Vertical cavity surface emitting laser and preparation method thereof

Abstract

The embodiment of the invention provides a vertical cavity surface emitting laser which can be applied to the technical field of semiconductor lasers. The laser comprises a substrate which is provided with a first surface and a second surface which are oppositely arranged; the N pixels are located on the first surface of the substrate, N is a positive integer larger than or equal to 2, and at least parts of at least two adjacent pixels are arranged at intervals; the top lining is located on the side, away from the substrate, of the first electrode pixel; and an adhesive layer on the first surface of the substrate, covering at least a portion of a side surface of the pixel and contacting a side surface of the top liner close to the substrate. The top lining structure is introduced into the light-emitting surface of the vertical-cavity surface-emitting laser, so that heat generated by the second distributed Bragg reflector on the light-emitting surface can be directly conducted to the contacted top lining, the heat dissipation path of the laser is increased, and the heat dissipation capability of the laser is improved. The embodiment of the invention also provides a preparation method of the vertical cavity surface emitting laser.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor lasers, and in particular to a vertical cavity surface emitting laser and a preparation method thereof. Background Art

[0002] Generally speaking, the heat generated during the composite light emission process of the active area of ​​the Vertical-Cavity Surface-Emitting Laser (VCSEL) needs to be conducted to the substrate, and then conducted to the heat sink through the substrate to achieve heat dissipation, resulting in poor heat dissipation effect. With the increase in the power of vertical-cavity surface-emitting lasers, the requirements for heat dissipation efficiency are increasing. In addition, for low-divergence-angle VCSELs used in some specific scenarios, micro-nano structures are generally directly integrated on the surface to achieve heat dissipation, but the integrated micro-nano structure increases the difficulty of the preparation process of VCSEL devices and affects the power consumption of the device.

[0003] The existing vertical cavity surface emitting laser structure and preparation method cannot increase the heat dissipation efficiency of the laser while reducing the process difficulty. For example, in the patent with application number CN 202210751501.8, a flip-chip VCSEL chip structure and its manufacturing method are disclosed, wherein the structure includes a substrate, a first Bragg reflector layer, a quantum well layer, a second Bragg reflector layer and a dielectric film layer. The substrate has a first surface and a second surface arranged opposite to each other, and a microlens structure with a focusing function is formed on the first surface; the first Bragg reflector layer is arranged on the second surface of the substrate; the quantum well layer is arranged on the side of the first Bragg reflector layer away from the substrate; the second Bragg reflector layer is arranged on the side of the quantum well layer away from the first Bragg reflector layer; the dielectric film layer covers the sidewalls of the second Bragg reflector layer, the quantum well layer and the first Bragg reflector layer and extends to the second surface of the substrate, and the dielectric film layer partially covers the surface of the second Bragg reflector layer away from the quantum well layer. This scheme forms a lens on a gallium arsenide (GaAs) substrate, which has restrictions on the laser wavelength, for example, it is not suitable for using wavelengths below 940nm, which affects the light extraction efficiency.

[0004] In the patent with application number CN 202010045074.2, a VCSEL device with a transparent top substrate and positive and negative electrodes on the back and a method for preparing the same are disclosed, including: an oxidized channel on the epitaxial layer and a VCSEL unit mesa structure defined by the oxide layer; a transparent top substrate located on the epitaxial layer and an optical element disposed on the transparent top substrate; a through hole formed on the back of the epitaxial layer; and a positive electrode and a negative electrode on the back of the epitaxial layer. This solution bonds a sapphire transparent top substrate to the front of the VCSEL, leads the front electrode to the back, and adds a lead preparation process.

[0005] At the same time, the heat dissipation of the existing VCSEL structure, especially the heat dissipation of the light emitting surface, causes the performance of the VCSEL to be significantly reduced. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] In order to solve at least one of the above-mentioned technical problems arising from the heat dissipation of a vertical cavity surface emitting laser in the prior art, an embodiment of the present invention provides a vertical cavity surface emitting laser and a preparation method thereof. A top lining structure is introduced on the light-emitting surface of the vertical cavity surface emitting laser, so that the heat generated by the second distributed Bragg reflector on the light-emitting surface can be directly conducted to the contacting top lining, thereby increasing the heat dissipation path of the laser and improving the heat dissipation capacity of the laser.

[0008] (II) Technical solution

[0009] In view of the above technical problems, an embodiment of the present invention provides a vertical cavity surface emitting laser and a method for manufacturing the same.

[0010] According to a first aspect of the present invention, a vertical cavity surface emitting laser is provided, comprising: a substrate having a first surface and a second surface arranged opposite to each other; N picture elements, located on the first surface of the substrate, wherein N is a positive integer greater than or equal to 2, and at least a portion of at least two adjacent picture elements are spaced apart at a predetermined interval; a top liner, located on a side of the picture element away from the substrate; and an adhesive layer, located on the first surface of the substrate, covering at least a portion of the side surface of the picture element and contacting a surface of the top liner on a side close to the substrate.

[0011] In some exemplary embodiments, at least a portion of any two adjacent picture elements are spaced apart at a predetermined interval to form N-1 inner gaps; an outer gap is formed between the adhesive layer, the top lining, and the outermost picture elements; and the vertical cavity surface emitting laser also includes a heat conducting portion, which is respectively located in the N-1 inner gaps and the outer gap.

[0012] In some exemplary embodiments, the method further includes: a first electrode located on the second surface of the substrate.

[0013] In some exemplary embodiments, at least one pixel includes: a first distributed Bragg reflector, located on a first surface of a substrate; a quantum well active region, located on a side of the first distributed Bragg reflector away from the substrate, the quantum well active region including a tunnel junction, an active region and an oxide layer arranged periodically in sequence; a second distributed Bragg reflector, located on a side of the oxide layer away from the substrate; and a second electrode, located on a side of the second distributed Bragg reflector away from the substrate, wherein the side of the second distributed Bragg reflector away from the substrate is a light emitting surface.

[0014] In some exemplary embodiments, the top substrate includes: a light-transmitting layer located on a side of the second electrode away from the substrate, wherein the reflectivity of the light-transmitting layer to lasers with a wavelength greater than or equal to 600 nm is less than 3%; the thermal conductivity of the light-transmitting layer is greater than the thermal conductivity of the second distributed Bragg reflector; the electrical conductivity of the light-transmitting layer is greater than the electrical conductivity of the second distributed Bragg reflector; the material of the light-transmitting layer includes silicon carbide; the thickness of the light-transmitting layer is 200 μm-300 μm; and the surface of the light-transmitting layer away from the substrate includes a microlens array structure, the microlens array structure includes N microlenses arranged in an array, wherein the position of the microlens corresponds to the laser emission window of the pixel, so that the period of the microlens matches the period of the pixel, thereby achieving the purpose of compressing the laser divergence angle.

[0015] In some exemplary embodiments, the top substrate further includes: a graphene layer, wherein the graphene layer is located between the light-transmitting layer and the second electrode, wherein the number of graphene layers in the graphene layer is no more than 3 layers.

[0016] In some exemplary embodiments, the top substrate further includes: an anti-reflection film located between the graphene layer and the second distributed Bragg reflector, and the height of the anti-reflection film is flush with that of the second electrode.

[0017] According to a second aspect of the present invention, a method for preparing a vertical cavity surface emitting laser is provided, comprising: preparing a picture element: growing a first distributed Bragg reflector, a quantum well active region, a second distributed Bragg reflector and a second electrode in sequence on a first surface of a substrate to obtain N picture elements, wherein N is a positive integer greater than or equal to 2, and at least a portion of at least two adjacent picture elements are arranged at a predetermined interval; forming a heat-conducting portion: filling the heat-conducting portion in the gaps between adjacent picture elements and on the sides of the outermost picture elements, and the height of the heat-conducting portion is flush with the surface of the second electrode away from the substrate; forming an adhesive layer: growing an adhesive layer on the exposed sides of the picture element and the heat-conducting portion, and the height of the heat-conducting portion is not lower than the height of the surface of the second electrode away from the substrate; forming a top liner: pressing a pre-prepared top liner to a side surface of the picture element away from the substrate, and the top liner covers the picture element, the heat-conducting portion and the adhesive layer; and preparing a first electrode: forming the first electrode on the second surface of the substrate, wherein the quantum well active region includes a tunnel junction, an active region and an oxide layer arranged periodically in sequence; and the first surface and the second surface are two surfaces arranged opposite to each other on the substrate.

[0018] In some exemplary embodiments, the top lining includes a light-transmitting layer, and a method for pre-preparing the top lining includes preparing a microlens array structure on a surface of the light-transmitting layer away from the substrate, wherein the microlens array structure includes N microlenses arranged in an array; the position of the microlens corresponds to the laser emission window of the pixel, so that the period of the microlens matches the period of the pixel, thereby achieving the purpose of compressing the laser divergence angle.

[0019] In some exemplary embodiments, the top substrate also includes a graphene layer, and the pre-preparation method of the top substrate also includes: forming a graphene layer on the opposite surfaces of the light-transmitting layer and the microlens array structure; in the process of pressing the pre-prepared top substrate to the side surface of the pixel away from the substrate, the graphene layer contacts the side surface of the pixel away from the substrate.

[0020] (III) Beneficial effects

[0021] It can be seen from the above technical solutions that a vertical cavity surface emitting laser and a preparation method thereof provided by an embodiment of the present invention have at least one of the following beneficial effects:

[0022] (1) By introducing a top liner structure on the light-emitting surface of a vertical cavity surface emitting laser, the heat generated by the second distributed Bragg reflector on the light-emitting surface can be directly transferred to the contacting top liner, thereby increasing the heat dissipation path of the laser and improving the heat dissipation capacity of the laser.

[0023] (2) The top substrate includes a light-transmitting layer, and the material of the light-transmitting layer is silicon carbide. As a high-refractive-index material, silicon carbide helps to form an effective DBR structure, thereby improving reflectivity and light output quality. The high thermal conductivity of silicon carbide also helps to dissipate heat from the VCSEL device, thereby reducing the impact of thermal effects on light output quality.

[0024] (3) The top substrate further includes a graphene layer, which can further reduce the thermal resistance of the VCSEL device (array) and thus improve its performance. At the same time, the graphene is grown on the silicon carbide layer, and then an electrical connection is formed between the graphene layer and the second electrode through an adhesive layer, thereby avoiding the problems of interface contact and inconsistent thermal expansion coefficients. Furthermore, graphene is also beneficial for improving current uniformity. Since graphene has good lateral conductivity, its lateral conductivity is higher than that of the best conductive metal - silver. Therefore, by injecting current into the VCSEL device through graphene, the problem of uneven electric injection in the conventional VCSEL array structure can be improved, so that the current can be expanded laterally and the current can be injected uniformly.

[0025] (4) By filling an anti-reflection film between the second distributed Bragg reflector and the graphene layer so that the upper and lower surfaces of the anti-reflection film are in contact with the surface of the graphene layer and the second distributed Bragg reflector respectively, the laser transmittance can be enhanced and the reflection loss can be reduced.

[0026] (5) Filling the heat-conducting part between the pixels can improve the heat dissipation capacity of each pixel. At the same time, the upper surface of the heat-conducting part is flush with the second electrode, and the lower surface is located on the first distributed Bragg reflector or the substrate. On the one hand, the graphene layer and the heat-conducting part can directly form heat conduction to improve the heat dissipation efficiency; on the other hand, the graphene layer and the light-transmitting layer can be supported by the heat-conducting part and the second electrode to ensure the mechanical stability and reliability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the cross-sectional structure of a first vertical cavity surface emitting laser according to an embodiment of the present invention is shown;

[0028] Figure 2 A schematic diagram schematically shows the relationship between the thickness of the SiC layer and the temperature of the active region according to an embodiment of the present invention;

[0029] Figure 3 A schematic diagram of the cross-sectional structure of a second vertical cavity surface emitting laser according to an embodiment of the present invention is shown;

[0030] Figure 4 A schematic diagram of a process of manufacturing a vertical cavity surface emitting laser according to an embodiment of the present invention is shown;

[0031] Figure 5 A schematic diagram of a two-dimensional simulation of the heat generation of a vertical cavity surface emitting laser including a graphene-silicon carbide top substrate according to an embodiment of the present invention is schematically shown;

[0032] Figure 6 A schematic diagram schematically shows a three-dimensional simulation comparison of the heat generation of a vertical cavity surface emitting laser including a graphene-silicon carbide top substrate according to an embodiment of the present invention and a conventional packaging structure;

[0033] Figure 7 A schematic diagram schematically shows a two-dimensional simulation diagram of current density distribution of a vertical cavity surface emitting laser according to an embodiment of the present invention; and

[0034] Figure 8 The two-dimensional simulation diagram of the current density distribution of the traditional packaging structure is schematically shown.

[0035] Description of reference numerals:

[0036] 1-first electrode; 2-substrate; 3-pixel; 31-first distributed Bragg reflector; 32-quantum well active region; 321-tunnel junction; 322-active region; 323-oxide layer; 33-second distributed Bragg reflector; 34-second electrode; 4-top substrate; 41-light-transmitting layer; 411-microlens array structure; 42-graphene layer; 43-anti-reflection film; 5-adhesive layer; 6-thermal conductive part. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The working principle of the vertical cavity surface emitting laser (VCSEL) is: based on epitaxial technology, a wavelength-level resonant cavity is formed by stacking reflective N-DBR (N-type distributed Bragg reflector), tunnel junction and quantum well active area, and output P-DBR (P-type distributed Bragg reflector) in the vertical direction of the substrate. This structural design enables the laser to obtain effective gain in the cavity and finally output. The current starts from the P electrode, penetrates the P-DBR (light emitting surface), passes through the active area 322, and then passes through the N-DBR, finally reaches the substrate and flows to the N-terminal electrode on the surface of the substrate. Since the resistivity of the P-DBR as the light emitting surface is high, its heat generation is relatively large. In the standard VCSEL design, the P-DBR is far away from the substrate and the heat sink, which limits its heat dissipation efficiency.

[0039] Figure 1 The cross-sectional structure diagram of the first vertical cavity surface emitting laser according to the embodiment of the present invention is schematically shown.

[0040] like Figure 1 As shown, the first vertical cavity surface emitting laser according to the embodiment of the present invention comprises: a substrate 2 having a first surface and a second surface arranged oppositely; N picture elements 3 (picture element 3 refers to a single laser emitting unit constituting a vertical cavity surface emitting laser) located on the first surface of the substrate 2, wherein N is a positive integer greater than or equal to 2, and at least a portion of at least two adjacent picture elements 3 are arranged at a predetermined interval; a top substrate 4 located on the side of the picture element 3 away from the substrate 2; and an adhesive layer 5 located on the first surface of the substrate 2, the adhesive layer 5 covering at least a portion of the side of the picture element 3 and contacting with a side surface of the top substrate 4 close to the substrate 2, and a first electrode 1 located on the second surface of the substrate 2, wherein an outer gap is formed between the adhesive layer 5, the top substrate 4 and the outermost picture element 3. Optionally, the substrate 2 comprises at least one of a gallium arsenide substrate 2, an aluminum nitride substrate 2, a silicon carbide substrate 2 and a diamond transfer substrate 2. The device formed by the pixel 3 in the embodiment of the present invention includes a single-junction or multi-junction vertical cavity surface emitting laser, and the vertical cavity surface emitting laser includes an array pixel 3 vertical cavity surface emitting laser or a single-tube pixel 3 vertical cavity surface emitting laser.

[0041] In an embodiment of the present invention, by introducing a top substrate 4 structure on the light-emitting surface of the vertical cavity surface emitting laser, the heat generated by the second distributed Bragg reflector 33 on the light-emitting surface can be directly conducted to the contacting top substrate 4, thereby increasing the heat dissipation path of the laser and improving the heat dissipation capacity of the laser.

[0042] In some exemplary embodiments, at least one pixel 3 includes: a first distributed Bragg reflector 31, located on the first surface of the substrate 2; a quantum well active region 32, located on the side of the first distributed Bragg reflector 31 away from the substrate 2, the quantum well active region 32 includes a tunnel junction 321, an active region 322 and an oxide layer 323 arranged periodically in sequence; a second distributed Bragg reflector 33, located on the side of the oxide layer 323 away from the substrate 2; and a second electrode 34, located on the side of the second distributed Bragg reflector 33 away from the substrate 2, wherein the side of the second distributed Bragg reflector 33 away from the substrate 2 is a light emitting surface.

[0043] In some exemplary embodiments, at least a portion of any two adjacent picture elements 3 are arranged at a predetermined spacing to form N-1 inner gaps; and the vertical cavity surface emitting laser further includes a heat conducting portion 6, wherein the heat conducting portion 6 is respectively located in the N-1 inner gaps and the outer gaps. Filling the heat conducting portion 6 between the picture elements 3 can improve the heat dissipation capacity of each picture element 3. At the same time, the upper surface of the heat conducting portion 6 is flush with the second electrode 34, and the lower surface is located on the first distributed Bragg reflector 31 or the substrate 2. On the one hand, the top substrate 4 and the heat conducting portion 6 are directly heat-conducted to improve the heat dissipation efficiency; on the other hand, the top substrate 4 can be supported by the heat conducting portion 6 and the second electrode 34 to ensure the mechanical stability and reliability of the device. Optionally, the material of the heat conducting portion 6 includes gold (Au).

[0044] In some exemplary embodiments, the top substrate 4 includes: a light-transmitting layer 41, which is located on the side of the second electrode 34 away from the substrate 2, and the light-transmitting layer 41 has excellent light transmittance to laser, and has excellent thermal and electrical conductivity. The reflectivity of the light-transmitting layer 41 to lasers with a wavelength greater than or equal to 600nm is less than 3%; the thermal conductivity of the light-transmitting layer 41 is greater than the thermal conductivity of the second distributed Bragg reflector 33; the electrical conductivity of the light-transmitting layer 41 is greater than the electrical conductivity of the second distributed Bragg reflector 33. The thickness of the light-transmitting layer 41 is selected according to the heat dissipation requirements. Preferably, the material of the light-transmitting layer 41 is silicon carbide (SiC). This is because SiC has excellent electrical and thermal conductivity, is a common substrate 2 material in semiconductor processes, and has excellent light transmittance to lasers with a wavelength of 600nm and above. Therefore, forming the light-transmitting layer 41 with SiC can improve the heat dissipation capacity of the second distributed Bragg reflector 33, and has a low impact on the laser transmission efficiency, and is particularly suitable for high-power VCSELs. Adding a silicon carbide layer to the light-emitting surface of the VCSEL device (array), if designed properly, can be used as a high refractive index material to help form an effective DBR structure, thereby improving reflectivity and light output quality. The high thermal conductivity of silicon carbide also helps dissipate heat in the VCSEL device, thereby reducing the impact of thermal effects on light output quality. However, if the thickness or refractive index of the silicon carbide layer does not match, additional losses will be introduced, affecting the light coupling efficiency and light output quality. The relationship between the thickness of the SiC layer and the temperature of the active area 322 is shown in the figure below. Figure 2 As shown by Figure 2 It can be seen that when the thickness of the light-transmitting layer 41 (SiC layer) is between 100 μm and 200 μm, as the thickness of the SiC layer increases, the temperature of the active area 322 drops fastest. After the thickness of the SiC layer is greater than 300 μm, as the thickness of the SiC layer increases, the temperature fluctuation of the active area 322 is small. Considering factors such as process, heat dissipation effect and cost, in this embodiment, the SiC thickness is preferably 200-300 μm.

[0045] In the embodiment of the present invention, the second electrode 34 and the Au heat-conducting portion 6 are directly connected to the light-transmitting layer 41. The second electrode 34 and the Au heat-conducting portion 6 directly transfer heat to the SiC light-transmitting layer 41. The Au heat-conducting portion 6 can transfer part of the heat to the substrate 2 to improve the heat dissipation efficiency, which is beneficial to ensure the stable optical performance of the VCSEL device.

[0046] Preferably, the lower surface of the light-transmitting layer 41 is designed according to the size of the pixel 3, and a pattern electrode is formed around the pixel 3 to achieve ohmic connection between the light-transmitting layer 41 and the second electrode 34. The pattern electrode is an electrode designed according to a specific shape and layout, which can achieve current injection and uniform distribution of current density. This is a well-known technology and will not be described in detail.

[0047] Figure 3The cross-sectional structure diagram of a second vertical cavity surface emitting laser according to an embodiment of the present invention is schematically shown.

[0048] like Figure 3 As shown, Figure 1 Compared to the VCSEL shown, Figure 3 The top substrate 4 of the vertical cavity surface emitting laser shown also includes: a graphene layer 42, the graphene layer 42 is located between the light-transmitting layer 41 and the second electrode 34, the upper surface of the graphene layer 42 is in contact with the lower surface of the light-transmitting layer 41, and the lower surface of the graphene layer 42 is in contact with the second electrode 34. The second electrode 34 on the light-emitting surface of the VCSEL device directly contacts the graphene layer 42 of the top substrate 4. The second electrode 34 is electrically connected to the top substrate 4. Optionally, an anti-reflection film 43 is filled between the upper surface of the second distributed Bragg reflector 33 (the light-emitting surface of the pixel 3) and the graphene layer 42, and the upper and lower surfaces of the anti-reflection film 43 are in contact with the graphene layer 42 and the upper surface of the second distributed Bragg reflector 33, respectively. The anti-reflection film 43 can enhance the laser transmittance and reduce reflection loss.

[0049] The graphene layer 42 is first formed on the upper surface or the lower surface of the light-transmitting layer 41, and then loaded onto the light-emitting surface of the pixel 3. There are many methods for preparing the graphene layer 42 on the surface of the light-transmitting layer 41, for example, epitaxial growth method (solid source molecular beam epitaxy), chemical vapor deposition method, pulsed electron beam bombardment method, atomic layer deposition (ALD), etc., or spin coating the graphene transparent conductive adhesive layer 5 on the surface of the light-transmitting layer 41.

[0050] In some exemplary embodiments, the surface of the light-transmitting layer 41 away from the substrate 2 includes a microlens array structure 411, and the microlens array structure 411 includes N microlenses arranged in an array, wherein the position of the microlens corresponds to the laser emission window of the pixel 3, so that the period of the microlens matches the period of the pixel 3, thereby achieving the purpose of compressing the laser divergence angle.

[0051] An adhesive layer 5 is provided on the outer side of the Au heat conductive part 6 at the outer periphery of the outer pixel 3. The adhesive layer 5 surrounds the outer periphery of all the outer pixels 3. Moreover, the height of the adhesive layer 5 and the Au heat conductive part 6 is flush with the height of the second electrode 34, and the adhesive layer 5 is in direct contact with the graphene layer 42 of the top substrate 4. Therefore, the adhesive layer 5 can adhere and fix the entire graphene layer 42 / transparent layer 41, and make the graphene layer 42 located on the upper surface of the second electrode 34. The adhesive layer 5 is used to make the positions of the graphene layer 42 and the second electrode 34 relatively fixed and electrically connected. Such a structure not only avoids the problem of the graphene layer 42 and the second electrode 34 being unable to grow directly on the second electrode 34 due to the compatibility problem of the materials, but also avoids the problem caused by the different thermal expansion coefficients, while simplifying the process and reducing the cost.

[0052] Specifically, the lower surface of the adhesive layer 5 contacts the upper surface of the substrate 2 , the upper surface of the adhesive layer 5 contacts the lower surface of the graphene layer 42 , and the side surfaces of the adhesive layer 5 contact the outer pixel 3 and the exposed side surfaces of the outer heat conducting portion 6 .

[0053] In the embodiment of the present invention, part of the heat generated by the second distributed Bragg reflector 33 on the light-emitting surface of the pixel 3 is directly conducted to the top substrate 4 in contact with it, and the other part is conducted laterally from the side to the Au heat-conducting part 6 in contact with it, and then conducted from the Au heat-conducting part 6 to the top substrate 4 and the substrate 2. Due to the high thermal conductivity of graphene and SiC materials, the heat generated by the second distributed Bragg reflector 33 can be conducted away in the shortest path (first heat-conducting path), and there is also a second heat-conducting path from the Au heat-conducting part 6 to the graphene layer 42, and a third heat-conducting path from the Au heat-conducting part 6 to the substrate 2. Therefore, the design of the three heat-conducting paths in this embodiment significantly improves the heat dissipation capacity compared with the design of only the third heat-conducting path in the conventional technology. In particular, this embodiment is suitable for high-power VCSEL devices, which can improve their heat dissipation capacity and ensure stable optical performance.

[0054] In addition, the first electrode 1 and the light-transmitting layer 41 are respectively connected to the external electrodes, and the current is injected into the second electrode 34 by the graphene layer 42, and the top of the VCSEL emits light. It should be noted that the emitted light is emitted outward through the top substrate 4, and the divergence angle is compressed by the microlens array structure 411 of the light-transmitting layer 41. Part of the heat generated by the pixel 3 is transferred from the substrate 2 to the external heat sink, part of it is transferred from the light-emitting surface to the top substrate 4, and part of it is transferred from the side to the Au heat-conducting part 6 and then to the top substrate 4. Therefore, the VCSEL structure provided in the embodiment of the present invention can directly dissipate the heat on the upper surface of the VCSEL device, while meeting the design requirements of light extraction efficiency and compressed light beam divergence angle.

[0055] In an embodiment of the present invention, graphene is used to further reduce the thermal resistance of the VCSEL device (array), thereby improving its performance. The thickness of the graphene layer 42 is nanometer-level, only a few nanometers thick. Although graphene has high electron mobility and good thermal conductivity, its application in VCSEL has long been limited, mainly because the preparation process of graphene is complicated, and it is difficult to maintain uniformity and quality consistency when growing over a large area. In addition, the interface contact between graphene and semiconductor materials is not an ideal contact, which affects the injection efficiency of carriers and the overall performance of VCSEL. At the same time, the thermal expansion coefficient of graphene does not match the thermal expansion coefficient of commonly used semiconductor materials, resulting in stress at the interface when the temperature changes, affecting the long-term stability of the device. Therefore, the present invention avoids the problem of inconsistent interface contact and thermal expansion coefficient by pre-growing graphene on the SiC light-transmitting layer 41, and then forming an electrical connection between the graphene layer 42 and the second electrode 34 through the adhesive layer 5. Optionally, the graphene layer 42 used in the present invention is nano-scale graphene, which is easy to grow evenly on the SiC light-transmitting layer 41, thereby ensuring production efficiency and quality.

[0056] In the embodiment of the present invention, the presence of the graphene layer 42 is also beneficial to improving the uniformity of the current. Since graphene has good lateral conductivity, the lateral conductivity is even higher than that of the metal with the best conductivity, silver. Therefore, by injecting current into the pixel 3 through the graphene layer 42, the problem of uneven electric injection in the conventional pixel 3 array can be improved, so that the current is expanded laterally and the current is injected uniformly. Therefore, the presence of the graphene layer 42 can, on the one hand, improve the uniformity of the current injection of different pixels 3 in the pixel 3 array, and on the other hand, improve the uniformity of the current injection of a single pixel 3 in the pixel 3 array.

[0057] It should be noted that according to the VCSEL structure of the embodiment of the present invention, the graphene layer 42 and the SiC light-transmitting layer 41 stacked on the light-emitting surface have negligible effects on the light-emitting quality. SiC crystal is a wide bandgap material, and its intrinsic absorption coefficient in the near-infrared band is very small and can be ignored; in the near-infrared band, the refractive index of SiC crystal is about 2.5. Although the refractive index difference between SiC and pixel 3 and air will affect the transmittance, this effect can be eliminated by coating the surface of pixel 3 and the surface of SiC (anti-reflection film 43); in the visible and near-infrared regions, due to the electronic band structure of graphene, the opacity of graphene is 2.3%. Moreover, when the number of layers is small, the transmittance of the few-layer graphene can be simply expressed as (1-0.023n)×100% (n is the number of layers). Therefore, the number of the graphene layers 42 of the graphene layer 42 in the present invention is less than or equal to 3 layers (ie, 1 to 3 layers, preferably 1 layer), which can ensure that the optical loss is small enough to meet the application requirements.

[0058] In summary, according to the vertical cavity surface emitting laser of the embodiment of the present invention, a SiC light-transmitting layer 41 covered with a graphene layer 42 is introduced on the light-emitting surface of the vertical cavity surface emitting laser (VCSEL). This technology utilizes the high light transmittance, electrical conductivity and thermal conductivity efficiency of SiC and graphene under lasers with a wavelength of 600nm and above, and significantly improves the heat dissipation capacity of the VCSEL device. High transmittance means that the SiC light-transmitting layer 41 and the graphene layer 42 will not hinder the emission of the laser, and can also provide heat dissipation. The high electrical conductivity of the graphene layer 42 contributes to the effective transmission of current and reduces resistance loss. Both SiC and graphene have excellent thermal conductivity (especially the thermal conductivity of graphene exceeds 5000 W / (m•K), which is one of the materials with the highest thermal conductivity known to date), and can effectively conduct heat away from the active region 322 of the laser to improve heat dissipation performance. This sophisticated multi-layer structure design not only takes advantage of the material properties but also simplifies the process, reflecting the complex integration and application of optical, electronic and thermal management technologies at the micro-nano scale.

[0059] Figure 4 The flowchart of the method for preparing a vertical cavity surface emitting laser according to an embodiment of the present invention is schematically shown.

[0060] like Figure 4 As shown, the method for preparing a vertical cavity surface emitting laser according to an embodiment of the present invention can be used to prepare Figure 1 and Figure 3 The vertical cavity surface emitting laser shown includes steps S110 to S150.

[0061] In step S110, a picture element 3 is prepared: a first distributed Bragg reflector 31, a quantum well active area 32232, a second distributed Bragg reflector 33 and a second electrode 34 are grown in sequence on the first surface of the substrate 2 to obtain N picture elements 3, wherein N is a positive integer greater than or equal to 2, and at least a portion of at least two adjacent picture elements 3 are arranged at a predetermined interval; the quantum well active area 32232 includes a tunnel junction 321, an active area 322 and an oxide layer 323 that are periodically arranged in sequence.

[0062] In step S120 , a heat conducting portion 6 is formed: the heat conducting portion 6 is filled in the gaps between adjacent picture elements 3 and the sides of the outermost picture elements 3 , and the height of the heat conducting portion 6 is flush with the surface of the second electrode 34 away from the substrate 2 .

[0063] In step S130 , an adhesive layer 5 is formed: the adhesive layer 5 is grown on the exposed sides of the pixel 3 and the heat conducting portion 6 , and the height of the heat conducting portion 6 is not lower than the height of the surface of the second electrode 34 away from the substrate 2 .

[0064] In step S140 , a top liner 4 is formed: the pre-prepared top liner 4 is pressed onto a surface of the pixel 3 that is away from the substrate 2 , and the top liner 4 covers the pixel 3 , the heat conducting portion 6 , and the adhesive layer 5 .

[0065] In some exemplary embodiments, the top lining 4 includes a light-transmitting layer 41, and the pre-preparation method of the top lining 4 includes preparing a microlens array structure 411 on the surface of the light-transmitting layer 41 away from the substrate 2, wherein the microlens array structure 411 includes N microlenses arranged in an array; the position of the microlens corresponds to the laser emission window of the pixel 3, so that the period of the microlens matches the period of the pixel 3, thereby achieving the purpose of compressing the laser divergence angle.

[0066] In some exemplary embodiments, the top substrate 4 also includes a graphene layer 42, and the pre-preparation method of the top substrate 4 also includes: forming the graphene layer 42 on the opposite surfaces of the light-transmitting layer 41 and the microlens array structure 411; in the process of pressing the pre-prepared top substrate 4 to the side surface of the pixel 3 away from the substrate 2, the graphene layer 42 is in contact with the side surface of the pixel 3 away from the substrate 2.

[0067] Optionally, methods for preforming the graphene layer 42 on the surface of the light-transmitting layer 41 include growth, deposition and bonding methods, especially solid source molecular beam epitaxy, chemical vapor deposition, pulsed electron beam bombardment, atomic layer deposition, etc.

[0068] In step S150 , a first electrode 1 is prepared: the first electrode 1 is formed on the second surface of the substrate 2 , wherein the first surface and the second surface are two surfaces on the substrate 2 that are arranged opposite to each other.

[0069] It can be understood that the first distributed Bragg reflector 31 in the vertical cavity surface emitting laser according to the embodiment of the present invention can be an N-type distributed Bragg reflector, the corresponding second distributed Bragg reflector 33 is a P-type distributed Bragg reflector, the first electrode 1 is an N-electrode, and the second electrode 34 is a P-electrode. Alternatively, the first distributed Bragg reflector 31 is a P-type distributed Bragg reflector, the corresponding second distributed Bragg reflector 33 is an N-type distributed Bragg reflector, the first electrode 1 is a P-electrode, and the second electrode 34 is an N-electrode.

[0070] Figure 5 A schematic diagram of a two-dimensional simulation of the heat generation of a vertical cavity surface emitting laser including a graphene-silicon carbide top substrate according to an embodiment of the present invention is schematically shown.

[0071] Figure 6 A schematic diagram of a three-dimensional simulation comparison of the heat generation of a vertical cavity surface emitting laser including a graphene-silicon carbide top substrate according to an embodiment of the present invention and a conventional packaging structure is schematically shown.

[0072] like Figure 5and Figure 6 The maximum temperature of the conventional packaging structure is 374K. The maximum temperature of the vertical cavity surface emitting laser according to the embodiment of the present invention is 344K under the same power and the same heat dissipation conditions, and the temperature has dropped by 30K. The reduction in temperature can significantly improve the output performance of the VCSEL. Because as the temperature increases, the emission wavelength of the VCSEL will move toward the long-wave direction (the specific value depends on the temperature drift coefficient), the threshold current will increase (the specific value depends on the temperature coefficient of the threshold current), and the output power and slope efficiency will decrease accordingly (the specific reduction depends on the design and material of the laser). It should be noted that the use of Figure 6 When the three-dimensional model in the embodiment of the present invention is used to simulate and calculate the heat generation of the VCSEL and the conventional packaging structure, a 1mm×1mm area is taken as an example, and the calculation amount is 1 / 4 of the overall structure.

[0073] Figure 7 A schematic diagram of a two-dimensional simulation of current density distribution of a vertical cavity surface emitting laser according to an embodiment of the present invention is shown.

[0074] like Figure 7 As shown in the two-dimensional simulation schematic diagram of the current density distribution of the vertical cavity surface emitting laser according to the embodiment of the present invention, it can be seen that since there is a graphene layer 42 between the light-transmitting layer 41 (SiC layer) and the P electrode (second electrode 34), and graphene has high in-plane conductivity and transparency, the graphene layer 42 enables the current to be spread on the entire light-emitting surface of the VCSEL device, making the current density more evenly distributed on the entire device. Compared with the annular electrode of the conventional packaging structure (see Figure 8 ), the VCSEL with the graphene-silicon carbide top substrate 4 according to the embodiment of the present invention injects more uniform current into the active area 322. Moreover, an ohmic contact is formed between the P electrode and the semiconductor material, which can expand the surface current, reduce the preparation of the thick gold layer, improve the uniformity of the current density, and reduce the process difficulty and cost.

[0075] In summary, SiC has excellent transmittance to lasers with a wavelength of 600nm and above, and SiC itself has excellent electrical conductivity and thermal conductivity; moreover, graphene has high transmittance, electrical conductivity and thermal conductivity. The front of the VCSEL directly contacts the SiC covered with a graphene film, which improves the heat dissipation capacity of the second distributed Bragg reflector 33 and has a low impact on laser transmission, and is particularly suitable for high-power VCSELs. It can be understood that when there is no graphene layer 42, the SiC light-transmitting layer 41 can also be used to improve the heat dissipation capacity. However, the VCSEL with the graphene layer 42 has better current uniformity than the VCSEL without the graphene layer 42.

[0076] So far, the embodiments of the present invention have been described in detail with reference to the accompanying drawings.

[0077] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A vertical cavity surface emitting laser, characterized in that: include: A substrate having a first surface and a second surface disposed opposite to each other; N picture elements are located on the first surface of the substrate, wherein N is a positive integer greater than or equal to 2, and at least a portion of at least two adjacent picture elements are arranged at a predetermined interval; a top substrate, located on a side of the pixel away from the substrate; and The adhesive layer is located on the first surface of the substrate, covers at least a portion of the side surface of the picture element and contacts with a surface of the top substrate close to the substrate.

2. The vertical cavity surface emitting laser according to claim 1, characterized in that: At least a portion of any two adjacent pixels are arranged at a predetermined interval to form N-1 inner gaps; An outer gap is formed between the adhesive layer, the top liner and the outermost picture element; and The vertical cavity surface emitting laser further includes a heat conducting portion, and the heat conducting portion is respectively located in the N-1 inner gaps and the outer gap.

3. The vertical cavity surface emitting laser according to claim 1, characterized in that: Also includes: The first electrode is located on the second surface of the substrate.

4. The vertical cavity surface emitting laser according to any one of claims 1 to 3, characterized in that: At least one of the pixels comprises: A first distributed Bragg reflector is located on the first surface of the substrate; A quantum well active region, located on a side of the first distributed Bragg reflector away from the substrate, the quantum well active region comprising a tunnel junction, an active region and an oxide layer that are periodically arranged in sequence; A second distributed Bragg reflector is located on a side of the oxide layer away from the substrate; and a second electrode, located on a side of the second distributed Bragg reflector away from the substrate, Wherein, a side of the second distributed Bragg reflector away from the substrate is a light emitting surface.

5. The vertical cavity surface emitting laser according to claim 4, characterized in that: The top substrate comprises: a light-transmitting layer located on a side of the second electrode away from the substrate, Wherein, the reflectivity of the light-transmitting layer to lasers with a wavelength greater than or equal to 600 nm is less than 3%; The thermal conductivity of the light-transmitting layer is greater than the thermal conductivity of the second distributed Bragg reflector; The conductivity of the light-transmitting layer is greater than the conductivity of the second distributed Bragg reflector; The material of the light-transmitting layer includes silicon carbide; The thickness of the light-transmitting layer is 200 μm-300 μm; and The surface of the light-transmitting layer away from the substrate includes a microlens array structure, and the microlens array structure includes N microlenses arranged in an array, wherein the position of the microlens corresponds to the laser emission window of the pixel, so that the period of the microlens matches the period of the pixel, thereby achieving the purpose of compressing the laser divergence angle.

6. The vertical cavity surface emitting laser according to claim 5, characterized in that: The top substrate further comprises: a graphene layer, wherein the graphene layer is located between the light-transmitting layer and the second electrode. Wherein, the number of graphene layers of the graphene layer is no more than 3 layers.

7. The vertical cavity surface emitting laser according to claim 6, characterized in that: The top substrate further includes an anti-reflection film, which is located between the graphene layer and the second distributed Bragg reflector and has a height flush with that of the second electrode.

8. A method for preparing a vertical cavity surface emitting laser, characterized in that: include: Preparing a pixel: sequentially growing a first distributed Bragg reflector, a quantum well active region, a second distributed Bragg reflector, and a second electrode on a first surface of a substrate to obtain N pixels, wherein N is a positive integer greater than or equal to 2, and at least a portion of at least two adjacent pixels are arranged at a predetermined interval; Forming a heat-conducting portion: filling the heat-conducting portion in the gap between adjacent picture elements and the side of the outermost picture element, and the height of the heat-conducting portion is flush with the surface of the second electrode away from the substrate; Forming an adhesive layer: growing an adhesive layer on the exposed sides of the pixel and the heat conducting portion, wherein the height of the heat conducting portion is not lower than the height of the surface of the second electrode away from the substrate; Forming a top liner: pressing a pre-prepared top liner onto a surface of the pixel away from the substrate, wherein the top liner covers the pixel, the heat conducting portion and the adhesive layer; and Preparing a first electrode: forming a first electrode on the second surface of the substrate, Wherein, the quantum well active region includes a tunnel junction, an active region and an oxide layer which are periodically arranged in sequence; and The first surface and the second surface are two surfaces on the substrate that are arranged opposite to each other.

9. The method according to claim 8, characterized in that The top liner includes a light-transmitting layer. The pre-preparation method of the top liner includes preparing a microlens array structure on a surface of the light-transmitting layer away from the substrate. Wherein, the microlens array structure comprises N microlenses arranged in an array; The position of the microlens corresponds to the laser emission window of the pixel, so that the period of the microlens matches the period of the pixel, thereby achieving the purpose of compressing the laser divergence angle.

10. The method according to claim 9, characterized in that The top substrate further includes a graphene layer, and the pre-preparation method of the top substrate further includes: forming a graphene layer on the opposite surface of the light-transmitting layer and the microlens array structure; In the process of pressing the pre-prepared top substrate onto the surface of the pixel away from the substrate, the graphene layer is in contact with the surface of the pixel away from the substrate.

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