Infrared temperature sensor and preparation method thereof

Abstract

The invention discloses an infrared temperature sensor and a preparation method thereof, and belongs to the technical field of semiconductors. The infrared temperature sensor comprises a plurality of sensing units, each sensing unit comprises a substrate, a semiconductor layer, a barrier layer, a first electrode, a wave absorbing coating and a second electrode, the semiconductor layer, the barrier layer, the first electrode and the wave absorbing coating are sequentially stacked on the substrate, the second electrode is arranged on the side, away from the semiconductor layer, of the substrate, and the second electrode penetrates through the substrate and is electrically connected with the semiconductor layer. The sensing unit utilizes the pyroelectric effect of a semiconductor layer and a barrier layer, when the temperature changes, the self-polarization effect of a heterostructure formed by the semiconductor layer and the barrier layer enables electrons in a material to move in the direction perpendicular to the surface of the material, so that polarization surface charges are generated, and current is formed through a first electrode and a second electrode; and temperature detection is realized through the magnitude of the current.

Description

Technical Field

[0001] The present application belongs to the field of semiconductor technology, and in particular relates to an infrared temperature sensor and a preparation method thereof. Background Art

[0002] At present, temperature sensors still have problems such as low measurement accuracy, low sensitivity, or complex system and high manufacturing cost. Infrared temperature sensors in particular have low sensitivity and poor measurement accuracy, and their performance is greatly reduced or even fails in low temperature environments.

[0003] Based on this, how to improve the sensitivity of infrared temperature sensors has become an urgent problem to be solved in this field. Summary of the invention

[0004] The present application provides an infrared temperature sensor and a preparation method thereof, aiming to improve the sensitivity of the infrared temperature sensor and expand the measurement range of the infrared temperature sensor.

[0005] In a first aspect, the present application provides an infrared temperature sensor, comprising a plurality of sensing units. Each sensing unit comprises a substrate, a semiconductor layer, a barrier layer, a first electrode and an absorbing coating layer stacked in sequence on the substrate, and a second electrode disposed on a side of the substrate away from the semiconductor layer, wherein the second electrode penetrates the substrate and is electrically connected to the semiconductor layer.

[0006] In some embodiments, the materials of the semiconductor layer and the barrier layer both include Group IIIA-VA elements.

[0007] In some embodiments, the material of the semiconductor layer includes at least one of gallium nitride, gallium arsenide, or indium gallium arsenide, and the material of the barrier layer includes at least one of indium gallium nitride, aluminum gallium nitride, indium phosphide, aluminum gallium arsenide, or indium aluminum arsenide.

[0008] In some embodiments, the sensing unit further includes a buffer layer disposed between the substrate and the semiconductor layer, and the second electrode is electrically connected to the semiconductor layer through the buffer layer.

[0009] In some embodiments, the sensing unit further includes a passivation layer, the passivation layer covers a portion of the first electrode, and the absorbing coating penetrates the passivation layer and contacts the first electrode.

[0010] In some embodiments, the material of the absorbing coating includes at least one of carbon nanotubes, zinc oxide, lead zirconate titanate, or polyvinylidene fluoride.

[0011] In some embodiments, the infrared temperature sensor further includes a hollow portion, and the hollow portion is arranged around the sensing unit along a direction parallel to the plane where the substrate is located.

[0012] In some embodiments, the substrate includes a penetrating cavity, the second electrode is disposed on an inner wall of the cavity, and the second electrode is electrically connected to the semiconductor layer through the cavity.

[0013] In a second aspect, an embodiment of the present application further provides a method for preparing an infrared temperature sensor, wherein the infrared temperature sensor includes a plurality of sensing units, and forming the sensing units includes the following steps S10 to S20:

[0014] Step S10: sequentially forming a stacked semiconductor layer, a barrier layer, a first electrode and a microwave absorbing coating on a substrate.

[0015] Step S20: forming a second electrode on a side of the substrate away from the semiconductor layer, wherein the second electrode penetrates the substrate and is electrically connected to the semiconductor layer.

[0016] In some embodiments, after forming the absorbing coating layer and before forming the second electrode, the preparation method further includes steps S11 and S12:

[0017] Step S11: etching the semiconductor layer to form a hollow portion exposing the substrate; the hollow portion is arranged around the sensing unit in a direction parallel to the plane where the semiconductor layer is located.

[0018] Step S12: etching the substrate to form a cavity communicating with the hollow portion.

[0019] In addition, the process of forming the second electrode in step S20 includes: forming the second electrode on the inner wall of the cavity, and the second electrode is electrically connected to the semiconductor layer through the cavity.

[0020] In the infrared temperature sensor provided in the embodiment of the present application, the sensing unit includes a substrate, a semiconductor layer, a barrier layer, a first electrode and an absorbing coating layer stacked in sequence on one side of the substrate, and a second electrode on the other side of the substrate. The second electrode penetrates the substrate and is electrically connected to the semiconductor layer. The pyroelectric effect of the semiconductor layer and the barrier layer is utilized. When the temperature changes, the self-polarization effect of the heterostructure formed by the semiconductor layer and the barrier layer causes the electrons in the material to move in a direction perpendicular to the surface of the material, thereby generating polarized surface charges. The surface charges are discharged through the first electrode and the second electrode to form a current, and the temperature is detected by collecting the current size.

[0021] The above-mentioned sensing unit is more sensitive to temperature. Compared with the related art, a larger current can be formed under the same temperature change, so that the infrared temperature sensor has a higher sensitivity. In addition, by providing an absorbing coating, the absorption efficiency of the sensing unit to infrared waves can be improved, so that the temperature in the sensing unit rises rapidly, further improving the sensitivity and accuracy of the infrared temperature sensor, and expanding the measurement range of the infrared temperature sensor.

[0022] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0024] Figure 1 A top view of the infrared temperature sensor provided in an embodiment of the present application;

[0025] Figure 2 for Figure 1 A cross-sectional view of the mid-infrared temperature sensor along the section line AA';

[0026] Figure 3 A flow chart of a method for preparing an infrared temperature sensor provided in an embodiment of the present application;

[0027] Figures 4 to 11 A diagram of the steps for preparing an infrared temperature sensor provided in an embodiment of the present application. DETAILED DESCRIPTION

[0028] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in some embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments provided by the present application, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present application.

[0029] Unless the context requires otherwise, throughout the specification and claims, the term "comprising" is to be construed in an open, inclusive sense, ie, meaning "including, but not limited to."

[0030] In the following, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, unless otherwise specified, "plurality" means two or more.

[0031] When describing some embodiments, the term "connection" and its derivative expressions may be used. The term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For example, when describing some embodiments, the term "connection" may be used to indicate that two or more components are in direct physical or electrical contact with each other.

[0032] Additionally, the use of “based on” is meant to be open and inclusive, as a process, step, calculation, or other action “based on” one or more stated conditions or values ​​may, in practice, be based on additional conditions or values ​​beyond those stated.

[0033] It will be understood that when a layer or an element is referred to as being on another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may be present between the layer or element and the other layer or substrate.

[0034] Exemplary embodiments are described herein with reference to cross-sectional views that are idealized exemplary drawings. In the drawings, the thickness of layers and the area of ​​regions are exaggerated for clarity. Therefore, variations in shape relative to the drawings due to, for example, manufacturing techniques and / or tolerances are conceivable. Therefore, the exemplary embodiments should not be interpreted as being limited to the shapes of the regions shown herein, but include deviations in shape due to, for example, manufacturing. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to illustrate the actual shape of regions of the device, and are not intended to limit the scope of the exemplary embodiments.

[0035] Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0036] In the related art, infrared temperature sensors have low sensitivity, poor measurement accuracy, unsatisfactory performance in low temperature environments, and a small measurement range.

[0037] To solve the above problems, the present application provides an infrared temperature sensor, which includes a plurality of sensing units, such as Figure 1-2 As shown, Figure 1 This is a top view of the infrared temperature sensor provided in the embodiment of the present application. The dotted box in the figure corresponds to a sensing unit 100. Figure 2 for Figure 1 Cross-sectional view of the mid-infrared temperature sensor along section line AA'.

[0038] Taking a sensor unit 100 as an example, each sensor unit 100 includes a substrate 10 and a semiconductor layer 11, a barrier layer 12, a first electrode 13 and an absorbing coating layer 14 stacked in sequence on the substrate 10. The second electrode 15 of each sensor unit 100 is arranged on a side of the substrate 10 away from the semiconductor layer 11, and the second electrode 15 penetrates the substrate 10 and is electrically connected to the semiconductor layer 11.

[0039] In the sensing unit 100, the second electrode 15 that penetrates the substrate 10, and the semiconductor layer 11, the barrier layer 12, the first electrode 13 and the absorbing coating 14 that are sequentially stacked on the substrate 10 constitute a "measuring unit" that performs a temperature measurement function. Among them, the semiconductor layer 11 and the barrier layer 12 form a heterostructure. After the absorbing coating 14 absorbs infrared waves, the heat is conducted to the heterostructure through the first electrode 13, causing the temperature of the sensing unit 100 to rise. The temperature rise causes the heterostructure to undergo a self-polarization effect change. The self-polarization effect causes the electrons in the material to move in a direction perpendicular to the surface of the material, that is, along the Z-axis direction, thereby generating polarized surface charges on the surfaces of the semiconductor layer 11 and the barrier layer 12 that are opposite to each other. The surface charges are discharged through the first electrode 13 and the second electrode 15 to form a current. By collecting the current size, the temperature can be detected.

[0040] Compared with the related art, the infrared temperature sensor provided by the present application utilizes the characteristics of the heterogeneous structure to generate more charges under the pyroelectric effect, so that the infrared temperature sensor can pass a larger current when the temperature change is low, so that the infrared temperature sensor has a higher sensitivity and expands the measurement range of the infrared temperature sensor. In addition, the absorbing coating 14 can also improve the absorption efficiency of infrared waves, so that the temperature of the sensing unit 100 rises rapidly, which is conducive to further improving the sensitivity.

[0041] In some embodiments, the materials of the semiconductor layer 11 and the barrier layer 12 both include Group IIIA-VA elements, such as silicon, gallium, nitrogen, arsenic, germanium, and the like.

[0042] In some embodiments, the material of the semiconductor layer 11 includes at least one of gallium nitride, gallium arsenide or indium gallium arsenide, and the material of the barrier layer 12 includes at least one of indium gallium nitride, aluminum gallium nitride, indium phosphide, aluminum gallium arsenide or indium aluminum arsenide.

[0043] The single crystal structure material formed by the above materials has relatively excellent pyroelectric properties and electrostrictive effects, so that when the temperature change is low, the temperature sensor can also generate more polarized surface charges on the two opposite surfaces of the semiconductor layer 11 and the barrier layer 12, thereby forming current, thereby improving the sensitivity of the device.

[0044] In some embodiments, Figure 2 As shown, in order to avoid lattice mismatch and dislocation, the sensing unit also includes a buffer layer 16 disposed between the substrate 10 and the semiconductor layer 11. The buffer layer 16 is used to reduce lattice mismatch and dislocation density. On this basis, the second electrode 15 is electrically connected to the semiconductor layer 11 through the buffer layer 16, which can improve the performance and reliability of the device.

[0045] In some embodiments, Figure 2As shown, the sensing unit further includes a passivation layer 17, which covers part of the first electrode 13 and is used to isolate and protect the first electrode 13. The absorbing coating 14 penetrates the passivation layer 17 and contacts the first electrode 13. After the absorbing coating 14 absorbs infrared waves, the heat is conducted to the semiconductor layer 11 and the barrier layer 12 through the first electrode 13, so that the temperature of the "measurement unit" of the sensing unit 100 rises rapidly, the heterostructure undergoes a self-polarization effect change, and then generates current.

[0046] The material of the passivation layer 17 includes but is not limited to at least one of silicon nitride, silicon dioxide or aluminum oxide, and its thermal conductivity is slightly worse than that of the first electrode 13. Therefore, the portion of the passivation layer 17 covering the first electrode 13 is also beneficial to reducing the heat loss of the "measurement unit" of the sensing unit 100. The absorbing coating 14 absorbs the temperature rise caused by the infrared waves and retains as much as possible in the "measurement unit", thereby improving the stability of the infrared temperature sensor.

[0047] In addition, the exposed portion of the first electrode 13 is used for electrical connection with an external circuit.

[0048] In some embodiments, the material of the absorbing coating 14 includes at least one of carbon nanotubes, zinc oxide, lead zirconate titanate, or polyvinylidene fluoride. The above materials have good performance in absorbing infrared waves and are relatively sensitive to temperature changes. By absorbing infrared waves, the temperature of the "measuring unit" of the sensing unit 100 rises rapidly, and the temperature is detected under the pyroelectric effect, thereby improving the sensitivity of the infrared temperature sensor.

[0049] In some embodiments, Figure 1 and Figure 2 As shown, the infrared temperature sensor further includes a hollow portion K1 , which is arranged around the sensing unit 100 along a direction parallel to the plane where the substrate 10 is located.

[0050] The setting of the hollow portion K1 can reduce the conduction loss of heat in the solid, so that the temperature increased by the absorbing coating 14 after absorbing the infrared wave is retained as much as possible in the semiconductor layer 11 and the barrier layer 12 in the "middle part" surrounded by the hollow portion K1, so as to avoid the temperature rising and then dropping rapidly. The "middle part" here can be understood as the aforementioned "measurement unit". By setting the hollow portion K1, the result of the temperature increase can be effectively retained in the "measurement unit" of the sensing unit 100, which is conducive to the self-polarization effect of the heterostructure and the generation of a more stable current, thereby improving the measurement sensitivity and measurement accuracy.

[0051] In some embodiments, Figure 2As shown, the substrate 10 includes a penetrating cavity K2 , and the second electrode 15 is disposed on the inner wall of the cavity K2 . The second electrode 15 is electrically connected to the semiconductor layer 11 through the cavity K2 .

[0052] The provision of the cavity K2 can also reduce the conduction loss of heat in the "measurement unit" of the sensing unit 100 in the substrate 10. Exemplarily, in some embodiments, the hollow portion K1 and the cavity K2 work together to form the "measurement unit" of the sensing unit 100 into a suspended island structure.

[0053] For the sensing unit 100 formed as a suspended island structure, its "measuring unit" is connected to the infrared temperature sensor as a whole only through a "support arm". The "support arm" here refers to a stacked structure composed of a semiconductor layer 11 and a barrier layer 12 that exists between the hollow part K1 to ensure the connection between the "measuring unit" and the infrared temperature sensor as a whole.

[0054] The above-mentioned island structure can keep the temperature as much as possible in the semiconductor layer 11 and the barrier layer 12 of the "measurement unit", avoiding the temperature from rising and then dropping rapidly. In addition, the second electrode 15 is formed on the inner wall of the cavity K2, passing through the substrate 10 and electrically connected to the semiconductor layer 11. During the electron movement process, it is not necessary to pass through the substrate 10, and the current can be directly formed through the second electrode 15, which improves the electron movement efficiency and can improve the measurement accuracy and sensitivity of the infrared temperature sensor.

[0055] In a second aspect, the present application also provides a method for preparing an infrared temperature sensor, wherein the infrared temperature sensor comprises a plurality of sensing units, such as Figure 3 As shown, Figure 3 This is a flow chart of a method for preparing an infrared temperature sensor provided in an embodiment of the present application. Figures 4 to 11 A diagram of the steps for preparing an infrared temperature sensor provided in an embodiment of the present application.

[0056] The method for preparing the sensor unit comprises the following steps S10 to S20:

[0057] Step S10: Figures 4 to 8 As shown, a semiconductor layer 11 , a barrier layer 12 , a first electrode 13 and an absorbing coating layer 14 are sequentially formed on a substrate 10 .

[0058] For example, Figure 4 As shown, the material of the substrate 10 includes at least one of silicon or silicon carbide. In the process of forming the stacked structure, in order to avoid lattice mismatch and dislocation, a buffer layer 16 is further provided between the substrate 10 and the semiconductor layer 11. For example, the materials of the buffer layer 16, the semiconductor layer 11 and the barrier layer 12 all include gallium nitride.

[0059] Then, if Figure 5As shown, the barrier layer 12 is etched to form a desired morphology. For example, an inductively coupled plasma etching process can be used for etching, which can more accurately control the etching depth and achieve a more ideal etching effect.

[0060] Afterwards, if Figure 6 As shown, a first electrode 13 is formed. The first electrode 13 is electrically connected to the surface of the barrier layer 12 away from the substrate 10, and is used to extract surface charges when the device is working to form a current. The first electrode 13 is a metal material, and the material type includes but is not limited to at least one of gold, aluminum, platinum, molybdenum, etc. The thickness of the first electrode 13 ranges from 50nm to 1000nm.

[0061] Then, if Figure 7 As shown, a passivation layer 17 is formed by a plasma enhanced chemical vapor deposition process, and the passivation layer 17 is etched to form an opening V1 and an opening V2 exposing the first electrode 13. The material of the passivation layer 17 includes but is not limited to at least one of silicon nitride, silicon dioxide, aluminum oxide, etc., and the thickness of the passivation layer 17 ranges from 100nm to 500nm. The portion of the first electrode 13 exposed by the opening V2 can be used to electrically connect to an external circuit.

[0062] The passivation layer 17 can be used to protect the first electrode 13 , and the thermal conductivity of the material of the passivation layer 17 is slightly worse than that of the first electrode 13 . The provision of the passivation layer 17 is also beneficial to reducing heat loss.

[0063] like Figure 8 As shown, the absorbing coating 14 is formed so that the absorbing coating 14 contacts the first electrode 13 through the opening V1 of the passivation layer 17. The material of the absorbing coating 14 includes at least one of carbon nanotubes, zinc oxide, lead zirconate titanate or polyvinylidene fluoride, and the thickness of the absorbing coating 14 ranges from 5 nm to 500 nm.

[0064] Step S20: Figures 9 to 11 As shown, a second electrode 15 is formed on a side of the substrate 10 away from the semiconductor layer 11 , and the second electrode 15 penetrates the substrate 10 and is electrically connected to the semiconductor layer 11 .

[0065] Exemplarily, in some embodiments, after forming the absorbing coating layer 14 and before forming the second electrode 15, the preparation method further includes steps S11 and S12:

[0066] Step S11: Fig. 9 As shown, the semiconductor layer 11 is etched to form a hollow portion K1 exposing the substrate 10 ; along a direction parallel to the plane where the semiconductor layer 11 is located, the hollow portion K1 is arranged around the sensing unit 100 .

[0067] For example, Fig. 9As shown in FIG. 1 , when a buffer layer 16 is disposed between the semiconductor layer 11 and the substrate 10, the semiconductor layer 11 and the buffer layer 16 are etched by an inductively coupled plasma etching process to expose the substrate 10. The hollowed-out area after etching is the hollowed-out portion K1. Figure 1 As shown, the hollow portion K1 is disposed around the sensing unit 100. In other words, the hollow portion K1 surrounds the outside of the "measuring unit" and can be used to reduce the heat loss of the "measuring unit".

[0068] Step S12: Fig.10 As shown, the substrate 10 is etched to form a cavity K2 communicating with the hollow portion K1.

[0069] For example, deep silicon etching is performed on a side of the substrate 10 away from the semiconductor layer 11 , and the etching thickness is equal to the thickness of the substrate 10 . The cavity K2 formed by etching the substrate 10 is connected to the hollow portion K1 .

[0070] Finally, the process of forming the second electrode 15 in step S20 is as follows: Fig.11 As shown, a second electrode 15 is formed on the inner wall of the cavity K2 , and the second electrode 15 penetrates the substrate 10 and is electrically connected to the semiconductor layer 11 through the cavity K2 .

[0071] At this point, one sensor unit 100 is prepared.

[0072] In the embodiment of the present application, a "measurement unit" of each sensing unit in the infrared temperature sensor is formed by forming a second electrode 15, a semiconductor layer 11, a barrier layer 12, a first electrode 13 and an absorbing coating layer 14 stacked in sequence. The "measurement unit" uses the pyroelectric effect of the material to form polarized surface charges on the opposite sides of the semiconductor layer 11 and the barrier layer 12. The surface charges are respectively derived through the first electrode 13 and the second electrode 15 to form a current, thereby realizing the temperature detection function. In addition, the presence of the absorbing coating layer 14 can improve the absorption efficiency of infrared waves, so that the temperature of the infrared temperature sensor rises rapidly, thereby improving the sensitivity. Furthermore, by etching to form a hollow portion K1 and a cavity K2, the heat absorbed by the absorbing coating layer 14 is retained as much as possible in the "measurement unit" of the sensing unit 100, further improving the sensitivity and stability of the infrared temperature sensor.

[0073] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that a person skilled in the art can think of within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. An infrared temperature sensor, characterized in that: including a plurality of sensing units; The sensing unit includes a substrate, a semiconductor layer, a barrier layer, a first electrode and an absorbing coating layer stacked in sequence on the substrate, and a second electrode arranged on a side of the substrate away from the semiconductor layer, wherein the second electrode penetrates the substrate and is electrically connected to the semiconductor layer.

2. The infrared temperature sensor according to claim 1, characterized in that: The materials of the semiconductor layer and the barrier layer both include group IIIA-VA elements.

3. The infrared temperature sensor according to claim 1, characterized in that: The material of the semiconductor layer includes at least one of gallium nitride, gallium arsenide or indium gallium arsenide, and the material of the barrier layer includes at least one of indium gallium nitride, aluminum gallium nitride, indium phosphide, aluminum gallium arsenide or indium aluminum arsenide.

4. The infrared temperature sensor according to claim 1, characterized in that: The sensing unit further includes a buffer layer disposed between the substrate and the semiconductor layer, and the second electrode is electrically connected to the semiconductor layer through the buffer layer.

5. The infrared temperature sensor according to claim 1, characterized in that: The sensing unit further includes a passivation layer, wherein the passivation layer covers a portion of the first electrode; The absorbing coating penetrates the passivation layer and contacts the first electrode.

6. The infrared temperature sensor according to claim 1, characterized in that: The material of the wave absorbing coating includes at least one of carbon nanotubes, zinc oxide, lead zirconate titanate or polyvinylidene fluoride.

7. The infrared temperature sensor according to claim 1, characterized in that: The infrared temperature sensor further includes a hollow portion; Along a direction parallel to the plane where the substrate is located, the hollow portion is arranged around the sensing unit.

8. The infrared temperature sensor according to claim 1, characterized in that: The substrate comprises a through cavity, and the second electrode is arranged on an inner wall of the cavity; The second electrode is electrically connected to the semiconductor layer through the cavity.

9. A method for preparing an infrared temperature sensor, characterized in that: The infrared temperature sensor includes a plurality of sensing units; Forming the sensing unit includes: sequentially forming a stacked semiconductor layer, a barrier layer, a first electrode and a wave absorbing coating on a substrate; A second electrode is formed on a side of the substrate away from the semiconductor layer, and the second electrode penetrates the substrate and is electrically connected to the semiconductor layer.

10. The preparation method according to claim 9, characterized in that: After forming the radar absorbing coating and before forming the second electrode, the preparation method further comprises: The semiconductor layer is etched to form a hollow portion exposing the substrate; the hollow portion is arranged around the sensing unit in a direction parallel to the plane where the semiconductor layer is located; Etching the substrate to form a cavity communicating with the hollow portion; The second electrode is formed, comprising: The second electrode is formed on the inner wall of the cavity, and the second electrode is electrically connected to the semiconductor layer through the cavity.

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