Influence of sapphire substrate thickness on the characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors

Abstract

A standard AlGaN/AlN/GaN heterostructure field-effect transistor (HFET) on a 420μm thick sapphire substrate was fabricated, and then the sapphire substrate was thinned to several different thicknesses by grinding. When the remaining substrate thickness is more than 170μm, the characteristics of the substrate thinned AlGaN/AlN/GaN HFET are almost the same as the original device. However, when the substrate thickness is less than 170μm, the drain-to-source current, the threshold voltage, and the electron mobility of the two-dimensional electron gas (2DEG) in the channel are varied compared to the original one. It is attributed to the shrinkage of the GaN layer with the reduction of substrate thickness, which induces the decrease of both the 2DEG sheet density and the polarization charge sheet density, and a possible increase of dislocation scattering and the reduction of polarization Coulomb field scattering.