CN119092584B

CN119092584B - Epitaxial structure and preparation method of heterojunction photodetector

Info

Publication number: CN119092584B
Application number: CN202411135884.1A
Authority: CN
Inventors: 江灏; 彭琢雅; 吴勉; 吕泽升
Original assignee: Sun Yat Sen University
Current assignee: Sun Yat Sen University
Priority date: 2024-08-19
Filing date: 2024-08-19
Publication date: 2025-09-26
Anticipated expiration: 2044-08-19
Also published as: CN119092584A

Abstract

The invention relates to the field of semiconductor photodetectors, and provides an epitaxial structure of a heterojunction photodetector and a preparation method thereof, wherein the epitaxial structure comprises a substrate, an interface lower layer, an interface transition layer, an interface upper layer, an in-situ SiN _x passivation layer and an ohmic contact electrode from bottom to top, wherein an anode and a cathode of the ohmic contact electrode are deposited on the surface of the in-situ SiN _x passivation layer, or the anode and the cathode of the ohmic contact electrode are deposited on the surface of the interface upper layer from which the in-situ SiN _x passivation layer is etched in advance. The method has the advantages that the in-situ grown thin SiN _x film with high film forming quality and no impurity atom introduction in the air environment is used as the passivation layer, so that the surface defects of the III-nitride photoelectric detector are reduced, and further the capture of the semiconductor surface defects to the photo-generated carriers is inhibited. The method not only effectively improves the serious continuous photoconductive effect in the detector caused by the surface defect and the response speed limit caused by the serious continuous photoconductive effect, but also obviously improves the light response stability of the detector and the uniformity of dark current of the on-chip device.

Description

Epitaxial structure of heterojunction photoelectric detector and preparation method

Technical Field

The invention relates to the technical field of semiconductor photodetectors, in particular to an epitaxial structure of a heterojunction photodetector and a preparation method thereof.

Background

The photoelectric detector is a device capable of converting an external optical signal into an internal electric signal of a device, and is widely applied to the fields of optical communication, environmental monitoring, biomedical imaging and the like. The basic working principle of the semiconductor photoelectric detector is that under the external illumination, the semiconductor material can absorb photons to generate electron-hole pairs, so that the conductivity of the semiconductor material is affected, namely, the conductivity of the semiconductor in the light and dark states is different. Photodetectors can be divided into two broad categories, non-gain type and gain type, where the non-gain device type includes schottky barrier photodiodes, PIN photodiodes, and schottky contact metal-semiconductor-metal (MSM) type photodiodes, and the gain type devices include avalanche photodiodes, bipolar heterojunction photodiodes, field effect heterojunction photodiodes, and the like.

In the current process of high-speed development of the informatization technology, numerous application scenes require that the photoelectric detector has high responsivity and can detect weak light, so that the photoelectric detector is required to have higher internal gain. Due to the strong spontaneous polarization and piezoelectric polarization effects in the wurtzite structure III nitride semiconductor, the heterojunction composed of the III nitride semiconductors with different components can enable the epitaxial thin film layers on two sides of the heterointerface to be in a high-resistance state by forming a polarized electric field, and electron-hole pairs generated by illumination can weaken the electric field, so that the epitaxial thin film layer generating light absorption can restore conductivity, carrier transport is generated (the epitaxial layer can be called as a light absorption and transport layer), namely the polarized electric field plays a role of a light-operated built-in grid, and the heterojunction phototransistor with a field effect is formed. The heterojunction phototransistor of the single pole type has a photoconductive gain in addition to a grating control gain, and thus high responsivity can be obtained.

Although the above-described III-nitride heterojunction polarization effect-based phototransistor detector has high gain and high responsivity, it generally exhibits a strong persistent photoconductive (Photoconductivity, PPC) effect, i.e., the response current of the detector needs to be delayed for a period of time to rise to a steady state peak value and then decay to a steady state dark current value during the incident/withdrawal of an optical signal. For devices with severe PPC effects, the response current can only recover the initial dark current value after hours to days after the light is removed. This is because deep level defects and localized states in the epitaxial layer capture photogenerated minority carriers under continuous light, induce multi-carrier continuous injection, and their release rate of carriers is slow after light is removed, resulting in severe PPC effects. The PPC not only can deteriorate the response speed of the photoelectric detector and limit the application of the PPC in optical communication and optical logic calculation, but also can influence the weak light response characteristic and the periodic light response stability of the detector due to the effect caused by the defects, and seriously influence the practicability of the detector. For example, maintaining a high value of response current in the dark state after illumination can affect the detection of subsequent weak light signals by the device, while gradual ramp-up of the response peak can affect the sequential light signals of the detector, and at the same time, the on-chip uniformity of the detector can be affected because defects are typically unevenly distributed.

For heterojunction photodetectors, the defects that cause PPC are mainly from the surface, interface, and bulk of the epitaxial layer. Wherein defects in the body and interface can be suppressed by improvement of epitaxial growth, whereas surface defects are unavoidable from the point of view of crystal structure and can be reduced and controlled only by processing. Among these, surface passivation is an effective way. The preparation of dielectric film passivation layers such as ex-situ SiO _x、Al₂O₃、SiN_x is a relatively common method at present, and is to take out an epitaxial structure from a Metal Organic Chemical Vapor Deposition (MOCVD) or Molecular Beam Epitaxy (MBE) cavity for subsequent passivation layer deposition. However, the epitaxial wafer is removed from the growth chamber, the surface of the epitaxial layer is pre-reacted with oxygen in the air or impurities are adsorbed, so that an additional surface state is caused, and the ex-situ passivation layer is usually obtained at a lower temperature, so that defects and impurity charges in the layer are more and the passivation layer has poor quality.

Therefore, an in-situ surface passivation method is developed to inhibit surface defects of semiconductor materials, which has important significance for effectively relieving the PPC effect of the heterojunction photoelectric detector and improving the practical performance of the detector including response speed, response stability and on-chip uniformity.

Disclosure of Invention

The invention aims to reduce the surface defects of an epitaxial layer of a heterojunction photoelectric detector, and provides an epitaxial structure of the heterojunction photoelectric detector and a preparation method thereof, so that the surface defects are effectively controlled, and meanwhile, the subsequent process steps are not required to be added, thereby relieving the PPC effect of a device and improving the light response speed, light response stability and on-chip uniformity of the device.

In order to achieve the technical effects, the epitaxial structure of the heterojunction photoelectric detector comprises a substrate, an interface lower layer, an interface transition layer, an interface upper layer, a SiN _x in-situ passivation layer and an ohmic contact electrode from bottom to top, wherein an anode and a cathode of the ohmic contact electrode are deposited on the surface of the SiN _x in-situ passivation layer, or the anode and the cathode of the ohmic contact electrode are deposited on the surface of the interface upper layer where the SiN _x in-situ passivation layer is etched in advance. Ohmic contact can be formed by conventional ohmic contact deposition and heat treatment alloy processes. The interface upper layer is a light absorption and transport layer.

Further, the value of x in the SiN _x in-situ passivation layer is 0.5-1.5.

The SiN _x in-situ passivation layer is prepared from SiH ₄ and NH ₃ by a metal organic chemical vapor deposition method, and can be grown on the surface of the device in situ after the epitaxial structure of the device grows, and the passivation layer below the electrode does not need to be etched in advance.

Further, the interface lower layer, the interface transition layer and the interface upper layer of the detector epitaxial structure are all made of III-nitride semiconductor materials, and the interface lower layer, the interface transition layer and the interface upper layer form a heterojunction.

Further, the interface transition layer is a III-group nitride layer with the forbidden band width gradually changing from the interface lower layer to the interface upper layer through component adjustment, the thickness range is between 0 and 50 nm, when the thickness is 0, a abrupt heterojunction is formed between the interface lower layer and the interface upper layer, and when the thickness is not 0, a gradual change heterojunction is formed.

The upper and lower layers of the interface are III-nitride materials, and the polarization intensities of the two layers are different, so that positive/negative polarization charges can be generated at the interface of the two layers by utilizing polarization effect, and the III-nitride semiconductor materials are grown on polar surfaces or semi-polar surfaces, wherein the polar surfaces are arranged according to the metal polar direction, namely, the polar surfaces grow along the [0001] crystal direction.

Further, the interface upper layer is a single-layer interface upper layer, and the interface upper layer is an n-type doped layer. The doping mode of the n-type doping layer comprises uniform doping, alternating doping and linear gradual change doping, and the equivalent electron concentration range in the n-type doping layer is 3×10 ¹⁷cm^-3 to 8×10 ¹⁸cm^-3.

Further, the interface upper layer is a double-layer interface upper layer, and the interface upper layer is composed of an undoped barrier layer with a wider forbidden bandwidth and a channel layer with a narrower forbidden bandwidth.

If the interface upper layer is a single n-type doped layer, such as an AlGaN material, the Al component of AlGaN of the interface lower layer should be higher than that of the interface upper layer. Due to the existence of piezoelectric and spontaneous polarization, negative polarization charges are generated at the interface, which can raise the energy band at the interface and generate a built-in electric field pointing to the interface, so that electrons on the upper layer of the interface are exhausted, and the interface is in a high-resistance state in no illumination, and has lower dark current. When in-band response illumination is applied, electron-hole pairs are generated on the upper layer of the interface, under the action of an electric field, photo-generated electrons drift to the surface to increase the electric conduction, and photo-generated holes drift to the interface to shield the effect of negative polarized charges of the interface, so that the electric conduction of the epitaxial layer is further reduced, and the device has higher photocurrent.

If the interface upper layer is a bilayer of barrier layer/channel layer, for example, alGaN material, the Al component of the barrier layer in the bilayer is higher than that of the channel layer, then two-dimensional electron gas (2 DEG) is induced between the bilayers. Further, if AlGaN having an Al composition higher than that of the upper interface layer is selected as the lower interface layer, negative charges are generated at the interfaces of the upper and lower layers, and the 2DEG is depleted in the dark state. Under illumination, the 2DEG is supplemented by the photo-generated electrons under the action of an electric field, and the negative polarization charge effect is weakened by the photo-generated holes, so that the conductivity of the channel layer in the upper layer of the interface is recovered.

In the technical scheme, the in-situ SiN _x tunneling passivation layer has the advantages of high film forming quality, introduction of impurity atoms (such as oxygen atoms and the like) in an air-free environment and the like, can effectively reduce the surface defects of the heterojunction photoelectric detector, and has the advantage of not increasing the complexity of an ohmic contact preparation process. Both types of heterojunction photodetectors are surface devices, and carrier transport is strongly affected by surface state concentrations. Under illumination, photo-generated carriers drift to the surface of the device under the action of a built-in polarized electric field, trap energy levels in surface defects can capture the drifted carriers to provide partial defect-associated photoconductive gain, but the response speed of the device can be reduced, so that the PPC effect and the periodic photoresponse in the device are unstable. Therefore, the PPC of the high-gain heterojunction photoelectric detector can be effectively relieved by preparing the thin SiN _x tunneling passivation layer in situ, and the response speed, the light response stability and the on-chip uniformity can be remarkably improved.

Preferably, the lattice structure of the group III nitride material is wurtzite structure, and the material has piezoelectric polarization and spontaneous polarization effects, including GaN、AlN、Al_xGa_1-xN、In_xGa_1-xN、Al_xIn_1-xN、Al_xIn_yGa_1-x-yN materials, wherein 0≤x≤1, and 0≤y≤1.

Preferably, the upper and lower layers of the interface may be Al_xGa_1-xN/Al_yGa_1-yN、In_yGa_1-yN/In_xGa_1-xN、InGaN/AlGaN and other heterojunctions with polarization differences, respectively. When x is more than or equal to 0 and less than or equal to 1, negative charges exist at the upper and lower interfaces, and when y is more than or equal to 0 and less than or equal to 1, positive charges exist at the upper and lower interfaces.

Preferably, if the upper interfacial layer is an n-doped layer, the layer may be composed of a uniformly doped layer and an unintentionally doped layer of the same composition, wherein the carrier concentration of the unintentionally doped layer is lower than 5 x 10 ¹⁷cm^-3.

Preferably, when the interfacial upper layer is doped n-type, si can be used for uniform doping with doping concentrations above 1 x 10 ¹⁷cm^-3 and below 5x 10 ¹⁹cm^-3, as moderate doping concentrations can maintain both higher carrier concentration and mobility and maintain the device in a depleted state in the dark state.

Preferably, in the 2DEG structure, the barrier layer/channel layer included in the upper layer of the double-layer interface can be Al _xGa_1-xN/Al_yGa_1-yN、In_yGa_1-yN/In_xGa_1-x N, wherein y < x < 1, and the interface between the barrier layer and the channel layer can form positive charges, so that the 2DEG is induced.

Preferably, in the 2DEG structure, alN, gaN, inN with a thickness of 1-2 nm a can be inserted between the barrier layer and the channel layer in the upper layer of the double-layer interface as a space layer, which plays roles of reducing alloy scattering and increasing carrier concentration.

Preferably, in the 2DEG structure, a layer of 10 nm gradient component AlGaN and InGaN can be inserted between the upper layer and the lower layer of the interface as an interface transition layer so as to reduce the relaxation degree of the upper layer of the interface, thereby ensuring that the upper layer interface and the lower layer interface have more negative polarization charges and playing a better role in exhausting the upper layer channel of the interface.

Preferably, when the interfacial upper layer is n-doped or unintentionally doped, the negative and Yang Oum contact electrodes on the SiN _x passivation layer are both metal stacks of Ti/Al/Ni/Au or V/Al/V/Au, with a thickness of 15/80/20/60 nm. Under illumination, the SiN _x passivation layer is thinner, so that carriers can be tunneled and transported to the metal electrode, and the electrode and the upper layer of the interface form good ohmic contact.

Preferably, when the interface upper layer is n-type doped, the thickness of the interface upper layer is set so that the total amount of carriers in the interface upper layer is smaller than the total amount of negative polarized charges in the interface upper layer and the interface lower layer, so as to ensure that the doped carriers are exhausted.

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 bilayer interface should be smaller than the total amount of negative polarized charges at the upper and lower interfaces to ensure that the 2DEG is depleted.

The invention further aims to provide a preparation method of the heterojunction photoelectric detector epitaxial structure, which comprises the following steps:

After the appointed epitaxial structure grows in the MOCVD cavity, closing the metal source, opening the Si source, and continuing to grow the SiN _x passivation layer on the original structure in situ, wherein the specific steps are as follows:

(1) Closing the metal source, setting NH ₃ flow (F ₁) and Si source flow (F ₂) to specified values, keeping the carrier gas atmosphere as hydrogen, setting the cavity temperature as T ₁, and keeping the flow and the temperature of the flowmeter stable;

(2) Introducing NH ₃ and Si sources into the MOCVD cavity to prepare an in-situ SiN _x passivation layer, wherein the growth time is t ₁, and the corresponding thickness is d ₁;

(3) After the growth is completed, the Si source is closed, the NH ₃ flow is kept unchanged, and the SiN _x passivation layer is annealed while the temperature is reduced.

Preferably, the NH ₃ flow rate for growing SiN _x is 0.04 mol/min < F ₁ <0.37 mol/min, the Si source for growing SiN _x is SiH ₄, the flow rate is 0.02 mu mol/min < F ₁ <0.36 mu mol/min, and the ratio of the corresponding group V source to the group IV source is changed within the range of 10 ⁵-10⁷.

Preferably, the growth time 455 s < t ₁ <7000 s corresponds to a thickness of 1 nm < d ₁ <6 nm.

Compared with the prior art, the invention has the beneficial effects that:

(1) An in-situ passivation method for significantly improving the PPC effect of a heterojunction photoelectric detector is provided. The thin SiN _x tunneling passivation layer prepared in situ by using MOCVD has the advantages of high film forming quality, no impurity atoms in the air environment and the like, and on the premise of not influencing the subsequent device process steps, the surface defects of the III-nitride photoelectric detector are reduced, the capture of the semiconductor surface defects to photo-generated carriers is further inhibited, the response of the device to light is accelerated, and meanwhile, the recombination of the photo-generated carriers after the light is removed is promoted, so that the PPC effect limiting the frequency characteristic and weak light response of the device is effectively relieved.

(2) The SiN _x in-situ passivation layer significantly improves the stability of the detector periodic photoresponse process. Due to the reduction of surface defects after passivation, the light and dark current of the device is always stable in the process of switching on/off the lamp for many times, and continuous rising of the light and dark current in the circulating process does not occur, so that the stability of the device in operation in a practical application scene is improved.

(3) The SiN _x in-situ passivation layer significantly improves the uniformity of dark current for the detector at different locations on the chip. Because the concentration of surface defects is different at different locations on the passivation front, the dark current values of the devices at the corresponding locations also differ significantly. And by preparing the SiN _x in-situ passivation layer, the surface defects of all positions on the chip are inhibited, and the dark current values of devices at different positions tend to be consistent, which is beneficial to improving the utilization rate of the devices on the chip.

(4) The in-situ preparation of the SiN _x passivation layer in the MOCVD chamber also has the advantage of simple process. The passivation layer may be prepared directly after the epitaxial structure has been grown without subsequent wet processing or in-situ passivation layer growth in a PECVE, LPCVD chamber. Meanwhile, the ohmic contact electrode can be directly prepared on the thin tunneling passivation layer, so that the process complexity is greatly reduced.

Drawings

Fig. 1 is a schematic diagram showing the epitaxial structure of the heterojunction photodetectors in embodiment 1 and embodiment 2 of the present invention.

Fig. 2 is a graph showing the decay of heterojunction photodetector current with time after light is removed in accordance with example 1 of the present invention.

FIG. 3 is a graph showing the periodic light response at different light intensities according to example 1 of the present invention.

Fig. 4 shows the standard deviation of dark current at different on-chip locations for example 1 of the present invention.

Fig. 5 is a schematic diagram of the epitaxial structure of the heterojunction photodetectors in examples 3 and 5 of the present invention.

Fig. 6 is a schematic diagram of the epitaxial structure of the heterojunction photodetector in embodiment 4 of the present invention.

Fig. 7 is a schematic diagram of the epitaxial structure of the heterojunction photodetector in embodiment 6 of the present invention.

Reference numerals are 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 are for illustrative purposes only and are not to be construed as limiting the invention. For better illustration of the following embodiments, some parts of the drawings may be omitted, enlarged or reduced, and not represent the actual product size, and it will be understood by those skilled in the art that some well-known structures in the drawings and their descriptions may be omitted.

In order to more clearly and easily illustrate the application of the inventive technique, embodiments are mainly given by taking AlGaN and InGaN base semiconductors as examples, which are not meant to exclude other group III nitride semiconductor materials.

Example 1

As shown in fig. 1, this embodiment discloses a uid-AlGaN-based double-layer interface upper layer heterojunction photodetector with a thin SiN _x in-situ passivation layer grown on the surface. The epitaxial structure of the device sequentially comprises a c-plane sapphire substrate layer 101, a uid-AlN buffer layer, a uid-AlGaN interface transition layer 103, a ui-Al _0.49Ga_0.51 N, a ui-Al _0.56Ga_0.44 N, a second interface upper layer 105, a barrier layer, a SiN _x in-situ passivation layer 106, a positive contact electrode 107 and a negative contact electrode 108, wherein the thickness of the interface lower layer 102 is 400 nm, the thickness of the ui-AlGaN interface transition layer 103 is 10 nm, the interface upper layer 200 comprises a first interface upper layer 104 and a second interface upper layer 105, the ui-Al _0.49Ga_0.51 N is used as the first interface upper layer 104, the first interface upper layer 104 is a channel layer, the thickness of the first interface upper layer 104 is 70 nm, the ui-Al _0.56Ga_0.44 N is used as the second interface upper layer 105, the second interface upper layer 105 is a barrier layer, the thickness of the SiN _x is 15 nm, the thickness of the in-situ passivation layer 106 is 1 nm, the thicknesses of the positive contact electrode 107 and the negative contact electrode 108 are Ti/Al/Ni/Au metal stacks, and the thicknesses of the layers are 15/80/20/60 nm respectively.

In the device structure disclosed in this embodiment, the value of x in the SiN _x in-situ passivation layer is 0.5-1.5, and the group III nitride epitaxial layers obtained by growth are all [0001] oriented, so that stronger polarization effects including spontaneous polarization and piezoelectric polarization exist in each nitride epitaxial layer. Since the thickness of the ui-AlN layer at the lower interface layer is 400 nm a, the stress of the sapphire substrate is relaxed, only spontaneous polarization exists, and the graded layer can keep the relaxation degree of the ui-Al _0.49Ga_0.51 N layer at the upper interface layer relatively low, so that more polarization negative charges are generated at the ui-Al _0.49Ga_0.51 N/ui-AlN interface. Similarly, the uid-Al _0.56Ga_0.44N/uid-Al_0.49Ga_0.51 N interface would generate a polarized positive charge, presumably to induce 2DEG. However, the polarized negative charge at the ui-Al _0.49Ga_0.51 N/ui-AlN interface and at the ui-Al _0.56Ga_0.44 N surface will raise the energy band of the heterojunction as a whole, thereby depleting the 2DEG, and keeping the ui-Al _0.49Ga_0.51 N channel high-resistance in the dark state, i.e., the device has a small dark current. Under illumination, photo-generated carriers generated by the upper layer of the double-layer interface can be separated to the surface and the interface under the action of a polarized electric field, so that the effect of negative charges on the surface and the interface is shielded, and the channel of the device is recovered to a low-resistance state, namely the device has higher photocurrent.

Because the active layer participating in absorption in the device of the embodiment is positioned on the surface, the photogenerated carriers are easily affected by the surface state in the transportation process, thereby affecting the performance of the device.

Therefore, on the basis of the working principle of the device, the thin SiN _x passivation layer is grown on the surface of the device in situ, and the thin SiN _x passivation layer can effectively reduce surface defects, so that the performance of the device is obviously improved. It is worth mentioning that the ohmic contact electrode Ti/Al/Ni/Au can be directly deposited on the passivation layer surface without pre-etching the SiN _x layer under the metal, thanks to the thickness of the SiN _x layer of only 1:1 nm.

In addition, the same structure device without growing SiN _x in-situ passivation layer is selected as a control, and related performance tests are carried out on the device without passivation (W/O) and the device with passivation (W).

FIG. 2 is a graph of current decay over time for unpassivated (W/O) and passivated (W) devices after light removal, where the light wavelengths and intensities are 260 nm, 700 μW/cm ², respectively. It can be seen that the unpassivated device exhibited a severe PPC effect with current decaying only 1 order of magnitude after 20 s a while the passivated device decayed more than 4 orders of magnitude, indicating that the SiN _x passivation layer effectively reduced surface defects, promoted recombination of photo-generated carriers after removal of the illumination, and thus significantly alleviated PPC.

Fig. 3 (a) and 3 (b) reflect the periodic response of unpassivated (W/O) and passivated (W) devices, respectively, at different light intensities, with an illumination on/off time of 20/20 s in a single period. The test results show that the photocurrent is continuously increased with the on time during each period. The continuous rise in photocurrent after the illumination is turned on results from the continuous trapping of holes by defects in weak light. Thus, a relatively small increase in photocurrent reflects a lower concentration of defects in the device after passivation. In addition, at each light intensity, the passivated device shows excellent photocurrent time dependent stability, and the current of the unpassivated device not only rises significantly in a periodic manner, but also fluctuates, which is related to the higher surface defect concentration of the unpassivated device.

Fig. 4 is the standard deviation of dark current for the unpassivated (W/O) and passivated (W) devices at different on-chip locations. The standard deviation of dark current of the device after passivation is much smaller than before passivation at each voltage, which indicates that passivation improves the uniformity of dark current at different positions on the chip. Because the concentration of surface defects is different at different locations on the passivation front, the dark current values of the devices at the corresponding locations also differ significantly. And by preparing the SiN _x in-situ passivation layer, the surface defects of all positions on the chip are inhibited, and the dark current values of devices at different positions tend to be consistent, which is beneficial to improving the utilization rate of the devices on the chip.

Example 2

As shown in fig. 1, this embodiment discloses a uid-InGaN-based double-layer interface upper layer heterojunction photodetector with a thin SiN _x in-situ passivation layer grown on the surface. The epitaxial structure of the device is a c-plane sapphire substrate layer 201, a uid-GaN buffer layer is simultaneously used as an interface lower layer 102, and the thickness of the device is 3 mu m from bottom to top; the thickness of the ui-InGaN interface transition layer 103 is 10nm, the thickness of the interface upper layer 200 is 10% from 0% to 20%, the interface upper layer 200 consists of a first interface upper layer 104 and a second interface upper layer 105, the ui-In _0.2Ga_0.8 N is used as the first interface upper layer 104, the first interface upper layer 104 is a channel layer, the thickness of the ui-InGaN is 80 nm, the ui-GaN is used as the second interface upper layer 105, the second interface upper layer 105 is a barrier layer, the thickness of the SiN _x In-situ passivation layer 206 is 15nm, the thickness of the SiN In-situ passivation layer is 1nm, the anode contact electrode 107 and the cathode contact electrode 108 are Ti/Al/Ni/Au metal stacks, and the metal thickness of each layer is 15/80/20/60 nm respectively.

In the device structure disclosed in this embodiment, the value of x in the SiN _x in-situ passivation layer is 0.5-1.5, and the group III nitride epitaxial layers obtained by growth are all [0001] oriented, so that stronger polarization effects including spontaneous polarization and piezoelectric polarization exist in each nitride epitaxial layer. Since the thickness of the ui-GaN layer at the lower layer of the interface is 3 mu m, the layer has relaxed the stress of the sapphire substrate, only spontaneous polarization exists, and the graded layer can keep the relaxation degree of the ui-In _0.2Ga_0.8 N at the upper layer of the interface relatively low, so that more polarization negative charges are generated at the ui-In _0.2Ga_0.8 N/ui-GaN interface. Similarly, a polarized positive charge is generated between the channel In the upper interface layer and the barrier layer (uid-GaN/uid-In _0.2Ga_0.8 N), which is supposed to induce the generation of 2DEG. However, the polarized negative charge at the ui-In _0.2Ga_0.8 N/ui-GaN interface and at the ui-GaN surface will raise the energy band of the heterojunction as a whole, and further deplete the 2DEG, so that the ui-In _0.2Ga_0.8 N channel keeps high resistance In the dark state, i.e. the device has a smaller dark current. Under illumination, photo-generated carriers generated by the upper layer of the double interfaces can be separated to the surfaces and the interfaces under the action of a polarized electric field, and the effect of negative charges on the surfaces and the interfaces is shielded, so that a channel of the device is recovered to a low-resistance state, namely the device has higher photocurrent.

Example 3

As shown in fig. 5, this embodiment discloses an n-AlGaN-based single layer interface upper layer heterojunction photodetector with a thin SiN _x in-situ passivation layer grown on the surface. The epitaxial structure of the device sequentially comprises a c-plane sapphire substrate layer 101, a uid-AlN buffer layer, an interface lower layer 102, an interface upper layer 200, an interface upper layer 80 and a doping concentration 1×10 ¹⁸cm^-3;SiN_x in-situ passivation layer 106, an interface upper layer 86, a positive contact electrode 107 and a negative contact electrode 108, wherein the c-plane sapphire substrate layer 101, the uid-AlN buffer layer and the interface lower layer 102 are sequentially arranged from bottom to top, the thickness is 400: 400 nm, si is adopted for N-type uniform doping, the Al _0.49Ga_0.51 N is adopted as the interface upper layer 200, the thickness is 80: 80 nm, the doping concentration is 1×10 ¹⁸cm^-3;SiN_x in-situ passivation layer 106, the thickness is 1: 1 nm, the positive contact electrode 107 and the negative contact electrode 108 are Ti/Al/Ni/Au metal stacks, and the metal thicknesses of the layers are 15/80/20/60 nm respectively.

In the device structure disclosed in this embodiment, the value of x in the SiN _x in-situ passivation layer is 0.5-1.5, and the group III nitride epitaxial layers obtained by growth are all [0001] oriented, so that stronger polarization effects including spontaneous polarization and piezoelectric polarization exist in each nitride epitaxial layer. Since the interface underlayer uid-AlN has a thickness of 400 nm, this layer has relaxed the stress of the sapphire substrate, and only spontaneous polarization exists. The thickness of the upper layer of the interface is 80 nm, the stress of AlN at the lower layer of the interface is larger, the relaxation degree is lower, and the AlN at the lower layer of the interface has spontaneous polarization and opposite piezoelectric polarization, so that polarized negative charges are generated at the interface of the upper layer and the lower layer of the interface. In the dark state, the polarized negative charge will raise the energy band of the heterojunction, thereby depleting the electrons in the upper layer of the interface. Under illumination, photo-generated electron-hole pairs are generated in the upper layer of the interface, the photo-generated electrons drift to the surface under the action of a polarized electric field to participate in conduction, and the photo-generated holes are transported to the interface to shield the action of polarized negative charges, so that the conductivity of the upper layer of the interface is further improved.

Example 4

As shown in fig. 6, this embodiment discloses a heterojunction photodetector with a thin SiN _x in-situ passivation layer n-AlGaN-based double-layer interface upper layer grown on the surface. The epitaxial structure of the device sequentially comprises a c-plane sapphire substrate layer 101, a uid-AlN buffer layer, an interface lower layer 102, a thickness of 400 nm, an interface upper layer 200, a positive contact electrode 107 and a negative contact electrode 108, wherein the interface lower layer 102 is sequentially arranged from bottom to top, the interface upper layer 200 consists of a first interface upper layer 104 and a second interface upper layer 105, the uid-AlGaN with 49% of Al components is the first interface upper layer 104, the epitaxial layer with the same components and adopting Si to carry out n-type uniform doping is the second interface upper layer 105, the thicknesses are respectively 10 nm and 80 nm, the n-type doping concentration is 1×10 ¹⁸cm^-3;SiN_x, the thickness is 1 nm, the positive contact electrode 107 and the negative contact electrode 108 are both Ti/Al/Ni/Au metal stacks, and the metal thicknesses of the layers are 15/80/20/60 nm respectively.

In the device structure disclosed in this embodiment, the value of x in the SiN _x in-situ passivation layer is 0.5-1.5, and the group iii nitride epitaxial layers are all grown in the [0001] orientation, so that stronger polarization effects (including spontaneous polarization and piezoelectric polarization) exist in each nitride epitaxial layer. Since the interface underlayer uid-AlN has a thickness of 400 nm, this layer has relaxed the stress of the sapphire substrate, and only spontaneous polarization exists. The total thickness of the upper layer of the interface with the same components is 90 nm, the upper layer of the interface is stressed by the compression stress of AlN at the lower layer of the interface, the relaxation degree is low, and the upper layer of the interface has spontaneous polarization and opposite piezoelectric polarization, so that the interface of the upper layer and the lower layer of the interface can generate polarized negative charges. In the dark state, the polarized negative charge will raise the energy band of the heterojunction, thereby depleting the electrons in the upper layer of the interface. Under illumination, photo-generated electron-hole pairs are generated in the upper layer of the interface, the photo-generated electrons drift to the surface under the action of a polarized electric field to participate in conduction, and the photo-generated holes are transported to the interface to shield the action of polarized negative charges, so that the conductivity of the upper layer of the interface is further improved. It should be noted that the interfacial upper layer of this embodiment further includes an unintentionally doped layer of the same composition as the n-type layer, which is mainly used to reduce recombination of photo-generated holes by the interfacial defect, thereby further promoting recovery of conductivity of the interfacial upper layer under illumination.

Example 5

As shown in fig. 5, this embodiment discloses a uid-InGaN-based single-layer interface upper layer heterojunction photodetector with a thin SiN _x in-situ passivation layer grown on the surface. The epitaxial structure of the device sequentially comprises a c-plane sapphire substrate layer 101, a uid-GaN buffer layer, an interface lower layer 102, a uid-In _0.2Ga_0.8 N, an SiN _x In-situ passivation layer 106, a positive contact electrode 107 and a negative contact electrode 108, wherein the thickness of the sapphire substrate layer 101 is 3 mu m, the thickness of the uid-In _0.2Ga_0.8 N is 120 nm, the thickness of the SiN _x In-situ passivation layer 106 is 1 nm, the thicknesses of the positive contact electrode 107 and the negative contact electrode 108 are Ti/Al/Ni/Au metal stacks, and the thicknesses of the metals of the layers are 15/80/20/60 nm respectively.

In the device structure disclosed in this embodiment, the value of x in the SiN _x in-situ passivation layer is 0.5-1.5, and the group iii nitride epitaxial layers are all grown in the [0001] orientation, so that stronger polarization effects including spontaneous polarization and piezoelectric polarization exist in each nitride epitaxial layer. Since the interface underlayer uid-GaN thickness is 3 μm, this layer has relaxed the stress of the sapphire substrate, and only spontaneous polarization exists. The thickness of the upper layer of the interface is 120 nm, the GaN layer is stressed by the GaN layer under the interface, the relaxation degree is low, and the GaN layer has spontaneous polarization and opposite piezoelectric polarization, so that the interface between the upper layer and the lower layer of the interface generates polarized negative charges. In the dark state, the polarized negative charge will raise the energy band of the heterojunction, thereby depleting the electrons in the upper layer of the interface. Under illumination, photo-generated electron-hole pairs are generated in the upper layer of the interface, the photo-generated electrons drift to the surface under the action of a polarized electric field to participate in conduction, and the photo-generated holes are transported to the interface to shield the action of polarized negative charges, so that the conductivity of the upper layer of the interface is further improved.

Example 6

As shown in fig. 7, this embodiment discloses a heterojunction photodetector with a thin SiN _x in-situ passivation layer uid-InGaN-based single-layer interface upper layer grown on the surface. The epitaxial structure of the device sequentially comprises a c-plane sapphire substrate layer 101, a uid-GaN buffer layer, a uid-InGaN interface transition layer 103, a uid-InGaN interface transition layer 106, a SiN _x In-situ passivation layer 106, a positive contact electrode 107 and a negative contact electrode 108, wherein the c-plane sapphire substrate layer 101, the uid-GaN buffer layer simultaneously serves as an interface lower layer 102, the thickness is 3 mu m, in is increased from 0% to 20%, the thickness is 30 nm, the uid-In _0.2Ga_0.8 N serves as an interface upper layer 200, the thickness is 120 nm, the SiN _x In-situ passivation layer 106 is 1 nm, the positive contact electrode 107 and the negative contact electrode 108 are Ti/Al/Ni/Au metal stacks, and the metal thickness of each layer is 15/80/20/60 nm.

In the device structure disclosed in this embodiment, the value of x in the SiN _x in-situ passivation layer is 0.5-1.5, and the group iii nitride epitaxial layers are all grown in the [0001] orientation, so that stronger polarization effects including spontaneous polarization and piezoelectric polarization exist in each nitride epitaxial layer. Since the interface underlayer uid-GaN thickness is 3 μm, this layer has relaxed the stress of the sapphire substrate, and only spontaneous polarization exists. The graded layer can keep the relaxation degree of the ui-In _0.2Ga_0.8 N on the upper layer of the interface relatively low, and the graded layer is subjected to larger compressive stress, so that more polarized negative charges are generated at the ui-In _0.2Ga_0.8 N/ui-GaN interface. In the dark state, the polarized negative charge will raise the energy band of the heterojunction, thereby depleting the electrons in the upper layer of the interface. Under illumination, photo-generated electron-hole pairs are generated in the upper layer of the interface, the photo-generated electrons drift to the surface under the action of a polarized electric field to participate in conduction, and the photo-generated holes are transported to the interface to shield the action of polarized negative charges, so that the conductivity of the upper layer of the interface is further improved.

Example 7

The embodiment provides a preparation method of an epitaxial structure of a heterojunction photoelectric detector, which is characterized by comprising the following steps:

s1, growing an interface lower layer, an interface transition layer and an interface upper layer on a substrate through metal organic chemical vapor deposition;

S2, closing a metal source, setting NH ₃ flow F ₁ and Si source flow F ₂ to specified values, keeping the carrier gas atmosphere as hydrogen, setting the cavity temperature as T ₁, and keeping the flow and the temperature of the flowmeter stable;

S3, introducing NH ₃ and Si sources into the epitaxial cavity to prepare an in-situ SiN _x passivation layer, wherein the growth time is t ₁, and the corresponding thickness is d ₁;

And S4, after the growth is completed, closing the Si source, keeping the NH ₃ flow unchanged, and annealing the SiNx passivation layer while cooling.

Further, the NH ₃ flow F ₁ satisfies 0.04 mol/min < F ₁ <0.37 mol/min;

The Si source is SiH ₄, the Si source flow F ₂ is 0.02 mu mol/min < F ₂ <0.36 mu mol/min, and the corresponding ratio of the group V source to the group IV source flow is changed within the range of 10 ⁵-10⁷.

Further, the growth time t ₁ satisfies 455 s < t ₁ <7000 s, and the corresponding thickness d ₁ satisfies 1 nm < d ₁ <6 nm.

Claims

1. A method for preparing a heterojunction photodetector epitaxial structure, comprising the following steps:

S1. growing an interface lower layer, an interface transition layer, and an interface upper layer on a substrate by metal organic chemical vapor deposition;

S2. Turn off the metal source, set the NH ₃ flow rate F ₁ and the Si source flow rate F ₂ to the specified values, keep the carrier gas atmosphere at hydrogen, set the chamber temperature to T ₁ , and wait until the flow meter flow and temperature remain stable;

S3, introducing NH ₃ and Si source into the epitaxial cavity to prepare an in-situ SiN _x passivation layer, with a growth time of t ₁ and a corresponding thickness of d ₁ ;

S4. After the growth is completed, the Si source is turned off while keeping the NH ₃ flow rate unchanged, and the SiN _x passivation layer is annealed while the temperature is lowered;

The NH ₃ flow rate F ₁ satisfies: 0.04 mol/min<F ₁ <0.37 mol/min;

The Si source is SiH ₄ , and the Si source flow rate F ₂ satisfies: 0.02 μmol/min<F ₂ <0.36 μmol/min, and the flow rate ratio of the corresponding Group V source to the Group IV source varies in the range of 10 ⁵ -10 ⁷ ;

The value of x in the SiN _x in-situ passivation layer is 0.5-1.5.

2 . The method for preparing a heterojunction photodetector epitaxial structure according to claim 1 , wherein the growth time t ₁ satisfies: 455 s< t ₁ <7000 s, and the corresponding thickness d ₁ satisfies: 1 nm< d ₁ <6 nm.

3. A heterojunction photodetector epitaxial structure prepared by the preparation method of claim 1, characterized in that it comprises, from bottom to top, 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;

The anode and cathode of the ohmic contact electrode are deposited on the surface of the _SiNx in-situ passivation layer.

Alternatively, the anode and cathode of the ohmic contact electrode are deposited on the upper surface of the interface where the SiN _x in-situ passivation layer is etched away in advance.

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

5. The heterojunction photodetector epitaxial structure according to claim 3 is characterized in that the interface transition layer is a Group III nitride layer whose band gap width gradually changes from the lower interface layer to the upper interface layer through composition adjustment, 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.

6 . The heterojunction photodetector epitaxial structure according to claim 3 , wherein the interface upper layer is a single-layer interface upper layer, and the interface upper layer is an n-type doped layer.

7. The heterojunction photodetector epitaxial structure according to claim 3, characterized in that the interface upper layer is a double-layer interface upper layer, and the interface upper layer is composed of a non-doped wide bandgap barrier layer and a narrow bandgap channel layer.

8. The heterojunction photodetector epitaxial structure according to claim 6, wherein the doping methods of the n-type doping layer include uniform doping, alternating doping, and linear gradient doping, and the equivalent electron concentration in the n-type doping layer ranges from 3×10 ¹⁷ cm ^-3 to 8×10 ¹⁸ cm ^-3 .