TCAD-Based Investigation of a-GaOx UV Phototransistors

Amorphous gallium oxide thin-film transistor photodetectors are promising for ultraviolet detection because of their wide bandgap and low dark current. Magnetron sputtering is compatible with low-temperature processing, but device performance is sensitive to sputtering conditions. Poor parameter choices can introduce oxygen vacancies and interface charges, degrading optoelectronic performance. Here, a three-factor, three-level orthogonal design is used to vary sputtering power, Ar/O2 flow ratio, and film thickness. Nine device sets are fabricated and compared based on transfer characteristics and transient photocurrent–time (I-t) responses measured at a wavelength of 254 nm, with clear differences observed among process combinations. To identify the origin of these differences, representative samples with significant responsivity variations were modeled using TCAD. By fitting the simulated I-t curves to measured transients, the interface fixed charge density and defect-state densities were extracted, and the photon absorption distribution of different samples was analyzed. This analysis, from both defect and UV absorption perspectives, revealed the reasons for the differences in responsivity. The absorption coefficients at 254 nm measured by ellipsometry for the two samples were also compared, and the absorption trends observed in both the simulation and ellipsometry were consistent, confirming the accuracy of the simulation results. This work presents an integrated experimental and TCAD approach for process optimization and mechanistic analysis of a-GaOx TFT-PDs.