AlGaN-based structures on sapphire for visible blind Schottky-barrier UV photodetectors: toward high-performance device applications

Abstract

Al x Ga 1-x N material system, whose bandgap lies in the 3.42 - 6.2 eV range, is extremely interesting for visible and solar blind UV photodetector applications. This paper describes the device performances of Al x Ga 1-x N (x=0-35%) UV Schottky barrier photodetectors for visible-blind applications grown on c-oriented sapphire, with a detailed balance with the basic materials properties. Conventional low temperature grown AlN or GaN were used in all applications. High quality Schottky barrier photodiodes made of Epitaxial Lateral Overgrown (ELOG) GaN are also presented. All Schottky barrier devices show a fast time response (15 ns for Al 0.22 Ga 0.78 N(Si) photodiodes grown on AlN nucleation layers), a high UV-visible rejection factor (>3 orders of magnitude for AlGaN(Si) photodiodes grown on GaN or AlN nucleation layers, and rising up to 5 orders of magnitude for the GaN ELOG material), and high absolute values of above bandgap reponsivities (up to 130 mA/W for GaN ELOG materials). A new application of AlGaN UV Schottky barrier photodetectors to monitor the biological action of the solar UV radiation, as well as the device performance of high quality GaN and AlGaN Metal Semiconductor Metal with cutoff wavelengths as short as 310 nm, are described in detail.