Photoelectric detector based on gradient oxygen vacancy Ga2O3 double heterojunction and preparation method

Abstract

The application discloses a kind of gradient oxygen vacancy Ga2O3 double heterojunction-based photoelectric detector and preparation method thereof, mainly solve the problem that the current β-Ga2O3 base solar blind ultraviolet photoelectric detector responsivity, light dark current ratio and response speed are difficult to consider simultaneously.The β-Ga2O3 layer, oxygen vacancy-rich β-Ga2O3 layer, step-shaped MoS2 layer and WSe2 layer are sequentially arranged on the substrate to form β-Ga2O3 / MoS2 heterojunction and MoS2 / WSe2 two-dimensional heterojunction, constitute double heterojunction, and electrodes are arranged on MoS2 layer and WSe2 layer respectively.The application combines gradient oxygen vacancy regulation, double heterojunction structure and layered electrode structure to improve device light gain, carrier separation and transport efficiency and electrode collection efficiency, thereby achieving high responsivity and fast response of the device, and is suitable for solar blind ultraviolet photoelectric detection field.

Description

Technical Field

[0001] This invention belongs to the field of electronic technology, and more specifically relates to a photodetector based on a gradient oxygen vacancy Ga2O3 double heterojunction and its fabrication method within the field of semiconductor electronic device technology. This invention can be used for solar-blind ultraviolet photodetection, achieving detection characteristics of low dark current, high responsivity, and fast response.

[0002] Background Technology: With the development of photoelectric detection technology, applications such as ultraviolet communication, flame early warning, space exploration, environmental monitoring, and high-voltage discharge detection place higher demands on the sensitivity, response speed, and anti-interference capabilities of detectors. To effectively identify weak deep ultraviolet signals against a solar background, photodetectors operating in the solar-blind ultraviolet band are typically employed. Currently, β-Ga2O3 is widely used in solar-blind ultraviolet photodetectors due to its ultra-wide bandgap, strong solar-blind ultraviolet absorption, and good chemical and thermal stability. However, existing β-Ga2O3-based photodetectors still face the challenge of simultaneously improving responsivity, response speed, and photocurrent-to-dark-current ratio. Ordinary heterojunction or double heterojunction structures mainly rely on the band difference between the two two-dimensional materials to separate photogenerated carriers and improve response speed, but lack targeted control over the carrier transfer process at the interface between β-Ga2O3 and the two-dimensional material, and have limited optical gain methods, resulting in low responsivity. However, simply adjusting the oxygen vacancy concentration in β-Ga2O3 can easily cause a contradiction between photoconductive gain, dark current, and sustained photoconductive effect, resulting in improved responsivity but high dark current and long response time, which further limits the improvement of the overall performance of the device.

[0003] In their paper "Ultra-Fast Gallium Oxide Solar-Blind Photodetector with Novel Thermal Pulse Treatment" (Advanced Materials, 2025, 37), Lili Luo et al. proposed a gallium oxide solar-blind ultraviolet photodetector employing thermal pulse treatment. This device utilizes thermal pulse treatment to form a vertically layered crystal structure and oxygen vacancy distribution in a Ga2O3 thin film, resulting in a high oxygen vacancy concentration on the surface and a relatively low oxygen vacancy concentration in the internal region. This structure leverages the trapping and release of photogenerated electrons by surface-side oxygen vacancy-related defect states under illumination, improving photocurrent and responsivity. Simultaneously, the relatively low oxygen vacancy region within the film mitigates the persistent photoconductivity caused by the overall high defect concentration, thus alleviating the challenge of simultaneously achieving high responsivity and response speed in gallium oxide solar-blind ultraviolet photodetectors. However, the device in this paper still has some shortcomings. It mainly focuses on the longitudinal distribution control of oxygen vacancies in a single Ga2O3 thin-film photodetector, which cannot achieve spatial separation of photogenerated electrons and holes. This easily leads to recombination of photogenerated carriers. In addition, it adopts a conventional metal-semiconductor-metal structure, which has a high dark current level and the rise and fall times are still on the order of milliseconds. The limitation that it is difficult to balance oxygen vacancy gain and continuous photoconductivity still has room for optimization, which limits the further improvement of the device's high responsivity and fast response capability.

[0004] Xi'an University of Electronic Science and Technology proposed a photodetector based on a double heterojunction, namely "Photodetector based on double heterojunction and its fabrication method" (application number CN202210816620.7, application date 2022.07.12, publication number CN115148844A, publication date 2022.10.04; authorization announcement number CN115148844B, authorization announcement date 2024.02.06). This device has a MoS2 layer on a β-Ga2O3 layer and a WSe2 layer on top of the MoS2 layer, forming a heterojunction between the β-Ga2O3 and MoS2 layers, and a two-dimensional heterojunction between the MoS2 and WSe2 layers. This achieves separation of photogenerated carriers, reduces dark current, and improves the device's response speed. However, the shortcomings of this patented technology are as follows: the device mainly relies on the band difference between the β-Ga2O3 / MoS2 heterojunction and the MoS2 / WSe2 two-dimensional heterojunction for carrier separation. The anode and cathode of the device are located at both ends of the WSe2 layer and the MoS2 layer, mainly to draw out the overall photocurrent, which leads to current recombination. Therefore, there is still room for further optimization in terms of carrier stratification and collection. The insufficient optical gain means also limit the simultaneous improvement of device responsivity and photocurrent-to-dark ratio. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a photodetector based on a gradient oxygen vacancy Ga2O3 double heterojunction and its fabrication method. This invention aims to solve the problems in existing β-Ga2O3-based solar-blind ultraviolet photodetectors, such as the difficulty in simultaneously achieving oxygen vacancy gain and sustained photoconductivity, insufficient separation and collection of photogenerated electrons and holes, and the difficulty in simultaneously improving responsivity, photocurrent ratio, and response speed.

[0006] The idea behind this invention is to sequentially deposit a β-Ga₂O₃ layer, an oxygen-vacancy-rich β-Ga₂O₃ layer, a MoS₂ layer, and a WSe₂ layer on a substrate, and to deposit a first electrode and a second electrode on the exposed area of ​​the MoS₂ layer and the WSe₂ layer, respectively. The β-Ga₂O₃ layer serves as a solar-blind ultraviolet light absorption layer, used to absorb solar-blind ultraviolet light and generate photogenerated carriers. The oxygen-vacancy-rich β-Ga₂O₃ layer is located on the side of the β-Ga₂O₃ layer closest to the MoS₂ layer, forming an oxygen vacancy-rich region on the β-Ga₂O₃ surface after treatment, with the oxygen vacancy concentration gradually decreasing away from the MoS₂ layer. The oxygen-vacancy-rich β-Ga2O3 layer is located near the β-Ga2O3 / MoS2 contact interface. Its oxygen vacancy-related defect states can capture and release photogenerated electrons under illumination, enhancing the photoconductivity gain and effective electron concentration on the β-Ga2O3 surface side. This allows for the provision of more photogenerated carriers for transport near the β-Ga2O3 / MoS2 interface. At the same time, since the oxygen vacancies are mainly confined to the side of the β-Ga2O3 layer near the MoS2 layer, rather than being uniformly distributed throughout the entire β-Ga2O3 layer, the increase in dark current and the persistent photoconductivity effect caused by the high defect concentration in the main region can be reduced. This solves the problem of the difficulty in balancing oxygen vacancy gain and response speed. Based on the aforementioned interface-side carrier supply enhancement, this invention involves a MoS2 layer disposed on an oxygen-rich vacancy β-Ga2O3 layer, forming a β-Ga2O3 / MoS2 heterojunction. This allows photogenerated carriers generated in the β-Ga2O3 absorption layer to enter the MoS2 two-dimensional transport layer and participate in lateral transport. A WSe2 layer is disposed on the MoS2 layer and covers a portion of the MoS2 layer, forming a MoS2 / WSe2 two-dimensional heterojunction. The band difference between the two two-dimensional materials promotes the spatial separation of photogenerated electrons and holes, thereby reducing the recombination probability of electrons and holes. A first electrode is electrically connected to the MoS2 layer, and a second electrode is electrically connected to the WSe2 layer, allowing the separated carriers to be transported along the MoS2 and WSe2 layers respectively and collected by the corresponding electrodes, thereby reducing carrier recombination and loss during transport and collection. This invention combines gradient oxygen vacancy surface gain, β-Ga2O3 / MoS2 interface carrier supply, MoS2 / WSe2 two-dimensional heterojunction carrier separation, and layered electrode collection to enable the device to improve the efficiency of photogenerated carrier generation, transport, and collection while suppressing the adverse effects of overall high oxygen vacancy concentration. This improves the problem that existing β-Ga2O3-based solar-blind ultraviolet photodetectors are difficult to improve simultaneously in terms of responsivity, photocurrent ratio, and response speed.

[0007] The solar-blind ultraviolet photodetector of the present invention includes a substrate, a β-Ga₂O₃ layer, an oxygen-vacancy-rich β-Ga₂O₃ layer, a MoS₂ layer, a WSe₂ layer, a first electrode, and a second electrode. The β-Ga₂O₃ layer is disposed on the substrate as a solar-blind ultraviolet light absorption layer. The oxygen-vacancy-rich β-Ga₂O₃ layer is disposed on the side of the β-Ga₂O₃ layer near the MoS₂ layer, serving to form an oxygen vacancy gradient modulation region on the surface of the β-Ga₂O₃ layer, thereby enhancing photoconductivity gain and interface carrier supply. The MoS₂ layer is disposed on the oxygen-vacancy-rich β-Ga₂O₃ layer, and the WSe₂ layer... A layer is disposed on the MoS2 layer and covers only one side of the MoS2 layer. The β-Ga2O3 layer and the MoS2 layer form a β-Ga2O3 / MoS2 heterojunction, and the MoS2 layer and the WSe2 layer form a MoS2 / WSe2 two-dimensional heterojunction. This dual heterojunction is used for interfacial carrier transport and spatial distribution control of photogenerated carriers. The first electrode is disposed on the side of the MoS2 layer not covered by the WSe2 layer and is electrically connected to the MoS2 layer. The second electrode is disposed on the WSe2 layer and is electrically connected to the WSe2 layer, and is used to collect photogenerated carriers from the MoS2 layer and the WSe2 layer, respectively.

[0008] Furthermore, the substrate is any one of a sapphire substrate, a SiO2 / Si substrate, a quartz substrate, or an insulating silicon substrate.

[0009] Furthermore, the thickness of the β-Ga2O3 layer is 30nm to 300nm, the thickness of the MoS2 layer is 0.7nm to 10nm, and the thickness of the WSe2 layer is 1nm to 50nm.

[0010] Furthermore, the oxygen vacancy-related defect state density in the oxygen-rich vacancy β-Ga2O3 layer is 1×10⁻⁶. 20 cm -3 ~1×10 21 cm -3 The oxygen vacancy-related defect state density in the main region of the β-Ga2O3 layer is 1×10⁻⁶. 18 cm -3 ~5×10 20 cm -3 .

[0011] Furthermore, the thickness of the oxygen-vacancy-rich β-Ga2O3 layer is 3 nm to 30 nm.

[0012] Furthermore, the MoS2 layer and the WSe2 layer form a MoS2 / WSe2 two-dimensional heterojunction, with the MoS2 layer serving as a photogenerated electron transport channel and the WSe2 layer serving as a photogenerated hole transport channel; the first electrode is electrically connected to the MoS2 layer and the second electrode is electrically connected to the WSe2 layer, for collecting photogenerated carriers separated by the MoS2 / WSe2 two-dimensional heterojunction under an applied bias voltage.

[0013] The first electrode and the second electrode are made of the same metal material or the same metal stack structure. The metal material is one of Au, Ti, Ni, Pt, Cr, and Al, and the metal stack structure is a stack structure formed by two or more metals selected from Au, Ti, Ni, Pt, Cr, and Al.

[0014] The method for fabricating the photodetector of the present invention includes the following steps:

[0015] S1, the substrate is cleaned and dried;

[0016] S2, a β-Ga2O3 thin film is grown on the substrate to form a β-Ga2O3 layer with a thickness of 30nm to 300nm;

[0017] S3, perform thermal pulse treatment on the side of the β-Ga2O3 layer away from the substrate to form an oxygen-vacancy-rich β-Ga2O3 layer in the surface region of the β-Ga2O3 layer that is intended to contact the MoS2 layer; the thickness of the oxygen-vacancy-rich β-Ga2O3 layer is 3nm to 30nm, so that the oxygen vacancies are mainly distributed in the surface region extending from the surface of the β-Ga2O3 layer into the interior of the β-Ga2O3 layer.

[0018] S4, a MoS2 layer with a thickness of 0.7 nm to 10 nm is transferred onto an oxygen-vacancy-rich β-Ga2O3 layer;

[0019] S5, a WSe2 layer with a thickness of 1nm to 50nm is transferred onto the MoS2 layer, so that the WSe2 layer only covers one side of the MoS2 layer, and the other side of the MoS2 layer is not covered by the WSe2 layer.

[0020] S6, a first electrode is fabricated on the side of the MoS2 layer not covered by the WSe2 layer, and the first electrode is electrically connected to the MoS2 layer; a second electrode is fabricated on the WSe2 layer, and the second electrode is electrically connected to the WSe2 layer; the first electrode and the second electrode are made of the same metal material or the same metal stack structure, and are located on the lateral sides of the device respectively.

[0021] Further, the thermal pulse treatment in step S3 includes introducing a hydrogen-oxygen mixed gas into the surface side of the β-Ga2O3 layer and generating a short-duration thermal pulse by ignition, thereby forming an oxygen vacancy enrichment region on the surface side of the β-Ga2O3 layer; wherein, the volume ratio of hydrogen to oxygen in the hydrogen-oxygen mixed gas is 1.5:1 to 3:1, preferably 2:1; the number of short-duration thermal pulses is 1 to 30, preferably 3 to 18; the duration of a single thermal pulse is 0.01s to 5s; and the interval between two adjacent thermal pulses is 0.1s to 60s.

[0022] Furthermore, the β-Ga2O3 layer is prepared by magnetron sputtering, the MoS2 layer and WSe2 layer are formed by PDMS-assisted dry transfer, and the first electrode and the second electrode are formed by thermal evaporation, electron beam evaporation or magnetron sputtering.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] First, because this invention sets an oxygen-rich vacancy β-Ga2O3 layer on the side of the β-Ga2O3 layer close to the MoS2 layer, oxygen vacancies are mainly enriched near the β-Ga2O3 / MoS2 contact interface. This overcomes the increased dark current and persistent photoconductivity effect caused by the overall high defect concentration in the main body region in the prior art. As a result, the solar-blind ultraviolet photodetector of this invention has high optical gain while reducing dark current and weakening the photoconductivity effect. This is beneficial for balancing high responsivity and fast response speed.

[0025] Secondly, because this invention employs a double heterojunction structure composed of a β-Ga2O3 / MoS2 heterojunction and a MoS2 / WSe2 two-dimensional heterojunction, and further utilizes layered electrodes to collect different types of charge carriers separated by the MoS2 / WSe2 two-dimensional heterojunction in a layered manner, it overcomes the shortcomings of high carrier recombination probability and low photocurrent output efficiency in existing technologies. This allows the solar-blind ultraviolet photodetector of this invention to reduce carrier recombination and loss during transmission and collection, and to collect charge carriers more efficiently, setting multiple potential barriers and depletion regions for charge carriers in the dark state. This is beneficial for further improving the device's response speed and reducing dark current.

[0026] Third, the solar-blind ultraviolet photodetector of the present invention combines a double heterojunction structure, layered electrode arrangement and oxygen vacancy control, overcoming the shortcomings of existing photodetectors such as high dark current, insufficient photogenerated carrier separation efficiency and difficulty in simultaneously improving responsivity, response speed and detectivity. This enables the solar-blind ultraviolet photodetector of the present invention to enhance carrier separation and collection capabilities under illumination conditions while suppressing dark-state carrier transport, and has the characteristics of low dark current, high responsivity and fast response. This is beneficial for the application of this device in the field of high-sensitivity and low-noise ultraviolet photodetection.

[0027] Fourth, in the simulation experiments of this invention, the responsivity of the solar-blind ultraviolet photodetector under the simulated condition of a first electrode voltage of +5 V is 268.04 A / W, and the external quantum efficiency is 1.31 × 10⁻⁶. 5 %, with a specific detectivity of 5.54 × 10⁻⁶. 13 Jones, with a light-to-dark current ratio of 7.33 × 10⁻⁶. 4 The above results are used to illustrate that the structure of the present invention has high photoresponse capability, low dark-state leakage current, and superior overall detection performance under the simulation conditions, and are not intended to limit the performance of actual fabricated devices. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the solar-blind ultraviolet photodetector of the present invention;

[0029] Figure 2 This is a schematic diagram of the fabrication process of the solar-blind ultraviolet photodetector of the present invention;

[0030] Figure 3 This is a comparison diagram of simulated dark current of the device in the embodiment of the present invention;

[0031] Figure 4 This is a simulation response time test diagram of the solar-blind ultraviolet photodetector of the present invention. Detailed Implementation

[0032] To more accurately describe the implementation of the present invention, the present invention will be fully described and explained below in conjunction with the accompanying drawings and embodiments.

[0033] Reference Figure 1 The present invention provides a further description of a photodetector structure based on a gradient oxygen vacancy Ga2O3 double heterojunction.

[0034] Figure 1 The device of the present invention comprises, from bottom to top, a substrate 1, a β-Ga2O3 layer 2, an oxygen-vacancy-rich β-Ga2O3 layer 3, a MoS2 layer 4, and a WSe2 layer 5. The β-Ga2O3 layer 2 is deposited or grown on top of the substrate 1. The oxygen-vacancy-rich β-Ga2O3 layer 3 is formed on the surface region of the β-Ga2O3 layer 2 away from the substrate 1. The MoS2 layer 4 is transferred over the oxygen-vacancy-rich β-Ga2O3 layer 3. The WSe2 layer 5 is transferred over the MoS2 layer 4 and only covers a portion of the MoS2 layer 4, leaving an exposed area of ​​the MoS2 layer 4 not covered by the WSe2 layer 5. A first electrode 6 is disposed on the exposed area of ​​the MoS2 layer 4 and electrically connected to the MoS2 layer 4; a second electrode 7 is disposed on the WSe2 layer 5 and electrically connected to the WSe2 layer 5.

[0035] A β-Ga2O3 / MoS2 heterojunction structure with an interface-side gradient oxygen vacancy distribution is formed by a β-Ga2O3 layer 2, an oxygen-rich β-Ga2O3 layer 3, and a MoS2 layer 4. In this structure, the oxygen-rich β-Ga2O3 layer 3 is not a separate material layer independent of the β-Ga2O3 layer 2, but rather a modified region on the surface side of the β-Ga2O3 layer 2. Its oxygen vacancy concentration is higher than that of the main region of the β-Ga2O3 layer 2, and gradually decreases away from the MoS2 layer 4. A MoS2 / WSe2 two-dimensional heterojunction structure is formed by the MoS2 layer 4 and the WSe2 layer 5 to promote the spatial separation of photogenerated electrons and holes. The first electrode 6 and the second electrode 7 are connected to the MoS2 layer 4 and the WSe2 layer 5, respectively, for the stratified collection of the separated charge carriers.

[0036] The substrate 1 is any one of sapphire substrate, SiO2 / Si substrate, quartz substrate, or insulating silicon substrate. The thickness of the β-Ga2O3 layer 2 is 30–300 nm. The thickness of the oxygen-vacancy-rich β-Ga2O3 layer 3 is 3–30 nm, preferably 5–20 nm, more preferably 8–12 nm. The thickness of the MoS2 layer 4 is 0.7–10 nm. The thickness of the WSe2 layer 5 is 1–50 nm. The first electrode 6 and the second electrode 7 adopt a stacked structure of one or more metals selected from Au, Ti, Ni, Pt, Cr, and Al.

[0037] In the device structure of Embodiment 1 of the present invention, the substrate 1 is a sapphire substrate, the thickness of the β-Ga2O3 layer 2 is 100nm, the thickness of the oxygen-vacancy-rich β-Ga2O3 layer 3 is 10nm, the thickness of the MoS2 layer 4 is 2nm, the thickness of the WSe2 layer 5 is 10nm, and the first electrode 6 and the second electrode 7 are both made of Ti / Au multilayer metal, wherein the thickness of the Ti layer is 5nm and the thickness of the Au layer is 50nm.

[0038] Reference Figure 2 The preparation processes of the three embodiments of the present invention are further described below:

[0039] Example 1: The substrate is a sapphire substrate, the thickness of the β-Ga2O3 layer is 100nm, the thickness of the oxygen-rich vacancy β-Ga2O3 layer is 10nm, the thickness of the MoS2 layer is 2nm, the thickness of the WSe2 layer is 10nm, and the first electrode and the second electrode are both gallium oxide-based double heterojunction solar-blind ultraviolet photodetectors made of Ti / Au stacked metals.

[0040] Step 1: Select a substrate and perform pretreatment.

[0041] A sapphire substrate was selected as substrate 1 and was sequentially immersed in deionized water, acetone and ethanol for ultrasonic cleaning, each cleaning lasting 10-15 minutes. After cleaning, it was dried with a nitrogen gun for later use.

[0042] Step 2: Prepare a β-Ga2O3 layer on the substrate.

[0043] The pretreated sapphire substrate was placed in the vacuum chamber of a magnetron sputtering apparatus, and a β-Ga2O3 layer was grown on the sapphire substrate using magnetron sputtering. The magnetron sputtering process conditions were as follows: sputtering power of 120W, sputtering temperature of 550℃, Ga2O3 ceramic target, working pressure of 3Pa, argon flow rate of 20sccm, oxygen flow rate of 2sccm, sputtering time of 30min, and chamber vacuum of 5×10⁻⁶. -4 Pa. After deposition, a β-Ga2O3 layer with a thickness of approximately 100 nm is formed.

[0044] Step 3: Form an oxygen-rich vacancy β-Ga2O3 layer 3 on the surface side of β-Ga2O3 layer 2.

[0045] A substrate 1 with a β-Ga2O3 layer 2 is placed on the support stage of a thermal pulse processing device, with the side of the β-Ga2O3 layer 2 away from the substrate 1 facing the thermal pulse application area. A hydrogen-oxygen mixture gas, in which the volume ratio of hydrogen to oxygen is 2:1, is introduced into the thermal pulse application area. A short-duration thermal pulse is generated by arc ignition, so that the thermal pulse mainly acts on the surface side of the β-Ga2O3 layer 2. The process conditions for the thermal pulse processing are: 9 short-duration thermal pulses, a single thermal pulse duration of 0.1 s, and an interval of 5 s between two adjacent thermal pulses. After processing, an oxygen-rich vacancy β-Ga2O3 layer 3 with a thickness of approximately 10 nm is formed on the surface side of the β-Ga2O3 layer 2.

[0046] Step 4: Transfer MoS2 layer 4 onto oxygen-rich vacancy β-Ga2O3 layer 3.

[0047] Bulk MoS2 material was adhered to with adhesive tape and repeatedly torn to obtain MoS2 sheets with a thickness of approximately 2 nm. The exfoliated MoS2 sheets were then attached to a PDMS support to form a PDMS / MoS2 composite material. The PDMS / MoS2 composite material was fixed on a microscopic transfer platform, and the sample with an oxygen-vacancy-rich β-Ga2O3 layer 3 was fixed on the sample stage. The position of the transfer platform was observed and adjusted using a microscopic system to align the MoS2 sheets with the target area of ​​the oxygen-vacancy-rich β-Ga2O3 layer 3. Subsequently, the MoS2 sheets were brought into contact with and adhered to the oxygen-vacancy-rich β-Ga2O3 layer 3, and the PDMS support was slowly separated, leaving the MoS2 layer 4 on top of the oxygen-vacancy-rich β-Ga2O3 layer 3.

[0048] Step 5: Transfer WSe2 layer 5 onto MoS2 layer 4.

[0049] The bulk WSe2 material was adhered to with adhesive tape and repeatedly torn to obtain WSe2 sheets with a thickness of approximately 10 nm. The exfoliated WSe2 sheets were then attached to a PDMS carrier to form a PDMS / WSe2 composite material. The WSe2 layer 5 was transferred onto the MoS2 layer 4 using a micro-transfer platform, so that the WSe2 layer 5 covered a portion of the MoS2 layer 4, while leaving exposed areas of the MoS2 layer 4 not covered by the WSe2 layer 5.

[0050] Step six: Prepare the first electrode 6 and the second electrode 7.

[0051] Electrode masks were applied over the exposed area of ​​MoS2 layer 4 and over WSe2 layer 5 to define the positions of the first electrode 6 and the second electrode 7, respectively. The sample was placed in the vacuum chamber of an electron beam evaporation apparatus, with the deposition current set to 100 A, the deposition rate to 0.7 nm / s, and the chamber vacuum level to 6 × 10⁻⁶. -4 Pa, tray rotation speed 12 r / min. Ti / Au multilayer metal was deposited using electron beam evaporation. The Ti layer thickness was 5 nm, and the Au layer thickness was 50 nm. After deposition, the mask was removed, allowing the first electrode 6 to be formed on the exposed area of ​​the MoS2 layer 4 and electrically connected to it. The second electrode 7 was formed on top of the WSe2 layer 5 and electrically connected to it. Device fabrication was completed.

[0052] Example 2: A gallium oxide-based double heterojunction solar-blind ultraviolet photodetector was fabricated with a SiO2 / Si substrate, a β-Ga2O3 layer thickness of 80 nm, an oxygen-vacancy-rich β-Ga2O3 layer thickness of 8 nm, a MoS2 layer thickness of 1.4 nm, a WSe2 layer thickness of 12 nm, and both the first and second electrodes being Cr / Au stacked metals.

[0053] Step 1, Pre-treat the substrate.

[0054] SiO2 / Si substrate was selected as substrate 1. It was then placed in acetone, ethanol and deionized water for ultrasonic cleaning, each cleaning lasting 10 minutes. After cleaning, it was dried with a nitrogen gun for later use.

[0055] Step 2: Prepare a β-Ga2O3 layer 2 on the substrate.

[0056] The pretreated SiO2 / Si substrate was placed in the vacuum chamber of a magnetron sputtering apparatus, and a β-Ga2O3 layer was grown on the SiO2 / Si substrate using magnetron sputtering. The magnetron sputtering process conditions were as follows: sputtering power of 90W, sputtering temperature of 550℃, Ga2O3 ceramic target, working pressure of 3Pa, argon flow rate of 20sccm, oxygen flow rate of 1sccm, sputtering time of 25min, and chamber vacuum of 5×10⁻⁶. -4Pa. After deposition, a β-Ga2O3 layer with a thickness of approximately 80 nm is formed.

[0057] Step 3: Form an oxygen-rich vacancy β-Ga2O3 layer 3 on the surface side of β-Ga2O3 layer 2.

[0058] A thermal pulse treatment was performed on the side of the β-Ga2O3 layer 2 away from the substrate 1 to form an oxygen-vacancy-rich β-Ga2O3 layer 3 on the surface of the β-Ga2O3 layer 2. The process conditions for the thermal pulse treatment were: a hydrogen to oxygen volume ratio of 2:1, 6 short thermal pulses, a single thermal pulse duration of 0.08 s, and an interval of 5 s between adjacent thermal pulses. After the thermal pulse treatment, an oxygen-vacancy-rich β-Ga2O3 layer 3 with a thickness of approximately 8 nm was formed on the surface of the β-Ga2O3 layer 2.

[0059] Step 4: Transfer MoS2 layer 4 onto oxygen-rich vacancy β-Ga2O3 layer 3.

[0060] A PDMS-assisted dry transfer method was used to transfer a MoS2 layer 4 with a thickness of approximately 1.4 nm onto an oxygen-vacancy-rich β-Ga2O3 layer 3, thereby bringing the MoS2 layer 4 into contact with the oxygen-vacancy-rich β-Ga2O3 layer 3.

[0061] Step 5: Transfer WSe2 layer 5 onto MoS2 layer 4.

[0062] A PDMS-assisted dry transfer method was used to transfer a WSe2 layer 5 with a thickness of approximately 12 nm onto a MoS2 layer 4, with the WSe2 layer 5 covering a portion of the MoS2 layer 4, leaving exposed areas of the MoS2 layer 4 that were not covered by the WSe2 layer 5.

[0063] Step 6: Prepare the first electrode 6 and the second electrode 7.

[0064] Electron masks were applied over the exposed area of ​​MoS2 layer 4 and over WSe2 layer 5 to define the positions of the first electrode 6 and the second electrode 7, respectively. A Cr / Au multilayer metal was deposited using electron beam evaporation. The Cr layer was 5 nm thick, and the Au layer was 50 nm thick. After deposition, the mask was removed, allowing the first electrode 6 to be formed on the exposed area of ​​MoS2 layer 4 and electrically connected to it, and the second electrode 7 to be formed on top of WSe2 layer 5 and electrically connected to it. The device fabrication was then complete.

[0065] Example 3: A quartz substrate was fabricated with a β-Ga2O3 layer thickness of 150 nm, an oxygen-vacancy-rich β-Ga2O3 layer thickness of 12 nm, a MoS2 layer thickness of 5 nm, a WSe2 layer thickness of 20 nm, and both the first and second electrodes were gallium oxide-based double heterojunction solar-blind ultraviolet photodetectors made of Ni / Au stacked metals.

[0066] Step A: Pre-treat the substrate.

[0067] A1) A quartz substrate was selected as substrate 1 and was placed in acetone, ethanol and deionized water in sequence for ultrasonic cleaning to remove surface organic matter and particulate impurities.

[0068] A2) After cleaning, use a nitrogen gun to dry it for later use.

[0069] Step B: Prepare a β-Ga2O3 layer 2 on the substrate.

[0070] B1) The pretreated quartz substrate is placed in the vacuum chamber of the magnetron sputtering equipment, and Ga2O3 ceramic target is used as the sputtering target.

[0071] B2) Magnetron sputtering was used, with a sputtering power of 120W, a sputtering temperature of 650℃, a working pressure of 4.5Pa, an argon flow rate of 20sccm, an oxygen flow rate of 2sccm, a sputtering time of 45min, and a chamber vacuum of 5×10⁻⁶. -4 Under Pa process conditions, a β-Ga2O3 layer with a thickness of approximately 150 nm was grown on a quartz substrate.

[0072] Step C: An oxygen-rich vacancy β-Ga2O3 layer 3 is formed on the surface side of β-Ga2O3 layer 2.

[0073] C1) The quartz substrate with the β-Ga2O3 layer 2 is placed on the support stage of the thermal pulse processing device, with the side surface of the β-Ga2O3 layer 2 away from the substrate 1 facing the thermal pulse action area.

[0074] C2) A hydrogen-oxygen mixture is introduced into the thermal pulse application area, and a short-duration thermal pulse is generated by electric arc ignition. The volume ratio of hydrogen to oxygen in the hydrogen-oxygen mixture is 1.8:1.

[0075] C3) Under the process conditions of 15 short-time thermal pulses, 0.1s for each thermal pulse, and 8s for the interval between two adjacent thermal pulses, the surface side of β-Ga2O3 layer 2 is treated to form an oxygen-rich vacancy β-Ga2O3 layer 3 with a thickness of about 12nm on the surface side of β-Ga2O3 layer 2.

[0076] Step D: Prepare a MoS2 / WSe2 two-dimensional heterojunction.

[0077] D1) Use adhesive tape to pick up the bulk MoS2 material and repeatedly tear it to obtain a MoS2 sheet with a thickness of about 5nm; attach the MoS2 sheet to the PDMS carrier to form a PDMS / MoS2 composite material.

[0078] D2) Using a micro-transfer platform, the MoS2 layer 4 is transferred onto the oxygen-rich vacancy β-Ga2O3 layer 3, so that the MoS2 layer 4 and the oxygen-rich vacancy β-Ga2O3 layer 3 come into contact.

[0079] D3) Use adhesive tape to pick up the bulk WSe2 material and repeatedly tear it to obtain a WSe2 sheet with a thickness of about 20nm; attach the WSe2 sheet to the PDMS carrier to form a PDMS / WSe2 composite material.

[0080] D4) Using a micro-transfer platform, the WSe2 layer 5 is transferred onto the MoS2 layer 4, so that the WSe2 layer 5 covers a portion of the MoS2 layer 4, while leaving the MoS2 layer 4 with an exposed area for subsequent fabrication of the first electrode 6.

[0081] Step E: Prepare the first electrode 6 and the second electrode 7.

[0082] E1) Define the patterned areas of the first electrode 6 and the second electrode 7 by photolithography, electron beam exposure or masking.

[0083] E2) Electron beam evaporation is used in an evaporation chamber with a vacuum of 5 × 10⁻⁶. -4 Ni / Au multilayer metal was deposited under Pa conditions. The Ni layer thickness was 10 nm and the Au layer thickness was 60 nm.

[0084] E3) Form the first electrode 6 on the exposed area of ​​the MoS2 layer 4 and electrically connect it to the MoS2 layer 4; form the second electrode 7 on the WSe2 layer 5 and electrically connect it to the WSe2 layer 5. The device fabrication is complete.

[0085] The effects of this invention can be further illustrated by the following simulation results.

[0086] I. Simulation conditions.

[0087] The simulation software is Silvaco TCAD.

[0088] The material parameters of sapphire substrate, β-Ga2O3, MoS2, WSe2, Au and Ti used in the simulation were all obtained from the Silvaco database and published journal articles.

[0089] In the optoelectronic simulation process, the surface of the photodetector is illuminated with solar-blind ultraviolet light, and the illumination range covers the effective photosensitive area of ​​the device.

[0090] The simulation device includes a substrate 1, a β-Ga2O3 layer 2, an oxygen-rich vacancy β-Ga2O3 layer 3, a MoS2 layer 4, a WSe2 layer 5, a first electrode 6, and a second electrode 7.

[0091] An oxygen-rich vacancy β-Ga2O3 layer 3 is disposed on the side of β-Ga2O3 layer 2 close to MoS2 layer 4, and its thickness is approximately 10 nm.

[0092] The first electrode 6 is electrically connected to the MoS2 layer 4, and the second electrode 7 is electrically connected to the WSe2 layer 5. The applied bias voltage is -5 to +5V.

[0093] II. Simulation Content and Result Analysis.

[0094] Simulation 1: Under the above conditions, the current characteristics of the device in the embodiment of the present invention were simulated under dark and light conditions. The results are as follows: Figure 3 As shown.

[0095] Depend on Figure 3 As can be seen, the gallium oxide-based double heterojunction solar-blind ultraviolet photodetector of this invention maintains a low dark current in the dark state, while the current increases significantly under illumination, exhibiting excellent solar-blind ultraviolet light response characteristics. When the first electrode voltage is +5 V, the dark current of the device of this invention is approximately 3.66 × 10⁻⁶. -12 A, Under illumination, the photocurrent is approximately 2.68 × 10⁻⁶. -7 A, the photocurrent-to-dark-current ratio is approximately 7.33 × 10⁻⁶. 4 .

[0096] The results of simulation experiment 1 show that the device of the present invention can obtain significant photocurrent output while maintaining a low dark-state leakage current, which is beneficial to improving the device's weak light detection capability and signal-to-noise ratio.

[0097] Simulation 2: Under the above conditions, the transient optical response characteristics of the gallium oxide-based double heterojunction solar-blind ultraviolet photodetector of the present invention were simulated, and the results are as follows. Figure 4 As shown.

[0098] Depend on Figure 4 As can be seen, the gallium oxide-based double heterojunction solar-blind ultraviolet photodetector of this invention exhibits a rapid current increase after illumination is turned on and a rapid decay after illumination is turned off, demonstrating a fast photoresponse and turn-off process. Based on the transient current curve, its 10%–90% rise time is approximately 73.2 μs, and its 90%–10% fall time is approximately 521.0 μs.

[0099] The results of simulation experiment 2 show that the device of the present invention has a response speed on the order of microseconds, indicating that its double heterojunction structure, interface oxygen vacancy control region and layered electrode structure can synergistically promote the separation, transport and collection of photogenerated carriers, thereby improving the transient response performance of the device.

[0100] Under simulation conditions with a first electrode voltage of +5 V, the responsivity of the device of this invention is 268.04 A / W, and the external quantum efficiency is 1.31 × 10⁻⁶.5 %, with a specific detectivity of 5.54 × 10⁻⁶. 13 Jones, with a light-to-dark current ratio of 7.33 × 10⁻⁶. 4 The above results are intended to illustrate that the structure of the present invention has high photoresponse capability, low dark-state leakage current, and superior overall detection performance under the same simulation conditions, and are not intended to limit the performance of actual fabricated devices.

[0101] The operating process of the device of this invention is as follows: β-Ga2O3 layer 2 absorbs solar-blind ultraviolet light and generates photogenerated electrons and holes; oxygen-rich vacancy β-Ga2O3 layer 3 regulates the interface defect states, local charge distribution, and band bending between β-Ga2O3 layer 2 and MoS2 layer 4; the MoS2 / WSe2 two-dimensional heterojunction promotes the spatial separation of photogenerated electrons and holes; the first electrode 6 is electrically connected to MoS2 layer 4 to collect carriers transported along MoS2 layer 4; the second electrode 7 is electrically connected to WSe2 layer 5 to collect carriers transported along WSe2 layer 5. The above structures collectively reduce the carrier recombination probability, improve photocurrent output efficiency, and enhance the device turn-off speed.

[0102] The above descriptions are merely a few specific examples of the present invention and do not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and detail without departing from the principles and structure of the present invention. For example, in addition to the sapphire substrate, SiO2 / Si substrate, and quartz substrate used in the present invention, other insulating substrates can also be used; in addition to Ti / Au, Cr / Au, or Ni / Au multilayer metals, the first electrode 6 and the second electrode 7 can also use Au, Pt, Al, or other metal multilayer structures; in addition to the PDMS-assisted dry transfer method, other two-dimensional material transfer methods can also be used for the MoS2 layer 4 and WSe2 layer 5; the number of thermal pulse treatments and the single treatment time can be adjusted according to the target thickness and oxygen vacancy concentration of the oxygen-rich β-Ga2O3 layer 3. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A photodetector based on a gradient oxygen vacancy Ga2O3 double heterojunction, comprising a substrate (1), a β-Ga2O3 layer (2), an oxygen-vacancy-rich β-Ga2O3 layer (3), a MoS2 layer (4), a WSe2 layer (5), a first electrode (6), and a second electrode (7); characterized in that, The β-Ga2O3 layer (2) is disposed on the substrate (1) as a solar-blind ultraviolet light absorption layer; the oxygen-vacancy-rich β-Ga2O3 layer (3) is disposed on the side of the β-Ga2O3 layer (2) near the MoS2 layer (4) to form an oxygen vacancy gradient modulation region on the surface side of the β-Ga2O3 layer (2), thereby enhancing photoconductivity gain and interfacial carrier supply; the MoS2 layer (4) is disposed on the oxygen-vacancy-rich β-Ga2O3 layer (3), and the WSe2 layer (5) is disposed on the MoS2 layer (4) and covers only one side of the MoS2 layer (4), forming a β-Ga2O3 / MoS2 heterojunction, MoS2 layer (4) and WSe2 layer (5) form a MoS2 / WSe2 two-dimensional heterojunction. This dual heterojunction is used for interface carrier transport and spatial distribution control of photogenerated carriers. The first electrode (6) is disposed on the side of MoS2 layer (4) not covered by WSe2 layer (5) and electrically connected to MoS2 layer (4). The second electrode (7) is disposed on WSe2 layer (5) and electrically connected to WSe2 layer (5) and is used to collect photogenerated carriers from MoS2 layer (4) and WSe2 layer (5) respectively.

2. The photodetector according to claim 1, characterized in that, The substrate (1) is any one of sapphire substrate, SiO2 / Si substrate, quartz substrate or insulating silicon substrate.

3. The photodetector according to claim 1, characterized in that, The thickness of the β-Ga2O3 layer (2) is 30nm to 300nm, the thickness of the MoS2 layer (4) is 0.7nm to 10nm, and the thickness of the WSe2 layer (5) is 1nm to 50nm.

4. The photodetector according to claim 1, characterized in that, The oxygen vacancy-related defect state density in the oxygen-rich vacancy β-Ga2O3 layer (3) is 1×10 20 cm -3 ~1×10 21 cm -3 The oxygen vacancy-related defect state density in the main region of the β-Ga2O3 layer (2) is 1×10 18 cm -3 ~5×10 20 cm -3 .

5. The photodetector according to claim 1, characterized in that, The thickness of the oxygen-rich vacancy β-Ga2O3 layer (3) is 3 nm to 30 nm.

6. The photodetector according to claim 1, characterized in that, The MoS2 layer (4) and the WSe2 layer (5) form a MoS2 / WSe2 two-dimensional heterojunction. The MoS2 layer (4) serves as a photogenerated electron transport channel, and the WSe2 layer (5) serves as a photogenerated hole transport channel. The first electrode (6) is electrically connected to the MoS2 layer (4), and the second electrode (7) is electrically connected to the WSe2 layer (5), which are used to collect photogenerated carriers separated by the MoS2 / WSe2 two-dimensional heterojunction under an applied bias voltage.

7. The photodetector according to claim 1, characterized in that, The first electrode (6) and the second electrode (7) are made of the same metal material or the same metal stack structure. The metal material is one of Au, Ti, Ni, Pt, Cr and Al. The metal stack structure is a stack structure formed by two or more metals of Au, Ti, Ni, Pt, Cr and Al.

8. The method for fabricating a photodetector according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1, the substrate (1) is cleaned and dried; S2, a β-Ga2O3 thin film is grown on the substrate (1) to form a β-Ga2O3 layer (2) with a thickness of 30nm to 300nm. S3, perform thermal pulse treatment on the side of the β-Ga2O3 layer (2) away from the substrate (1) to form an oxygen-vacancy-rich β-Ga2O3 layer (3) on the surface region of the β-Ga2O3 layer (2) that is intended to contact the MoS2 layer (4); the thickness of the oxygen-vacancy-rich β-Ga2O3 layer (3) is 3nm to 30nm, so that the oxygen vacancies are mainly distributed in the surface region extending from the surface of the β-Ga2O3 layer (2) into the interior of the β-Ga2O3 layer (2); S4, a MoS2 layer (4) with a thickness of 0.7 nm to 10 nm is transferred onto an oxygen-rich vacancy β-Ga2O3 layer (3); S5, a WSe2 layer (5) with a thickness of 1nm to 50nm is transferred onto the MoS2 layer (4), so that the WSe2 layer (5) only covers one side of the MoS2 layer (4), and the other side of the MoS2 layer (4) is not covered by the WSe2 layer (5). S6, a first electrode (6) is prepared on the side of the MoS2 layer (4) not covered by the WSe2 layer (5), so that the first electrode (6) is electrically connected to the MoS2 layer (4); a second electrode (7) is prepared on the WSe2 layer (5), so that the second electrode (7) is electrically connected to the WSe2 layer (5); the first electrode (6) and the second electrode (7) are made of the same metal material or the same metal stack structure, and are located on the lateral sides of the device respectively.

9. The preparation method according to claim 8, characterized in that, The thermal pulse treatment in step S3 includes introducing a hydrogen-oxygen mixed gas into the surface side of the β-Ga2O3 layer (2) and generating a short-time thermal pulse by ignition, thereby forming an oxygen vacancy enrichment region on the surface side of the β-Ga2O3 layer (2); wherein, the volume ratio of hydrogen to oxygen in the hydrogen-oxygen mixed gas is 1.5:1 to 3:1, preferably 2:1; the number of short-time thermal pulses is 1 to 30, preferably 3 to 18; the duration of a single thermal pulse is 0.01s to 5s; and the interval between two adjacent thermal pulses is 0.1s to 60s.

10. The preparation method according to claim 8, characterized in that, The β-Ga2O3 layer (2) is prepared by magnetron sputtering, the MoS2 layer (4) and WSe2 layer (5) are formed by PDMS-assisted dry transfer, and the first electrode (6) and the second electrode (7) are formed by thermal evaporation, electron beam evaporation or magnetron sputtering.

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