Surface Plasmon-Enhanced GaN Metal–Insulator–Semiconductor Ultraviolet Detectors With Ag Nanoislands Embedded in a Silicon Dioxide Gate Layer

GaN metal-insulator-semiconductor ultraviolet (UV) photodetectors (PDs) with silver (Ag) nanoislands on a silicon dioxide (SiO₂) gate layer were fabricated and characterized. Samples with different Ag mass thickness values were prepared on SiO₂/sapphire template substrates and characterized by transmission spectral to confirm the surface plasmon resonance (SPR) effect. By examining the transmission spectra of Ag nanoislands on the SiO₂/sapphire substrates, two transmission dips were observed in each spectrum. The transmission dip in the blue region was more significant than that in the UV region, but visible light with photon energy less than the bandgap of GaN was not absorbed to generate significant response. By introducing the Ag nanoislands, the UV-to-visible rejection ratio (R_UV/vis) of spectral responsivity was at least ten times higher than those of PDs without Ag nanoislands. The R_UV/vis enhancement was mainly due to the increase in UV response caused by SPR at approximately 360 nm induced by Ag nanoislands to enhance UV-light absorption.