Ultraviolet bandpass Al0.17 Ga0.83 NGaN heterojunction phototransitors with high optical gain and high rejection ratio

Ultraviolet Al0.17 Ga0.83 NGaN -based heterojunction phototransistors (HPTs) grown by metal-organic vapor-phase epitaxy were demonstrated. The HPTs showed a bandpass spectral responsivity ranging from 280 to 390 nm. With a bias voltage of 6 V, the responsivity at an incident of 340 nm was as high as 1500 AW, corresponding to a quantum gain of 5.47× 103. In contrast to GaN-based photoconductors, the HPTs also featured high contrast in spectral response. With a bias voltage of 3 V, the spectral response showed high rejection ratios of approximately 4× 105 and 1× 104 for the long-wavelength side (340400 nm) and the short-wavelength side, respectively. The high contrast of spectral response for the long-wavelength side could be due to the long trapping time of holes blocked by the base-emitter heterojunction and the low defect-to-band response that is caused by defect-related gap states.