High temperature electron transport properties of AlGaN/GaN heterostructures based on unintentionally doped and semi-insulating GaN buffer layer

Abstract

High temperature electron transport properties of Al0.35Ga0.65N/GaN heterostructures grown on unintentionally doped (UID) and semi-insulating (SI) GaN buffer layer (BL) have been investigated. Electron sheet density and electron mobility dependence on temperature have been systematically measured by Hall effect measurement. It is found that the electron mobility of AlGaN/GaN heterostructure is mainly limited by the longitudinal optical (LO) phonon scattering at high temperature. The sheet carrier density of AlGaN/GaN heterostructure based on UID-BL increases gradually with the increase of temperature, while it decreases firstly, and then increases for the sample based on SI-BL. It is indicated by the analysis of the high temperature resistance properties for the corresponding UID-GaN and SI-GaN films, that the effect of the background carrier-limited electron mobility increases gradually for the UID-BL sample, while for the SI-BL sample the electron mobility is mainly limited by the additional dislocation scattering around room temperature but the background carrier limited effect increases after 600 K. This is meaningful for investigating the high temperature property of the devices based on AlGaN/GaN heterostructure. Moreover, the theoretical calculation indicates that, the two dimensional gas (2DEG) has expanded to the AlGaN barrier layer and the deeper position of the GaN buffer layer, and the electron occupation in the first subband decreases to 81% at 700 K.