Substantial improvement of InGaN/GaN visible-light polarization-induced self-depletion phototransistor by thermally oxidized Al2O3

Atomic layer deposited (ALD) Al2O3 acting as gate dielectric and surface passivation is widely adopted in power electronics but seldom used in optoelectronic fields for its sophisticated and expensive technology. Herein, a simple but efficient Al2O3 passivation is used in the fabrication of InGaN/GaN visible-light (VL) polarization-induced self-depletion field effect phototransistors (FEPTs), for suppressing the surface leakage and recombination. The Al2O3 layer obtained by thermal oxidation (TO) of 2-nm-thick thermally evaporated metal Al shows high electrical insulation and even better passivation effect than the ALD-Al2O3. As a result, the dark current of TO-Al2O3 passivated device decreases by about 2 orders of magnitudes; meanwhile, the photoresponse increases by about 65%. Under a weak VL illumination of 6.8 μW/cm2, the InGaN/GaN FEPT exhibits a large photo-to-dark current ratio of 3.1 × 108 and an ultrahigh shot-noise-limited detectivity of 1.9 × 1018 jones. In addition, the FEPTs exhibit a strong wavelength selectivity with a 600 nm/400 nm spectral response rejection ratio exceeding 5 × 105. All these performances show huge potential in emerging VL applications that are limited by the insufficiencies of current Si photodetectors.