A high performance Ga2O3 thin film active solar-blind ultraviolet detector and its preparation method

Abstract

The present invention provides a Ga2O3 thin film active solar-blind ultraviolet detector with ultra-large photocurrent and ultra-high detection rate and a preparation method thereof. The present invention is completed by epitaxially growing a layer of Ga2O3 thin film on a sapphire substrate by pulsed laser deposition technology (PLD), and then by a specific annealing process and a micro-nano processing process. The active solar-blind ultraviolet photodetector prepared by the present invention has a significant photoelectric response only to deep ultraviolet rays in the solar-blind area. When the device is working, it has an ultra-large photocurrent and an ultra-high detection rate, and the working performance is stable. It can be used to solve technical problems involving solar-blind ultraviolet signal detection such as fire monitoring, missile tail flame tracking, and high-voltage corona detection.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor photoelectric devices, and in particular relates to a high-performance Ga2O3 thin-film photoelectric detector capable of detecting solar-blind ultraviolet signals and a preparation method thereof. Background Art

[0002] More than 99% of the energy in the solar radiation spectrum is concentrated in the 0.2-10μm band, and the ultraviolet band less than 400nm accounts for only 5% of the total energy. Among them, the deep ultraviolet signal below 280nm is completely absorbed by the ozone layer during the process of passing through the atmosphere, so that the ultraviolet light in this band is almost attenuated to zero near the surface, so this band is called the solar-blind ultraviolet region. Compared with the visible band and infrared band, the detection of the solar-blind ultraviolet band can achieve the requirements of no background signal interference, low false alarm rate, and high sensitivity, which means that this technology has a high social application value.

[0003] Solar-blind ultraviolet detection technology is of strategic significance in national defense, military and engineering applications. For example, solar-blind ultraviolet photoelectric detectors play a vital role in defense fields such as missile warning and space-based warning, as well as in power grid fields such as high-voltage corona detection and drone inspection. In addition, the application scenarios of solar-blind ultraviolet photoelectric detectors also include fire monitoring, space communications, meteorological monitoring and environmental testing.

[0004] Ultraviolet detectors have a history of nearly 100 years. Early photomultiplier tubes were large in size, easily affected by the environment, had a short working life, and there were few products on the market, so their application range was relatively limited. Silicon-based photodetectors are currently the most widely used type of products, but the detection of ultraviolet signals requires additional filters and current amplification components, which invisibly increases the production cost. At the same time, silicon-based detectors are prone to failure in extreme environments such as high temperatures. The wide-bandgap photodetectors developed in recent years have made up for the shortcomings of the former. They are not only sensitive to ultraviolet signals, but also easy to miniaturize. They are the key direction of detector development in recent years.

[0005] Ga2O3 is a natural wide bandgap oxide with an ultra-wide bandgap of 4.85eV, corresponding to an absorption wavelength below 260nm, and can detect solar-blind ultraviolet radiation with high selectivity. Not only that, the material also has excellent mobility and relatively stable chemical properties, making it suitable for high-speed response detection tasks in harsh environments. Therefore, in the market demand for high-sensitivity, high-detection rate, and miniaturized ultraviolet photodetectors, Ga2O3 as a preferred material for the preparation of solar-blind ultraviolet photodetectors highlights its extraordinary comparative advantages.

[0006] In the prior art, Ga2O3 solar-blind photodetectors are mainly thin-film devices. Although there are many related reports, most of them still cannot have the performance of large photocurrent and high detection rate (Xie, C.; Lu, XT; Ma, MR; Tong, XW; Zhang, ZX; Wang, L.; Wu, CY; Yang, WH; Luo, LB Catalyst-free vapor-solid deposition growth of β-Ga2O3 nanowires for DUV photodetector and image sensor application. Adv. Opt. Mater. 2019, 7, 1901257., Qin, Y.; Long, SB; He, QM; Dong, H.; Jian, GZ; Zhang, Y.; Hou, XH; Tan, PJ; Zhang, ZF; Lu, YJ et al. Amorphous gallium oxide-based gate-tunable high-performance thin film phototransistor for solar-blind imaging.Adv.Electron.Mater.2019,5,1900389.), which limits the realization of many application scenarios. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a high-performance Ga2O3 thin film photodetector which can generate ultra-large photocurrent for solar-blind ultraviolet signals and has ultra-high detection rate and a preparation method thereof.

[0008] In order to achieve the above purpose, the technical solution of the present invention is:

[0009] A Ga2O3 thin film active solar-blind ultraviolet detector with ultra-large photocurrent and ultra-high detection rate and a preparation method thereof, comprising the following steps:

[0010] (1) A small amount of polyvinyl alcohol aqueous solution and Ga2O3 polycrystalline powder are mixed, fully ground, poured into an isostatic pressing mold, pressed into a flake solid, and then placed in a high-temperature muffle furnace for calcination in air at 1250-1450°C for 12-36 hours to obtain a high-purity Ga2O3 polycrystalline target; the concentration of the polyvinyl alcohol aqueous solution is 0.1-1% of the mass of pure water, and the volume of the polyvinyl alcohol aqueous solution added is 1-5% of the mass of the Ga2O3 polycrystalline powder;

[0011] (2) Under oxygen partial pressure conditions, the high-purity Ga2O3 polycrystalline target material is adhered to a stainless steel target holder, the Al2O3 substrate is fixed on a heating table with silver paste, the heating table heating rate and growth temperature are controlled, the flow controller is adjusted to control the background oxygen partial pressure in the PLD growth chamber, and a Ga2O3 film is grown on the Al2O3 polished substrate using pulsed laser deposition technology;

[0012] (3) After the Ga2O3 film is grown, it is not necessary to take it out in time, and an in-situ high temperature and high oxygen pressure annealing process is performed in the PLD growth chamber with the help of a heating stage;

[0013] (4) subjecting the annealed Ga2O3 film to a standard photolithography process through a laser direct writing photolithography system, developing a preset interdigital electrode pattern, and using electron beam evaporation to prepare positive and negative electrodes to complete a photodetector;

[0014] Optionally, in step (1), the uniformly mixed powder is poured into a stainless steel isostatic pressing mold for pressing at a pressure of 6-10 MPa, and then calcined.

[0015] Optionally, in step (1), the heating rate of calcination is 5-20°C / min, and the cooling rate is 2-10°C / min.

[0016] Optionally, in step (2), the Al2O3 substrate is a single-sided / double-sided polished single crystal substrate, the polished surface is a c-plane, the surface roughness is <0.1nm, and the size is 5-10mm×5-10mm×0.4-0.6mm.

[0017] Optionally, in step (2), the heating stage heating rate is 10-25°C / min, and the growth temperature of the heating stage is maintained at 500-750°C;

[0018] Optionally, in step (2), the background vacuum of the PLD growth chamber is <10 -5 Pa, the flow controller controls the background oxygen partial pressure of high-purity oxygen to maintain at 0.133-13.33Pa;

[0019] Optionally, in step (2), the PLD control panel sets the laser outlet energy to 150-400 mJ, the number of pulses to 5000-40000, the pulse frequency to 1-20 Hz, and the laser energy density to 1-2 J / cm 2 ;

[0020] Optionally, in step (2), the thickness of the grown Ga2O3 film is 0.1-0.4 μm;

[0021] Optionally, in step (3), the annealing temperature is 500-700°C, and the flow controller is adjusted to control the background oxygen partial pressure at 10 4-10 5 Pa, annealing time is controlled at 1-60min, and the cooling rate of the heating stage is 5-25℃ / min;

[0022] Optionally, in step (4), the finger width of the interdigitated electrode pattern is 5-100 μm, the finger spacing is 5-100 μm, and the finger length is 2-4.5 mm;

[0023] Optionally, in step (4), the positive and negative electrode materials are titanium and gold, and the background vacuum of the electron beam evaporation growth chamber is 10 -7 -10 -6 Pa, the thickness of the titanium layer is 5-50nm, and the thickness of the gold layer is 20-100nm.

[0024] The working principle of the Ga2O3 thin film active solar-blind ultraviolet detector with ultra-large photocurrent and ultra-high detectivity prepared by the above preparation method is:

[0025] A certain bias is applied to both ends of the interdigital electrodes. In a dark environment, there are no photogenerated carriers inside the detector, the intrinsic resistance is quite large, and there is only a weak current. At 20V, the circuit current is in the pA level. Under the irradiation of solar-blind ultraviolet light, the Ga2O3 film is excited by light and generates a large number of photogenerated carriers. Under the action of the external bias, the photogenerated carriers move in a directional manner to generate photocurrent, and the resistance decreases sharply. At 20V, the circuit current is in the mA level, which is fed back by the external circuit as a light response signal to realize the detection of the light signal.

[0026] The beneficial effects of the present invention are:

[0027] 1. The present invention optimizes the performance of Ga2O3 thin film by using an annealing process under specific oxygen pressure and temperature conditions, effectively reducing the oxygen defect concentration of the film and significantly suppressing the dark current. Through subsequent specific electrode processes, the device's ability to capture photogenerated carriers is significantly improved, the photocurrent and responsiveness are improved, and the photoelectric performance of the device is greatly improved, with a switching ratio of more than 10 8 , the detection rate exceeds 10 16 Jones, greatly improving the detection performance of a single device.

[0028] 2. The Ga2O3 thin film photodetector of the present invention only responds to solar-blind light, particularly to the deep ultraviolet band of <260nm, has good wavelength selectivity, fast response speed, good repeatability, and high stability, and can meet the stringent detection requirements for solar-blind ultraviolet signals in engineering or national defense.

[0029] 3. The present invention uses a c-plane Al2O3 substrate, which is low-cost. The relevant thin film growth technology can be directly transferred to the construction of similar thin film devices. The photodetector structure design and process flow are simple and can be seamlessly connected with existing semiconductor processing technology without the need for additional customized equipment. It has significant market application prospects.

[0030] 4. The present invention reduces the probability of the film being contaminated by the environment, simplifies the complexity of equipment operation, saves preparation process time, further optimizes the film quality, reduces intrinsic defects in the film, and greatly improves the performance indicators of subsequent optoelectronic devices by using a new in-situ high oxygen pressure annealing method.

[0031] 5. The film produced by the present invention has excellent crystallinity and smooth surface roughness, which is conducive to the continued growth of other heterojunction material films or superlattice structures on the upper layer of the film to construct new semiconductor devices.

[0032] 6. The electrode pattern design and process adopted in the present invention have excellent ability to capture photogenerated carriers. At the same time, relying on the Schottky barrier at the contact interface between the electrode material and the Ga2O3 film, the dark current can be further reduced while improving the detection rate of the device. The electrode pattern design and process are expected to change the problem of generally low output performance in the current devices of this type. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a simplified schematic diagram of the front view structure of the Ga2O3 thin film active solar-blind ultraviolet photodetector prepared in Example 1 of the present invention and Comparative Examples 1 and 2.

[0034] Figure 2 are the electrode patterns used in Example 1 and Comparative Example 1 of the present invention, and the electrode pattern used in Comparative Example 2;

[0035] Figure 3 is the XRD diagram of Ga2O3 thin films prepared in Example 1 of the present invention and Comparative Examples 1 and 2;

[0036] Figure 4 is a current-voltage (IV) characteristic curve of the Ga2O3 thin film photodetector prepared in Example 1 of the present invention and Comparative Examples 1 and 2;

[0037] Figure 5 is a current-time curve diagram of the Ga2O3 thin film photodetector prepared in Example 1 of the present invention and Comparative Examples 1 and 2;

[0038] Figure 6 It is the valence band cutoff edge of the X-ray photoelectron absorption spectrum of the Ga2O3 thin film samples prepared in Example 1 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The embodiments described below are implemented based on the technical requirements of the present invention, and detailed implementation methods and operation steps are given. It should be noted that the present invention is not limited to the following specific embodiments, and the numbering meaning of each method step is only expressed to distinguish the different method steps described, rather than to limit the arrangement order of any method steps or to limit the scope of implementation of the present invention. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

[0040] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments.

[0041] Example 1

[0042] The specific preparation method of the Ga2O3 thin film active solar-blind ultraviolet detector of this embodiment is as follows:

[0043] (1) Target synthesis: 6 g of Ga2O3 powder and 0.2 ml of 0.5% mass fraction polyvinyl alcohol aqueous solution were weighed and ground in an agate mortar for 60 min. The mixed powder was then poured into a stainless steel isostatic pressing mold and pressed into a 1-inch diameter disc with a tablet press at a pressure of 10 MPa. The disc was then placed in a high-temperature muffle furnace and calcined in air at 1350°C for 24 h with a heating rate of 10°C / min and a cooling rate of 5°C / min.

[0044] (2) A 5×5×0.5 mm single-side polished c-Al2O3 substrate was fixed on a heating table with silver paste. After the silver paste was completely dry, the heating table was placed in a vacuum growth chamber of a pulsed laser deposition system.

[0045] (3) Use mechanical pump and molecular pump to pump the background vacuum of the chamber to <10 -5 Pa. Turn on the heater, heat the heating stage to 650°C at a heating rate of 25°C / min and maintain the temperature constant.

[0046] (4) Turn on the flow controller to introduce oxygen into the growth chamber to maintain the background oxygen partial pressure in the chamber at 1 Pa. Set the laser energy to 200 mJ, the number of pulses to 20,000 pulses, and the pulse frequency to 5 Hz.

[0047] (5) After the deposition, the background oxygen partial pressure was maintained at 1 Pa, the heating stage was cooled to 600 °C at a cooling rate of 25 °C / min, and the flow controller was turned on to introduce oxygen into the growth chamber to maintain the background oxygen partial pressure in the chamber at 10 4 Pa, and maintained for 20 min. Then, the heating stage was cooled to 200 °C at a cooling rate of 25 °C / min, and the background pressure in the cavity was restored to 10 -5Pa. The heating stage was taken out to obtain a high-purity Ga2O3 film with a thickness of 200 nm.

[0048] (6) The annealed Ga2O3 film is subjected to a standard photolithography process through a laser direct writing photolithography system to develop a preset interdigitated electrode pattern, wherein the interdigitated electrode pattern has a finger width of 5 μm, a finger spacing of 25 μm, a finger length of 4 mm, and a development depth of 1 μm.

[0049] (7) Then, the positive and negative electrodes were prepared using electron beam evaporation equipment. Titanium was first plated. The background vacuum of the electron beam evaporation growth chamber was 5×10 -6 Pa, the thickness of the titanium layer is 20nm, and then gold is evaporated to a thickness of 50nm. After the electrode is plated, the organic mask part is washed off with acetone to complete the preparation of the Ga2O3 thin film photodetector.

[0050] Comparative Example 1

[0051] A Ga2O3 thin film active day-blind ultraviolet detector for comparison was prepared in a method substantially the same as in Example 1, except that after the deposition in step (5) was completed, the background oxygen partial pressure was maintained at 1 Pa, the heating stage was directly cooled to 200°C at a cooling rate of 25°C / min, and then taken out, and steps (6) and (7) remained unchanged.

[0052] Comparative Example 2

[0053] A Ga2O3 thin film active day-blind ultraviolet detector for comparison is prepared in a method substantially the same as in Example 1, except that, when developing the preset interdigitated electrode pattern in step (6), the finger width in the interdigitated electrode pattern is 150 μm, the finger spacing is 200 μm, and the finger length is 2.5 mm, and step (7) remains unchanged.

[0054] Figure 1 A simplified schematic diagram of the front-view structure used in the embodiments and comparative examples of the Ga2O3 thin film active day-blind ultraviolet photodetector of the present invention is given, including an Al2O3 substrate, a Ga2O3 thin film grown on the Al2O3 substrate, and positive and negative electrodes arranged on the Ga2O3 thin film. The Ga2O3 thin film is developed to form a preset interdigitated electrode pattern, and a titanium / gold stack is deposited to form positive and negative electrodes.

[0055] Figure 2 Different interdigitated electrode patterns used in Example 1 of the present invention and Comparative Example 2 are given, wherein the colored area is the metal-plated electrode portion, and the middle area is the exposed Ga2O3 thin film photosensitive area. By applying a potential to one of the thicker areas at both ends and grounding the other end, a uniform electric field can be formed between the fingers, causing the photogenerated carriers in the photosensitive area to drift in a directional manner under the action of the electric field, and finally be received by the electrode to form a photocurrent.

[0056] Figure 3 XRD patterns of Ga2O3 films prepared in Example 1 and Comparative Examples 1 and 2 of the present invention are given. The X-ray diffraction data shown in the figure show that the heteroepitaxial film grown on the low-cost sapphire substrate is single-phase, and the (-201) oriented β-Ga2O3 film has a rocking curve with a calculated full width at half maximum (FWHM) of 1.6° for (-201), indicating that they all have high crystallinity. The signals of all comparative examples are basically equivalent to those of the embodiments, indicating that changing the annealing conditions does not significantly affect the crystal structure of the Ga2O3 film.

[0057] Figure 4 The current-voltage (IV) characteristic curves of the Ga2O3 thin film solar-blind ultraviolet photodetectors prepared in Example 1 of the present invention and Comparative Examples 1 and 2 are given. The bias voltage applied during the test is 20V, wherein the dark current is obtained by testing in a dark box environment, and the photocurrent is obtained by irradiating a xenon lamp light source with 240nm solar-blind ultraviolet light separated by a monochromator. The device prepared in Example 1 of the present invention has a dark current as low as ~50pA, very low background noise, a photocurrent of up to an ultra-high 6mA, and an on / off ratio of more than 10 8 , the detection rate can reach 1.9×10 16 cm·Hz 0.5 ·W -1 According to Comparative Examples 1 and 2, it is found that the photocurrent of Comparative Example 1, which does not implement the operation of Example 1, exceeds 60 mA and the dark current exceeds 2 mA. Although the photocurrent is larger, the on-off ratio is significantly smaller, and the corresponding detection rate is also significantly reduced, which is only 2.9×10 13 cm·Hz 0.5 ·W -1 The corresponding annealing process will effectively improve the detector's detection rate index. In Comparative Example 2, which does not implement the operation of Example 1, the photocurrent is only ~45μA, and the on / off ratio exceeds 10 5 , the detection rate is only 2.3×10 14 cm·Hz 0.5 ·W -1 In this comparative example, it is obvious that the photocurrent is significantly smaller, which affects the detection rate index. In summary, only by completing the specific operations of Example 1 can a Ga2O3 thin film solar-blind ultraviolet photodetector with both ultra-large photocurrent and ultra-high detection rate index be obtained.

[0058] Figure 5The photocurrent variation curve obtained by irradiating the Ga2O3 thin film solar-blind ultraviolet photodetector prepared by Example 1 of the present invention and Comparative Examples 1 and 2 with 240nm solar-blind ultraviolet light over time is shown in the figure, and the external bias voltage of the test is 20V. The time taken for the device to rise (fall) from 10% (90%) of the stable photocurrent value to 10% (90%) is defined as the response speed. The calculation shows that the rise time of the device of Example 1 and Comparative Example 2 obtained by the present invention is 1.1s, and the fall time is 0.1s. The rise time of the device of Comparative Example 1 is 1s, and the fall time exceeds 10s, which is not conducive to the application of the device. Example 1 can stably output a photocurrent of 6mA under continuous switching, while the device of Comparative Example 2 can only stably output a photocurrent of ~45μA. In summary, the device prepared by Example 1 of the present invention has a faster response speed, a larger photocurrent output, and stable device operation.

[0059] Figure 6 The valence band cutoff edge of the high-resolution X-ray photoelectron spectrum of the Ga2O3 film corresponding to Example 1 of the present invention and Comparative Example 1 is given to determine the change of the valence band binding energy under different annealing conditions. Through linear extrapolation, it can be determined that the valence band top binding energy of the Ga2O3 film sample prepared in Example 1 is 4.42eV, and the valence band top binding energy of the Ga2O3 film sample prepared in Comparative Example 1 is 4.54eV, and the difference between the two is 0.12eV. The smaller the binding energy, the lower the carrier concentration near the surface of the sample, and it can be inferred that the dark current is lower, thus forming a premise for a higher detection rate. From the results, it can be seen that the Ga2O3 film day-blind ultraviolet photodetector obtained in Example 1 has a very low intrinsic carrier concentration while having high photoconductivity, and has device performance indicators of ultra-large photocurrent and ultra-high detection rate, which meets the detection requirements of semiconductor deep ultraviolet optoelectronic devices and has great application prospects in this field.

[0060] The above embodiments are only used to further illustrate a high-performance Ga2O3 thin film active day-blind ultraviolet detector and a preparation method thereof of the present invention, but the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a high-performance Ga2O3 thin film active solar-blind ultraviolet detector, characterized in that The following steps are involved: (1) Preparation of high-purity Ga2O3 polycrystalline target; (2) Under oxygen partial pressure conditions, using the high-purity Ga2O3 polycrystalline target material, a Ga2O3 thin film is grown on an Al2O3 substrate using a pulsed laser deposition technique, wherein the pulsed laser deposition method specifically comprises: a. Fix the Al2O3 substrate on a heating platform, and heat the platform at a rate of 10-25°C / min until the temperature is maintained constant at 500-750°C; b. PLD growth chamber background vacuum degree <10 -5 Pa, oxygen is introduced into the growth chamber, and the background oxygen partial pressure in the chamber is maintained at 0.133-13.33 Pa; c. Set the laser output energy to 150-400 mJ, the number of pulses to 5000-40000, the pulse frequency to 1-20 Hz, and the laser energy density to 1-2 J / cm 2 , growing a Ga2O3 film on an Al2O3 substrate, wherein the thickness of the grown Ga2O3 film is 0.1-0.4 μm; (3) After the growth is completed, the Ga2O3 film is subjected to in-situ high temperature and high oxygen pressure annealing in the PLD growth chamber. The annealing temperature is 500-700 °C, and the background oxygen partial pressure in the chamber is maintained at 10 4 -10 5 Pa, annealing time 1-60min, heating stage cooling rate 5-25℃ / min; (4) Developing a preset electrode pattern on the annealed Ga2O3 film, and depositing metal to prepare positive and negative electrodes, wherein the preset electrode pattern is developed by a laser direct writing process, and the developed preset electrode pattern is a forked-finger electrode, wherein the finger width is 5-100 μm, the finger spacing is 5-100 μm, and the finger length is 2-4.5 mm.

2. The preparation method according to claim 1, characterized in that: In step (1), a polyvinyl alcohol aqueous solution and a Ga2O3 polycrystalline powder are mixed, ground evenly, and poured into an isostatic pressing mold, and a pressure of 5-15 MPa is applied to press the mixture into a flaky solid. The flaky solid is calcined in air at a heating rate of 5-20°C / min, a solid phase sintering temperature of 1250-1450°C, a sintering time of 12-36h, and a cooling rate of 2-10°C / min to obtain a high-purity Ga2O3 polycrystalline target.

3. The preparation method according to claim 1, characterized in that: In step (2), the Al2O3 substrate is a single-sided / double-sided polished single crystal substrate, the polished surface is the c-plane, and the surface roughness is <0.1nm; the size of the Al2O3 substrate is 5-10 mm×5-10 mm×0.4-0.6 mm.

4. The preparation method according to claim 1, characterized in that: In step (4), the material of the positive and negative electrodes is titanium / gold stacked, prepared by electron beam evaporation process, and the background vacuum of the growth chamber of the electron beam evaporation process is 10 -7 -10 -6 Pa, the thickness of the titanium layer is 5-50 nm, and the thickness of the gold layer is 20-100 nm.

5. A Ga2O3 thin film active solar-blind ultraviolet detector prepared according to the preparation method according to any one of claims 1 to 4, characterized in that: It includes an Al2O3 substrate, a Ga2O3 film grown on the Al2O3 substrate, and positive and negative electrodes arranged on the Ga2O3 film. The thickness of the Ga2O3 film is 0.1-0.4 μm. The Ga2O3 film is developed to form a preset interdigitated electrode pattern, wherein the finger width is 5-100 μm, the finger spacing is 5-100 μm, and the finger length is 2-4.5 mm.

Images