Piezoelectric carrier confinement by lattice mismatch at ZnO/Zn0.6Mg0.4O heterointerface

This paper describes a strong piezoelectric carrier confinement at a ZnO/Zn(0.6)Mg(0.4)O heterointerface grown on an a-plane sapphire substrate by molecular beam epitaxy. A ZnO/Zn(0.6)Mg(0.4)O double-heterojunction structure was grown without intentional doping and the formation of a deep potential well for electrons was confirmed using cathodolumineseence and transmittance spectra. PhotoLuminescence spectra at 4.5 K consisted of an intense near-band-edge emission at 3.359 eV and a broad and weak peak on the low-energy side. The results of Hall effect measurement revealed that the conduction is n-type with a high carrier concentration of similar to1.2 x 10(13) cm(-2). The mobilities are similar to170cm(2)/V(.)s at 300 K and similar to400cm(2) /V(.)s at 77 K without deterioration at lower temperatures; these values are much higher than those of a thick single-layer ZnO film grown on an a-plane sapphire substrate. We attribute these optical and electrical properties to the formation of two-dimensional electron gas at the ZnO/Zn(0.6)Mg(0.4)O heterointerface by the piezoelectric polarization in a strained ZnO well.