Ga2O3-based embedded electrode solar blind ultraviolet photoelectric detector and preparation method thereof

Abstract

The invention discloses a Ga2O3-based embedded electrode solar-blind ultraviolet photoelectric detector and a preparation method thereof, the photoelectric detector takes c-plane sapphire as a substrate, a patterned SrRuO3 film with an interdigital electrode structure is deposited on the surface of the substrate to serve as an embedded electrode, the interdigital electrode structure comprises a positive electrode strip and a negative electrode strip, and the positive electrode strip and the negative electrode strip are arranged on the substrate. A plurality of interdigital pairs are formed between the two electrode strips, and a Ga2O3 film is deposited on the patterned SrRuO3 film to serve as a light absorption layer. The device is simple in preparation process and high in repeatability, and the prepared photoelectric detector has excellent solar blind ultraviolet light detection performance, low dark current and high response speed and has huge application potential.

Description

Technical Field

[0001] The invention relates to the field of photoelectric detectors, and in particular to a Ga2O3-based embedded electrode solar-blind ultraviolet photoelectric detector. Background Art

[0002] Deep ultraviolet (DUV) photodetectors can be applied in the fields of missile tracking, flame detection, environmental monitoring, etc., and are gaining more and more attention. The biggest advantage of DUV photodetectors is the accuracy of detecting weak signals, because DUV radiation (200-280nm) is almost non-existent in the near-Earth atmosphere. In the past few decades, wide bandgap materials including AlGaN, ZnMgO, diamond and β-Ga2O3 have been used to make DUV photodetectors. Among them, β-Ga2O3 has the advantages of larger bandgap, better physical stability and higher breakdown electric field. Various forms of β-Ga2O3 materials (nanowires, nanorod arrays, thin films and bulks) have been widely studied for the manufacture of DUV photodetectors. From a practical point of view, thin film materials are easier to prepare than nanomaterials and bulks in enterprise production and are suitable for device manufacturing processes. Many researchers have focused their attention on the preparation of high-performance DUV photodetectors using β-Ga2O3 thin films.

[0003] So far, it is still a challenge to prepare high-performance DUV photodetectors using β-Ga2O3 thin films. There are many factors that affect the performance of DUV photodetectors based on β-Ga2O3 thin films, including substrate pretreatment, β-Ga2O3 crystal quality, β-Ga2O3 film thickness, film electrode structure and size, and contact conditions between metal electrodes and β-Ga2O3. Among these factors, the type and structure of the electrode have a significant impact on the electrical and optical properties of β-Ga2O3, and are one of the important factors in improving the performance of photodetectors. MSM photodetectors have the advantages of simple manufacturing, low dark current generated by back-to-back Schottky barriers, fast response speed, and compatibility with traditional micro-fabrication processes.

[0004] It is well known that the high performance of MSM-type photodetectors usually requires a fast response time, however, it is often limited by the transmission time of photogenerated carriers in the MSM structure. To overcome this defect, some strategies have been proposed and implemented, such as introducing high-density recombination centers in the material, reducing the electrode spacing, and reducing the thickness of the active layer. These methods combined with nanofabrication technology can obtain ultrafast photodetectors, but these devices may also lead to poor responsiveness. In fact, adopting new electrode structures is an alternative way to address this limitation. These traditional MSM-type photodetectors usually use planar electrodes, which may lead to non-uniform electric field distribution in the light absorption area. The electric field in the planar MSM-type photodetector decreases with increasing depth, resulting in an increase in the collection time of photogenerated carriers deep in the active layer. Compared with traditional planar electrodes, embedded electrodes that are partially or fully embedded in the semiconductor material can effectively enhance the electric field inside the device. However, electrodes are often made of metal materials such as Au, Ag and Pt. When using embedded electrodes to grow gallium oxide thin films, gallium oxide needs to be deposited in an oxygen atmosphere. The metal electrodes will be oxidized, and under high-temperature annealing, the metal will further diffuse onto the defective channel material, reducing the switching ratio of the device. Therefore, using conductive metal oxides with better chemical and thermal stability to replace traditional metal materials as electrodes for photodetectors has its unique advantages. The use of metal oxide embedded electrodes provides a promising solution for improving the photoelectric properties of MSM photodetectors. Summary of the invention

[0005] In order to solve the adverse effect of the non-uniform electric field in the active layer on the separation or collection of photogenerated electron-hole pairs in an MSM-type Ga2O3 solar-blind ultraviolet photodetector manufactured by a planar metal electrode structure, the present invention provides a Ga2O3-based embedded electrode solar-blind ultraviolet photodetector, which aims to improve the photoelectric characteristics of the MSM-type photodetector through a metal oxide embedded electrode, and obtain a solar-blind ultraviolet photodetector with a simple preparation method, strong controllable growth conditions and excellent performance.

[0006] In order to achieve the purpose, the present invention adopts the following technical solutions:

[0007] A Ga2O3-based embedded electrode day-blind ultraviolet photodetector, characterized in that: the photodetector is based on c-plane sapphire, and a patterned SrRuO3 film with an interdigitated electrode structure is deposited on the surface of the substrate as an embedded electrode, the interdigitated electrode structure includes a positive electrode strip and a negative electrode strip, and a plurality of interdigitated pairs are formed between the two electrode strips; a Ga2O3 film is deposited on the patterned SrRuO3 film as a light absorption layer.

[0008] Furthermore, the thickness of the Ga2O3 film is 130-160nm, and the thickness of the patterned SrRuO3 film is 50-70nm.

[0009] Furthermore, the Ga2O3 film and the patterned SrRuO3 film are both deposited in situ using pulsed laser molecular beam epitaxy (L-MBE) technology. Due to the lattice mismatch between the materials, the Ga2O3 film deposited on the patterned SrRuO3 film is a-Ga2O3, and the Ga2O3 film deposited on the sapphire substrate at the spacing between adjacent interdigits is β-Ga2O3. The photosensitive area of ​​the prepared photodetector is the β-Ga2O3 film at the spacing between adjacent interdigits, while the a-Ga2O3 film on the SrRuO3 film has almost no contribution to the light response of the device.

[0010] Furthermore, the interdigital electrode structure has an interdigital spacing and width of 30-100 μm, and an interdigital length of 1-3 mm.

[0011] The present invention uses single-polished c-plane sapphire (α-Al2O3) as the substrate because it has good transmittance, thermal stability and chemical stability in the visible light wavelength range, high mechanical strength, mature production process and low manufacturing cost. According to a preferred embodiment of the present invention, the thickness of the single-polished c-plane sapphire is 0.5mm, and the total thickness deviation, curvature and warpage are all less than 10μm.

[0012] The present invention selects the perovskite structure compound SrRuO3 (abbreviated as SRO) with metallic conductivity as the electrode, whose room temperature resistivity is 280μΩ·cm, and has high conductivity, high chemical stability and high thermal stability.

[0013] The present invention selects Ga2O3 film as the light absorption layer, which is a wide-bandgap semiconductor with a direct bandgap, and the bandgap width at room temperature is about 4.9 eV.

[0014] The method for preparing the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector of the present invention comprises the following steps:

[0015] Step 1: Use a pulsed laser molecular beam epitaxy system to deposit a patterned SrRuO3 film with an interdigital electrode structure on a c-plane sapphire substrate. The deposition conditions are: laser frequency 5 Hz, laser energy 300 mJ, oxygen pressure 10 Pa, deposition temperature 600 ° C. After the deposition, the temperature is raised to 650 ° C and annealed at a constant temperature for 30 minutes.

[0016] Step 2: Use a pulsed laser molecular beam epitaxy system to deposit Ga2O3 thin film on the SrRuO3 thin film. The deposition conditions are: laser frequency 3 Hz, laser energy 400 mJ, oxygen pressure 3×10 -2Pa, deposition temperature was 750℃, after deposition, the temperature was raised to 800℃ and annealed at constant temperature for 30min.

[0017] The present invention screened the deposition conditions of SrRuO3 film and Ga2O3 film through XRD testing, and found that conditions such as laser frequency, laser energy, oxygen pressure, deposition temperature, annealing temperature, etc. will affect the crystallization quality of the film. The crystallization quality of the SrRuO3 film and Ga2O3 film obtained under the above process conditions is optimal.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] (1) The present invention designs and constructs a photodetector device with an embedded electrode structure, and proposes a new method for preparing a conductive oxide interdigital electrode by patterned deposition of SrRuO3 on a sapphire substrate, and then selectively epitaxially growing a Ga2O3 film thereon to prepare an MSM photodetector with an embedded electrode structure, which provides a promising solution for improving the photoelectric properties of MSM type photodetectors.

[0020] (2) The Ga2O3-based embedded electrode solar-blind UV photodetector designed by the present invention has excellent solar-blind UV detection performance, low dark current, and excellent UV-visible suppression ratio. In addition, the device has good stability and reproducibility and fast response speed. The electrode embedded in the semiconductor material can effectively enhance the electric field inside the device, thereby shortening the transmission distance of the photocarriers and significantly increasing the photocurrent.

[0021] (3) The device preparation process of the present invention is simple and easy. It adopts laser molecular beam epitaxy technology for deposition preparation. The growth conditions are highly controllable, the film thickness is precisely controllable, the obtained film has high density, and the layers of the film are in good contact. The preparation process is less affected by external environmental factors and has strong repeatability. The method is simple and has good compatibility with current semiconductor processes, making it easy to integrate the device on existing integrated circuit chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector prepared in Example 1 of the present invention.

[0023] Figure 2 This is the mask pattern used in the growth process of the conductive metal oxide SRO electrode in Example 1 of the present invention.

[0024] Figure 3 The ultraviolet absorption spectrum and bandgap width of the β-Ga2O3 film in Example 1 of the present invention.

[0025] Figure 4This is the XRD diagram of the β-Ga2O3 film in Example 1 of the present invention.

[0026] Figure 5 This is an atomic force microscope morphology image of the β-Ga2O3 film prepared in Example 1 of the present invention.

[0027] Figure 6 The typical current-voltage characteristic curve of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector in Example 1 of the present invention is shown in the figure. It can be seen that under 254nm light (light intensity of 17.8mW / cm 2 ), the device has significant photovoltaic characteristics, with a dark current of 22.2pA at a voltage of 10V.

[0028] Figure 7 This is the current-time characteristic curve of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector in Example 1 of the present invention under 10V bias and different light intensities of 254nm.

[0029] Figure 8 This is the time response spectrum of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector in Example 1 of the present invention under incident light with a frequency of 1 kHz. It can be seen from the figure that the rise time and fall time of the device are 16 μs and 21 μs respectively.

[0030] Fig. 9 This is the It photoresponse curve under 254nm light at 10V bias in Example 1 of the present invention.

[0031] Fig.10 1 is the effect of different bias voltages on the detector photocurrent under 254nm light in Example 1 of the present invention.

[0032] Fig.11 The relationship between the responsivity and specific detection rate of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector and the light intensity in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] The embodiments of the present invention are described in detail below. The embodiments described below are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the embodiments described below.

[0034] Example 1

[0035] like Figure 1As shown, this embodiment provides a Ga2O3-based embedded electrode solar-blind ultraviolet photodetector, which uses c-plane sapphire as a substrate, and deposits a patterned SrRuO3 film with a forked electrode structure on the substrate surface as an embedded electrode, the forked electrode structure includes a positive electrode strip and a negative electrode strip, and a plurality of forked finger pairs are formed between the two electrode strips; a Ga2O3 film is deposited on the patterned SrRuO3 film as a light absorption layer. Among them, the Ga2O3 film deposited on the patterned SrRuO3 film is a-Ga2O3, and the Ga2O3 film deposited on the sapphire substrate at the interval between adjacent forked fingers is β-Ga2O3.

[0036] The photoelectric detector of this embodiment is manufactured according to the following steps:

[0037] 1. Ultrasonic cleaning of the c-surface sapphire substrate with a size of 10×10×0.5 mm. The specific operation process is as follows: ultrasonic cleaning in deionized water for 5 minutes; ultrasonic cleaning in acetone solution for 10 minutes; ultrasonic cleaning in deionized water for 5 minutes; ultrasonic cleaning in ethanol solution for 10 minutes; ultrasonic cleaning in deionized water for 5 minutes. Take out and dry for later use.

[0038] 2. Fix the cleaned sapphire substrate on the sample holder of the pulsed laser molecular beam epitaxy system, and then transfer it to the sample stage of the deposition chamber for use.

[0039] 3. Prepare SrRuO3 target and Ga2O3 target (both specifications are , purity 99.99%), fix the two targets on the target holder, and then transfer them into the target stage of the deposition chamber at one time for use.

[0040] 4. Adjustment of the optical path: The laser emitted by the excimer laser is focused by a lens and directly irradiates the target surface through a quartz window at 45°. The spot size is adjusted so that the highest point of the plasma plume generated by the target irradiated by the laser is located at 2 / 3 of the distance from the target to the substrate.

[0041] 5. Turn on the heating system and raise the temperature to 600℃. Preheat at a constant temperature for 30 minutes. Turn on the laser, set the laser frequency to 5Hz, and the laser energy to 300mJ. While the substrate is preheated, turn on the oxygen pressure system and adjust the oxygen pressure to 10Pa. Bombard the SRO target with a laser to start deposition. After 20 minutes, the deposition is terminated to obtain a SRO film with a thickness of about 60nm on the substrate. During this process, there is a MASK between the target and the substrate to mask the SRO film so that it can be deposited in a pattern. The mask pattern is as follows: Figure 2 As shown, the finger spacing and width of the interdigital electrode structure are 50 μm, and the interdigital length is 2 mm. After the deposition is completed, the oxygen pressure is kept constant, the temperature is raised to 650°C for constant temperature annealing for 30 minutes, the heating system is turned off, and the temperature is naturally cooled to room temperature.

[0042] 6. Turn on the heating system, adjust the temperature to 750°C, and preheat for 30 minutes. While the substrate is preheating, turn on the oxygen pressure system and adjust the oxygen pressure to 3×10 -2 Pa; turn on the laser, set the laser frequency to 3Hz, set the laser energy density to 400mJ, and use the laser to bombard the Ga2O3 target for sputtering, so that a layer of Ga2O3 film is deposited on the SrRuO3 film. The deposition is completed after 2h, and the thickness of the obtained Ga2O3 film is about 150nm. For the convenience of testing, part of the SrRuO3 film electrode strip area is exposed. After the deposition is completed, keep the oxygen pressure unchanged, heat to 800℃ and anneal at a constant temperature for 30min, then turn off the heating system and wait for it to cool down to room temperature naturally. After the sapphire substrate has grown thin films twice, the device has been prepared and can be tested without subsequent operations such as evaporation electrodes.

[0043] The absorption spectrum of the β-Ga2O3 film prepared in this example is as follows Figure 3 As shown in the figure, it can be seen that the absorption cutoff edge of the β-Ga2O3 film is near 300nm, and the absorption rate in the visible light region is less than 10%. The inset in the figure is the bandgap width of the sample calculated by the absorption spectrum. The actual bandgap width of the β-Ga2O3 film is 4.9eV.

[0044] The XRD characterization of the β-Ga2O3 film prepared in this example is as follows Figure 4 As shown in the figure, it can be seen that the diffraction pattern has basically no impurity peaks, and the film is along ( 01) surface epitaxial growth. In addition, the half-width of the diffraction peak is small, the film has good crystallinity and no impurity phase. The β-Ga2O3 film was selected on the c-plane sapphire substrate ( 01) Surface preferential growth.

[0045] The atomic force microscope morphology of the β-Ga2O3 film prepared in this example is shown in Figure 5 As shown, it can be seen intuitively from the figure that the distance between the maximum peaks and valleys is 4.6nm, indicating that the surface roughness of the β-Ga2O3 film is low.

[0046] The photoelectric properties of the Ga2O3-based embedded electrode solar-blind UV photodetector prepared in this example were tested by a semiconductor characterization system (Keithley4200-SCS) and an oscilloscope (DPO2012B, Tektronix). It was equipped with a 254nm LED light source with a power of 12W. After calibration by an energy meter (LS125, Linshang), the light intensity variation range was 0.05-28mW / cm 2 The frequency of the chopper (DCS540, Zolix) is (20Hz-2kHz). At a light intensity of 10mW / cm2 , 254nm monochromatic light, it shows obvious photovoltaic characteristics, such as Figure 6 As shown, the dark current is 22.2pA when the voltage is 10V.

[0047] The current-time characteristic curves of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector prepared in this embodiment under 10V bias and different light intensities of 254nm are shown in Figure 2. Figure 7 As shown, the photoresponse exhibits obvious light intensity-dependent characteristics. With the increase of light intensity, the photocurrent gradually increases, which can be explained by the increase in the number of photocarriers under higher light intensity.

[0048] The time response spectrum of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector prepared in this embodiment under 254nm light with an incident frequency of 1kHz is shown in Figure 8 As shown, it can be seen that the device rise time and fall time are 16μs and 21μs respectively.

[0049] The It curve of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector prepared in this embodiment under 10V bias and 254nm light irradiation is as follows: Fig. 9 As shown. The photodetector has a fast response speed to ultraviolet light and has good repeatability and stability.

[0050] The effect of different bias voltages on the photocurrent of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector prepared in this example under 254nm light is shown in the following figure. Fig.10 The data in the figure reveal that the photocurrent of the device increases monotonically with the increase of bias voltage. This phenomenon can be attributed to the increase in the mobility of photogenerated carriers under high bias voltage and the hindered recombination of photogenerated electrons and holes caused by the strong electric field under high bias conditions.

[0051] The dependence of the light response of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector prepared in this example on the incident light power density at 254 nm is as follows: Fig.11 As shown, the applied bias voltage V ds =10V. At P = 100μW / cm 2 Under the illumination of , the device’s responsivity R = 6.98 mA / W, and the specific detection rate D* = 2.46×10 11 Jones, at which point the quality factors are the largest. It can be observed that as the incident light power density increases, the device's responsivity and specific detectivity decrease. 2 Under the illumination of , the device's responsivity decreases to R = 1.53 mA / W and the specific detection rate D* = 5.39 × 10 10Jones. Since D* is related to R, it shows a similar decreasing trend as the incident light power decreases.

[0052] Comparative Example 1

[0053] In this comparative example, a planar photodetector is prepared as a comparison. A β-Ga2O3 film is first deposited on a c-plane sapphire substrate as a light absorption layer, and then a patterned SrRuO3 film with a forked electrode structure is deposited thereon as an electrode. The deposition conditions of the film are the same as those in Example 1.

[0054] Comparative Example 2

[0055] In this comparative example, a photodetector with Au as an embedded electrode is prepared as a comparison. The c-plane sapphire is used as the substrate, and a patterned Au film with a forked electrode structure is evaporated on the surface of the substrate as the embedded electrode. The forked electrode structure includes a positive electrode strip and a negative electrode strip, and a plurality of forked finger pairs are formed between the two electrode strips. A Ga2O3 film is deposited on the Au film as a light absorption layer, and the deposition conditions of the film are the same as those in Example 1.

[0056] Table 1: Performance comparison of photoelectric detection devices prepared in the embodiment and the comparative example

[0057]

[0058] Table 1 shows the main properties of Ga2O3-based embedded conductive metal oxide electrodes, planar electrodes, and embedded metal electrode photodetectors prepared in the examples and comparative examples. It can be seen that the Ga2O3 photodetector with embedded conductive metal oxide electrodes has excellent solar-blind ultraviolet light detection performance, lower dark current, greater responsivity, and faster response speed compared with other electrode type devices.

[0059] The above contents are only a preferred embodiment of the present invention and are not intended to limit the present invention. Without departing from the spirit and principle of the present invention, those skilled in the art may make various modifications and improvements to the present invention, and these modifications and improvements shall be included in the protection scope of the present invention.

Claims

1. A Ga2O3-based embedded electrode solar-blind ultraviolet photodetector, characterized in that: The photodetector is based on c-plane sapphire, and a patterned SrRuO3 film with an interdigitated electrode structure is deposited on the surface of the substrate as an embedded electrode. The interdigitated electrode structure includes a positive electrode strip and a negative electrode strip, and a plurality of interdigitated pairs are formed between the two electrode strips. A Ga2O3 film is deposited on the patterned SrRuO3 film as a light absorption layer.

2. The Ga2O3-based embedded electrode solar-blind ultraviolet photodetector according to claim 1, characterized in that: The Ga2O3 film deposited on the patterned SrRuO3 film is a-Ga2O3, and the Ga2O3 film deposited on the sapphire substrate at the gap between adjacent interdigits is β-Ga2O3.

3. The Ga2O3-based embedded electrode solar-blind ultraviolet photodetector according to claim 1, characterized in that: The thickness of the Ga2O3 film is 130-160nm, and the thickness of the patterned SrRuO3 film is 50-70nm.

4. The Ga2O3-based embedded electrode solar-blind ultraviolet photodetector according to claim 1, characterized in that: The Ga2O3 film and the patterned SrRuO3 film are both obtained by in-situ deposition using pulsed laser molecular beam epitaxy technology.

5. The Ga2O3-based embedded electrode solar-blind ultraviolet photodetector according to claim 1, characterized in that: The interdigital electrode structure has an interdigital spacing and width of 30-100 μm, and an interdigital length of 1-3 mm.

6. A method for preparing the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector according to any one of claims 1 to 5, characterized in that: The steps include: Step 1: Deposit a patterned SrRuO3 film with an interdigital electrode structure on a c-plane sapphire substrate using a pulsed laser molecular beam epitaxy system; Step 2: Using a pulsed laser molecular beam epitaxy system to deposit a Ga2O3 film on the SrRuO3 film, the preparation of the ultraviolet photodetector is completed.

7. The preparation method according to claim 6, characterized in that: The deposition conditions of the patterned SrRuO3 film in step 1 are: laser frequency 5 Hz, laser energy 300 mJ, oxygen pressure 10 Pa, deposition temperature 600°C, and after the deposition, the temperature is raised to 650°C and annealed at a constant temperature for 30 minutes.

8. The preparation method according to claim 6, characterized in that: The deposition conditions of Ga2O3 film in step 2 are: laser frequency 3 Hz, laser energy 400 mJ, oxygen pressure 3×10 -2 Pa, deposition temperature was 750℃, after deposition, the temperature was raised to 800℃ and annealed at constant temperature for 30min.

9. Use of the Ga2O3-based embedded electrode solar-blind ultraviolet photodetector according to any one of claims 1 to 5 in deep ultraviolet light detection.

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