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

Ultraviolet Al0.17Ga0.83N/GaN-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 A/W, corresponding to a quantum gain of 5.47 x 10(3). 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 x 10(5) and 1 x 10(4) for the long-wavelength side (340/400 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. (c) 2008 American Institute of Physics.