Surface acoustic wave ultraviolet detector and preparation method thereof

Abstract

The invention relates to the technical field of semiconductor photoelectric detectors, in particular to a surface acoustic wave ultraviolet detector and a preparation method thereof. The detector comprises a substrate, an epsilon-phase gallium oxide layer and a metal electrode layer which are arranged from bottom to top, the metal electrode layer comprises two groups of energy converters and reflecting gratings which are symmetrically arranged, the energy converter at one end is used for receiving radio frequency signals, and the energy converter at the other end is used for connecting direct current bias voltage. According to the surface acoustic wave ultraviolet detector, the interaction of the acoustic-electric effect and the piezoelectric effect of the surface acoustic wave is utilized. The method has the advantages that on one hand, technical means such as doping, surface treatment or high-temperature annealing do not need to be introduced into the epsilon-phase gallium oxide film; and on the other hand, one end of the transducer is used for receiving a radio frequency signal, the excited surface acoustic wave is propagated in the epsilon-phase gallium oxide layer, and the surface acoustic wave with a specific frequency is selectively enhanced when the surface acoustic wave reaches the reflecting grating. The surface acoustic wave can promote the separation of photon-generated carriers and inhibit electron-hole recombination, thereby effectively improving the performance of the detector.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor photoelectric detectors, and in particular to a surface acoustic wave ultraviolet detector and a preparation method thereof. Background Art

[0002] Solar-blind ultraviolet photodetectors have important applications in secure communications, fire warning, environmental monitoring and other fields. In recent years, significant progress has been made in the development of solar-blind ultraviolet photodetectors constructed from wide-bandgap semiconductors. These all-solid-state photodetectors are considered to be alternatives to photomultiplier tubes, but they are limited by high operating voltage, fragility and external optical filters. Available wide-bandgap semiconductors with band gaps exceeding 4.4 eV include alloyed MgZnO (3.35~7.8 eV), alloyed AlGaN (3.4~6.2 eV), and gallium oxide Ga2O3 (4.5~4.9 eV). Gallium oxide has attracted much attention due to its ultra-wide band gap and remarkable thermal and chemical stability. Gallium oxide has α Mutually, β Mutually, c Mutually, d Mutually, e Mutually, k Equivalent to 6 different crystal phase structures, e Phase gallium oxide is second only to β Metastable phase of gallium oxide. e Phase gallium oxide β Compared with the phase GaO, it has a similar wide bandgap (~4.9eV), higher lattice symmetry, lower anisotropy and lower growth temperature. e The unique piezoelectric properties of gallium oxide (piezoelectric coefficient is 0.94 C / m 2 ) and ferroelectric properties (residual polarization intensity is 5~6 μC / cm) can be used as both a piezoelectric layer and a photosensitive layer, making it possible to improve the performance of the detector by using surface acoustic wave propagation.

[0003] Surface acoustic waves are elastic waves that propagate along the surface of a piezoelectric material when an alternating voltage is applied between interdigitated electrodes. Surface acoustic wave devices can interact with the piezoelectric field accompanying the propagation of surface acoustic waves through the acoustic-electric effect. Studies have shown that surface acoustic waves can promote the separation of photogenerated carriers and suppress electron-hole recombination, and this modulation does not cause changes or deterioration in the structure or composition of the semiconductor material. In addition, e Phase gallium oxide has a relative dielectric constant significantly lower than other conventional piezoelectric materials e r =3.6, which can efficiently convert electrical energy and mechanical energy. Therefore, after comprehensive consideration, it is believed that based on e Gallium oxide-based surface acoustic wave ultraviolet detectors may meet people's needs for high-performance ultraviolet detection.

[0004] In recent years, people have devoted themselves to developing high-performance e Phase GaO2 thin film solar-blind detectors, but it is still a big challenge to simultaneously achieve low dark current, high specific detectivity, high UV-visible suppression ratio and fast response speed. e The presence of a large number of oxygen vacancies in the phase-phase gallium oxide film is one of the reasons for the above problems. Thermal annealing under oxygen is a passivation e One of the common methods to remove oxygen vacancy defects in phase-phase gallium oxide. However, e The metastable characteristics of phase gallium oxide make it difficult to completely suppress the adverse effects of oxygen vacancy defects on its photoelectric detection performance by high-temperature oxygen annealing. Some research results show that the introduction of impurities into gallium oxide can significantly suppress oxygen vacancy defects. e Doping Zn in GaO2 films improves e The crystal quality and stability of the metastable structure of phase gallium oxide inhibit the formation of oxygen vacancies, making the prepared Zn-doped e The performance of photodetectors with MSM (metal-oxide-metal) structures based on phase-phase gallium oxide thin films has been improved. In addition, it has been proposed that a thin layer of aluminum oxide can be used as a capping layer to effectively passivate the epitaxial e By introducing an aluminum oxide layer, e The dark current of the photodetector with phase-gallium oxide MSM structure is significantly reduced by more than 3 orders of magnitude, and the photocurrent and response speed are improved at the same time. Although these methods are feasible, they undoubtedly increase the production cost and increase the complexity of production technology. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a surface acoustic wave ultraviolet detector and a preparation method thereof.

[0006] The first object of the present invention is to provide a surface acoustic wave ultraviolet detector, comprising a substrate arranged from bottom to top, e Phase gallium oxide layer and metal electrode layer; The metal electrode layer includes two groups of transducers and reflection grids that are symmetrically arranged. The transducer at one end is used to receive radio frequency signals, and the transducer at the other end is used to connect to a DC bias voltage. The transducer is a uniform transducer or a non-uniform transducer. The reflection grid is a short-circuit reflection grid or an open-circuit reflection grid.

[0007] Preferably, the thickness of the metal electrode layer is 50-500 nm; the material of the metal electrode layer is at least one of molybdenum, nickel, gold, titanium, aluminum or platinum; the frequency band of the surface acoustic wave excited by the metal electrode layer is a very high frequency band of 30-300 MHZ.

[0008] Preferably, eThe thickness of the phase gallium oxide layer is 0.1~10 μm.

[0009] Preferably, e The thickness of the phase gallium oxide layer is 300 nm; and the substrate is sapphire.

[0010] Preferably, the transducer is a uniform transducer; the width of the interdigital fingers of the transducer is a and interdigital spacing p Equal, the corresponding resonant sound wave wavelength l =4 a =4 p ; The finger length of the transducer is 50~60 μm.

[0011] Preferably, the finger width of the transducer a =5 μm, the number of interdigital pairs is 100.

[0012] Preferably, the reflective grid is a short-circuit reflective grid, and the number of the short-circuit reflective grids is 60.

[0013] The second object of the present invention is to provide a method for preparing a surface acoustic wave ultraviolet detector, which specifically comprises the following steps: S1. Cleaning the substrate, and placing the substrate in a metal organic chemical vapor deposition reaction chamber after cleaning; S2. Perform on substrate e Growth of phase gallium oxide layers; S3. e Apply photoresist on the phase gallium oxide layer, cover the photoresist with a mask, perform pre-baking, exposure, post-baking, and development; etch the area of ​​the photoresist not covered by the mask to make a metal electrode pattern; S4. Depositing metal on the metal electrode pattern area by electron beam deposition; S5. Perform a stripping process to obtain a metal electrode layer, thereby completing the preparation of the surface acoustic wave ultraviolet detector.

[0014] Preferably, in step S2 e The growth temperature of the phase gallium oxide film is 600~650 ℃, the growth time is 150~200 minutes, and the growth pressure is 800~900 Pa.

[0015] Preferably, in step S1, the organic gallium source reacted in the reaction chamber is triethylgallium, the temperature of the organic source cold trap is set to 8-15°C, the carrier gas flow rate of the organic gallium source is 5-5.5 sccm, and the oxygen flow rate is 500 sccm; the deposited metal target in step S4 is platinum, and the deposition time is 20 minutes.

[0016] Compared with the prior art, the present invention can achieve the following beneficial effects: The present invention proposes a method based on e The surface acoustic wave detector based on phase GaO thin film is grown on c-plane sapphire substrate by metal oxide chemical vapor deposition (MOCVD) technology. e Phase gallium oxide film, and prepare metal electrodes on the film surface to construct a surface acoustic wave ultraviolet detector, using the interaction between the acoustic-electric effect and the piezoelectric effect of the surface acoustic wave to improve e The performance of phase GaO photodetector. The advantages are: on the one hand, no need to e The GaO2 film is introduced by doping, surface treatment or high temperature annealing. On the other hand, one end of the transducer is used to receive the RF signal, and the surface acoustic wave excited by the transducer is e The photons propagate through the gallium oxide thin film layer and selectively enhance the surface acoustic waves of a specific frequency when they propagate to the reflector. The surface acoustic waves can promote the separation of photogenerated carriers, suppress the advantages of electron-hole recombination, and effectively improve the performance of the detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is an overall schematic diagram of a surface acoustic wave ultraviolet detector structure provided according to an embodiment of the present invention.

[0018] Figure 2 It is a cross-sectional schematic diagram of a surface acoustic wave ultraviolet detector structure provided according to an embodiment of the present invention.

[0019] Figure 3 It is a schematic plan view of a metal electrode layer in a surface acoustic wave ultraviolet detector provided according to an embodiment of the present invention.

[0020] Figure 4 1 is an XRD diagram of an ε-phase gallium oxide thin film of a surface acoustic wave ultraviolet detector provided according to an embodiment of the present invention.

[0021] Figure 5 3 is a SEM image of an ε-phase gallium oxide thin film of a surface acoustic wave ultraviolet detector provided according to an embodiment of the present invention.

[0022] Figure 6 This is an AFM image of an ε-phase gallium oxide thin film of a surface acoustic wave ultraviolet detector provided according to an embodiment of the present invention.

[0023] Figure 7 It is a current-voltage test diagram of a surface acoustic wave ultraviolet detector provided according to an embodiment of the present invention in a dark environment / light environment under a DC bias voltage of -5~5V.

[0024] Figure 8 It is a light response diagram of a surface acoustic wave ultraviolet detector provided according to an embodiment of the present invention at different light power densities under different DC bias voltages.

[0025] Figure 9 is the parameter S of the surface acoustic wave ultraviolet detector provided by the embodiment of the present invention in a dark environment 12 Test chart.

[0026] Figure 10 The surface acoustic wave ultraviolet detector provided by the embodiment of the present invention has an optical power density of 1 mW / cm 2 Parameter S under different light wavelengths 12 Test chart of peak variation.

[0027] Figure 11 The parameter S of the surface acoustic wave ultraviolet detector provided by the embodiment of the present invention under different radiation intensities with a light wavelength of 255 nm is 12 Test chart of peak variation.

[0028] Figure 12 The present invention is a schematic diagram of the surface acoustic wave separation of photogenerated carriers and suppression of electron-hole recombination of the surface acoustic wave ultraviolet detector provided according to an embodiment of the present invention; (A) shows the separation and recombination of carriers in the photosensitive layer under the irradiation of ultraviolet light without the influence of surface acoustic waves; (B) shows that when the photosensitive layer is irradiated with ultraviolet light, the surface acoustic wave causes the bending of the energy band of the photosensitive layer, thereby promoting the separation of photogenerated carriers and suppressing the recombination of electrons and holes.

[0029] Figure 13 According to the embodiment of the present invention, the e The results of X-ray powder diffractometer testing of the phase gallium oxide layer.

[0030] Reference numerals: 1.Metal electrode layer; 2. e Phase gallium oxide layer; 3. substrate; 101. Transducer; 102. Reflection grid. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0032] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0033] The present invention provides a surface acoustic wave ultraviolet detector, comprising a substrate arranged from bottom to top, eThe metal electrode layer includes two sets of transducers and reflective grids which are symmetrically arranged, wherein the transducer at one end is used to receive RF radio frequency signals, and the other end is used to receive DC bias voltage; The thickness of the metal electrode layer is 50-500 nm; the material of the metal electrode layer is a metal material with high conductivity and strong adhesion, including at least one of molybdenum, nickel, gold, titanium, aluminum or platinum; the frequency band of the surface acoustic wave excited by the metal electrode layer is a very high frequency band of 30-300 MHZ; The transducer is a uniform transducer or a non-uniform transducer; The reflector is a short-circuit reflector or an open-circuit reflector; In a specific embodiment, the transducer is a uniform transducer, the reflector is a short-circuit reflector; the width of the transducer fingers is a =5 μm, pitch p =5 μm, finger length l =56 μm, corresponding to the wavelength of the resonant sound wave l =4 a =4 p =20 μm, acoustic aperture W=44 μm; distance between reflection grating and transducer x The diameter of the transducer is 5 μm, the number of transducer finger pairs at the left and right ends is 100, and the number of short-circuit reflective gratings is 60; e The thickness of the phase gallium oxide layer is 0.1-10 μm; in a specific embodiment, e The thickness of the phase gallium oxide layer is 300nm; The substrate material is sapphire.

[0034] The preparation method of the surface acoustic wave ultraviolet detector comprises the following steps: S1. The substrate was ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 5 minutes to remove organic matter and impurities on the surface of the substrate, and then the substrate was dried with high-purity nitrogen and placed in a metal-organic chemical vapor deposition (MOCVD) reaction chamber; S2. Perform on substrate e Growth of phase gallium oxide layers; S3. e Apply photoresist on the phase gallium oxide layer, cover the photoresist with a mask, perform pre-baking, exposure, post-baking, and development; etch the area of ​​the photoresist not covered by the mask to make a metal electrode pattern; S4. Depositing metal on the metal electrode pattern area by electron beam deposition; S5. Perform a lift-off process to obtain a metal electrode layer, thereby completing the preparation of the surface acoustic wave ultraviolet detector.

[0035] In step S1, the organic gallium source reacted in the reaction chamber is triethylgallium, the organic source cold trap temperature is set to 10° C., the carrier gas flow rate of the organic gallium source is 5.3 sccm, and the oxygen flow rate is 500 sccm, which is an oxygen-rich condition.

[0036] In step S2 e The growth temperature of the phase gallium oxide film is 600-650°C, the growth time is 150-200 minutes, and the growth pressure is 800-900 Pa; in a specific embodiment, the growth temperature is 630°C, the growth time is 180 minutes, and the growth pressure is 820 Pa.

[0037] The deposition condition in step S4 is room temperature, the metal target is platinum, and the deposition time is 20 minutes.

[0038] Example 1 Figure 1-Figure 3 A surface acoustic wave ultraviolet detector is shown, comprising a substrate 3 arranged from bottom to top, e The metal electrode layer 1 comprises two sets of transducers 101 and reflectors 102 which are symmetrically arranged; the transducer 101 is a uniform transducer, and the reflector 102 is a short-circuit reflector; the interdigital width of the transducer 101 is a =5 μm, pitch p =5 μm, finger length l =56 μm, corresponding to the wavelength of the resonant sound wave l =4 a =4 p =20 μm, acoustic aperture W=44 μm; the distance between the reflection grating 102 and the transducer 101 x The diameter is 5μm, the number of transducer finger pairs at the left and right ends is 100, and the number of short-circuit reflective gratings is 60; The preparation method specifically comprises the following steps: S1. The substrate 3 is ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 5 minutes to remove organic matter and impurities on the surface of the substrate, and then the substrate 3 dried with high-purity nitrogen is placed in a metal-organic chemical vapor deposition (MOCVD) reaction chamber; The organic gallium source reacted in the reaction chamber is triethylgallium, the temperature of the organic source cold trap is set to 10°C, the carrier gas flow rate of the organic gallium source is 5.3 sccm, and the oxygen flow rate is 500 sccm, which is an oxygen-rich condition.

[0039] S2. Performed on substrate 3 e Growth of phase gallium oxide layer 2; eThe growth temperature of the phase gallium oxide film is 630 °C, the growth time is 180 minutes, and the growth pressure is 820 Pa; e The phase gallium oxide layer 2 serves as both the piezoelectric layer and the photosensitive layer of the surface acoustic surface ultraviolet wave detector, which can avoid the problem of poor quality of the photosensitive layer caused by the large lattice mismatch between the photosensitive layer and the traditional piezoelectric substrate (such as lithium niobate) leading to limited detector performance. e The results of X-ray powder diffractometer testing of the phase gallium oxide film are as follows Figure 4 As shown, it was found that under this growth condition, the grown gallium oxide film is a single e Mutually; e The results of the scanning tunneling microscope test of the phase gallium oxide film are as follows Figure 5 As shown, it was found that under this growth condition, the growth e The surface of the phase gallium oxide film is flat and the thickness is 300 nm; e The surface of the phase gallium oxide film was tested by atomic force microscopy. Figure 6 As shown in the figure, it is found that under this growth condition, the surface of the grown gallium oxide film has high flatness and the roughness is as low as 0.182 nm. This shows that the integration of the photosensitive layer and the piezoelectric layer of the surface acoustic surface ultraviolet wave detector can realize the preparation of a high-quality photosensitive layer.

[0040] S3. e Apply photoresist on the phase gallium oxide layer 2, cover the photoresist with a mask, perform pre-baking, exposure, post-baking, and development; etch the area of ​​the photoresist not covered by the mask to make a metal electrode pattern; S4. Depositing metal on the metal electrode pattern area by electron beam deposition; S5. Perform a lift-off process to obtain the metal electrode layer 1, thereby completing the preparation of the surface acoustic wave ultraviolet detector.

[0041] The performance of the prepared surface acoustic wave ultraviolet detector was tested, and the results are as follows: Figure 7 This is a current-voltage test diagram of the surface acoustic wave ultraviolet detector in a dark environment / light environment under a DC bias voltage of -5~5 V. It can be seen from the figure that the light / dark suppression ratio of the surface acoustic wave ultraviolet detector of the present invention can reach 10 7 , indicating that the output characteristics of the surface acoustic wave ultraviolet detector are good.

[0042] Figure 8 2 is a light response diagram of the surface acoustic wave ultraviolet detector at different DC bias voltages and different optical power densities. It can be seen from the figure that the response of the surface acoustic wave ultraviolet detector of the present invention to 254 nm ultraviolet light is as high as 10 2 , indicating that the surface acoustic wave ultraviolet detector has a good response to ultraviolet light.

[0043] Figure 9 is the parameter S of the surface acoustic wave ultraviolet detector in a dark environment 12 It can be seen from the figure that the surface acoustic wave ultraviolet detector of the present invention can be excited to produce a surface acoustic wave of 270.9 MHz, indicating that the surface acoustic wave can be e Phase propagation on the surface of gallium oxide thin films.

[0044] Figure 10 The surface acoustic wave ultraviolet detector is a light power density of 1 mW / cm 2 Parameter S under different light wavelengths 12 The test graph of peak value change. It can be seen from the graph that the surface acoustic wave ultraviolet detector of the present invention only responds to light in the solar-blind ultraviolet band.

[0045] Figure 11 is the parameter S of the surface acoustic wave ultraviolet detector under different radiation intensities at a wavelength of 255 nm. 12 The test graph of peak value change. It can be seen from the graph that the intensity of the surface acoustic wave of the surface acoustic wave ultraviolet detector of the present invention changes differently under the influence of 255 nm ultraviolet light of different optical power densities.

[0046] Figure 12 The schematic diagram of the surface acoustic wave ultraviolet detector is that the surface acoustic wave separates the photogenerated carriers and suppresses the electron-hole recombination. It can be seen from the figure that the surface acoustic wave ultraviolet detector of the present invention is to excite the surface acoustic wave to make e The energy band of the phase-phase gallium oxide is bent, which promotes the separation of photogenerated carriers, inhibits electron-hole recombination, and improves the performance of the detector.

[0047] Example 2 e The experiment to determine the growth temperature of the phase gallium oxide layer is as follows: Using MOCVD to grow different growth temperatures e Phase gallium oxide film (640 ℃, 630 ℃, 620 ℃, 600 ℃), the growth time is 120 minutes, the growth pressure is 820 Pa; the organic source is triethylgallium, the organic source cold trap temperature is set to 10 ℃, the carrier gas flow rate of the organic source gallium source is 5.3 sccm, the oxygen flow rate is 500 sccm, which is an oxygen-rich condition; the different growth temperatures e The X-ray powder diffractometer test showed that when the growth temperature was 630 °C, the e Phase gallium oxide film growth quality is best (such as Figure 13 Therefore, the growth temperature was selected as 630 °C for the preparation e The temperature of the gallium oxide layer.

[0048] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0049] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A surface acoustic wave ultraviolet detector, characterized in that: Including a substrate arranged from bottom to top, ε Phase gallium oxide layer and metal electrode layer; The metal electrode layer includes two groups of transducers and reflection grids that are symmetrically arranged. The transducer at one end is used to receive radio frequency signals, and the transducer at the other end is used to connect to a DC bias voltage. The transducer is a uniform transducer or a non-uniform transducer. The reflection grid is a short-circuit reflection grid or an open-circuit reflection grid.

2. A surface acoustic wave ultraviolet detector according to claim 1, characterized in that: The thickness of the metal electrode layer is 50-500 nm; the material of the metal electrode layer is at least one of molybdenum, nickel, gold, titanium, aluminum or platinum; the frequency band of the surface acoustic wave excited by the metal electrode layer is a very high frequency band of 30-300 MHZ.

3. A surface acoustic wave ultraviolet detector according to claim 1, characterized in that: Said ε The thickness of the phase gallium oxide layer is 0.1~10 μm.

4. A surface acoustic wave ultraviolet detector according to claim 3, characterized in that: Said ε The thickness of the phase gallium oxide layer is 300 nm; and the substrate is sapphire.

5. The surface acoustic wave ultraviolet detector according to claim 1, characterized in that: The transducer is a uniform transducer; the width of the interdigital fingers of the transducer is a and interdigital spacing p Equal, the corresponding resonant sound wave wavelength λ =4 a =4 p ; The finger length of the transducer is 50~60 μm.

6. A surface acoustic wave ultraviolet detector according to claim 5, characterized in that: The finger width of the transducer a =5 μm, the number of interdigital pairs is 100.

7. A surface acoustic wave ultraviolet detector according to claim 6, characterized in that: The reflective grid is a short-circuit reflective grid, and the number of the short-circuit reflective grids is 60.

8. The method for preparing a surface acoustic wave ultraviolet detector according to claim 1, characterized in that: The specific steps include: S1. Cleaning the substrate, and placing the substrate in a metal organic chemical vapor deposition reaction chamber after cleaning; S2. Perform on substrate ε Growth of phase gallium oxide layers; S3. ε A photoresist is applied on the phase gallium oxide layer, a mask is covered on the photoresist, and pre-baking, exposure, post-baking and development are performed; Etching the area of ​​the photoresist not covered by the mask to produce a metal electrode pattern; S4. Depositing metal on the metal electrode pattern area by electron beam deposition; S5. Perform a stripping process to obtain a metal electrode layer, thereby completing the preparation of the surface acoustic wave ultraviolet detector.

9. The method for preparing a surface acoustic wave ultraviolet detector according to claim 8, characterized in that: In step S2 ε The growth temperature of the phase gallium oxide film is 600~650 ℃, the growth time is 150~200 minutes, and the growth pressure is 800~900 Pa.

10. The method for preparing a surface acoustic wave ultraviolet detector according to claim 9, characterized in that: In the step S1, the organic gallium source reacted in the reaction chamber is triethylgallium, the temperature of the organic source cold trap is set to 8-15°C, the carrier gas flow rate of the organic gallium source is 5-5.5 sccm, and the oxygen flow rate is 500 sccm; the deposited metal target in the step S4 is platinum, and the deposition time is 20 minutes.

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