Properties of InGaN deposited on glass at low temperature

Abstract

We have investigated the properties of InGaN grown at low temperature on glass substrates by a plasma enhanced MBE process. The goal of this study was to evaluate the potential of InGaN as an oxide-free, transparent conductor material which could be deposited at or slightly above room temperature with minimal interaction or damage to the underlying material. InxGa 1-xN films deposited on glass, even without substrate heating, are highly crystalline, but the crystallinity as measured by x-ray degrades at x < 0.5. The microstructure observed by TEM of InGaN films deposited on unheated substrates is highly columnar, with typical column widths of ∼10 nm. The optical absorption spectra of InGaN/glass have a distinct absorption edge at the bandgap, but also high background absorption in the bandgap. In xGa1-xN grown on glass (x > 0.5) is conductive due to its high electron concentration. InN electron Hall mobilities > 20 cm 2Ns when grown at 400°C, and ∼ 7 cm2Ns on unheated substrates were obtained. The addition of GaN degraded the electrical properties of the films to a greater extent than it improved the transparency. As a result, the best transparent conductor films were pure InN which, when deposited at 400°C, were half as transparent in the green as an indium tin oxide film having the same sheet resistance.