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

Abstract

Ultraviolet ${\mathrm{Al}}_{0.17}{\mathrm{Ga}}_{0.83}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ -based heterojunction phototransistors (HPTs) grown by metal-organic vapor-phase epitaxy were demonstrated. The HPTs showed a bandpass spectral responsivity ranging from $280\text{to}390\mathrm{nm}$ . With a bias voltage of $6\mathrm{V}$ , the responsivity at an incident of $340\mathrm{nm}$ was as high as $1500\mathrm{A}∕\mathrm{W}$ , corresponding to a quantum gain of $5.47\times {10}^3$ . In contrast to GaN-based photoconductors, the HPTs also featured high contrast in spectral response. With a bias voltage of $3\mathrm{V}$ , the spectral response showed high rejection ratios of approximately $4\times {10}^5$ and $1\times {10}^4$ for the long-wavelength side $(340∕400\mathrm{nm})$ 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.