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Xiao Y, Yang S S, Cheng L Y, et al. Research progress of solar-blind UV photodetectors based on amorphous gallium oxide[J]. Opto-Electron Eng, 2023, 50(6): 230005. doi: 10.12086/oee.2023.230005
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Research progress of solar-blind UV photodetectors based on amorphous gallium oxide
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Abstract
The Solar-blind UV detection has wide application scenarios and unique market values in the civil and military fields, such as space security communication, ozone hole detection, missile attack warning and so on. Gallium oxide (Ga2O3) has an extremely wide band gap (4.4-5.3 eV), almost covering the entire solar-blind UV region, and is considered as one of the most promising materials for the preparation of solar-blind UV photodetectors. Compared with single crystal or epitaxy materials, amorphous gallium oxide (a-Ga2O3) has a lower deposition temperature, a relatively simple preparation process, and a much wider range of applicable substrates. Therefore, it has become a new research hot spot in the field of the Ga2O3 solar-blind UV detection in most recent years. In this paper, the basic characteristics and most common preparation methods of a-Ga2O3 are introduced firstly, and then the research progress and present situations of the a-Ga2O3-based solar-blind UV photodetector are introduced in details from the perspective of device structures. At present, a-Ga2O3 based solar-blind UV photodetectors are mainly divided into MSM, junction, TFT and array types. By the optimization of device structures, the photodetection performance has been significantly improved. MSM device is the most widely used because of its simple structure and high responsivity. By constructing Schottky junction or heterojunction, the junction-type devices own the characteristics of fast response speed, low dark current, and self-power supply. TFT devices can suppress the dark current, amplify the gain and improve the recovery speed by applying gate voltage. Array-type devices can be used for large-area imaging. Finally, the future development trends of the a-Ga2O3 solar-blind UV photodetector are summarized. -
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References
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Overview
Due to the absorption of ozone in the stratosphere, ultraviolet radiation of 200-280 nm barely reaches the ground, so this band is usually called as the solar-blind region. The ultraviolet detector working in the solar-blind region naturally has the advantages of low background noise, high anti-interference ability, and all-weather operation. Moreover, due to the absorption of the atmosphere, the transmission distance of communication signal in the solar-blind region is controllable, and the risk of eavesdropping is low. Therefore, the solar-blind UV photodetector has very important application value in the fields of UV monitoring, space safety communication, and optical imaging.
Gallium oxide (Ga2O3) has an extremely wide band gap (4.4-5.3 eV), almost covering the entire solar-blind UV region, and is considered as one of the most ideal materials for the preparation of solar-blind UV photodetectors. Compared with the single crystal or epitaxy materials, amorphous gallium oxide (a-Ga2O3) thin film has lower preparation temperature, more flexible substrate selection, and better uniformity. Therefore, it has become a new research hotspot in the field of Ga2O3 solar-blind UV detection in most recent years.
The a-Ga2O3-based solar-blind UV photodetectors are mainly divided into MSM, junction, TFT and array types. The MSM device is based on two back-to-back Schottky diodes, often with interfingered metal electrodes. It is the most widely used because of its simple structure and high responsivity. Junction-type devices are mainly constructed in two ways, one is to form a heterojunction with another semiconductor, and the other is to form a Schottky junction with metal. Under the influence of built-in electric field, the photogenerated electron-hole pairs are separated rapidly, which guarantees the device a faster response speed. Meanwhile, dark current can also be suppressed due to the existence of barrier at the interface. The TFT device is added with a control gate on the basis of the structure of the two-terminal device. The suitable selection of gate voltage can make carriers accumulate in the channel, thus amplifying the gain. In addition, the application of gate voltage pulse might accelerate the non-equilibrium carriers’ recombination and improve the recovery speed of the device. Array devices construct several detector units into a large area array to realize solar-blind UV imaging.
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Xiao Y, Yang S S, Cheng L Y, et al. Research progress of solar-blind UV photodetectors based on amorphous gallium oxide[J]. Opto-Electron Eng, 2023, 50(6): 230005. doi: 10.12086/oee.2023.230005
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Figure 1.
Crystal structures of amorphous, mixed, and crystalline Ga2O3[36]
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Figure 2.
(a) Schematic diagram and photograph of the gallium-oxide MSM photodetectors; (b) TEM images of the gallium oxide films deposited by RFMS and MBE; (c) I-V characteristics and (d) transient response of the MSM photodetectors based on a-Ga2O3 and β-Ga2O3 thin films[30]
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Figure 3.
(a) I-V curves in dark and (b) under UV 254 nm light illumination; (c) Temporal response tests of the PDs with KrF pulse laser illumination at 10 V bias[32]
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Figure 4.
(a) I−V characteristics and (b) I-T characteristics of the devices fabricated at various growth temperatures[58]; (c) Responsive characteristics and (d) I-T characteristics of the devices fabricated at various growth temperatures[59]
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Figure 5.
(a) Film roughness fitting results from XRR and AFM; (b) Top: fitting curve of film density from SE and XRR. Medium: the variation trend of the a-GaOx bandgap. Bottom: Variation trend of Ga/O ratio based on XPS analysis[60]
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Figure 6.
(a) The I-V characteristics of the detectors based on a-GaOx film and Mg: GaOx film under dark and 255 nm illumination conditions; (b) Time-dependent photocurrent of devices based on different amorphous films[42]
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Figure 7.
(a) Schematic illustration of the flexible photodetector; (b) SEM image of the Ag NWs electrode; (c) Variations in photocurrent of the device[68]
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Figure 8.
(a) Schematic of the a-Ga2O3/ITO prototype device; (b) I−V characteristics of the devices fabricated at various growth temperatures in dark; (c) Schematic of band alignment of the Ga2O3/ITO heterojunction; (d) The I–T characteristic of the detector[70]
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Figure 9.
(a) Schematic diagram of the a-Ga2O3/p-Si heterojunctions photodetector, the enlarged view shows a cross-sectional view of the device; (b) The I–T characteristic of the detector without oxygen plasma treatment; (c) The I–T characteristic of the detector with oxygen plasma treatment[71]
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Figure 10.
(a) Schematic diagram of the fabrication steps of 3D urchin-like VO-Ga2O3/ZnO; (b) The I–T characteristic of the detector[72]
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Figure 11.
(a) Schematic structure of the GR/a-Ga2O3 flexible PD; (b) Schematics of the band diagram and the carrier transport mechanism of the GR/a-Ga2O3 under light irradiation[73]
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Figure 12.
(a) Cross-section image of the as-fabricated GaOx phototransistor; (b) IDS-VG transfer characteristics measured at different VDS in the dark and under 254 nm light illumination[74]
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Figure 13.
(a) IDS-VGS curves and IGS-VGS curves of the a-Ga2O3 TFTs with and without channel patterned; (b) Suppression of the PPC with a positive gate pulse[75]
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Figure 14.
(a) The photomask with letters “CAS” and (b) the image obtained from the imaging system[74]; (c) Schematic diagram of the optical imaging system and (d) the obtained "C" pattern [82]; (e) Schematic diagram of the PDs array and (f) the obtained "E" pattern [83]
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Figure 15.
(a) Schematic of the 3D Ga2O3 photodetector array, photograph and microscope image of an individual photodetector cell; (b) I-T curves of the photodetector at 15 V without bending and after 500 and 2000 bending cycles[80]
- Figure .
