCSELs) have been widely used in fields such as optical communication, optical interconnection, and optical sensing due to their easy integration characteristics. The main application scenario in the field of optical sensing is lidar. High-power VCSEL devices are the main technical direction for future applications in lidar. High-power VCSELs usually require cascading multiple active layers to achieve. However, currently, the confinement factor of the oxide layer in multi-junction VCSEL devices with cascaded multiple active layers is relatively high, resulting in a large emission angle of the multi-junction VCSEL device, which limits the usage scenarios of the multi-junction VCSEL device. Summary of the Invention

[0003] Based on this, it is necessary to provide a multi-junction VCSEL device, a VCSEL chip, a lidar system, and a light source thereof for the problem of the large divergence angle of the multi-junction VCSEL device in the prior art.

[0004] In a first aspect, the present application provides a multi-junction VCSEL device, comprising:

[0005] A substrate;

[0006] A bottom mirror structure and a top mirror structure stacked on the substrate; the bottom mirror structure and the top mirror structure define a resonant cavity structure for generating a standing wave;

[0007] The resonant cavity structure includes a plurality of active regions and a plurality of optical confinement layers. Each of the optical confinement layers is located on the side of the corresponding active region away from the substrate, and the optical confinement layer is located at the trough of the standing wave. The optical confinement layer is used to define the light-emitting region of the multi-junction VCSEL device;

[0008] A plurality of optical field modulation layers, which are arranged adjacent to the optical confinement layer. The optical field modulation layer is configured to divide the optical field in the resonant cavity structure into at least three segments, and the intensity of each segment of the optical field is different.

[0009] In one embodiment, the optical field modulation layer includes a photonic crystal structure or a periodically stacked first DBR structure.

[0010] In one embodiment, the bottom mirror structure and the top mirror structure respectively include a periodically stacked second DBR structure;

[0011] Among them, the refractive index of the high refractive index film layer in the first DBR structure is higher than that of the high refractive index film layer in the second DBR structure.

[0012] In one embodiment, the active region includes at least one multi-quantum well structure, and the refractive index of the optical confinement layer is lower than that of the multi-quantum well structure closest to the optical field modulation layer in the active region and lower than that of the low refractive index film layer in the first DBR structure.

[0013] In one embodiment, when the optical field modulation layer includes a periodically stacked first DBR structure, the periodically stacked first DBR structure is composed of Al x Ga （1-x） As / Al y Ga （1-y） As alternately, and the number of stacking periods is between 3 pairs and 10 pairs, 0≤x<y≤1.

[0014] In one embodiment, at least one of the side of the optical confinement layer close to the substrate and the side far from the substrate is provided with the optical field modulation layer.

[0015] In one embodiment, when the optical field modulation layer is located on the side of the optical confinement layer far from the substrate, a tunnel junction layer is further provided between the optical field modulation layer and the optical confinement layer.

[0016] In one embodiment, when one optical field modulation layer is provided on each side of the optical confinement layer, one of the optical field modulation layers located on the side of the optical confinement layer close to the substrate and the side far from the substrate includes a photonic crystal structure, and the other optical field modulation layer includes a periodically stacked first DBR structure.

[0017] In one embodiment, the resonant cavity structure includes three active regions and three optical confinement layers; the three active regions include a first active region, a second active region, and a third active region arranged in sequence along the direction away from the substrate, and the two optical confinement layers include a first optical confinement layer, a second optical confinement layer, and a third optical confinement layer;

[0018] The first optical confinement layer is located between the first active region and the second active region, the second optical confinement layer is located between the second active region and the third active region, and the third optical confinement layer is located on the side of the third active region close to the top mirror structure.

[0019] In one embodiment, the first active region includes three multi-quantum well structures, the second active region includes two multi-quantum wells, and the third active region includes two multi-quantum well structures; and adjacent multi-quantum well structures within each active region are connected by a tunnel junction layer.

[0020] In one embodiment, the multi-junction VCSEL device includes two optical field modulation layers. Among them, the first optical field modulation layer is disposed between the first active region and the first optical confinement layer, and the second optical field modulation layer is disposed between the second active region and the second optical confinement layer.

[0021] In one embodiment, the optical confinement layer includes any one of an air column type optical confinement layer, an oxidation confinement type optical confinement layer, an ion implantation type optical confinement layer, and a tunnel junction type optical confinement layer.

[0022] In one embodiment, the oxidation confinement type optical confinement layer includes an unoxidized region made of AlGaAs material with a high Al component and an oxidized region made of alumina material. The oxidized region is disposed outside the unoxidized region, and the unoxidized region forms a light-emitting region for effective current injection.

[0023] In one embodiment, the tunnel junction type optical confinement layer includes at least one highly doped N-type structure layer and at least one highly doped P-type structure layer.

[0024] In one embodiment, the materials of the N-type structure layer and the P-type structure layer are selected as Al x Ga 1-x As, and the doping concentration of the N-type structure layer and the P-type structure layer is greater than 1e 18 cm -3 , where 0 ≤ x ≤ 1.

[0025] In a second aspect, the present application provides a VCSEL chip, and the VCSEL chip includes a positive electrode, a negative electrode, and the multi-junction VCSEL device as described above;

[0026] Among them, the positive electrode and the negative electrode are electrically connected to the bottom mirror structure and the top mirror structure of the multi-junction VCSEL device respectively; or

[0027] The positive electrode and the negative electrode are electrically connected to the top mirror structure and the bottom mirror structure of the multi-junction VCSEL device respectively;

[0028] The positive electrode and the negative electrode are located on opposite sides of the light-emitting side of the VCSEL chip.

[0029] In a third aspect, the present application provides a VCSEL chip, including at least one laser array; the laser array includes a plurality of multi-junction VCSEL devices as described above; the laser array is a regularly arranged array, or a randomly arranged array, or an array having a plurality of addressable sub-arrays.

[0030] In a fourth aspect, the present application provides a light source for a lidar system, including at least one multi-junction VCSEL device as described above or at least one VCSEL chip as described above.

[0031] In a fifth aspect, the present application provides a lidar, including a transmitting component and a receiving component, and the transmitting component uses the light source for the lidar system as described above.

[0032] For the above multi-junction VCSEL device, VCSEL chip, lidar system and its light source, by inserting a plurality of optical field regulation layers in the resonant cavity structure of the multi-junction VCSEL device, the optical field in the resonant cavity structure can be divided into at least three segments. By setting the structure and / or composition of the optical field regulation layer, flexible adjustment of the optical field intensity of each segment of the optical field can be achieved. Since the photoelectric confinement layer is located at the trough of the standing wave, the electric field intensity at the photoelectric confinement layer can be made relatively low. Moreover, due to the segmentation effect of the optical field regulation layer on the optical field, the optical field intensity at the optical field regulation layer is also relatively weak, so the optical field intensity of the adjacent photoelectric confinement layer can also be restricted. Based on the positive correlation between the confinement factor of the film layer and the electric field intensity and optical field intensity at its location, the above setting method effectively reduces the confinement factor of the photoelectric confinement layer, thereby achieving the suppression of high-order modes and achieving the effect of a low divergence angle. Therefore, the present application provides a multi-junction VCSEL device with a relatively small confinement factor of the photoelectric confinement layer and a relatively large confinement factor of the active region, thereby improving the performance of the multi-junction VCSEL device in terms of divergence angle and threshold current. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments or related technologies. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0034] Figure 1 FIG. 1 is one of the schematic structural diagrams of a multi-junction VCSEL device according to an embodiment;

[0035] Figure 2 FIG. 2 is another schematic structural diagram of a multi-junction VCSEL device according to an embodiment;

[0036] Figure 3The third schematic structural diagram of a multi-junction VCSEL device according to an embodiment;

[0037] Figure 4 The refractive index and optical field intensity diagrams of a multi-junction VCSEL device according to an embodiment.

[0038] Description of component labels:

[0039] Substrate: 100; Bottom mirror structure: 200; Top mirror structure: 300; Active region: 400; Multiple quantum well structure: 401; First active region: 410; Second active region: 420; Third active region: 430; Optical confinement layer: 500; First optical confinement layer: 510; Second optical confinement layer: 520; Third optical confinement layer: 530; Optical field regulation layer: 600; First optical field regulation layer: 610; Second optical field regulation layer: 620; Tunnel junction layer: 700. Detailed implementation manners

[0040] To facilitate the understanding of the present application, the present application will be described more comprehensively below with reference to the relevant drawings. Embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the disclosure of the present application is more thorough and comprehensive.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application in this specification are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0042] It should be understood that when an element or layer is referred to as being "on", "adjacent to", "connected to", or "coupled to" another element or layer, it can be directly on, adjacent to, connected, or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on", "directly adjacent to", "directly connected to", or "directly coupled to" another element or layer, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers, doping types, and / or portions, these elements, components, regions, layers, doping types, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, doping type, or portion from another element, component, region, layer, doping type, or portion. Thus, without departing from the teachings of the present invention, the first element, component, region, layer, doping type, or portion discussed below may be referred to as the second element, component, region, layer, or portion; for example, the first doping type may be referred to as the second doping type, and similarly, the second doping type may be referred to as the first doping type; the first doping type and the second doping type are different doping types. For instance, the first doping type may be P-type and the second doping type may be N-type, or the first doping type may be N-type and the second doping type may be P-type.

[0043] Spatial relationship terms such as "under", "below", "lower", "beneath", "above", "upper", etc. are used herein to describe the relationship of one element or feature shown in the figures to other elements or features. It should be understood that, in addition to the orientation shown in the figures, spatial relationship terms also encompass different orientations of the device during use and operation. For example, if the device in the figures is flipped, an element or feature described as "under" or "beneath" or "underneath" another element or feature will be oriented "on" the other element or feature. Thus, the exemplary terms "under" and "beneath" can include both an upper and a lower orientation. Additionally, the device may also include other orientations (such as a 90-degree rotation or other orientations), and the spatial descriptors used herein are to be interpreted accordingly.

[0044] As used herein, the singular forms "a", "an", and "the" may also include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprises / include" or "has" etc. specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. At the same time, in this specification, the term "and / or" includes any and all combinations of the related listed items.

[0045] An embodiment of the present application provides a multi-junction VCSEL device. A multi-junction VCSEL device refers to a vertical cavity surface emitting laser (VCSEL) with a stacked structure of multiple PN junctions. Figure 1 It is one of the schematic structural diagrams of a multi-junction VCSEL device in an embodiment. Refer to Figure 1 , the multi-junction VCSEL device includes a substrate 100, a bottom mirror structure 200, a resonant cavity structure, and a top mirror structure 300 that are sequentially disposed on the substrate 100. The resonant cavity structure is defined by the bottom mirror structure 200 and the top mirror structure 300, that is, the region between the bottom mirror structure 200 and the top mirror structure 300 is the resonant cavity. The resonant cavity is used to generate a standing wave. A standing wave is a wave formed by the superposition of two coherent waves propagating in opposite directions along the same straight line. Specifically, when the phases of the two waves are the same, their amplitudes are added to form a wave belly (i.e., a wave peak). When the phases of the two waves are opposite, their amplitudes are subtracted to form a wave node (i.e., a wave valley). Therefore, the positions of the wave peaks and wave valleys of the standing wave are fixed.

[0046] Among them, the material of the substrate 100 includes but is not limited to GaAs, InP, Si, etc. The bottom mirror structure 200 and the top mirror structure 300 may include a film layer with a periodically varying refractive index to achieve efficient reflection or transmission of light within a specific wavelength range. The film layer with a periodically varying refractive index can be composed of semiconductor materials, dielectric materials, metal-dielectric hybrid materials, etc. For example, the bottom mirror structure 200 can be an N-type semiconductor layer, and the top mirror structure 300 can be a P-type semiconductor layer. Another example is that the bottom mirror structure 200 can be a P-type semiconductor layer, and the top mirror structure 300 can be an N-type semiconductor layer. Optionally, the materials of the N-type semiconductor layer and the P-type semiconductor layer can be but are not limited to GaAs, AlGaAs, etc., and are not limited here as long as they can define the resonant cavity, and all belong to the protection scope of this embodiment. Specifically, the resonant cavity structure includes a plurality of active regions 400, a plurality of optical confinement layers 500, and a plurality of optical field control layers 600.

[0047] The number of active regions 400 can be, for example, 2, 3, 4, etc. Figure 1Three active regions 400 in a multi-junction VCSEL device are shown, namely a first active region 410, a second active region 420, and a third active region 430. The active regions 400 are used to generate stimulated emission photons, and the emitted photons are continuously reflected in a resonant cavity defined by a bottom mirror structure 200 and a top mirror structure 300, and are continuously enhanced during the reflection process, so as to finally emit laser light at a specific wavelength and with sufficient energy. Multiple active regions 400 in the multi-junction VCSEL device can emit light simultaneously, so that the light fields can be effectively superimposed between the multiple active regions 400, thereby optimizing the overall distribution of the light field.

[0048]

[0049] Furthermore, the above formula (1) is the calculation formula for the confinement factor of the target film layer. Wherein, is the confinement factor of the target film layer, is the thickness of the target film layer in the z-axis direction, is the thickness of the entire light field in the z-axis direction, is the refractive index of the target film layer in the z-axis direction, is the refractive index of the entire light field in the z-axis direction, is the light field intensity in the z-axis direction. The z-axis direction is the light emission direction. It can be understood that on the premise that the thickness, refractive index, and light field intensity of the entire light field are basically unchanged, the integration result of the denominator in the calculation formula (1) is basically unchanged.

[0050] When the target film layer is the active region 400, since multiple active regions 400 are provided in the multi-junction VCSEL device, the thickness of the active region 400 in the z-axis direction is relatively large, so that the integration result of the numerator in the confinement factor calculation formula (1) will increase accordingly, so that the confinement factor of the active region 400 is relatively large, which further helps photons to obtain gain more fully, enabling the multi-junction VCSEL device to emit laser light at a lower injection current.

[0051] The number of the optoelectronic confinement layers 500 is not greater than the number of the active regions 400, and can be, for example, 2, 3, 4, etc. Figure 1Shows three optical confinement layers 500 in a multi-junction VCSEL device, namely the first optical confinement layer 510, the second optical confinement layer 520, and the third optical confinement layer 530. The optical confinement layer 500 is used to define the light-emitting region of the multi-junction VCSEL device. Specifically, the optical confinement layer 500 is located on the side of the corresponding active region 400 away from the substrate 100 to restrict the flow of current, so that the current only flows within the light-emitting region defined by the optical confinement layer 500, thereby reducing unnecessary energy consumption, further reducing the threshold current, and increasing the current density. Moreover, the optical confinement layer 500 can also confine the optical field within the light-emitting region defined by the optical confinement layer 500, reducing light scattering and diffraction, thereby optimizing the divergence angle of the VCSEL and improving the beam quality. Continuing to refer to the calculation formula (1), when the target film layer is the optical confinement layer 500, since the optical confinement layer 500 is disposed at the trough of the standing wave, the electric field at the optical confinement layer 500 is small, and the electric field strength is positively correlated with the optical field strength. Therefore, the integral result of the numerator in the calculation formula (1) of the confinement factor will decrease accordingly. Since the integral result of the denominator remains basically unchanged, the confinement factor of the optical confinement layer 500 is small, which helps to reduce the divergence angle of the multi-junction VCSEL device.

[0052] The number of optical field regulation layers 600 is not greater than the number of optical confinement layers 500. For example, it can be 2, 3, 4, etc. The optical field regulation layer 600 is used to divide the optical field in the resonant cavity structure into at least three segments, and the intensity of each segment of the optical field is different. Figure 1 Shows two optical field regulation layers 600 in a multi-junction VCSEL device, namely the first optical field regulation layer 610 and the second optical field regulation layer 620. The two optical field regulation layers 600 can divide the optical field in the resonant cavity structure into three segments. Among them, the optical field regulation layer 600 is disposed adjacent to the optical confinement layer 500. It can be understood that the closer the distance between the optical confinement layer 500 and the optical field regulation layer 600, the greater the degree of reducing the diffusion of the current on the surface of the active region 400 after passing through the optical confinement layer 500. Therefore, in this embodiment, by setting the optical field regulation layer 600 between the optical confinement layer 500 and the active region 400, the confinement factor of the optical confinement layer 500 can be effectively regulated on the premise of better reducing current diffusion. By setting the structure and / or composition of the optical field regulation layer 600, the optical field intensity of each segment of the optical field can be flexibly adjusted. Based on different optical field distributions, different scenario applications can be realized, thereby improving the applicability of the multi-junction VCSEL device to different scenarios.

[0053] In the embodiments of the application, by inserting a plurality of optical field regulation layers 600 into the resonant cavity structure of a multi-junction VCSEL device, the optical field in the resonant cavity structure can be divided into at least three segments. By setting the structure and / or composition of the optical field regulation layer 600, flexible adjustment of the optical field intensity of each segment of the optical field can be achieved. Since the optoelectronic confinement layer 500 is located at the trough of the standing wave, the electric field intensity at the optoelectronic confinement layer 500 can be made relatively low. Moreover, due to the segmenting effect of the optical field regulation layer 600 on the optical field, the optical field intensity at the optical field regulation layer 600 is also relatively weak. Therefore, it is also possible to limit the optical field intensity of the optoelectronic confinement layer 500 located between two optical field regulation layers 600. Based on the positive correlation between the confinement factor of the film layer and the electric field intensity and optical field intensity at its location, the above setting method effectively reduces the confinement factor of the optoelectronic confinement layer 500, thereby achieving suppression of high-order modes and achieving the effect of a low divergence angle. Therefore, the present application provides a multi-junction VCSEL device with a relatively small confinement factor of the optoelectronic confinement layer 500 and a relatively large confinement factor of the active region 400, thereby improving the performance of the multi-junction VCSEL device in terms of divergence angle and threshold current.

[0054] In one of the embodiments, the optical field regulation layer 600 includes a photonic crystal structure or a periodically stacked first DBR structure. Specifically, the periodically stacked DBR (Distributed Bragg Reflector) structure realizes efficient reflection or transmission of light within a specific wavelength range through the periodic stacking of multiple layers of materials with different refractive indices. Among them, the optical thickness of each layer in the periodically stacked first DBR structure is 1 / 4 of the lasing wavelength. The material of the periodically stacked first DBR structure includes any one of semiconductor materials and metals. Exemplarily, the first DBR structure of semiconductor materials is, for example, composed of alternately stacked GaAs and AlGaAs with different refractive indices, or composed of alternately stacked InGaAs and GaAsP with different refractive indices, or composed of alternately stacked InGaAs and AlGaAs with different refractive indices. The first DBR structure of metals is, for example, composed of alternately stacked silver and aluminum with different refractive indices. Since the photonic crystal has a periodic change in dielectric constant by itself, a photonic bandgap can be formed, and thus, by controlling the position and width of the bandgap, reflection or transmission of light within a specific wavelength range can be achieved. In some embodiments, the optical field regulation layer 600 can also be composed of dielectric materials, metal-dielectric hybrid materials, etc., which are not limited herein.

[0055] In one embodiment, the bottom mirror structure 200 includes a periodically stacked second DBR structure, that is, it includes a plurality of mirrors with an optical thickness of a quarter of the lasing wavelength, and the plurality of mirrors are alternately arranged with high and low refractive indices. The top mirror structure 300 also includes a periodically stacked second DBR structure, that is, a plurality of mirrors with an optical thickness of a quarter of the lasing wavelength, and the plurality of mirrors are alternately arranged with high and low refractive indices. It can be understood that the components, the number of stacking periods, etc. of the second DBR structure of the bottom mirror structure 200 and the second DBR structure of the top mirror structure 300 can be the same or different, and this embodiment does not make a limitation. Among them, the materials of the top mirror structure 300 and the bottom mirror structure 200 can be dielectric materials with electrical insulation properties, for example, it can include silicon nitride, silicon oxide, aluminum oxide, titanium oxide, etc. The materials of the top mirror structure 300 and the bottom mirror structure 200 can also be semiconductor materials, for example, it can include GaAs and AlGaAs.

[0056] Further, the refractive index of the high refractive index film layer in the first DBR structure is higher than that of the high refractive index film layer in the second DBR structure. It can be understood that on the premise that the refractive indices of the low refractive index film layers in the first DBR structure and the second DBR structure are the same or close, increasing the refractive index of the high refractive index film layer in the first DBR structure can make the refractive index difference inside the first DBR structure greater than the refractive index difference inside the second DBR structure, so that the first DBR structure has a higher reflection coefficient to achieve the light field segmentation function of the light field control layer.

[0057] Figure 2 is the second schematic diagram of the structure of a multi-junction VCSEL device in an embodiment. Refer to Figure 2 , in one embodiment, at least one multi-quantum well structure 401 is provided in each active region 400. That is, the active region 400 can include only one multi-quantum well structure 401, or can include a composite structure composed of a plurality of multi-quantum well structures 401 arranged in layers. The composite structure can be, but is not limited to, composed of material layers of GaAs and AlGaAs, InGaAs and GaAsP, or InGaAs and AlGaAs arranged in layers. The multi-quantum well structure 401 is used to convert electrical energy into light energy to generate laser light.

[0058] It can be understood that the multi - quantum well structure 401 is the place where laser gain amplification occurs. The central position of the multi - quantum well structure 401 can be aligned with the position where the optical field is the strongest to achieve a greater amplification effect. Further, in the case where a segmented optical field includes multiple multi - quantum well structures 401, the confinement factors of the multi - quantum well structures 401 in the same segment of the optical field are within the same preset range, that is, the confinement factors of each multi - quantum well structure 401 are maintained at the same level, so that the contribution of each multi - quantum well structure 401 to light emission is similar. It can be understood that similar light - emission contributions mean that the current injection in each multi - quantum well structure 401 is more uniform, which helps to reduce the threshold current of the multi - junction VCSEL device, thereby reducing the power consumption of the multi - junction VCSEL device and extending its service life. Moreover, when the contribution of each multi - quantum well structure 401 to light emission is similar, the distribution of carriers in each multi - quantum well structure 401 will be more uniform, which helps to reduce the recombination loss of carriers, thereby improving the overall light - emission efficiency of the multi - junction VCSEL device.

[0059] In one embodiment, the refractive index of the optical - electrical confinement layer is lower than the refractive index of the multi - quantum well structure closest to the optical - field control layer in the active region and lower than the refractive index of the low - refractive - index film layer in the first DBR structure.

[0060] In one embodiment, there are multiple multi - quantum well structures 401 between the bottom mirror structure 200 and the nearest optical - field control layer 600. Since there are multiple multi - quantum well structures 401 between the bottom mirror structure 200 and the nearest optical - field control layer 600, it is equivalent to increasing the thickness of the active region 400 in the Z - axis direction, so that the confinement factor in the active region 400 divided by the optical - field control layer 600 changes little, ensuring that the reduction of the confinement factor in the active region 400 is small. In one embodiment, there are three multi - quantum well structures 401 between the bottom mirror structure 200 and the nearest first optical - field control layer 610.

[0061] In one embodiment, the active regions 400 are connected by a tunnel - junction layer 700. That is, the tunnel - junction layer 700 is located between two adjacent multi - quantum well structures 401. The tunnel - junction layer 700, as a current path, can limit the flow position of the current, making the current flow more in the central region near the central axis of the multi - junction VCSEL device, reducing the diffusion of the current from the central region to the outside, which is conducive to the laser emitting from the center of the multi - junction VCSEL device. Moreover, the tunnel - junction layer 700 can also reduce the non - radiative recombination of carriers at the tunnel - junction layer 700, ensuring that more current is used to generate useful photons, thereby increasing the probability of radiative recombination and improving the optical - field quality.

[0062] In one embodiment, the resonant cavity structure includes three active regions 400 and three optical confinement layers 500. Among them, the three active regions 400 include a first active region 410, a second active region 420, and a third active region 430 arranged in sequence along the direction away from the substrate 100, and the three optical confinement layers 500 include a first optical confinement layer 510, a second optical confinement layer 520, and a third optical confinement layer 530. The first optical confinement layer 510 is located between the first active region 410 and the second active region 420, the second optical confinement layer 520 is located between the second active region 420 and the third active region 430, and the third optical confinement layer 530 is located on the side of the third active region 430 close to the top mirror structure 300. Further, the first active region 410 includes three multi-quantum well structures 401, the second active region 420 includes two multi-quantum well structures 401, and the third active region 430 includes two multi-quantum well structures 401. Among them, adjacent multi-quantum well structures 401 in each active region 400 are connected by a tunnel junction layer 700. Further, the multi-junction VCSEL device includes two optical field modulation layers 600. Among them, the first optical field modulation layer 610 is disposed between the first active region 410 and the first optical confinement layer 510, and the second optical field modulation layer 620 is disposed between the second active region 420 and the second optical confinement layer 520.

[0063] In one embodiment, when the optical field modulation layer 600 includes a periodically stacked first DBR structure, the periodically stacked first DBR structure is composed of Al x Ga （1-x） As / Al y Ga （1-y） As alternately. Specifically, by adjusting the proportion of aluminum and gallium in the AlGaAs material system, the refractive index and bandgap of the periodically stacked first DBR structure can be precisely controlled, so as to realize the reflection or transmission of light of a specific wavelength. Further, the number of stacking periods is between 3 pairs and 10 pairs, 0≤x<y≤1. Among them, a pair includes two adjacent film layers with different refractive indices. For example, if the number of stacking periods of the optical field modulation layer 600 is 3 pairs, then the first DBR structure of an optical field modulation layer 600 includes an Al x Ga （1-x） As layer, an Al y Ga （1-y） As layer, an Al x Ga （1-x） As layer, an Al y Ga （1-y） As layer, an Al x Ga （1-x） As layer and an Al y Ga （1-y）The As layer. It can be understood that, the more the number of stacking periods of the first DBR structure of the optical field modulation layer 600, the lower the confinement factor of the optical and electrical confinement layer 500, but at the same time, the problem of current spreading will be aggravated, thus the influence on the light-emitting efficiency of the active region 400 after the optical and electrical confinement layer 500 becomes greater. Therefore, in this embodiment, each optical field modulation layer 600 is respectively configured to include 3 to 10 pairs of stacking periods, so as to have a lower confinement factor of the optical and electrical confinement layer 500 on the premise that the problem of current spreading is controllable. It should be noted that, the number of stacking periods of the first DBR structure of each optical field modulation layer 600 can be the same or different, and can be specifically set according to the requirements for the optical field, which is not limited herein.

[0064] In one embodiment, at least one of the side of the optical and electrical confinement layer 500 close to the substrate 100 and the side far from the substrate 100 is provided with an optical field modulation layer 600. That is to say, the optical field modulation layer 600 can be provided on one side of the optical and electrical confinement layer 500, or an optical field modulation layer 600 can be respectively provided on both sides of the optical and electrical confinement layer 500. Exemplarily, when an optical field modulation layer 600 is respectively provided on both sides of the optical and electrical confinement layer 500, one of the optical field modulation layers 600 located on the side of the optical and electrical confinement layer 500 close to the substrate 100 and the side far from the substrate 100 includes a photonic crystal structure, and the other optical field modulation layer 600 includes a periodically stacked first DBR structure. Another exemplarily, when an optical field modulation layer 600 is respectively provided on both sides of the optical and electrical confinement layer 500, the optical field modulation layers 600 on both sides are both periodically stacked first DBR structures or both photonic crystal structures. That is to say, the specific type of each optical field modulation layer 600 can be set according to needs, without being limited to the same structure of the two optical field modulation layers 600 adjacent to the same optical and electrical confinement layer 500, both being periodically stacked first DBR structures or both photonic crystal structures. By respectively selecting the specific type of each optical field modulation layer 600, it is easier to achieve the required reflection coefficient, thus more flexibly realizing the required multi-segment optical field.

[0065] Figure 3 FIG. 3 is a schematic structural diagram of a multi-junction VCSEL device according to an embodiment, refer to Figure 3, in one embodiment, when the optical field modulation layer 600 is located on the side of the optoelectronic confinement layer 500 away from the substrate 100, a tunnel junction layer 700 is further provided between the optical field modulation layer 600 and the optoelectronic confinement layer 500. The tunnel junction layer 700, as the current path, can limit the current flow position, enabling the current to flow more in the central region near the central axis of the multi-junction VCSEL device, reducing the diffusion of the current from the central region to the outside, which is beneficial for the laser to emit from the center of the multi-junction VCSEL device. Moreover, the tunnel junction layer 700 can also reduce the non-radiative recombination of carriers at the tunnel junction layer 700, ensuring that more current is used to generate useful photons, thereby increasing the probability of radiative recombination and improving the optical field quality.

[0066] Moreover, by providing the tunnel junction layer 700 between the optical field modulation layer 600 and the optoelectronic confinement layer 500, the change rate of the optical field intensity at the optoelectronic confinement layer 500 and the optical field modulation layer 600 can be slowed down, so that the optical field intensity at the optoelectronic confinement layer 500 and the optical field modulation layer 600 can continuously remain at a lower position. It can be understood that if the process results in a certain offset in the position of the optoelectronic confinement layer 500 in the optical field, it may cause the optoelectronic confinement layer 500 not to be located at the trough of the standing wave. Based on the positive correlation between the confinement factor and the optical field intensity, when the offset causes the optical intensity at the optoelectronic confinement layer 500 to increase, the confinement factor of the optoelectronic confinement layer 500 will increase, thus affecting the performance of the multi-junction VCSEL device. In addition, taking the tunnel junction layer 700 adjacent to the first optoelectronic confinement layer 510 as an example, since the multi-quantum well structure 401 on the side of the first active region 410 away from the substrate 100 adjacent to the first optoelectronic confinement layer 510 is heavily doped with P-type. And in the tunnel junction layer 700 adjacent to the first optoelectronic confinement layer 510, its side adjacent to the first optoelectronic confinement layer 510 is also heavily doped with P-type. Therefore, if the tunnel junction layer 700 is provided on the side of the first optoelectronic confinement layer 510 close to the substrate 100, it will cause the two P-type heavily doped regions to be too close, and the P-type heavily doped region has certain light absorption characteristics, and the two P-type heavily doped regions with a closer distance will further enhance the light absorption, resulting in a decline in the performance of the multi-junction VCSEL device. In the embodiment of the application, the tunnel junction layer 700 is provided on the side of the first optoelectronic confinement layer 510 away from the substrate 100, which can effectively improve the above-mentioned light absorption problem.

[0067] In one embodiment, when the optical field modulation layers 600 on both sides of the optical-electric confinement layer 500 are both periodically stacked first DBR structures, the stacking periods of the first DBR structures in the optical field modulation layers 600 on both sides are different. Specifically, the periodically stacked first DBR structure includes alternately stacked first DBR functional layers and second DBR functional layers with different refractive indexes. When the refractive indexes of the first DBR functional layers of the two optical field modulation layers 600 adjacent to the same optical-electric confinement layer 500 are the same, and the refractive indexes of the second DBR functional layers of each optical field modulation layer 600 are the same, the stacking periods of the first DBR structures of the two optical field modulation layers 600 adjacent to the same optical-electric confinement layer 500 are different.

[0068] Further, the components of the elements affecting the refractive index in the first DBR functional layers of the two optical field modulation layers 600 adjacent to the same optical-electric confinement layer 500 can be made the same, so that the refractive indexes of the first DBR functional layers of each optical field modulation layer 600 are the same. Similarly, the components of the elements affecting the refractive index in the second DBR functional layers of each optical field modulation layer 600 can be made the same, so that the refractive indexes of the second DBR functional layers of each optical field modulation layer 600 are the same. Taking the first DBR functional layer as Al x Ga （1-x） As and the second DBR functional layer as Al y Ga （1-y） As as an example, where 0 ≤ x < y ≤ 1. The x value of the first DBR functional layer in one optical field modulation layer 600 can be made the same as the x value of the first DBR functional layer in the other optical field modulation layer 600, and the y value of the second DBR functional layer in one optical field modulation layer 600 can be made the same as the y value of the second DBR functional layer in the other optical field modulation layer 600. Exemplarily, the two optical field modulation layers 600 can both be composed of alternately stacked Al 0.25 Ga 0.75 As / Al 0.5 Ga 0.5 As.

[0069] The number of stacking periods of the first DBR structure of the two optical field modulation layers 600 adjacent to the same optoelectronic confinement layer 500 can be different. It can be that the number of stacking periods of the first DBR structure of the optical field modulation layer 600 closer to the substrate 100 is greater than that of the first DBR structure of the optical field modulation layer 600 farther from the substrate 100, or it can be that the number of stacking periods of the first DBR structure of the optical field modulation layer 600 farther from the substrate 100 is greater than that of the first DBR structure of the optical field modulation layer 600 closer to the substrate 100. There is no limitation here. It can be understood that the greater the number of stacking periods of the first DBR structure of the optical field modulation layer 600, the more interfaces the photons will reflect at, that is, the reflection coefficient of the optical field modulation layer 600 will be changed. Therefore, the difference in the number of stacking periods of the first DBR structures of the two optical field modulation layers 600 adjacent to the same optoelectronic confinement layer 500 means that the reflection coefficients of the two optical field modulation layers 600 are different, so that the photons generated in the active region 400 can be emitted from one of the optical field modulation layers 600 after obtaining the required gain, so as to realize the flexible control of the optical field intensity.

[0070] The optoelectronic confinement layer 500 includes any one of an air column type optoelectronic confinement layer 500, an oxidation confinement type optoelectronic confinement layer 500, an ion implantation type optoelectronic confinement layer 500, and a tunnel junction type optoelectronic confinement layer 500. Among them, the air column type optoelectronic confinement layer 500 realizes the confinement of current and light through air columns. The air columns are hollow structures formed by dry etching technology, and their refractive index is lower than that of the surrounding semiconductor materials, so as to effectively confine the light in the central region. The ion implantation type optoelectronic confinement layer 500 changes its electrical properties by implanting ions into the semiconductor material to form a high-resistance region, and the high-resistance region can limit the flow of current, thereby indirectly limiting the light generation region.

[0071] In one embodiment, the oxidation confinement type optoelectronic confinement layer 500 includes an unoxidized region made of AlGaAs material with a high Al component and an oxidized region made of alumina material. The oxidized region is provided outside the unoxidized region, and the unoxidized region forms a light-emitting region for effective current injection. Among them, the semiconductor layer of the unoxidized region in the optoelectronic confinement layer 500 can be understood as an opening, and the opening is used to define the light-emitting region of the multi-junction VCSEL device. When the current enters, the current can only flow to the active region 400 through the opening in the optoelectronic confinement layer 500, so as to realize the confinement of the current injection path and the optical mode field. Further, through a selective oxidation process, the AlGaAs layer with a high aluminum component can be converted into alumina to form the peripheral unoxidized region. Further, the opening sizes of different optoelectronic confinement layers 500 can be the same or different. In the case where the openings of multiple optoelectronic confinement layers 500 are different, the light-emitting region defined by the optoelectronic confinement layer 500 with the smallest opening is used as the light-emitting region of the multi-junction VCSEL device.

[0072] In one embodiment, the tunnel junction type optoelectronic confinement layer 500 includes at least one highly doped N-type structural layer and at least one highly doped P-type structural layer. Specifically, a potential barrier is formed between the highly doped N-type structural layer and the highly doped P-type structural layer, and electrons are allowed to pass through the potential barrier by tunneling effect, thereby achieving lateral confinement of the current. In one embodiment, the materials of the N-type structural layer and the P-type structural layer are selected as Al x Ga 1-x As, and the doping concentration of the N-type structural layer and the P-type structural layer is greater than 1e 18 cm -3 ^-3^, where 0 ≤ x ≤ 1.

[0073] Figure 4 FIG. is a refractive index and optical field intensity diagram of a multi-junction VCSEL device according to an embodiment. Referring to Figure 4 , in this embodiment, based on the first DBR structure formed by the periodic stacking of the optical field modulation layer 600, the refractive index at the optical field modulation layer 600 changes periodically. Among them, the first optical field modulation layer 610 and the second optical field modulation layer 620 include the first DBR structure, and the bottom mirror structure 200 and the top mirror structure 300 include the second DBR structure. The refractive index of the high refractive index film layer in the first DBR structure is higher than that of the high refractive index film layer in the second DBR structure. The refractive index of the first optoelectronic confinement layer 510 is lower than that of the multi-quantum well structure 401 closest to the first optical field modulation layer 610 in the second active region 420, and lower than that of the low refractive index film layer in the first DBR structure of the first optical field modulation layer 610. The refractive index of the second optoelectronic confinement layer 520 is lower than that of the multi-quantum well structure 401 closest to the second optical field modulation layer 620 in the third active region 430, and lower than that of the low refractive index film layer in the first DBR structure of the second optical field modulation layer 620. Moreover, the optical field intensities of the active regions 400 on both sides of the same optical field modulation layer 600 are different, indicating that the optical field modulation layer 600 effectively divides the optical field in the resonant cavity. Specifically, the optical field intensity of each active region 400 shows a gradually decreasing trend along the direction away from the substrate 100.

[0074] The embodiment of the present application further provides a VCSEL chip, which may be a flip-chip VCSEL chip. The VCSEL chip includes a positive electrode, a negative electrode, and the multi-junction VCSEL device as described above. Exemplarily, the positive electrode and the negative electrode are electrically connected to the bottom mirror structure 200 and the top mirror structure 300 of the multi-junction VCSEL device respectively, and the positive electrode and the negative electrode are located on the side opposite to the light-emitting side of the VCSEL chip. Another example is that the positive electrode and the negative electrode are electrically connected to the top mirror structure 300 and the bottom mirror structure 200 of the multi-junction VCSEL device respectively, and the positive electrode and the negative electrode are located on the side opposite to the light-emitting side of the VCSEL chip. Based on the foregoing multi-junction VCSEL device, the VCSEL chip of this embodiment can have better performance in terms of divergence angle and threshold current. In addition, the flip-chip VCSEL chip can be connected to the substrate and the carrier through bumps, which can reduce the need for wire bonding, thereby not only simplifying the packaging technology but also reducing the system inductance of the flip-chip VCSEL chip, contributing to improving the overall optoelectronic conversion efficiency of the flip-chip VCSEL chip.

[0075] The embodiment of the present application further provides a VCSEL chip, and the VCSEL chip includes at least one laser array. The laser array includes a plurality of multi-junction VCSEL devices as described above. The laser array is a regularly arranged array, or a randomly arranged array, or an array with multiple addressable sub-arrays. Based on the foregoing multi-junction VCSEL device, the VCSEL chip of this embodiment can have better performance in terms of divergence angle and threshold current.

[0076] The embodiment of the present application further provides a light source for a lidar system, including at least one multi-junction VCSEL device as described above or at least one VCSEL chip as described above.

[0077] The embodiment of the present application further provides a lidar system, including a transmitting component and a receiving component, and the transmitting component uses the light source for the lidar system as described above.

[0078] Embodiments of the invention are described herein with reference to cross-sectional illustrations that are schematic illustrations of ideal embodiments (and intermediate structures) of the invention. It is to be expected that variations in the shapes of the illustrated regions may result, for example, from manufacturing techniques and / or tolerances. Accordingly, embodiments of the invention should not be construed as limited to the particular shapes of regions shown herein but include shape deviations resulting, for example, from manufacturing techniques. For example, an implantation region shown as rectangular will typically have rounded or curved features at its edges and / or an implantation concentration gradient, rather than a binary change from the implantation region to the non-implantation region. Similarly, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions shown in the figures are substantially schematic, and their shapes do not represent the actual shapes of regions of the device and do not limit the scope of the invention.

[0079] In the description of this specification, the descriptions referring to the terms "some embodiments", "other embodiments", "ideal embodiments", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0080] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features of the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0081] The above embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A multi-junction VCSEL device, characterized in that, Comprising: A substrate; A bottom mirror structure and a top mirror structure stacked on the substrate; The bottom mirror structure and the top mirror structure define a resonant cavity structure for generating a standing wave; The resonant cavity structure includes a plurality of active regions and a plurality of optical confinement layers. Each of the optical confinement layers is located on the side of the corresponding active region away from the substrate, and the optical confinement layer is located at the trough of the standing wave. The optical confinement layer is used to define the light-emitting region of the multi-junction VCSEL device; A plurality of optical field modulation layers. Each of the optical field modulation layers is disposed between the corresponding optical confinement layer and the corresponding active region and is adjacent to the corresponding optical confinement layer. The optical field modulation layer is configured to divide the optical field in the resonant cavity structure into at least three segments, and the intensity of each segment of the optical field is different; Wherein, the confinement factor of the optical confinement layer satisfies the following calculation formula: Γ ox Γ is the confinement factor of the optoelectronic confinement layer, l is the thickness of the optoelectronic confinement layer in the z-axis direction, p is the thickness of the entire optical field in the z-axis direction, n2(z) is the refractive index of the optoelectronic confinement layer in the z-axis direction, n(z) is the refractive index of the entire optical field in the z-axis direction, E 2 (z) is the optical field intensity in the z-axis direction, and the z-axis direction refers to the light emission direction.

2. The multi-junction VCSEL device according to claim 1, characterized in that, The optical field modulation layer includes a photonic crystal structure or a periodically stacked first DBR structure.

3. The multi-junction VCSEL device according to claim 2, wherein The bottom mirror structure and the top mirror structure respectively include a periodically stacked second DBR structure; Wherein, the refractive index of the high refractive index film layer in the first DBR structure is higher than the refractive index of the high refractive index film layer in the second DBR structure.

4. The multi-junction VCSEL device according to claim 2, characterized in that, The active region includes at least one multi-quantum well structure. The refractive index of the optical confinement layer is lower than the refractive index of the multi-quantum well structure in the active region closest to the optical field modulation layer and lower than the refractive index of the low refractive index film layer in the first DBR structure.

5. The multi-junction VCSEL device according to claim 2, wherein, When the light field modulation layer includes a periodically stacked first DBR structure, the periodically stacked first DBR structure is composed of alternating Al x Ga (1-x) As / Al y Ga (1-y) As, and the number of stacking periods is between 3 pairs and 10 pairs, where 0 ≤ x < y ≤ 1.

6. The multi-junction VCSEL device according to claim 2, wherein, At least one of the side of the optical confinement layer close to the substrate and the side away from the substrate is provided with the optical field modulation layer.

7. The multi-junction VCSEL device according to claim 6, wherein When the optical field modulation layer is located on the side of the optical confinement layer away from the substrate, a tunnel junction layer is further provided between the optical field modulation layer and the optical confinement layer.

8. The multi-junction VCSEL device according to claim 6, wherein When one optical field modulation layer is provided on each side of the optical confinement layer, one of the optical field modulation layers located on the side of the optical confinement layer close to the substrate and the side away from the substrate includes a photonic crystal structure, and the other optical field modulation layer includes a periodically stacked first DBR structure.

9. The multi-junction VCSEL device according to any one of claims 1-8, characterized in that, The resonant cavity structure includes three active regions and three optical confinement layers; the three active regions include a first active region, a second active region, and a third active region arranged in sequence along the direction away from the substrate, and the two optical confinement layers include a first optical confinement layer, a second optical confinement layer, and a third optical confinement layer; The first optical confinement layer is located between the first active region and the second active region, the second optical confinement layer is located between the second active region and the third active region, and the third optical confinement layer is located on the side of the third active region close to the top mirror structure.

10. The multi-junction VCSEL device according to claim 9, characterized in that, The first active region includes three multi-quantum well structures, the second active region includes two multi-quantum wells, and the third active region includes two multi-quantum well structures; and adjacent multi-quantum well structures in each active region are connected by a tunnel junction layer.

11. The multi-junction VCSEL device according to claim 9, characterized in that, The multi-junction VCSEL device includes two optical field modulation layers. Among them, the first optical field modulation layer is disposed between the first active region and the first optical and electrical confinement layer, and the second optical field modulation layer is disposed between the second active region and the second optical and electrical confinement layer.

12. The multi-junction VCSEL device according to any one of claims 1-8, wherein, The optical and electrical confinement layer includes any one of an air column type optical and electrical confinement layer, an oxidation confinement type optical and electrical confinement layer, an ion implantation type optical and electrical confinement layer, and a tunnel junction type optical and electrical confinement layer.

13. The multi-junction VCSEL device according to claim 12, wherein The oxidation confinement type optical and electrical confinement layer includes an unoxidized region made of AlGaAs material with a high Al component and an oxidized region made of alumina material. The oxidized region is disposed outside the unoxidized region, and the unoxidized region forms a light-emitting region for effective current injection.

14. The multi-junction VCSEL device according to claim 12, wherein, The tunnel junction type optical and electrical confinement layer includes at least one highly doped N-type structure layer and at least one highly doped P-type structure layer.

15. The multi-junction VCSEL device according to claim 14, wherein, The materials of the N-type structure layer and the P-type structure layer are selected as Al x Ga 1-x As, and the doping concentration of the N-type structure layer and the P-type structure layer is greater than 1e 18 cm -3 , where 0 ≤ x ≤ 1.

16. A VCSEL chip, characterized in that, The VCSEL chip includes a positive electrode, a negative electrode, and the multi-junction VCSEL device according to any one of claims 1-15; wherein, the positive electrode and the negative electrode are respectively electrically connected to the bottom mirror structure and the top mirror structure of the multi-junction VCSEL device; or The positive electrode and the negative electrode are respectively electrically connected to the top mirror structure and the bottom mirror structure of the multi-junction VCSEL device; The positive electrode and the negative electrode are located on opposite sides of the light-emitting side of the VCSEL chip.

17. A VCSEL chip, characterized in that, It includes at least one laser array; the laser array includes a plurality of multi-junction VCSEL devices according to any one of claims 1-15; the laser array is a regularly arranged array, or a randomly arranged array, or an array having a plurality of addressable sub-arrays.

18. A light source for a lidar system, characterized in that, It includes at least one multi-junction VCSEL device according to any one of claims 1-15 or at least one VCSEL chip according to claim 16 or 17.

19. A lidar, characterized in that, It includes a transmitting component and a receiving component, and the transmitting component uses the light source for a lidar system according to claim 18.

Images