Fig. 1. Schematic illustration of the preparation process for the PtNPs@Ga2O3/GaN detector array and the structural diagram of the detector unit.

Fig. 2. Ga2O3 nanorod characterization. (a) SEM image of Ga2O3 nanorods film. (b) SEM image and EDS mapping of a Ga2O3 nanorod. (c) Raman spectrum of Ga2O3 samples. (d) Comprehensive XPS spectrum of the Ga2O3 nanorods. (e) XPS analysis focusing on Ga 2p lines of Ga2O3 nanorods. (f) XRD pattern of Ga2O3 nanorods.

Fig. 3. Modification of PtNPs on the optical and photoelectric properties of Ga2O3 nanorods. (a) SEM image of the PtNPs@Ga2O3 nanorods. (b) Absorption spectra of Ga2O3 nanorods without and with PtNPs deposition. Inset: Tauc plot of absorption curve. (c) Semi-logarithmic I−V curves of MSM devices based on PtNPs-decorated and undecorated Ga2O3 nanorods in darkness and upon 254 nm light illumination. (d) Normalized absorbance spectrum of PtNPs. Inset: SEM image of PtNPs on a quartz substrate. The computed plasmonic mapping outcomes of a PtNP on Ga2O3; (e) |E|2/|E0|2 spatial distribution of the local electric field in the x–y plane, with the electric-field intensity distributed along the x-axis; (f) cross-sectional view of |E|2/|E0|2 in the x–z plane, with the electric-field intensity distributed along the z-axis.

Fig. 4. Photoresponse depiction of the PtNPs@Ga2O3/GaN detector array unit. (a) I−V curve of the Ga2O3/GaN heterojunction unit measured in the dark. (b) Irradiation wavelength-dependent photocurrent obtained at 0 V bias. (c) Light irradiance-dependent I−V curves upon 254 nm light illumination. (d) Light irradiance-dependent I−T curves under 254 nm light exposure at 0 V bias. (e) Device stability tests after 3 months of storage. (f) Energy-band diagram of the device at equilibrium, depicted at 0 V bias.

Fig. 5. Comparison of photodetection performances of the fabricated photodetection devices, in which Ga2O3 nanorods were either uncoated or coated with PtNPs. (a) Semi-logarithmic I−V curves of heterojunction detectors fabricated on account of Ga2O3 nanorods with and without PtNPs modification plotted in darkness and upon 254 nm light illumination. (b) Switching I−T curves of both the detectors under 254 nm light irradiation at 0 V bias. (c) Light irradiance-dependent photocurrents of the detectors when measured at 0 V bias. Light irradiance-dependent (d) R, (e) D∗, and (f) EQE in a self-biasing operation mode.

Fig. 6. Image sensing application of the PtNPs@Ga2O3/GaN detector arrays. (a) Variation of normalized photovoltage intensities with various modulation frequencies. (b) Device’s photoresponse characteristics exposed to pulsed light (254 nm) at the modulation frequencies of 100 and 500 Hz, respectively. (c) Amplification of the photoresponse curve at a modulation frequency of 100 Hz. (d) Diagrammatic representation of the experimental setup employing PtNPs@Ga2O3/GaN detector arrays as sensors for photoimaging measurements. (e) Statistical I−T curves of partial units in the detector array in the dark and upon 254 nm ultraviolet light exposure at 0 V bias. Inset, amplified I−T curves of photocurrent. (f) Images corresponding to optical masks “F,” “P,” “G,” and “A” were acquired from the array detector.

Fig. 7. Photoresponse properties of the pristine Ga2O3/GaN heterojunction detector. (a) Irradiation wavelength-dependent photocurrent obtained at 0 V bias. (b) Light irradiance-dependent I−V curves under 254 nm illumination. (c) Light irradiance-dependent I−T curves under 254 nm light exposure at 0 V bias. Device’s photoresponse characteristics to pulsed light (254 nm) at varying modulation frequencies of (d) 100 Hz and (e) 300 Hz. (f) Amplification of the photoresponse curve at 100 Hz.