Fig. 1. Crystal structure of β-Ga₂O3[45]

Fig. 2. Morphology of β-Ga₂O₃ nanowires and photoelectric response of device^[152]. (a) SEM image of the β-Ga₂O₃ nanowires grown on the Au-coated silicon substrate; (b) I-V curves of the detector under 254 nm light illumination and dark condition (inset); (c) time response of the device to light at 254 nm; (d) enlargement of the rising and falling edges for the light “on” and “off” for the first time

Fig. 3. Structural characteristics of Ga₂O₃ and performance of the device^[135]. (a) X-ray diffraction (XRD) pattern of the α-Ga₂O₃ grown on the sapphire substrate. The inset shows the schematic of the device structure; (b) spectral responsivity of the photodetectors at 5 V bias; (c) I-V characteristics of the devices in the dark (black line) and under illumination

Fig. 4. Structure and electrical characteristics of the device based on β-Ga₂O₃ flake^[72]. (a) Schematic of the preparation process of the β-Ga₂O₃ flake based solar-blind photodetector; (b) optical microscopy image of the device; (c) typical electrical properties of the β-Ga₂O₃ flake based FETs; (d) time-dependent photoresponse of the photodetector under illumination at different wavelengths; (e) responsivity as a function of wavelength

Fig. 5. Ga₂O₃ photodetector and its performance test. (a) Fabrication process of photodetector^[142]; (b) current-voltage (I-V) characteristics of photodetector. Filled and hollow dots represent current in the dark condition and 250 nm-light irradiationv, respectively^[142]; (c) responsivity and photocurrent response of the photodetector at reverse bias of 10 V^[142]; (d) photograph of the flame detector^[162]; (e) transient response of the detector^[162]; (f) signal from the flame detection system^[162]

Fig. 6. Performance of the Ga₂O₃ Schottky photodiode^[18]. (a) Dark I-V characteristics of the Au-Ga₂O₃ Schottky photodiode annealed at various temperatures; (b) spectral response of the device before and after annealing

Fig. 7. Crystal wafer of Ga₂O₃ and time response of the device^[163]. (a)(b) Epitaxial wafer and AFM image of the Ga₂O₃; (c) time response of the photodetector with the β-Ga₂O₃ MSM structure

Fig. 8. Configuration and its photoresponse of the narrow-band detector based on β-Ga₂O₃ single crystal^[166]. (a) AFM image of the (100) β-Ga₂O₃ single crystal; (b) configuration of the narrow-band detector combined with an orthogonally aligned filter; (c) photoresponsivity as a function of chopper modulation frequency; (d) fitting of waveform curves of transient photoresponse measured at 150 Hz

Fig. 9. Schematic diagram and measured I-V characteristic curves of the fabricated β-Ga₂O₃ photodetector. (a) Schematic diagram of the fabricated β-Ga₂O₃ photodetector; (b) measured I-V characteristic curves

Fig. 10. Structural schematic of the device and its spectral response ^[168]. (a) Structural schematic of β-Ga₂O₃ single-crystal photodiode; (b) spectral response of Ga₂O₃ photodiodes with and without a cap layer at reverse and forward biases of 3 V

Fig. 11. PL spectra of Ga₂O₃ films. (a) NIR PL spectra of Er∶Ga₂O₃ films with different concentrations^[171]; (b) PL spectra of Ce∶Ga₂O₃ films with different doping concentrations^[174]

Fig. 12. Electrical characteristics and spectral response of Ga₂O₃ solar-blind photodetectors. (a) I-V characteristics of the annealed β-Ga₂O₃ thin film at 800 ℃^[184]; (b) I-V curves of the MSM ε-Ga₂O₃ photodetector in the dark at variable temperatures^[136]; (c) R and D^* as functions of the wavelength of the MSM ε-Ga₂O₃ photodetector at a bias of 6 V^[136]; (d) magnified fall edge of the I-t characteristic curves^[136]

Fig. 13. I-V characteristics and spectral response of the device. (a) Current-voltage characteristics for various UV-light illumination intensities^[208]; (b) schematic diagram of the APD^[150]; (c) I-V characteristics of the device^[150]; (d) spectral response of the device at -6 V bias^[150]

Fig. 14. Principle of photoresponse and spectral response of the device. (a) Normalized transient photoresponse characteristics at room temperature^[212]; (b) photoconductive gain and avalanche multiplication gain for the device as functions of applied bias^[212]; (c) energy band diagram at high reverse bias under 254 nm illumination^[212]; (d) HRTEM images acquired from sample^[214]; (e) pulse photocurrent as a function of the time of the Ga₂O₃ thin-film photodetectors^[214]; (f) spectral responsivity of the device at bias of 5 V^[214]

Fig. 15. Fabrication process and photoelectric properties of β-Ga₂O₃ nanowires photodiode^[145]. (a) Schematic illustration of the fabrication of β-Ga₂O₃ nanowires array film and its vertical Schottky photodiode; (b) I-V characteristics of device in dark and under the illumination at 254 nm; (c) spectral response of the device

Fig. 16. Imaging and photoresponse of β-Ga₂O₃ photodetectors. (a) Spectral response of the diamond/β-Ga₂O₃ photodetector at 0 V bias^[148]; (b) image of the object with letters “UV” on a black paper and the image obtained from the imaging system^[148]; (c) I-V curves of the MoS₂/β-Ga₂O₃ heterojunction device^[151]; (d) time-dependent photoresponse of the device^[151]; (e) typical PEC system built for evaluating the photoresponse behaviors of the α-Ga₂O₃ NA/Cu₂O photodetector^[227]; (f) transient response current for the photodetector at zero bias^[227]

Fig. 17. Spectral response and impulse response of β-Ga₂O₃ photodetector. (a) Photocurrent and power density as functions of excitation wavelength^[230]; (b) spectral response of reference β-Ga₂O₃ photodetector at 1V bias and β-Ga₂O₃/PANI at zero bias^[230]; (c) spectral responsivity and corresponding absorption spectrum of the photodetector^[233]; (d) time response of the photodetector for the 248nm pulse laser without bias^[233]

Table 1. Summary of basic parameters of Ga₂O₃ polycrystalline^[15,42]

Table 2. Properties of β-Ga₂O₃ and other more commonly used semiconductors^[55]

Table 3. Summary of parameters of Ga₂O₃ thin films based photodetectors