Epitaxial structure of heterojunction photoelectric detector and preparation method

Abstract

The invention relates to the field of semiconductor photoelectric detectors, and provides an epitaxial structure of a heterojunction photoelectric detector and a preparation method, and the epitaxial structure comprises a substrate, an interface lower layer, an interface transition layer, an interface upper layer, a SiNx in-situ passivation layer and an ohmic contact electrode from bottom to top. The anode and the cathode of the ohmic contact electrode are deposited on the surface of the SiNx in-situ passivation layer, or the anode and the cathode of the ohmic contact electrode are deposited on the surface of the upper layer of the interface where the SiNx in-situ passivation layer is etched in advance. The method has the advantages that the in-situ growth thin SiNx film which is high in film forming quality and does not introduce impurity atoms in an air environment is used as the passivation layer, surface defects of the III-nitride photoelectric detector are reduced, and capture of photon-generated carriers by semiconductor surface defects is inhibited. According to the method, the serious continuous photoconductive effect in the detector caused by surface defects and the response speed limitation caused by the serious continuous photoconductive effect are effectively improved, and the photoresponse stability of the detector and the uniformity of dark current of an on-chip device are remarkably improved.

Description

Technical Field The present invention relates to the technical field of semiconductor photodetectors, and more specifically, to an epitaxial structure and a preparation method of a heterojunction photodetector. Background Art A photodetector is a device that can convert an external optical signal into an internal electrical signal of the device. It is now widely used in optical communications, environmental monitoring, biomedical imaging and other fields. The basic working principle of a semiconductor photodetector is that under external illumination, the semiconductor material absorbs photons to generate electron-hole pairs, which in turn affects the conductivity of the semiconductor material itself, that is, there is a difference in the conductivity of the semiconductor in the light and dark states. According to the different detector structures, photodetectors can be divided into two categories: non-gain type and gain type. Non-gain devices include Schottky barrier photodiodes, PIN photodiodes, and Schottky contact metal-semiconductor-metal (MSM) photodiodes. Gain devices include avalanche photodiodes, bipolar heterojunction phototransistors, field-effect heterojunction phototransistors, etc. In the current process of rapid development of information technology, many application scenarios require photodetectors to have high responsiveness and be able to detect weak light, which requires photodetectors to have high internal gain. Thanks to the strong spontaneous polarization and piezoelectric polarization effect in wurtzite structure III-nitride semiconductors, the heterojunction composed of III-nitride semiconductors of different components can form a polarization electric field to make the epitaxial thin film layers on both sides of the heterojunction present a high resistance state, and the electron-hole pairs generated by light can weaken the electric field, so that the epitaxial thin film layer that generates light absorption restores conductivity and generates carrier transport (therefore, the epitaxial layer can also be called a light absorption and transport layer), that is, the polarization electric field plays the role of a light-controlled built-in gate, thereby forming a heterojunction phototransistor with field effect. This unipolar heterojunction phototransistor has photoconductivity gain in addition to photograting gain, so it can obtain high responsiveness. Although the above-mentioned phototransistor detector based on III-nitride heterojunction polarization effect has high gain and the resulting high responsivity, it usually exhibits a strong persistent photoconductivity (PPC) effect, that is, in the process of light signal incidence to removal, the response current of the detector needs to be delayed for a period of time to rise to the steady-state peak, and then decay to the steady-state dark current value. For devices with severe PPC effect, the response current can only recover the initial dark current value after several hours to several days after the light is removed. This is because under continuous illumination, deep energy level defects and localized states in the epitaxial layer will capture photogenerated minority carriers and induce continuous injection of majority carriers, and after the light is removed, they release carriers at a slower speed, resulting in severe PPC effect. PPC will not only degrade the response speed of the photodetector, limiting its application in optical communication and optical logic computing, but also this defect-induced effect will affect the weak light response characteristics and periodic light response stability of the detector, seriously affecting the practicality of the detector. For example, a response current that remains high in the dark state after illumination will affect the device's detection of subsequent weak light signals, while the gradual rise in the response peak will affect the detector's sequential light signals; at the same time, since defects are usually non-uniformly distributed, they will affect the on-chip uniformity of the detector. For heterojunction photodetectors, the defects that cause PPC mainly come from the surface, interface and body of the epitaxial layer. Among them, the defects in the body and interface can be suppressed by improving the epitaxial growth, while the surface defects are unavoidable from the perspective of crystal structure and can only be reduced and controlled through process treatment. Among them, surface passivation is an effective way. Preparation of ex-situ SiO x 、Al2O3、SiN x The dielectric film passivation layer is a commonly used method at present. It is to take the epitaxial structure out of the metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) chamber and then perform the subsequent passivation layer deposition. However, the epitaxial layer surface of the epitaxial wafer taken out of the growth chamber will react with oxygen in the air or produce impurity adsorption in advance, resulting in additional surface states. In addition, the ex-situ passivation layer is usually obtained at a lower temperature, and there are more defects and impurity charges in the layer, and the passivation layer quality is poor. Therefore, developing an in-situ surface passivation method to suppress surface defects of semiconductor materials is of great significance for effectively alleviating the PPC effect of heterojunction photodetectors and improving the practical performance of detectors including response speed, response stability and on-chip uniformity. Summary of the invention The present invention aims to reduce the surface defects of the epitaxial layer of a heterojunction photodetector and provide an epitaxial structure and a preparation method for a heterojunction photodetector, so as to effectively control the surface defects without adding subsequent process steps, thereby alleviating the PPC effect of the device and improving the light response speed, light response stability and on-chip uniformity of the device. In order to achieve the above technical effects, the present invention provides an epitaxial structure of a heterojunction photodetector, which includes, from bottom to top, a substrate, an interface lower layer, an interface transition layer, an interface upper layer, a SiN x In-situ passivation layer and ohmic contact electrode; the anode and cathode of the ohmic contact electrode are deposited on SiN x The in-situ passivation layer surface, or the anode and cathode of the ohmic contact electrode are deposited on the pre-etched SiN x The upper surface of the interface of the in-situ passivation layer can form an ohmic contact by conventional ohmic contact deposition and heat treatment alloy process. The upper layer of the interface is a light absorption and transport layer. Furthermore, the SiN x The value of x in the in-situ passivation layer is 0.5-1.5. The SiN x The in-situ passivation layer is prepared by metal organic chemical vapor deposition method with SiH4 and NH3, and can be grown in-situ on the surface of the device after the epitaxial structure is grown, without the need to etch the passivation layer under the electrode in advance. Furthermore, the lower interface layer, the interface transition layer and the upper interface layer of the detector epitaxial structure are all made of Group III nitride semiconductor materials, and the lower interface layer, the interface transition layer and the upper interface layer form a heterojunction with each other. Furthermore, the interface transition layer is a Group III nitride layer whose bandgap width gradually changes from the lower interface layer to the upper interface layer by adjusting its composition, and its thickness ranges from 0 to 50 nm; when the thickness is 0, a sudden heterojunction is formed between the lower interface layer and the upper interface layer; when the thickness is not 0, a gradual heterojunction is formed. The upper interface layer and the lower interface layer are both group III nitride materials, and the polarization strengths of the two layers are different, so the polarization effect can be used to generate positive / negative polarization charges at the interface between the two layers; the group III nitride semiconductor materials used are all grown on polar planes or semi-polar planes, wherein the polar planes are arranged in the direction of metal polarity, that is, they grow along the

[0001] crystal direction. Furthermore, the interface upper layer is a single-layer interface upper layer, and the interface upper layer is an n-type doped layer. The doping methods of the n-type doped layer include: uniform doping, alternating doping and linear gradient doping. The equivalent electron concentration range of the n-type doped layer is 3×10 17 cm -3 to 8×10 18 cm -3 . Furthermore, the interface upper layer is a double-layer interface upper layer, and the interface upper layer is composed of a non-doped barrier layer with a relatively wide bandgap width and a channel layer with a relatively narrow bandgap width. If the upper layer of the interface is a single-layer n-type doped layer, taking AlGaN material as an example, the Al component of the lower layer of the interface AlGaN should be higher than that of the upper layer of the interface. Due to the existence of piezoelectric and spontaneous polarization effects, negative polarization charges will be generated at the interface, which will raise the energy band there and generate a built-in electric field pointing to the interface, thereby depleting the electrons in the upper layer of the interface, making it in a high-resistance state in the absence of light and having a lower dark current. When in-band response light is applied, electron-hole pairs will be generated in the upper layer of the interface. Under the action of the electric field, photogenerated electrons drift to the surface to increase conductivity, and photogenerated holes drift to the interface to shield the effect of the negative polarization charge on the interface, thereby further reducing the conductivity of the epitaxial layer and making the device have a higher photocurrent. If the upper layer of the interface is a double layer composed of a barrier layer / channel layer, taking AlGaN material as an example, the Al component of the barrier layer in the double layer is higher than that of the channel layer, then a two-dimensional electron gas (2DEG) will be induced between the double layers. Furthermore, if AlGaN with an Al component higher than that of the upper layer of the interface is selected as the lower layer of the interface, negative polarization charges will be generated at the interface between the upper and lower layers, thereby depleting 2DEG in the dark state. Under illumination, photogenerated electrons will replenish 2DEG under the action of the electric field, and photogenerated holes will weaken the effect of negative polarization charges and restore the conductivity of the channel layer in the upper layer of the interface. In this technical solution, in-situ SiN x The tunneling passivation layer has the advantages of high film quality and no introduction of impurity atoms (such as oxygen atoms) in the air environment. It can effectively reduce the surface defects of heterojunction photodetectors and has the advantage of not increasing the complexity of the ohmic contact preparation process. The above two types of heterojunction photodetectors are surface devices, and their carrier transport is strongly affected by the surface state concentration. Under illumination, the photogenerated carriers will drift to the surface of the device under the action of the built-in polarization electric field. The trap-type energy levels in the surface defects will capture the drifted carriers and provide partial defect-associated photoconductivity gain, but at the same time it will also reduce the response speed of the device, thereby causing the PPC effect and periodic light response instability in the device. Therefore, by in-situ preparation of thin SiN x By tunneling through the passivation layer, the PPC of high-gain heterojunction photodetectors can be effectively alleviated, and the response speed, photoresponse stability and on-chip uniformity can be significantly improved. Preferably, the lattice structure of the III-group nitride material is a wurtzite structure, and the material has piezoelectric polarization and spontaneous polarization effects, including GaN, AlN, Al x Ga 1-x N、In x Ga 1-x N、Al x In 1-x N、Alx In y Ga 1-x-y N material, where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1. Preferably, the upper and lower layers of the interface can be Al x Ga 1x N / Al y Ga 1y N, In y Ga 1y N / In x Ga 1x N, InGaN / AlGaN and other heterojunctions with polarization intensity differences. When 0 ≤ x < y ≤ 1, there are negative polarization charges at the upper and lower interfaces; when 0 ≤ y < x ≤ 1, there are positive polarization charges at the upper and lower interfaces. Preferably, if the upper layer of the interface is an n-type doped layer, this layer can be composed of a uniformly doped layer and an unintentionally doped layer of the same composition, where the carrier concentration of the unintentionally doped layer is lower than 5×10 17 cm 3 . Preferably, when the upper layer of the interface is doped with n-type, Si can be used for uniform doping, and the doping concentration is higher than 1×10 17 cm 3 、lower than 5×10 19 cm 3 , because a moderate doping concentration can not only maintain a high carrier concentration and mobility, but also keep the device in a depleted state in the dark. Preferably, in the 2DEG structure, the barrier layer / channel layer included in the upper layer of the double layer interface can be Al x Ga 1x N / Al y Ga 1 y N, In y Ga 1 y N / In x Ga 1x N, where 0 ≤ y < x ≤ 1, and positive polarization charges will be formed at the interface between the barrier layer and the channel layer, thereby inducing the generation of 2DEG. Preferably, in the 2DEG structure, AlN, GaN, InN with a thickness of 1 - 2 nm can be inserted between the barrier layer and the channel layer in the upper layer of the double layer interface as a spacer layer to reduce alloy scattering and increase the carrier concentration. Preferably, in the 2DEG structure, a 10 nm graded composition AlGaN, InGaN can be inserted between the upper and lower layers of the interface as an interface transition layer to reduce the relaxation degree of the upper layer of the interface, so as to ensure that there are more negative polarization charges at the upper and lower layer interfaces, which can better deplete the channel of the upper layer of the interface. Preferably, when the upper layer of the interface is n-type doped or unintentionally doped, SiN x For the passivation layer, both the cathode and anode ohmic contact electrodes are metal stacks of Ti / Al / Ni / Au or V / Al / V / Au, with a thickness of 15 / 80 / 20 / 60 nm. Under illumination, due to the relatively thin thickness of the SiN x passivation layer, carriers can be tunnel-transported to the metal electrodes, so that good ohmic contact is formed between the electrodes and the upper layer of the interface. Preferably, when the upper layer of the interface is n-type doped, the thickness of the upper layer of the interface is set to satisfy that the total amount of carriers in the upper layer of the interface is less than the total amount of negative-polarized charges at the upper and lower layer interfaces, so as to ensure that the doped carriers are depleted. Preferably, in the 2DEG structure, the total amount of positive-polarized charges at the interface between the barrier layer and the channel layer in the upper layer of the double layer should be less than the total amount of negative-polarized charges at the upper and lower interfaces, so as to ensure that the 2DEG is depleted. Another object of the present invention is to provide a method for preparing a heterojunction photodetector epitaxial structure: After growing the specified epitaxial structure in the MOCVD chamber, turn off the metal source, turn on the Si source, and continue to in-situ grow SiN x passivation layer on the original structure. The specific steps are as follows: (1) Turn off the metal source, set the NH3 flow rate (F1) and the Si source flow rate (F2) to specified values, keep the carrier gas atmosphere as hydrogen, and set the chamber temperature to T1 until the flow rate and temperature of the flow meter are stable; (2) Introduce NH3 and the Si source into the MOCVD chamber to prepare an in-situ SiN x passivation layer, with a growth time of t1 and a corresponding thickness of d1; (3) After growth is completed, turn off the Si source, and while keeping the NH3 flow rate unchanged, perform an annealing treatment on the SiN x passivation layer while cooling down. Preferably, for the growth of SiN x the NH3 flow rate used is 0.04 mol / min < F1 < 0.37 mol / min; for the growth of SiN x the Si source used is SiH4, and its flow rate is 0.02 μmol / min < F1 < 0.36 μmol / min, and the flow rate ratio of the group V source to the group IV source varies within the range of 10 5 -10 7 range. Preferably, the growth time is 455 s < t1 < 7000 s, and the corresponding thickness is 1 nm < d1 < 6 nm. Compared with the prior art, the beneficial effects of the present invention are: (1) An in-situ passivation method is provided to significantly improve the PPC effect of heterojunction photodetectors. x The tunneling passivation layer has the advantages of high film quality and no impurity atoms in the air environment. Without affecting the subsequent device process steps, it reduces the surface defects of the III-nitride photodetector, thereby inhibiting the capture of photogenerated carriers by semiconductor surface defects. This not only accelerates the device's response to light, but also promotes the recombination of photogenerated carriers after the light is removed, thereby effectively alleviating the PPC effect that limits the device's frequency characteristics and weak light response. (2)SiN x The in-situ passivation layer significantly improves the stability of the detector's periodic light response process. Due to the reduction of surface defects after passivation, the device's light and dark currents remain stable during multiple on / off cycles, and there is no continuous increase in light and dark currents during the cycle, which helps to improve the stability of the device in actual application scenarios. (3)SiN x The in-situ passivation layer significantly improves the uniformity of the dark current of the detector at different locations on the chip. Because the surface defect concentration at different locations on the chip is different before passivation, the dark current values ​​of the devices at the corresponding locations are also quite different. x With the in-situ passivation layer, surface defects at all locations on the chip are suppressed, and the dark current values ​​of devices at different locations tend to be consistent, which is beneficial to improving the utilization rate of on-chip devices. (4) In-situ preparation of SiN in MOCVD chamber x The passivation layer also has the advantage of simple process. The passivation layer can be prepared directly after the epitaxial structure is grown, without the need for subsequent wet processing, or the growth of an ex-situ passivation layer in a PECVE or LPCVD chamber. At the same time, the ohmic contact electrode can be directly prepared on the thin tunnel passivation layer, greatly reducing the process complexity. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 Schematic diagram of the epitaxial structure of the heterojunction photodetector in Example 1 and Example 2 of the present invention. Figure 2 This is a curve showing the decay of the current of the heterojunction photodetector over time after the light is removed in Example 1 of the present invention. Figure 3 This is the periodic light response curve of Example 1 of the present invention under different light intensities. Figure 4 : is the standard deviation of dark current at different on-chip locations in Example 1 of the present invention. Figure 5 Schematic diagram of the epitaxial structure of the heterojunction photodetector in Example 3 and Example 5 of the present invention. Figure 6Schematic diagram of the epitaxial structure of the heterojunction photodetector in Example 4 of the present invention. Figure 7 Schematic diagram of the epitaxial structure of the heterojunction photodetector in Example 6 of the present invention. Reference numerals: substrate 101, interface lower layer 102, interface transition layer 103, first interface upper layer 104, second interface upper layer 105, interface upper layer 200, SiN x In-situ passivation layer 106 , anode contact electrode 107 , cathode contact electrode 108 . DETAILED DESCRIPTION The drawings of the present invention are only for illustrative purposes and should not be construed as limiting the present invention. In order to better illustrate the following embodiments, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; it is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0001] In order to explain the application of the invention technology more clearly and easily, the present invention mainly provides embodiments by taking AlGaN and InGaN matrix semiconductors as examples, which does not mean that other Group III nitride semiconductor materials are not included. Example 1 like Figure 1 As shown, this embodiment discloses a method for growing a thin SiN x The uid-AlGaN-based double-layer interface upper layer heterojunction photodetector with in-situ passivation layer. The epitaxial structure of the device is, from bottom to top, a c-plane sapphire substrate layer 101; a uid-AlN buffer layer that also serves as an interface lower layer 102, with a thickness of 400nm; a uid-AlGaN interface transition layer 103 in which Al is reduced from 100% to 49%, with a thickness of 10nm; an interface upper layer 200 consisting of a first interface upper layer 104 and a second interface upper layer 105; a uid-Al 0.49 Ga 0.51 N is used as the first interface upper layer 104, which is a channel layer with a thickness of 70nm; uid-Al 0.56 Ga 0.44 N is used as the second interface upper layer 105, which is a barrier layer with a thickness of 15 nm; SiN x The in-situ passivation layer 106 has a thickness of 1 nm. The positive contact electrode 107 and the negative contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively. In the device structure disclosed in this embodiment, the SiN xThe value of x in the in-situ passivation layer is 0.5-1.5; the grown III-nitride epitaxial layers are all

[0001] oriented, so there is a strong polarization effect in each nitride epitaxial layer, including spontaneous polarization and piezoelectric polarization. Since the thickness of the uid-AlN layer under the interface is 400nm, the stress of the sapphire substrate has been relaxed in this layer, and only spontaneous polarization exists. The gradient layer can make the uid-AlN layer on the interface 0.49 Ga 0.51 N maintains a relatively low relaxation, thus 0.49 Ga 0.51 N / uid-AlN interface produces more polarized negative charges. 0.56 Ga 0.44 N / uid-Al 0.49 Ga 0.51 The N interface will generate polarized positive charges, which should induce 2DEG. 0.49 Ga 0.51 N / uid-AlN interface and uid-Al 0.56 Ga 0.44 The polarized negative charge on the N surface will raise the energy band of the heterojunction as a whole, thereby depleting the 2DEG and making the uid-Al 0.49 Ga 0.51 The N channel maintains high resistance in the dark state, that is, the device has a small dark current. Under light, the photogenerated carriers generated in the upper layer of the double-layer interface will separate to the surface and interface under the action of the polarization electric field, shielding the negative polarization charge on the surface and interface, thereby restoring the device channel to a low resistance state, that is, the device has a higher photocurrent. Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device. Therefore, based on the working principle of the device, this embodiment in-situ grows a thin SiN x Passivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiN x The thickness of the layer is only 1nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN under the metal x layer. In addition, the ungrown SiN x The same structure device with in-situ passivation layer was used as a control, and relevant performance tests were carried out on both the non-passivated (W / O) and passivated (W) devices. Figure 2The current decay curves of the unpassivated (W / O) and passivated (W) devices after the light is removed, where the light wavelength and light intensity are 260nm and 700μW / cm 2 It can be seen that the unpassivated device exhibits a serious PPC effect, and the current only decays by one order of magnitude after 20 seconds; while the passivated device decays by more than four orders of magnitude, which indicates that SiN x The passivation layer effectively reduces surface defects and promotes the recombination of photogenerated carriers after the light is removed, thus significantly alleviating PPC. Figure 3 (a) and Figure 3 (b) reflects the periodic response of the unpassivated (W / O) and passivated (W) devices under different light intensities, where the illumination on / off time in a single cycle is 20 / 20s. The test results show that in each cycle, the photocurrent continues to increase with the increase of the on time. After turning on the illumination, the continuous increase in photocurrent is due to the continuous capture of holes by defects under weak light. Therefore, the relatively small increase in photocurrent reflects that the passivated device has a lower concentration of defects. In addition, at all light intensities, the passivated devices show excellent time-dependent stability of the photocurrent, while the current of the unpassivated device not only shows a significant periodic increase, but also fluctuates, which is related to the higher surface defect concentration of the unpassivated device. Figure 4 is the standard deviation of dark current of unpassivated (W / O) and passivated (W) devices at different locations on the chip. At each voltage, the standard deviation of dark current of the passivated device is much smaller than that before passivation, which shows that passivation improves the uniformity of dark current at different locations on the chip. Because the surface defect concentration at different locations on the chip is different before passivation, the dark current values ​​of the devices at the corresponding locations are also quite different. By preparing SiN x With the in-situ passivation layer, surface defects at all locations on the chip are suppressed, and the dark current values ​​of devices at different locations tend to be consistent, which is beneficial to improving the utilization rate of on-chip devices. Example 2 like Figure 1 As shown, this embodiment discloses a method for growing a thin SiN x The uid-InGaN-based double-layer interface upper layer heterojunction photodetector with in-situ passivation layer. The epitaxial structure of the device is, from bottom to top, a c-plane sapphire substrate layer 201; a uid-GaN buffer layer that also serves as an interface lower layer 102, with a thickness of 3μm; a uid-InGaN interface transition layer 103 with In increasing from 0% to 20%, with a thickness of 10nm; an interface upper layer 200 consisting of a first interface upper layer 104 and a second interface upper layer 105; a uid-InGaN buffer layer that also serves as an interface lower layer 102, with a thickness of 3μm; a uid-InGaN interface transition layer 103 with In increasing from 0% to 20%, with a thickness of 10nm; a first interface upper layer 104 and a second interface upper layer 105; a uid-InGa 0.2 Ga 0.8N is used as the first interface upper layer 104, which is a channel layer with a thickness of 80nm; uid-GaN is used as the second interface upper layer 105, which is a barrier layer with a thickness of 15nm; SiN x The in-situ passivation layer 206 has a thickness of 1 nm. The positive contact electrode 107 and the negative contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively. In the device structure disclosed in this embodiment, the SiN x The value of x in the in-situ passivation layer is 0.5-1.5; the grown III-nitride epitaxial layers are all

[0001] oriented, so there is a strong polarization effect in each nitride epitaxial layer, including spontaneous polarization and piezoelectric polarization. Since the thickness of the lower uid-GaN layer of the interface is 3μm, the stress of the sapphire substrate has been relaxed in this layer, and only spontaneous polarization exists. The gradient layer can make the upper uid-In layer of the interface 0.2 Ga 0.8 N maintains a relatively low relaxation, thus in uid-In 0.2 Ga 0.8 N / uid-GaN interface produces more polarized negative charges. Similarly, the channel and barrier layers (uid-GaN / uid-In 0.2 Ga 0.8 N) will produce polarized positive charges, which should induce 2DEG. However, uid-In 0.2 Ga 0.8 The polarized negative charges at the N / uid-GaN interface and the uid-GaN surface will raise the energy band of the heterojunction as a whole, thereby depleting the 2DEG and making the uid-In 0.2 Ga 0.8 The N channel maintains high resistance in the dark state, that is, the device has a small dark current. Under light, the photogenerated carriers generated in the upper layer of the double interface will be separated to the surface and interface under the action of the polarization electric field, shielding the negative polarization charge on the surface and interface, thereby restoring the device channel to a low resistance state, that is, the device has a higher photocurrent. Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device. Therefore, based on the working principle of the device, this embodiment in-situ grows a thin SiN x Passivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiN x The thickness of the layer is only 1nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN under the metalx layer. Example 3 like Figure 5 As shown, this embodiment discloses a method for growing a thin SiN x n-AlGaN-based single-layer interface upper heterojunction photodetector with in-situ passivation layer. The epitaxial structure of the device is, from bottom to top, a c-plane sapphire substrate layer 101; a uid-AlN buffer layer that also serves as an interface lower layer 102 with a thickness of 400nm; an Al2O3 uniformly doped with Si for n-type 0.49 Ga 0.51 N is used as the upper interface layer 200, with a thickness of 80 nm and a doping concentration of 1×10 18 cm 3 ;SiN x The in-situ passivation layer 106 has a thickness of 1 nm. The positive contact electrode 107 and the negative contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively. In the device structure disclosed in this embodiment, the SiN x The value of x in the in-situ passivation layer is 0.5-1.5; the grown III-nitride epitaxial layers are all

[0001] oriented, so there is a strong polarization effect in each nitride epitaxial layer, including spontaneous polarization and piezoelectric polarization. Since the thickness of the lower interface layer uid-AlN is 400nm, the stress of the sapphire substrate has been relaxed in this layer, and only spontaneous polarization exists. The thickness of the upper interface layer is 80nm, which is subject to a large compressive stress of the lower interface layer AlN, and the relaxation degree is low. It has spontaneous polarization and piezoelectric polarization in opposite directions, so polarized negative charges will be generated at the interface between the upper and lower layers. In the dark state, the polarized negative charges will raise the energy band of the heterojunction, thereby depleting the electrons in the upper interface layer. Under illumination, photogenerated electron-hole pairs are generated in the upper interface layer. The photogenerated electrons drift to the surface under the action of the polarization electric field and participate in conduction. The photogenerated holes are transported to the interface to shield the effect of the polarized negative charges, thereby further improving the conductivity of the upper interface layer. Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device. Therefore, based on the working principle of the device, this embodiment in-situ grows a thin SiN x Passivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiN x The thickness of the layer is only 1nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN under the metal x layer. Example 4 like Figure 6 As shown, this embodiment discloses a method for growing a thin SiN x In-situ passivation layer n-AlGaN-based double-layer interface upper layer heterojunction photodetector. The epitaxial structure of the device is, from bottom to top, a c-plane sapphire substrate layer 101; a uid-AlN buffer layer also serves as an interface lower layer 102, with a thickness of 400nm; an interface upper layer 200 is composed of a first interface upper layer 104 and a second interface upper layer 105, wherein the uid-AlGaN with an Al component of 49% is the first interface upper layer 104, and an epitaxial layer with the same component and uniformly doped with Si for n-type is the second interface upper layer 105, with thicknesses of 10nm and 80nm, respectively, wherein the n-type doping concentration is 1×10 18 cm 3 ;SiN x The in-situ passivation layer 106 has a thickness of 1 nm. The positive contact electrode 107 and the negative contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively. In the device structure disclosed in this embodiment, the SiN x The value of x in the in-situ passivation layer is 0.5-1.5; the III-group nitride epitaxial layers are all obtained by

[0001] orientation growth, so there is a strong polarization effect (including spontaneous polarization and piezoelectric polarization) in each nitride epitaxial layer. Since the thickness of the lower interface layer uid-AlN is 400nm, the stress of the sapphire substrate has been relaxed in this layer, and only spontaneous polarization exists. The total thickness of the upper interface layer with the same composition is 90nm. It is subject to greater compressive stress from the lower interface layer AlN, has a lower degree of relaxation, and has spontaneous polarization and piezoelectric polarization in opposite directions. Therefore, polarized negative charges will be generated at the interface between the upper and lower layers. In the dark state, the polarized negative charges will raise the energy band of the heterojunction, thereby depleting the electrons in the upper interface layer. Under illumination, photogenerated electron-hole pairs are generated in the upper layer of the interface. The photogenerated electrons drift to the surface under the action of the polarized electric field and participate in the conduction. The photogenerated holes are transported to the interface to shield the polarized negative charge, thereby further improving the conductivity of the upper layer of the interface. It should be pointed out that the upper layer of the interface of this embodiment also includes an unintentionally doped layer of the same component as the n-type layer, which is mainly used to reduce the recombination of photogenerated holes by interface defects, thereby further promoting the recovery of the conductivity of the upper layer of the interface under illumination. Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device. Therefore, based on the working principle of the device, this embodiment in-situ grows a thin SiN x Passivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiNx The thickness of the layer is only 1nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN under the metal x layer. Example 5 like Figure 5 As shown, this embodiment discloses a method for growing a thin SiN x The uid-InGaN-based single-layer interface upper heterojunction photodetector with in-situ passivation layer. The epitaxial structure of the device is, from bottom to top, a C-plane sapphire substrate layer 101; a uid-GaN buffer layer that also serves as an interface lower layer 102 with a thickness of 3μm; 0.2 Ga 0.8 N is used as the upper interface layer 200 with a thickness of 120nm; SiN x The in-situ passivation layer 106 has a thickness of 1 nm. The positive contact electrode 107 and the negative contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively. In the device structure disclosed in this embodiment, the SiN x The value of x in the in-situ passivation layer is 0.5-1.5; the III-group nitride epitaxial layers are all obtained by

[0001] oriented growth, so there is a strong polarization effect in each nitride epitaxial layer, including spontaneous polarization and piezoelectric polarization. Since the thickness of the lower interface layer uid-GaN is 3μm, the stress of the sapphire substrate has been relaxed in this layer, and only spontaneous polarization exists. The thickness of the upper interface layer is 120nm, which is subject to a large compressive stress of the lower interface layer GaN, and the relaxation degree is low. It has spontaneous polarization and piezoelectric polarization in the opposite direction, so polarized negative charges will be generated at the interface between the upper and lower layers. In the dark state, the polarized negative charge will raise the energy band of the heterojunction, thereby depleting the electrons in the upper interface layer. Under illumination, photogenerated electron-hole pairs are generated in the upper interface layer. The photogenerated electrons drift to the surface under the action of the polarization electric field and participate in conduction. The photogenerated holes are transported to the interface to shield the effect of the polarized negative charge, thereby further improving the conductivity of the upper interface layer. Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device. Therefore, based on the working principle of the device, this embodiment in-situ grows a thin SiN x Passivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiN x The thickness of the layer is only 1nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN under the metal x layer. Example 6 like Figure 7 As shown, this embodiment discloses a method for growing a thin SiN x In-situ passivation layer uid-InGaN-based single-layer interface upper heterojunction photodetector. The epitaxial structure of the device is, from bottom to top, a c-plane sapphire substrate layer 101; a uid-GaN buffer layer that also serves as an interface lower layer 102, with a thickness of 3μm; a uid-InGaN interface transition layer 103 with In increasing from 0% to 20%, with a thickness of 30nm; 0.2 Ga 0.8 N is used as the upper interface layer 200 with a thickness of 120nm; SiN x The in-situ passivation layer 106 has a thickness of 1 nm. The positive contact electrode 107 and the negative contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively. In the device structure disclosed in this embodiment, the SiN x The value of x in the in-situ passivation layer is 0.5-1.5; the III-group nitride epitaxial layers are all grown in the

[0001] orientation, so there is a strong polarization effect in each nitride epitaxial layer, including spontaneous polarization and piezoelectric polarization. Since the thickness of the uid-GaN layer under the interface is 3μm, the stress of the sapphire substrate has been relaxed in this layer, and only spontaneous polarization exists. The gradient layer can make the uid-In layer on the interface 0.2 Ga 0.8 N maintains a relatively low relaxation and is subjected to a large compressive stress, which in turn 0.2 Ga 0.8 The N / uid-GaN interface generates more polarized negative charges. In the dark state, the polarized negative charges will raise the energy band of the heterojunction, thereby depleting the electrons in the upper layer of the interface. Under light, photogenerated electron-hole pairs are generated in the upper layer of the interface. The photogenerated electrons drift to the surface under the action of the polarized electric field and participate in conduction. The photogenerated holes are transported to the interface to shield the effect of the polarized negative charges, thereby further improving the conductivity of the upper layer of the interface. Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device. Therefore, based on the working principle of the device, this embodiment in-situ grows a thin SiN x Passivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiN x The thickness of the layer is only 1nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN under the metal xlayer Example 7 This embodiment provides a method for preparing an epitaxial structure of a heterojunction photodetector, which is characterized by including the following steps: S1. Grow an interface lower layer, an interface transition layer, and an interface upper layer on a substrate by metalorganic chemical vapor deposition; S2. Close the metal source, set the NH3 flow rate F1 and the Si source flow rate F2 to specified values, keep the carrier gas atmosphere as hydrogen, set the chamber temperature to T1, and wait for the flow rate and temperature of the flowmeter to stabilize; S3. Introduce NH3 and the Si source into the epitaxial chamber to prepare an in-situ SiN x passivation layer, with a growth time of t1 and a corresponding thickness of d1; S4. After growth is completed, close the Si source, while keeping the NH3 flow rate unchanged, and perform an annealing treatment on the SiNx passivation layer while cooling down. Further, the NH3 flow rate F1 satisfies: 0.04 mol / min < F1 < 0.37 mol / min; The Si source is SiH4, and the Si source flow rate F2 satisfies: 0.02 μmol / min < F2 < 0.36 μmol / min, and the flow rate ratio of the group V source to the group IV source varies within the range of 10 5 -10 7 range. Further, the growth time t1 satisfies: 455 s

Claims

1. An epitaxial structure of a heterojunction photodetector, characterized in that: From bottom to top, it includes substrate, lower interface layer, interface transition layer, upper interface layer, SiN x In-situ passivation layer and ohmic contact electrode; The anode and cathode of the ohmic contact electrode are deposited on SiN x In-situ passivation layer surface, Or the anode and cathode of the ohmic contact electrode are deposited on the SiN x The interface upper surface of the in-situ passivation layer.

2. The epitaxial structure of the heterojunction photodetector according to claim 1, characterized in that: The SiN x The value of x in the in-situ passivation layer is 0.5-1.

5.

3. The epitaxial structure of the heterojunction photodetector according to claim 1, characterized in that: The interface lower layer, the interface transition layer, and the interface upper layer of the detector epitaxial structure are all group-III nitride semiconductor materials, and the interface lower layer, the interface transition layer, and the interface upper layer form a heterojunction with each other.

4. The epitaxial structure of the heterojunction photodetector according to claim 1, characterized in that: The interface transition layer is a group-III nitride layer whose bandgap width gradually changes from the interface lower layer to the interface upper layer by composition adjustment, and its thickness ranges from 0 to 50 nm; when the thickness is 0, a step heterojunction is formed between the interface lower layer and the interface upper layer; when the thickness is not 0, a graded heterojunction is formed.

5. The epitaxial structure of the heterojunction photodetector according to claim 1, characterized in that: The interface upper layer is a single-layer interface upper layer, and the interface upper layer is an n-type doped layer.

6. The epitaxial structure of the heterojunction photodetector according to claim 1, characterized in that: The interface upper layer is a double-layer interface upper layer, and the interface upper layer is composed of an undoped wide bandgap barrier layer and a narrow bandgap channel layer.

7. The epitaxial structure of the heterojunction photodetector according to claim 5, characterized in that: The doping methods of the n-type doping layer include: uniform doping, alternating doping and linear gradient doping. The equivalent electron concentration range of the n-type doping layer is 3×10 17 cm -3 to 8×10 18 cm -3 .

8. The method for preparing a heterojunction photodetector epitaxial structure according to any one of claims 1 to 7, characterized in that: It includes the following steps: S1. Grow the interface lower layer, the interface transition layer, and the interface upper layer on the substrate by metalorganic chemical vapor deposition; S2. Close the metal source, set the NH3 flow rate F1 and the Si source flow rate F2 to specified values, keep the carrier gas atmosphere as hydrogen, set the chamber temperature to T1, and wait for the flow rate and temperature of the flowmeter to stabilize; S3, introducing NH3 and Si source into the epitaxial cavity to prepare in-situ SiN x Passivation layer, growth time is t1, corresponding thickness is d1; S4. After the growth is completed, turn off the Si source and keep the NH3 flow rate unchanged. x The passivation layer is annealed.

9. The method for preparing a heterojunction photodetector epitaxial structure according to claim 8, characterized in that: The NH3 flow rate F1 satisfies: 0.04 mol / min < F1 < 0.37 mol / min; The Si source is SiH4, and the flow rate F2 of the Si source satisfies: 0.02 μmol / min < F2 < 0.36 μmol / min, and the flow rate ratio of the Group V source to the Group IV source varies within the range of 10 5 -10 7 to 10.

10. The method for preparing a heterojunction photodetector epitaxial structure according to claim 8, characterized in that: The growth time t1 satisfies: 455 s < t1 < 7000 s, and the corresponding thickness d1 satisfies: 1 nm < d1 < 6 nm.

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