Highly sensitive radio-frequency UV sensor based on photocapacitive effect in GaN

We demonstrate a novel highly sensitive UV sensor based on RF LC oscillator with an optical frequency modulation due to the photocapacitive effect in an interdigitated aluminum-on-GaN/sapphire structure. In the range from 280 nm to 325 nm, the sensor exhibits extremely high sensitivity of 60 KHz/?W/cm² at low UV powers (?30 ?W). The maximum oscillator frequency shift of 4 MHz was observed at 375 nm corresponding to UV power density of 70 ?W/cm². This is at least two orders of magnitude higher than the values previously reported in literature for GaN-based SAW delay-line oscillators. The spectral response data from LC oscillator have been corroborated with direct measurements of photocapacitance and photoconductance values extracted from S-parameter measurements in both frequency and time domains. This sensor offers advantages of remote wireless signal transmission and high precision in frequency response measurements.