Multi-junction vertical cavity surface emitting laser and preparation method thereof

Abstract

The present invention relates to the field of laser technology, and discloses a multi-junction vertical cavity surface emitting laser and a preparation method thereof. The laser comprises a substrate layer, an epitaxial structure, a first oxide layer and a second oxide layer, wherein the epitaxial structure comprises a first reflector layer, an active layer comprising a plurality of barrier layers and a tunnel junction, and a second reflector layer; the first oxide layer having a first oxide hole is arranged on one side of the tunnel junction, the second oxide layer is arranged on the other side of the tunnel junction, and has a second oxide hole concentric with the first oxide hole, and the oxidation depth of the first oxide layer is greater than that of the second oxide layer; a tunnel junction, the first oxide layer and the second oxide layer form an integrated structure, which is placed in a trough of a standing wave field. An optical field limiting structure in which an oxide layer having a long upper portion and a short lower portion is arranged on both sides of the tunnel junction ensures that there are more high-order optical modes in the resonant cavity, which can effectively limit the lateral current, avoid the increase of the series resistance, shorten the effective cavity length of the standing wave field, and further improve the photoelectric conversion efficiency.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to a multi-junction vertical cavity surface emitting laser and a preparation method thereof. Background Art

[0002] In the light source market, the advantages of vertical-cavity surface-emitting laser (VCSEL) are: the active area is extremely small, which can achieve high packaging density and low threshold current; it is compatible with planarization process, has high yield and low cost, and can meet the application needs of the consumer market; the circular beam and small divergence angle make it easy to achieve high power density; the low temperature drift coefficient is conducive to the device to achieve stable performance in an ultra-wide temperature range of high and low temperatures. Therefore, VCSEL array chips are gradually becoming an important light source in a series of application fields such as sensing, laser heating, and laser heat treatment.

[0003] Photoelectric conversion efficiency is a comprehensive performance indicator, and its influencing factors include threshold current, slope efficiency, series resistance, operating voltage, etc. VCSEL array chips used in different scenarios have different levels of attention to multiple performance parameters. Sensing VCSEL array chips pay more attention to slope efficiency and divergence angle performance to achieve low radiation area applications, so their photoelectric conversion efficiency improvement is limited; heating VCSEL array chips require higher radiation power and larger radiation area, but because the Joule heat generated by VCSEL array chips under long pulse width or DC working conditions will directly affect the performance and reliability of the array chip, the photoelectric conversion efficiency needs to be further optimized to obtain a heating VCSEL array chip with high radiation power, high radiation area and high photoelectric conversion efficiency.

[0004] In related technologies, the optimization of photoelectric conversion efficiency is usually aimed at the efficiency optimization of low radiation area, which is reflected in the structural level of VCSEL: first, separate tunnel junctions and oxide layers are set, that is, the tunnel junctions and oxide layers correspond to different trough positions respectively. This design makes the tunnel junctions and oxide layers far away from the quantum wells in the active area, resulting in weakened current limitation and weakened light field limitation. Although the loss is reduced, it is also accompanied by a decrease in internal quantum efficiency, so the improvement of photoelectric conversion efficiency is limited. Secondly, multiple tunnel junctions are used to form more cascades of junctions. However, although the VCSEL with multiple tunnel junction cascades can obtain an exponential increase in gain materials, the multi-junction structure also means an exponentially increased turn-on voltage and a longer cavity length, which increases the series resistance and ultimately limits the improvement of photoelectric conversion efficiency. Summary of the invention

[0005] In view of this, the present invention provides a multi-junction vertical cavity surface emitting laser and a preparation method thereof to solve the problem of low photoelectric conversion efficiency of the multi-junction vertical cavity surface emitting laser.

[0006] In a first aspect, the present invention provides a multi-junction vertical cavity surface emitting laser, comprising: a substrate layer, an epitaxial structure, a first oxide layer and a second oxide layer, the epitaxial structure comprising a first reflector layer, an active layer and a second reflector layer which are stacked, the first reflector layer being arranged on the substrate layer, the active layer comprising a plurality of barrier layers and a plurality of tunnel junctions which are arranged at intervals from each other; the first oxide layer being arranged on a side surface of the tunnel junction away from the substrate layer, the first oxide layer having a first oxide hole penetrating the first oxide layer along a light emitting direction; the second oxide layer being arranged on a side surface of the tunnel junction close to the substrate layer, the second oxide layer having a second oxide hole penetrating the second oxide layer along a light emitting direction, the first oxide hole and the second oxide hole being concentric, and the oxidation depth of the first oxide layer being greater than the oxidation depth of the second oxide layer; any tunnel junction, the first oxide layer and the second oxide layer forming an integrated structure, the integrated structure being arranged between two adjacent barrier layers, and one integrated structure being correspondingly arranged in a trough of a standing wave field of the laser.

[0007] Beneficial effects: The multi-junction vertical cavity surface emitting laser of the present invention, on the one hand, forms a light field limiting structure with different oxide layers on both sides of the tunnel junction, which helps to enhance the lateral limiting effect of the resonant cavity on the standing wave field, weaken the leakage of the high-order light mode to both sides of the resonant cavity in the lateral direction, ensure that there are more high-order light modes in the resonant cavity, and realize the control of the light field resonant mode. The high-order light mode accounts for a large proportion, which is conducive to obtaining a larger gain volume, obtaining the maximum improvement of the slope efficiency and the improvement of the radiation area of ​​the entire device, and helping to improve the photoelectric conversion efficiency under a high radiation area. On the other hand, in the present invention, the first oxide layer with a larger oxidation depth is located on the side surface of the tunnel junction away from the substrate layer, that is, the first oxide layer with a smaller aperture first oxide hole is closer to the light exit hole, realizing effective limitation of the lateral current; under the premise that the first oxide layer forms a smaller light exit path, the second oxide layer arranged on the side surface of the tunnel junction close to the substrate layer has a smaller oxidation depth, thereby forming a second oxide hole with a larger aperture, balancing the excessive increase of the series resistance caused by the small light exit path. Therefore, a first oxide layer with a deeper oxidation is arranged on one side of the tunnel junction close to the light-exit hole, and a second oxide layer with a shallower oxidation is arranged on the other side, which can not only effectively limit the lateral current, but also avoid the increase of the series resistance, and finally improve the photoelectric conversion efficiency. In addition, the integrated structure consisting of the tunnel junction, the first oxide layer and the second oxide layer is arranged as a whole in a valley of the standing wave field, so that the wave number corresponding to each tunnel junction is shortened, the effective cavity length of the standing wave field is shortened, and the device series resistance caused by the increase of the effective cavity length is greatly reduced, and finally the photoelectric conversion efficiency is further improved.

[0008] In an optional implementation, the active layer further includes: a transition layer disposed between adjacent barrier layers; the transition layer is configured to adjust the position of the integrated structure in the standing wave field.

[0009] Beneficial effect: By adjusting the thickness of the transition layer, the position of the integrated structure as a whole in the standing wave field can be achieved, so that it can be better concentrated as a whole in a trough of the standing wave field. Without increasing the overall thickness of the device, the effective cavity length can be shortened and the device series resistance can be reduced, thereby improving the photoelectric conversion efficiency.

[0010] In an optional embodiment, the thickness of the integrated structure is within the range of 0%-30% of the energy distribution of the standing wave field.

[0011] Beneficial effect: Limiting the overall thickness of the integrated structure to 0%-30% of the energy distribution of the standing wave field can effectively avoid introducing additional doping losses and ensure the slope efficiency and photoelectric conversion efficiency of the laser.

[0012] In an optional implementation, the difference between the oxidation depth of the first oxide layer and the oxidation depth of the second oxide layer is set to Δd1, and the range of Δd1 is 0.5 μm~1 μm.

[0013] Beneficial effects: By placing the first oxide layer with a deeper oxidation depth above the tunnel junction, a better current limiting effect can be achieved; and the second oxide layer located below the tunnel junction can appropriately use a shorter oxidation depth due to the weakened lateral current expansion capability. Limiting the difference between the oxidation depth of the first oxide layer and the oxidation depth of the second oxide layer to between 0.5μm and 1μm can achieve the maximum improvement effect of photoelectric conversion efficiency. On the one hand, it can effectively avoid the small light output and increased device series resistance caused by the large difference; on the other hand, it can also avoid the insufficient limiting ability of the electric field and light field due to the small difference.

[0014] In an optional embodiment, the first oxide layer includes aluminum gallium arsenide having an aluminum component content ranging from 0.98 to 0.99, and the second oxide layer includes aluminum gallium arsenide having an aluminum component content ranging from 0.96 to 0.98.

[0015] Beneficial effect: By using aluminum gallium arsenide with different aluminum content, the first oxide layer and the second oxide layer with different oxidation depths are accurately formed, thereby effectively improving the photoelectric efficiency.

[0016] In an optional embodiment, the epitaxial structure further includes:

[0017] A third oxide layer is arranged on a side of the first reflector layer away from the substrate layer; the third oxide layer has a third oxide hole penetrating the third oxide layer, the third oxide hole is concentric with the first oxide hole, and the oxidation depth of the third oxide layer is less than the oxidation depth of the second oxide layer; and / or,

[0018] The fourth oxide layer is arranged on one side of the second reflector layer close to the substrate layer; the fourth oxide layer has a fourth oxide hole penetrating the fourth oxide layer, the fourth oxide hole is concentric with the first oxide hole, and the oxidation depth of the fourth oxide layer is less than the oxidation depth of the second oxide layer.

[0019] Beneficial effect: On the basis of the first oxide layer and the second oxide layer, a third oxide layer and a fourth oxide layer are further provided, which further increases the refractive index difference in the plane of the resonant cavity without reducing the light output path, weakens the leakage of high-order light modes to both sides of the resonant cavity in the lateral direction, and ensures that there are more high-order light modes in the resonant cavity, thereby helping to obtain a larger gain volume, maximize the improvement of slope efficiency and improve the radiation area of ​​the entire device, and ultimately achieve an improvement in photoelectric conversion efficiency under a high radiation area.

[0020] In an optional embodiment, the oxidation depth of the third oxide layer is equal to the oxidation depth of the fourth oxide layer; the difference between the oxidation depth of the third oxide layer or the oxidation depth of the fourth oxide layer and the oxidation depth of the second oxide layer is set to Δd2, and the range of Δd2 is 3μm~4μm.

[0021] Beneficial effect: The present invention sets the oxidation depth of the third oxide layer or the oxidation depth of the fourth oxide layer, and the difference between the oxidation depth of the second oxide layer and the oxidation depth is set to Δd2 between 3μm and 4μm, which helps to achieve the best improvement in photoelectric conversion efficiency. On the one hand, it avoids the poor effect of light field resonance mode control caused by too large a difference, that is, the lateral restriction effect of the resonant cavity on the standing wave field is not obvious, and it cannot ensure that the output light beam contains a sufficiently high proportion of high-order light modes; on the other hand, it avoids the current injection path being affected due to too small a difference, which brings additional lateral resistance in the second reflector layer, and ultimately leads to a significant reduction in the photoelectric conversion efficiency of the device.

[0022] In an optional embodiment, the epitaxial structure further includes: a contact layer disposed on a surface of the second reflector layer facing away from the substrate layer;

[0023] The epitaxial structure comprises a ridge structure, the ridge structure comprises a contact layer, a second reflector layer, an active layer and a portion of the first reflector layer, and the third oxide layer is located in the ridge structure.

[0024] Beneficial effects: A contact layer is provided at the topmost layer away from the substrate layer in the epitaxial structure. The contact layer facilitates good ohmic contact with the subsequently provided metal electrode, and further enables efficient current injection through connection with an external power source; the ridge structure facilitates more precise control of the oxidation depth.

[0025] In an optional embodiment, it also includes: a contact electrode layer, a passivation layer, a seed layer, a first electrode layer and a second electrode layer, the contact electrode layer is arranged on the side surface of the contact layer away from the substrate layer, the contact electrode layer includes a contact electrode hole, and the contact electrode hole is concentric with the first oxidation hole; the passivation layer covers the outer wall surface of the ridge structure and has an opening exposing at least part of the contact electrode layer; the seed layer covers the passivation layer and is connected to the contact electrode layer through the opening; the first electrode layer covers the seed layer and has a light output hole exposing at least part of the seed layer, the light output hole is concentric with the contact electrode hole, and in the direction perpendicular to the light output direction, the width dimension of the light output hole is smaller than the width dimension of the first oxidation hole; the second electrode layer is arranged on the side surface of the substrate layer away from the epitaxial structure.

[0026] Beneficial effects: The contact resistance of the contact electrode layer is small, and the contact electrode hole formed is used for laser emission. It is concentrically arranged with the first oxidation hole, the second oxidation hole, the third oxidation hole and the fourth oxidation hole to ensure smooth laser emission. A passivation layer is arranged on the outer wall of the ridge structure to achieve efficient reflection of photons inside the ridge structure, avoiding the escape of photons and affecting the light emission efficiency. The seed layer facilitates high-quality electrical connection between the subsequent electrode layer material on the light-emitting side and the epitaxial structure. Both the first electrode layer and the second electrode layer are made of metal gold, which has excellent conductivity and low contact resistance, and can achieve efficient electrical connection with the epitaxial structure when connected to an external power supply.

[0027] In a second aspect, the present invention further provides a method for preparing a multi-junction vertical cavity surface emitting laser, which is used to prepare the multi-junction vertical cavity surface emitting laser mentioned above, and the preparation method comprises:

[0028] forming a substrate layer;

[0029] An epitaxial structure is formed on the substrate layer, wherein the epitaxial structure includes a first reflector layer, an active layer and a second reflector layer which are stacked, wherein the first reflector layer is arranged on the substrate layer; and the active layer includes a plurality of barrier layers and a plurality of tunnel junctions which are arranged at intervals from each other.

[0030] A plurality of first oxide layers and a plurality of second oxide layers are formed in the active layer, wherein the first oxide layer is arranged on a side surface of the tunnel junction away from the substrate layer, and has a first oxide hole penetrating the first oxide layer along the light emitting direction; the second oxide layer is arranged on a side surface of the tunnel junction close to the substrate layer, and has a second oxide hole penetrating the second oxide layer along the light emitting direction, the first oxide hole and the second oxide hole are concentric, and the oxidation depth of the first oxide layer is greater than the oxidation depth of the second oxide layer; any tunnel junction, the first oxide layer and the second oxide layer form an integrated structure, the integrated structure is arranged between two adjacent barrier layers, and one integrated structure is correspondingly arranged in a trough of a standing wave field of a laser.

[0031] Beneficial effect: A multi-junction vertical cavity surface emitting laser is prepared by the preparation method of the present invention. On the one hand, a light field confinement structure with different oxide layers on both sides of the tunnel junction is formed, which helps to achieve control of the light field resonance mode and ensure that there are more high-order light modes in the resonance cavity, thereby obtaining a larger gain volume, a maximum improvement in slope efficiency, and an improvement in the radiation area of ​​the entire device, and ultimately improving the photoelectric conversion efficiency under a high radiation area. On the other hand, a first oxide layer with a deeper oxidation is set on one side of the tunnel junction close to the light port, and a second oxide layer with a shallower oxidation is set on the other side, which can not only effectively limit the lateral current, but also avoid the increase of the series resistance, and ultimately achieve the improvement of the photoelectric conversion efficiency. In addition, the integrated structure composed of the tunnel junction, the first oxide layer and the second oxide layer is set as a whole in a trough of the standing wave field, so that the wave number corresponding to each tunnel junction is effectively shortened, the effective cavity length of the standing wave field is shortened, and the device series resistance caused by the increase in the effective cavity length is greatly reduced, and the photoelectric conversion efficiency is further improved.

[0032] In an optional embodiment, after forming a plurality of first oxide layers and a plurality of second oxide layers in the active layer, the preparation method further comprises:

[0033] A third oxide layer is formed on a side of the first reflector layer away from the substrate layer, and / or a fourth oxide layer is formed on a side of the second reflector layer close to the substrate layer; the third oxide layer has a third oxide hole penetrating the third oxide layer, the third oxide hole is concentric with the first oxide hole, and the oxidation depth of the third oxide layer is less than the oxidation depth of the second oxide layer; the fourth oxide layer has a fourth oxide hole penetrating the fourth oxide layer, the fourth oxide hole is concentric with the first oxide hole, and the oxidation depth of the fourth oxide layer is less than the oxidation depth of the second oxide layer.

[0034] Beneficial effects: The third oxide layer and the fourth oxide layer can be prepared by the same method as the first oxide layer and the second oxide layer. On the basis of the first oxide layer and the second oxide layer, the third oxide layer and the fourth oxide layer are further provided, which further increases the refractive index difference in the plane of the resonant cavity without reducing the light output path, weakens the leakage of the high-order light mode to both sides of the resonant cavity in the lateral direction, and ensures that there are more high-order light modes in the resonant cavity, thereby helping to obtain a larger gain volume, maximize the improvement of slope efficiency, and improve the radiation area of ​​the entire device, and ultimately achieve an improvement in photoelectric conversion efficiency under a high radiation area.

[0035] In an optional embodiment, the epitaxial structure further includes a contact layer disposed on a surface of the second reflector layer facing away from the substrate layer; after forming the epitaxial structure on the substrate layer and before forming a plurality of first oxide layers and a plurality of second oxide layers in the active layer, the preparation method further includes:

[0036] forming a contact electrode layer on a surface of the contact layer facing away from the substrate layer, wherein the contact electrode layer comprises a contact electrode hole, and the contact electrode hole is concentric with the first oxidation hole;

[0037] A ridge structure is formed in the epitaxial structure, the ridge structure includes a contact layer, a second reflector layer, an active layer and a portion of the first reflector layer, the third oxide layer is located in the ridge structure, and the contact electrode layer is located on the ridge structure.

[0038] Beneficial effects: A contact layer is provided on the topmost layer away from the substrate layer in the epitaxial structure. The contact layer is of the same conductivity type as the second reflector layer directly contacting the contact layer below it. The contact layer facilitates good ohmic contact with the subsequently provided metal electrode, and then the connection with the external power supply enables efficient current injection. The contact resistance of the contact electrode layer is small, and the contact electrode hole formed is used for laser emission. The contact electrode hole is concentrically arranged with the first oxidation hole, the second oxidation hole, the third oxidation hole and the fourth oxidation hole to ensure smooth laser emission.

[0039] In an optional embodiment, after forming a third oxide layer on a side of the first reflector layer away from the substrate layer, and / or forming a fourth oxide layer on a side of the second reflector layer close to the substrate layer, the preparation method further comprises:

[0040] forming a passivation layer on an outer wall surface of the ridge structure, wherein the passivation layer has an opening exposing at least a portion of the contact electrode layer;

[0041] forming a seed layer on the passivation layer, wherein the seed layer is connected to the contact electrode layer through the opening;

[0042] Forming a first electrode layer on the seed layer, the first electrode layer having a light exit hole exposing at least a portion of the seed layer, the light exit hole being concentric with the contact electrode hole, and having a width dimension smaller than a width dimension of the first oxide hole in a direction perpendicular to the light exit direction;

[0043] A second electrode layer is formed on a surface of the substrate layer facing away from the epitaxial structure.

[0044] Beneficial effects: A passivation layer is set on the outer wall of the ridge structure to achieve efficient reflection of photons inside the ridge structure, preventing photons from escaping and affecting the light output efficiency. The seed layer facilitates high-quality electrical connection between the subsequent electrode layer material on the light output side and the epitaxial structure. Both the first electrode layer and the second electrode layer are made of metal gold, which has excellent conductivity and low contact resistance, and can achieve efficient electrical connection with the epitaxial structure when connected to an external power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 is a schematic structural diagram of a multi-junction vertical cavity surface emitting laser according to an embodiment of the present invention;

[0047] Figure 2 is a standing wave field and a refractive index distribution diagram of a multi-junction vertical cavity surface emitting laser according to an embodiment of the present invention;

[0048] Figure 3 It is a schematic structural diagram of a multi-junction vertical cavity surface emitting laser in the related art;

[0049] Figure 4 It is a standing wave field and refractive index distribution diagram of a multi-junction vertical cavity surface emitting laser in the related art;

[0050] Figure 5 is a schematic flow chart of a method for preparing a multi-junction vertical cavity surface emitting laser according to an embodiment of the present invention;

[0051] Figure 6 is a schematic diagram of the structure after forming a substrate layer and an epitaxial structure according to an embodiment of the present invention;

[0052] Figure 7 is a schematic structural diagram of an embodiment of the present invention after a contact electrode layer is formed on an epitaxial structure;

[0053] Figure 8is a schematic structural diagram of an embodiment of the present invention after a ridge structure is formed on an epitaxial structure;

[0054] Fig. 9 is a schematic diagram of the structure after a first oxide layer, a second oxide layer, a third oxide layer and a fourth oxide layer are formed in a ridge structure according to an embodiment of the present invention;

[0055] Fig.10 is a schematic diagram of a structure after a passivation layer is formed on an outer wall surface of a ridge structure according to an embodiment of the present invention;

[0056] Fig.11 It is a schematic diagram of the structure after a seed layer is formed on a passivation layer according to an embodiment of the present invention.

[0057] Description of reference numerals:

[0058] 100, standing wave field; 300, contrast oxide layer; 400, contrast standing wave field;

[0059] 1. Substrate layer;

[0060] 2. epitaxial structure; 200, ridge structure; 201, first reflector layer; 202, second reflector layer; 203, barrier layer; 204, tunnel junction; 205, transition layer; 206, contact layer;

[0061] 3. first oxide layer; 301. first oxide hole;

[0062] 4. second oxide layer; 401. second oxide hole;

[0063] 5. The third oxide layer; 501. The third oxide hole;

[0064] 6. Fourth oxide layer; 601. Fourth oxide hole;

[0065] 7. contact electrode layer; 701. contact electrode hole;

[0066] 8. passivation layer; 801. opening;

[0067] 9. Seed layer;

[0068] 10. first electrode layer; 1001. light exit hole;

[0069] 11. Second electrode layer. DETAILED DESCRIPTION

[0070] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only some structures related to the present invention are shown in the accompanying drawings, rather than all structures. In the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified for the purpose of clear expression, and some details may be omitted. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships between them are only exemplary, and may be deviated due to manufacturing tolerances or technical limitations in practice, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be an intermediate layer / element between them. In addition, if one layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0071] Photoelectric conversion efficiency PCE is a comprehensive performance indicator. According to its calculation formula , which affects the threshold current , Slope efficiency , Series resistance , Working voltage (V), etc. In the related art, the optimization of photoelectric conversion efficiency is usually aimed at the efficiency optimization of low radiation area. On the one hand, separate tunnel junctions and oxide layers are set, that is, the tunnel junctions and oxide layers correspond to different trough positions respectively, but this design makes the tunnel junctions and oxide layers far away from the quantum wells in the active area, resulting in weakened current limitation and weakened light field limitation. Although the loss is reduced, it is also accompanied by a decrease in internal quantum efficiency, so the improvement of photoelectric conversion efficiency is limited. On the other hand, multiple tunnel junctions are used to form more cascades of junctions. However, although the VCSEL with multiple tunnel junction cascades can obtain an exponential increase in gain materials, the multi-junction structure also means an exponentially increased turn-on voltage and a longer cavity length, which increases the series resistance and ultimately limits the improvement of photoelectric conversion efficiency.

[0072] Based on this, combined with the particularity of the VCSEL structure, that is, the existence of a single longitudinal mode and multiple transverse modes of the light field mode distribution in the resonant cavity, that is, the output light beam is the result of the superposition of multiple light modes. Due to the differences in the distribution position and distribution angle of high-order light modes and low-order light modes, high-order light modes can obtain a larger gain volume, and thus a larger gain coefficient.

[0073] Therefore, on the one hand, this embodiment achieves selective control of the light field mode by setting a plurality of different oxide layers in the active layer, retains more high-order light modes in the resonant cavity, and maximizes the gain volume; and because the proportion of high-order light modes increases, the radiation area of ​​the device can be effectively increased, and ultimately the photoelectric conversion efficiency under high radiation area is improved. On the other hand, the structural design is optimized to form an integrated structure of the tunnel junction and the upper and lower oxide layers. By adjusting the position of the integrated structure in the standing wave field of the resonant cavity, not only is the distance between it and the barrier layer in the active layer shortened, and the electric field and light field are restricted in the lateral direction, but also the effective cavity length can be shortened, and the series resistance and the power of waste heat generated can be reduced without sacrificing the slope efficiency, and ultimately the photoelectric conversion efficiency can be further improved.

[0074] A VCSEL device commonly used as a light source includes a plurality of multi-junction vertical cavity surface emitting lasers arranged in an array. In this embodiment, only a single multi-junction vertical cavity surface emitting laser is taken as an example for description.

[0075] Specific reference Figure 1 and Figure 2 The present embodiment provides a multi-junction vertical cavity surface emitting laser, comprising: a substrate layer 1, an epitaxial structure 2, a first oxide layer 3, and a second oxide layer 4, wherein the epitaxial structure 2 comprises a first reflector layer 201, an active layer, and a second reflector layer 202 which are stacked, the first reflector layer 201 being arranged on the substrate layer 1, the active layer comprising a plurality of barrier layers 203 and a plurality of tunnel junctions 204 which are arranged at intervals from each other; the first oxide layer 3 is arranged on a side surface of the tunnel junction 204 away from the substrate layer 1, and the first oxide layer 3 has a first oxide hole penetrating the first oxide layer 3 along a light emitting direction 301; the second oxide layer 4 is arranged on a side surface of the tunnel junction 204 close to the substrate layer 1, the second oxide layer 4 has a second oxide hole 401 penetrating the second oxide layer 4 along the light emitting direction, the first oxide hole 301 and the second oxide hole 401 are concentric, and the oxidation depth of the first oxide layer 3 is greater than the oxidation depth of the second oxide layer 4; any tunnel junction 204, the first oxide layer 3 and the second oxide layer 4 form an integrated structure, the integrated structure is arranged between two adjacent barrier layers 203, and one integrated structure is correspondingly arranged in a trough of the standing wave field 100 of the laser.

[0076] Specifically, the epitaxial structure 2 includes a first reflector layer 201, an active layer, and a second reflector layer 202 stacked in sequence on the surface of one side of the substrate layer 1. The light emitting direction is consistent with the stacking direction of each layer in the epitaxial structure 2, and the laser is emitted upward from one side of the substrate layer 1. The first reflector layer 201 and the second reflector layer 202 in the epitaxial structure 2 are both DBR reflectors, one of which is a P-type DBR, and the other is an N-type DBR. In this embodiment, the first reflector layer 201 is an N-type DBR, and the second reflector layer 202 is a P-type DBR. In the active layer located between the first reflector layer 201 and the second reflector layer 202, a plurality of barrier layers 203 and a plurality of tunnel junctions 204 are arranged at intervals from each other, that is, a tunnel junction 204 is arranged between each two adjacent barrier layers 203, and the overall structure presents a barrier layer 203, a tunnel junction 204, a barrier layer 203, etc., which are alternately repeated in sequence. It can be understood that a tunnel junction 204 is formed between every two adjacent barrier layers 203 arranged at intervals. On this basis, in this embodiment, on one hand, a first oxide layer 3 and a second oxide layer 4 are respectively arranged on the two side surfaces of each tunnel junction 204, so as to form a light field limiting structure in which oxide layers are arranged on both sides of the tunnel junction 204; and the first oxide layer 3 with a larger oxidation depth is arranged on the side surface of the tunnel junction 204 away from the substrate layer 1, that is, the first oxide layer 3 with a smaller aperture first oxide hole 301 is closer to the light exit hole 1001; on the premise that the first oxide layer 3 is arranged to form a smaller light exit path, the second oxide layer 4 arranged on the side surface of the tunnel junction 204 close to the substrate layer 1 has a smaller oxidation depth, forming a second oxide hole 401 with a larger aperture, and the first oxide hole 301 and the second oxide hole 401 are arranged concentrically to provide a smooth laser light exit path.

[0077] The multi-junction vertical cavity surface emitting laser of this embodiment is formed as follows Figure 1 The light field confinement structure shown in FIG. 1 is provided with different oxide layers on both sides of the tunnel junction 204. Compared with some solutions such as Figure 3 As shown, the structure of the contrast oxide layer 300 is only set on one side of the tunnel junction 204. The light field confinement structure in this embodiment helps to enhance the lateral confinement effect of the resonant cavity on the standing wave field 100, reduce the leakage of the high-order light mode to both sides of the resonant cavity in the lateral direction, ensure that there are more high-order light modes in the resonant cavity, and realize the control of the light field resonant mode. The high-order light mode accounts for a large proportion, which is conducive to obtaining a larger gain volume, obtaining the maximum improvement of the slope efficiency and the improvement of the radiation area of ​​the entire device, and helping to improve the photoelectric conversion efficiency under a high radiation area.

[0078] On the other hand, in the present embodiment, the first oxide layer 3 with a larger oxidation depth is located on the surface of the side of the tunnel junction 204 away from the substrate layer 1, that is, the first oxide layer 3 with a smaller aperture first oxide hole 301 is closer to the light output hole 1001, thereby effectively limiting the lateral current; under the premise that the first oxide layer 3 forms a smaller light output path, the second oxide layer 4 arranged on the surface of the side of the tunnel junction 204 close to the substrate layer 1 has a smaller oxidation depth, thereby forming a second oxide hole 401 with a larger aperture, balancing the excessive increase in series resistance caused by the small light output path. Therefore, a first oxide layer 3 with a deeper oxidation depth is arranged on the side of the tunnel junction 204 close to the light output hole 1001, and a second oxide layer 4 with a shallower oxidation depth is arranged on the other side, which can not only effectively limit the lateral current, but also avoid the increase in series resistance, thereby ultimately achieving an improvement in photoelectric conversion efficiency. In addition, compared with some schemes such as Figure 4 As shown, the tunnel junction 204 and the contrast oxide layer 300 are respectively aligned with two adjacent valleys of the contrast standing wave field 400, that is, the wave number corresponding to each tunnel junction 204 is 1λ, which will multiply the wave number in the multi-junction VCSEL, thereby increasing the effective cavity length. In this embodiment, the tunnel junction 204, the first oxide layer and the second oxide layer 4 form an integrated structure, and the integrated structure is disposed as a whole in a valley of the standing wave field 100, as shown in FIG. Figure 2 As shown, the wave number corresponding to each tunnel junction 204 is shortened to 0.5 λ, the effective cavity length of the standing wave field 100 is shortened, and the device series resistance caused by the increase in the effective cavity length is greatly reduced, and finally the photoelectric conversion efficiency is further improved.

[0079] refer to Figure 1 The active layer of this embodiment further includes a transition layer 205 disposed between adjacent barrier layers 203 ; the transition layer 205 is configured to adjust the position of the integrated structure in the standing wave field 100 .

[0080] Specifically, the active layer is formed by stacking a plurality of quantum well structures, each of which includes a barrier layer 203 and a transition layer 205 located on both sides of the barrier layer 203, and a tunnel junction 204 spaced from the barrier layer 203 is inserted into the transition layer 205 to form the active layer of the multi-junction cascade vertical cavity surface emitting laser. In this embodiment, the first oxide layer 3 and the second oxide layer 4 are respectively arranged on both sides of the tunnel junction 204 to form an integrated structure, and the integrated structure is located in the transition layer 205. Therefore, in this embodiment, the thickness of the transition layer 205 is adjusted to realize the position of the integrated structure as a whole in the standing wave field 100, so that it is better and more concentrated as a whole in a trough of the standing wave field 100, and the effective cavity length is shortened and the device series resistance is reduced without increasing the overall thickness of the device, thereby improving the photoelectric conversion efficiency.

[0081] As a preferred embodiment, Figure 2 As shown, in this embodiment, the thickness of the integrated structure is set to be within the range of 0%-30% of the energy distribution of the standing wave field 100.

[0082] Specifically, we can Figure 2 The broken line structure shown is understood as Figure 1 The structure shown is a simplified schematic diagram after being rotated 90°, so Figure 1 The thickness of the integrated structure shown in Figure 2 The width of the integrated structure shown in . The thickness of the oxide layer on both sides of the tunnel junction 204 is proportional to its doping level. The thicker the thickness, the higher the doping level. Therefore, it is necessary to limit the overall thickness of the integrated structure to 0%-30% of the energy distribution of the standing wave field 100, which can effectively avoid the introduction of additional doping loss and ensure the slope efficiency and photoelectric conversion efficiency of the laser.

[0083] In one embodiment, reference Figure 1 , the difference between the oxidation depth of the first oxide layer 3 and the oxidation depth of the second oxide layer 4 is set to Δd1, and the range of Δd1 is 0.5 μm~1 μm.

[0084] The difference in oxidation depth between the first oxide layer 3 and the second oxide layer 4 on the upper and lower sides of the tunnel junction 204 is set to Δd1. The tunnel junction 204 has a very obvious effect on the expansion of current. By placing the first oxide layer 3 with a deeper oxidation depth above the tunnel junction 204, a better current limiting effect can be achieved; and the second oxide layer 4 located below the tunnel junction 204 can appropriately use a shorter oxidation depth due to the weakening of the lateral current expansion capability. If Δd1 is too large, for example, the depth of the second oxide layer 4 is fixed, and the oxidation depth of the first oxide layer 3 becomes longer, the aperture of the first oxidation hole 301 will be too small, which will lead to a smaller light output, and the device string resistance will also increase, which is not conducive to the improvement of the photoelectric conversion efficiency; if Δd1 is too small, for example, the oxidation depth of the second oxide layer 4 is fixed, and the oxidation depth of the first oxide layer becomes shorter, the limiting ability of the electric field and the light field is insufficient. Therefore, in this embodiment, the difference Δd1 between the oxidation depths of the first oxide layer 3 and the second oxide layer 4 is limited to between 0.5μm and 1μm, which can achieve the maximum improvement effect of the photoelectric conversion efficiency.

[0085] In this embodiment, the first oxide layer 3 includes aluminum gallium arsenide with an aluminum component content ranging from 0.98 to 0.99, and the second oxide layer 4 includes aluminum gallium arsenide with an aluminum component content ranging from 0.96 to 0.98.

[0086] That is, by using aluminum gallium arsenide with different aluminum content, the first oxide layer 3 and the second oxide layer 4 with different oxidation depths are accurately formed, thereby achieving an effective improvement in photoelectric efficiency.

[0087] The multi-junction vertical cavity surface emitting laser of this embodiment, the epitaxial structure 2 also includes: a third oxide layer 5 and a fourth oxide layer 6, the third oxide layer 5 is arranged on the side of the first reflector layer 201 away from the substrate layer 1, the third oxide layer 5 has a third oxide hole 501 penetrating the third oxide layer 5, the third oxide hole 501 is concentric with the first oxide hole 301, and the oxidation depth of the third oxide layer 5 is less than the oxidation depth of the second oxide layer 4; the fourth oxide layer 6 is arranged on the side of the second reflector layer 202 close to the substrate layer 1, the fourth oxide layer 6 has a fourth oxide hole 601 penetrating the fourth oxide layer 6, the fourth oxide hole 601 is concentric with the first oxide hole 301, and the oxidation depth of the fourth oxide layer 6 is less than the oxidation depth of the second oxide layer 4.

[0088] like Figure 1 As shown, a plurality of third oxide layers 5 are arranged on one side of the first reflector layer 201 close to the active layer, and a plurality of fourth oxide layers 6 are arranged on one side of the second reflector layer 202 close to the active layer, and the oxidation depths of the third oxide layer 5 and the fourth oxide layer 6 are both less than the oxidation depth of the second oxide layer 4, that is, less than the oxidation depth of the first oxide layer 3. In this embodiment, on the basis of the first oxide layer 3 and the second oxide layer 4, the third oxide layer 5 and the fourth oxide layer 6 are further arranged, and the refractive index difference in the plane of the resonant cavity is further increased without reducing the light output path, and the leakage of the high-order light mode to the two sides of the resonant cavity in the lateral direction is weakened, so as to ensure that there are more high-order light modes in the resonant cavity, thereby facilitating the acquisition of a larger gain volume, the maximum improvement of the slope efficiency, and the improvement of the radiation area of ​​the entire device, and finally achieving the improvement of the photoelectric conversion efficiency under the high radiation area.

[0089] Of course, it is not excluded that a plurality of third oxide layers 5 are provided only on one side of the first reflector layer 201 close to the active layer, or a plurality of fourth oxide layers 6 are provided only on one side of the second reflector layer 202 close to the active layer.

[0090] Further, refer to Figure 1 In this embodiment, the oxidation depth of the third oxide layer 5 is equal to the oxidation depth of the fourth oxide layer 6; the difference between the oxidation depth of the third oxide layer 5 or the oxidation depth of the fourth oxide layer 6 and the oxidation depth of the second oxide layer 4 is set to Δd2, and the range of Δd2 is 3μm~4μm.

[0091] Specifically, in this embodiment, the third oxide layer 5 and the fourth oxide layer 6 both include aluminum gallium arsenide with an aluminum component content ranging from 0.7 to 0.9, so as to achieve an oxidation depth shorter than that of the second oxide layer 4, that is, at the oxidation depth level, the structure of the first oxide layer 3> the second oxide layer 4> the third oxide layer 5=the fourth oxide layer 6. In this embodiment, the oxidation depth of the third oxide layer 5 or the oxidation depth of the fourth oxide layer 6 is defined, and the difference between the oxidation depth of the second oxide layer 4 is set to Δd2. If Δd2 is too large, for example, the oxidation depth of the second oxide layer 4 is fixed, and the oxidation depths of the third oxide layer 5 and the fourth oxide layer 6 become shallower, the effect of controlling the light field resonance mode will be poor, that is, the lateral restriction effect of the resonant cavity on the standing wave field 100 is not obvious, and it is impossible to ensure that the output light beam contains a sufficiently high proportion of high-order light modes; if Δd2 is too small, for example, the oxidation depth of the second oxide layer 4 is fixed, and the oxidation depths of the third oxide layer 5 and the fourth oxide layer 6 become deeper, the current injection path will be affected, and additional lateral resistance will be brought to the second reflector layer 202. During the operation of the device, the waste heat generated by the lateral resistance of this part will greatly reduce the photoelectric conversion efficiency of the device. In this embodiment, the difference between the oxidation depth of the third oxide layer 5 or the oxidation depth of the fourth oxide layer 6 and the oxidation depth of the second oxide layer 4 is set to Δd2 between 3μm and 4μm, which helps to achieve the best improvement in photoelectric conversion efficiency.

[0092] like Figure 1 As shown, the above-mentioned epitaxial structure 2 also includes: a contact layer 206 arranged on the surface of the second reflector layer 202 facing away from the substrate layer 1; the epitaxial structure 2 also includes a ridge structure 200, the ridge structure 200 includes the contact layer 206, the second reflector layer 202, the active layer and part of the first reflector layer 201, and the third oxide layer 5 is located in the ridge structure 200.

[0093] Specifically, a contact layer 206 is provided at the topmost layer away from the substrate layer 1 in the epitaxial structure 2. The contact layer 206 and the second reflector layer 202 directly contacting thereunder are of the same conductivity type, that is, the contact layer 206 is also a P-type contact layer in this embodiment. The contact layer 206 is provided to facilitate good ohmic contact with the subsequently provided metal electrode, and further to achieve efficient current injection through connection with an external power source; the ridge structure 200 facilitates more precise control of the oxidation depth.

[0094] refer to Figure 1The multi-junction vertical cavity surface emitting laser of this embodiment further includes: a contact electrode layer 7, a passivation layer 8, a seed layer 9, a first electrode layer 10 and a second electrode layer 11, wherein the contact electrode layer 7 is arranged on a surface of the contact layer 206 facing away from the substrate layer 1, and the contact electrode layer 7 includes a contact electrode hole 701, and the contact electrode hole 701 is concentric with the first oxidation hole 301; the passivation layer 8 covers the outer wall surface of the ridge structure 200, and has an opening 801 exposing at least part of the contact electrode layer 7; the seed layer 9 covers the passivation layer 8, and is connected to the contact electrode layer 7 through the opening 801; the first electrode layer 10 covers the seed layer 9, and has a light exit hole 1001 exposing at least part of the seed layer 9, the light exit hole 1001 is concentric with the contact electrode hole 701, and in a direction perpendicular to the light exit direction, the width dimension of the light exit hole 1001 is smaller than the width dimension of the first oxidation hole 301; the second electrode layer 11 is arranged on a surface of the substrate layer 1 facing away from the epitaxial structure 2.

[0095] Exemplarily, the contact electrode layer 7 is a disc-shaped structure made of a metal material with a small contact resistance such as titanium (Ti), platinum (Pt), or gold (Au), and the diameter of the disc-shaped structure ranges from 20μm to 30μm; the contact electrode hole 701 formed between the disc-shaped structures is used for laser emission, and it is concentrically arranged with the first oxidation hole 301, the second oxidation hole 401, the third oxidation hole 501 and the fourth oxidation hole 601 to ensure smooth laser emission. The passivation layer 8 uses a silicon nitride film with a thickness between 400nm and 600nm, and then uses a standard photolithography process and an etching process to form an opening 801 above the contact electrode layer 7. The passivation layer 8 is arranged on the outer wall surface of the ridge structure 200 to achieve efficient reflection of photons inside the ridge structure 200, so as to prevent photons from escaping and affecting the light extraction efficiency. In this embodiment, titanium (Ti) or gold (Au) is deposited on the surface of the passivation layer 8 by a standard metal deposition process to form a seed layer 9, which facilitates the subsequent high-quality electrical connection between the electrode layer material located on the light-emitting side and the epitaxial structure 2. In this embodiment, the first electrode layer 10 and the second electrode layer 11 are both made of metal gold, which has excellent conductivity and low contact resistance, and can achieve efficient electrical connection with the epitaxial structure 2 when connected to an external power source.

[0096] The conversion efficiency of multi-junction VCSEL in the related art is generally below 40%. In this embodiment, a plurality of different oxide layer structures including the first oxide layer 3, the second oxide layer 4, the third oxide layer 5 and the fourth oxide layer 6 at specific positions are used, and the relative length design of the integrated structure based on the tunnel junction 204, the first oxide layer 3 and the second oxide layer 4 can effectively improve the photoelectric conversion efficiency of the multi-junction VCSEL with a high radiation area to more than 50%, and the process is compatible with the traditional VCSEL vertical process, the process is simple, and can meet the requirements of higher photoelectric conversion efficiency of laser heating and heat treatment VCSEL products.

[0097] refer to Figure 1 , Figure 2 as well as Figures 5 to 11 This embodiment also provides a method for preparing a multi-junction vertical cavity surface emitting laser, which is used to prepare the multi-junction vertical cavity surface emitting laser. Figure 5 The preparation method is a schematic flow chart, and the preparation method comprises the following steps:

[0098] Step S501, forming a substrate layer 1.

[0099] Exemplarily, the substrate layer 1 in this embodiment is a gallium arsenide substrate, and a plurality of array-arranged multi-junction vertical cavity surface emitting lasers of the VCSEL device are formed on the substrate layer 1 .

[0100] Step S502, forming an epitaxial structure 2 on the substrate layer 1, the epitaxial structure 2 includes a first reflector layer 201, an active layer and a second reflector layer 202 which are stacked, the first reflector layer 201 is arranged on the substrate layer 1; the active layer includes a plurality of barrier layers 203 and a plurality of tunnel junctions 204 which are arranged at intervals from each other.

[0101] For example, in this embodiment, the epitaxial structure 2 of the laser is grown on the gallium arsenide substrate layer 1 by metal organic chemical vapor deposition (MOCVD), such as Figure 6 shown.

[0102] Step S503, forming a plurality of first oxide layers 3 and a plurality of second oxide layers 4 in the active layer, wherein the first oxide layer 3 is arranged on a side surface of the tunnel junction 204 away from the substrate layer 1, and has a first oxide hole 301 penetrating the first oxide layer 3 along the light emitting direction; the second oxide layer 4 is arranged on a side surface of the tunnel junction 204 close to the substrate layer 1, and has a second oxide hole 401 penetrating the second oxide layer 4 along the light emitting direction, the first oxide hole 301 and the second oxide hole 401 are concentric, and the oxidation depth of the first oxide layer 3 is greater than the oxidation depth of the second oxide layer 4; any tunnel junction 204, the first oxide layer 3 and the second oxide layer 4 form an integrated structure, the integrated structure is arranged between two adjacent barrier layers 203, and one integrated structure is correspondingly arranged in a trough of the standing wave field 100 of the laser.

[0103] Exemplarily, the substrate layer 1 and the epitaxial structure 2 are placed in a wet oxidation furnace, and then water vapor is introduced into the chamber of the oxidation furnace. The wet oxidation furnace is controlled to heat up to the oxidation temperature. After a certain oxidation time, a first oxide layer 3 and a second oxide layer 4 are formed on both sides of the tunnel junction 204 of the active layer, and a first oxide hole 301 and a second oxide hole 401 with a certain width are formed at the center of the light exit hole 1001, wherein the aperture of the first oxide hole 301 is 15 μm to 25 μm, as shown in FIG. Fig. 9 shown.

[0104] The multi-junction vertical cavity surface emitting laser is prepared by the above-mentioned preparation method. On the one hand, Figure 1 The light field confinement structure with different oxide layers on both sides of the tunnel junction 204 shown helps to achieve control of the light field resonance mode and ensure the presence of more high-order light modes in the resonance cavity, thereby obtaining a larger gain volume, a maximum improvement in slope efficiency, and an improvement in the radiation area of ​​the entire device, and ultimately improving the photoelectric conversion efficiency under a high radiation area. On the other hand, a first oxide layer 3 with a deeper oxidation is provided on one side of the tunnel junction 204 close to the light exit hole 1001, and a second oxide layer 4 with a shallower oxidation is provided on the other side, which can not only effectively limit the lateral current, but also avoid the increase of the series resistance, and ultimately achieve an improvement in the photoelectric conversion efficiency. In addition, referring to Figure 2 In this embodiment, the integrated structure consisting of the tunnel junction 204, the first oxide layer and the second oxide layer 4 is disposed as a whole in a valley of the standing wave field 100, so that the wave number corresponding to each tunnel junction 204 is effectively shortened, thereby shortening the effective cavity length of the standing wave field 100 and greatly reducing the device series resistance caused by the increase in the effective cavity length, thereby further improving the photoelectric conversion efficiency.

[0105] In one embodiment, after step S503 of forming a plurality of first oxide layers 3 and a plurality of second oxide layers 4 in the active layer, the preparation method further comprises:

[0106] Step S504, forming a third oxide layer 5 on a side of the first reflector layer 201 away from the substrate layer 1, and / or forming a fourth oxide layer 6 on a side of the second reflector layer 202 close to the substrate layer 1; the third oxide layer 5 has a third oxide hole 501 penetrating the third oxide layer 5, the third oxide hole 501 is concentric with the first oxide hole 301, and the oxidation depth of the third oxide layer 5 is less than the oxidation depth of the second oxide layer 4; the fourth oxide layer 6 has a fourth oxide hole 601 penetrating the fourth oxide layer 6, the fourth oxide hole 601 is concentric with the first oxide hole 301, and the oxidation depth of the fourth oxide layer 6 is less than the oxidation depth of the second oxide layer 4.

[0107] like Fig. 9 As shown, the third oxide layer 5 and the fourth oxide layer 6 can also be formed in a wet oxidation furnace. On the basis of the first oxide layer 3 and the second oxide layer 4, the third oxide layer 5 and the fourth oxide layer 6 are further provided, which further increases the refractive index difference in the plane of the resonant cavity without reducing the light output path, weakens the leakage of the high-order light mode to both sides of the resonant cavity in the lateral direction, and ensures that there are more high-order light modes in the resonant cavity, thereby helping to obtain a larger gain volume, maximize the improvement of slope efficiency, and improve the radiation area of ​​the entire device, and finally achieve an improvement in photoelectric conversion efficiency under a high radiation area.

[0108] The epitaxial structure 2 of this embodiment further includes a contact layer 206 disposed on the surface of the second reflector layer 202 facing away from the substrate layer 1. The contact layer 206 is disposed on the uppermost layer of the epitaxial structure 2 away from the substrate layer 1. The contact layer 206 and the second reflector layer 202 directly contacting thereunder are of the same conductivity type. The contact layer 206 is disposed to facilitate good ohmic contact with the subsequently disposed metal electrode, and further to achieve efficient current injection through connection with an external power source.

[0109] After step S502 of forming the epitaxial structure 2 on the substrate layer 1 and before step S503 of forming a plurality of first oxide layers 3 and a plurality of second oxide layers 4 in the active layer, the preparation method further comprises:

[0110] refer to Figure 7 A contact electrode layer 7 is formed on the surface of the contact layer 206 facing away from the substrate layer 1 . The contact electrode layer 7 includes a contact electrode hole 701 . The contact electrode hole 701 is concentric with the first oxidation hole 301 .

[0111] First, a metal material with low contact resistance, such as titanium (Ti), platinum (Pt), or gold (Au), is deposited on the entire upper surface of the contact layer 206. Then, the metal material is partially removed through a standard photolithography process to form a plurality of disc-shaped structures. The diameter range of the disc-shaped structures is set between 20μm and 30μm. The contact electrode hole 701 formed between the disc-shaped structures is used for laser emission. The contact electrode hole 701 is concentrically arranged with the first oxidation hole 301, the second oxidation hole 401, the third oxidation hole 501 and the fourth oxidation hole 601 to ensure smooth laser emission.

[0112] A ridge structure 200 is formed in the epitaxial structure 2 , the ridge structure 200 includes a contact layer 206 , a second reflector layer 202 , an active layer and a portion of the first reflector layer 201 , a third oxide layer 5 is located in the ridge structure 200 , and a contact electrode layer 7 is located on the ridge structure 200 .

[0113] Exemplarily, a dry etching process is used to define a mesa structure to form a ridge structure 200, such as Figure 8 As shown. The diameter of the ridge structure 200 is between 30 μm and 50 μm, and the etching depth reaches the first reflector layer 201, thereby forming the basis of the VCSEL device with the common substrate layer 1. After the ridge structure 200 is formed, oxidation is performed on the sidewall surface of the ridge structure 200 to form the first oxide layer 3, the second oxide layer 4, the third oxide layer 5 and the fourth oxide layer 6, and the oxidation depth is easier to control.

[0114] In one embodiment, after step S504 of forming a third oxide layer 5 on a side of the first reflector layer 201 away from the substrate layer 1 and / or forming a fourth oxide layer 6 on a side of the second reflector layer 202 close to the substrate layer 1, the preparation method further comprises:

[0115] Step S505 , forming a passivation layer 8 on the outer wall surface of the ridge structure 200 , wherein the passivation layer 8 has an opening 801 exposing at least a portion of the contact electrode layer 7 .

[0116] refer to Fig.10 First, a silicon nitride film with a thickness of 400nm to 600nm is formed on the entire outer wall surface of the ridge structure 200, and can cover the upper surface of the first reflector layer outside the ridge structure 200; then, an opening 801 is formed on the silicon nitride film above the contact electrode layer 7 using a standard photolithography process and an etching process. A passivation layer 8 is provided on the outer wall surface of the ridge structure 200 to achieve efficient reflection of photons inside the ridge structure 200, and prevent photons from escaping and affecting light extraction efficiency.

[0117] Step S506 , forming a seed layer 9 on the passivation layer 8 , wherein the seed layer 9 is connected to the contact electrode layer 7 through the opening 801 .

[0118] refer to Fig.11 In this embodiment, titanium (Ti) or gold (Au) is deposited on the surface of the passivation layer 8 by a standard metal deposition process to form a seed layer 9, which facilitates the subsequent high-quality electrical connection between the electrode layer material on the light-emitting side and the epitaxial structure 2.

[0119] Step S507, forming a first electrode layer 10 on the seed layer 9, the first electrode layer 10 having a light emitting hole 1001 exposing at least a portion of the seed layer 9, the light emitting hole 1001 is concentric with the contact electrode hole 701, and in a direction perpendicular to the light emitting direction, the width dimension of the light emitting hole 1001 is smaller than the width dimension of the first oxidation hole 301.

[0120] refer to Figure 1 In this embodiment, the first electrode layer 10 is made of metal gold, which has excellent conductivity and low contact resistance, and can achieve efficient electrical connection with the epitaxial structure 2 when connected to an external power supply.

[0121] Step S508 , forming a second electrode layer 11 on a surface of the substrate layer 1 facing away from the epitaxial structure 2 .

[0122] refer to Figure 1 The second electrode layer 11 is made of metal gold like the first electrode layer 10, has excellent conductivity and low contact resistance, and can achieve efficient electrical connection with the epitaxial structure 2 when connected to an external power source.

[0123] The further functional description of each of the above structures is the same as that of the above corresponding embodiments and will not be repeated here.

[0124] In the above description, the technical details of the patterning and etching of each layer are not described in detail. However, those skilled in the art should understand that various technical means can be used to form layers, regions, etc. of desired shapes. In addition, in order to form the same structure, those skilled in the art can also design methods that are not completely the same as the methods described above. In addition, although the various embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage.

[0125] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A multi-junction vertical cavity surface emitting laser, characterized in that: include: substrate layer; An epitaxial structure, the epitaxial structure comprising a first reflector layer, an active layer and a second reflector layer which are stacked, the first reflector layer being arranged on the substrate layer; the active layer comprising a plurality of barrier layers and a plurality of tunnel junctions, the barrier layers and the tunnel junctions being arranged spaced apart from each other; A first oxide layer is arranged on a surface of a side of the tunnel junction away from the substrate layer, the first oxide layer having a first oxide hole penetrating the first oxide layer along a light emitting direction; A second oxide layer is arranged on a side surface of the tunnel junction close to the substrate layer, the second oxide layer has a second oxide hole that penetrates the second oxide layer along the light emitting direction, the first oxide hole and the second oxide hole are concentric, and the oxidation depth of the first oxide layer is greater than the oxidation depth of the second oxide layer; any of the tunnel junctions, the first oxide layer and the second oxide layer form an integrated structure, the integrated structure is arranged between two adjacent barrier layers, and one of the integrated structures is correspondingly arranged in a trough of the standing wave field of the laser.

2. The multi-junction vertical cavity surface emitting laser according to claim 1, characterized in that: The active layer further comprises: A transition layer is disposed between adjacent barrier layers; the transition layer is configured to adjust the position of the integrated structure in the standing wave field.

3. The multi-junction vertical cavity surface emitting laser according to claim 2, characterized in that: The thickness of the integrated structure is within the range of 0%-30% of the energy distribution of the standing wave field.

4. The multi-junction vertical cavity surface emitting laser according to claim 1, characterized in that: The difference between the oxidation depth of the first oxide layer and the oxidation depth of the second oxide layer is set to Δd1, and the range of Δd1 is 0.5 μm to 1 μm.

5. The multi-junction vertical cavity surface emitting laser according to claim 4, characterized in that: The first oxide layer includes aluminum gallium arsenide with an aluminum component content ranging from 0.98 to 0.99, and the second oxide layer includes aluminum gallium arsenide with an aluminum component content ranging from 0.96 to 0.

98.

6. The multi-junction vertical cavity surface emitting laser according to any one of claims 1 to 5, characterized in that: The epitaxial structure further comprises: A third oxide layer is arranged on a side of the first reflector layer away from the substrate layer; the third oxide layer has a third oxide hole penetrating the third oxide layer, the third oxide hole is concentric with the first oxide hole, and the oxidation depth of the third oxide layer is less than the oxidation depth of the second oxide layer; and / or A fourth oxide layer is arranged on a side of the second reflector layer close to the substrate layer; the fourth oxide layer has a fourth oxide hole penetrating the fourth oxide layer, the fourth oxide hole is concentric with the first oxide hole, and the oxidation depth of the fourth oxide layer is less than the oxidation depth of the second oxide layer.

7. The multi-junction vertical cavity surface emitting laser according to claim 6, characterized in that: The oxidation depth of the third oxide layer is equal to the oxidation depth of the fourth oxide layer; the difference between the oxidation depth of the third oxide layer or the oxidation depth of the fourth oxide layer and the oxidation depth of the second oxide layer is set to Δd2, and the range of Δd2 is 3μm~4μm.

8. The multi-junction vertical cavity surface emitting laser according to claim 7, characterized in that: The epitaxial structure further comprises: a contact layer disposed on a surface of the second reflector layer on a side away from the substrate layer; The epitaxial structure includes a ridge structure, the ridge structure includes the contact layer, the second reflector layer, the active layer and a portion of the first reflector layer, and the third oxide layer is located in the ridge structure.

9. The multi-junction vertical cavity surface emitting laser according to claim 8, characterized in that: Also includes: A contact electrode layer, arranged on a surface of the contact layer facing away from the substrate layer; The contact electrode layer comprises a contact electrode hole, and the contact electrode hole is concentric with the first oxidation hole; a passivation layer, the passivation layer covering an outer wall surface of the ridge structure and having an opening exposing at least a portion of the contact electrode layer; a seed layer, the seed layer covering the passivation layer and connected to the contact electrode layer through the opening; a first electrode layer, the first electrode layer covers the seed layer and has a light exit hole exposing at least a portion of the seed layer, the light exit hole is concentric with the contact electrode hole, and in a direction perpendicular to the light exit direction, the width of the light exit hole is smaller than the width of the first oxidation hole; A second electrode layer is provided on a surface of the substrate layer facing away from the epitaxial structure.

10. A method for preparing a multi-junction vertical cavity surface emitting laser, used for preparing the multi-junction vertical cavity surface emitting laser according to any one of claims 1 to 9, characterized in that: The preparation method comprises: forming a substrate layer; An epitaxial structure is formed on the substrate layer, wherein the epitaxial structure comprises a first reflector layer, an active layer and a second reflector layer which are stacked, wherein the first reflector layer is arranged on the substrate layer; and the active layer comprises a plurality of barrier layers and a plurality of tunnel junctions which are arranged at intervals from each other; A plurality of first oxide layers and a plurality of second oxide layers are formed in the active layer, wherein the first oxide layer is arranged on a side surface of the tunnel junction away from the substrate layer, and has a first oxide hole penetrating the first oxide layer along the light emitting direction; the second oxide layer is arranged on a side surface of the tunnel junction close to the substrate layer, and has a second oxide hole penetrating the second oxide layer along the light emitting direction, the first oxide hole and the second oxide hole are concentric, and the oxidation depth of the first oxide layer is greater than the oxidation depth of the second oxide layer; any of the tunnel junctions, the first oxide layer and the second oxide layer form an integrated structure, the integrated structure is arranged between two adjacent barrier layers, and one of the integrated structures is correspondingly arranged in a trough of a standing wave field of a laser.

11. The method for preparing a multi-junction vertical cavity surface emitting laser according to claim 10, characterized in that: After forming a plurality of first oxide layers and a plurality of second oxide layers in the active layer, the preparation method further comprises: A third oxide layer is formed on a side of the first reflector layer away from the substrate layer, and / or a fourth oxide layer is formed on a side of the second reflector layer close to the substrate layer; the third oxide layer has a third oxide hole penetrating the third oxide layer, the third oxide hole is concentric with the first oxide hole, and the oxidation depth of the third oxide layer is less than the oxidation depth of the second oxide layer; the fourth oxide layer has a fourth oxide hole penetrating the fourth oxide layer, the fourth oxide hole is concentric with the first oxide hole, and the oxidation depth of the fourth oxide layer is less than the oxidation depth of the second oxide layer.

12. The method for preparing a multi-junction vertical cavity surface emitting laser according to claim 11, characterized in that: The epitaxial structure further comprises a contact layer arranged on a surface of the second reflector layer on a side away from the substrate layer; After forming the epitaxial structure on the substrate layer and before forming a plurality of first oxide layers and a plurality of second oxide layers in the active layer, the preparation method further comprises: forming a contact electrode layer on a surface of the contact layer facing away from the substrate layer, wherein the contact electrode layer comprises a contact electrode hole, and the contact electrode hole is concentric with the first oxidation hole; A ridge structure is formed in the epitaxial structure, the ridge structure includes the contact layer, the second reflector layer, the active layer and a portion of the first reflector layer, the third oxide layer is located in the ridge structure, and the contact electrode layer is located on the ridge structure.

13. The method for preparing a multi-junction vertical cavity surface emitting laser according to claim 12, characterized in that: After forming a third oxide layer on a side of the first reflector layer away from the substrate layer, and / or forming a fourth oxide layer on a side of the second reflector layer close to the substrate layer, the preparation method further comprises: forming a passivation layer on an outer wall surface of the ridge structure, wherein the passivation layer has an opening exposing at least a portion of the contact electrode layer; forming a seed layer on the passivation layer, wherein the seed layer is connected to the contact electrode layer through the opening; forming a first electrode layer on the seed layer, wherein the first electrode layer has a light exit hole exposing at least a portion of the seed layer, the light exit hole is concentric with the contact electrode hole, and in a direction perpendicular to the light exit direction, the width of the light exit hole is smaller than the width of the first oxidation hole; A second electrode layer is formed on a surface of the substrate layer facing away from the epitaxial structure.

Images