Effect of special gate metals on polarization Coulomb field scattering in AlGaN/GaN high electron mobility transistors

Abstract

AlGaN/GaN HEMTs were fabricated using two special gate metals, Hf and W, as gate Schottky contact materials. Based on the measured I-V data and two-dimensional scattering theory, the electron mobility corresponding to polarization Coulomb field (PCF) scattering and other scattering mechanisms was calculated. The additional polarization charge (APC) due to the inverse piezoelectric effect (IPE) was also calculated. The differences in the effects of two special gate metals, Hf and W, on the PCF scattering intensity are analyzed from the aspects of Young’s modulus and work function of the metal. It was found that compared with W metal, Hf metal has a smaller Young’s modulus and weaker ability to resist elastic deformation, which makes the AlGaN barrier layer in contact with Hf more easily deformed due to IPE, resulting in more APC under the Hf metal Schottky contact. On the other hand, Hf has a smaller work function compared to W metal, so the 2DEG density is higher. The influence of special gate metals Hf and W on the PCF scattering intensity is the result of the combined effect of these two factors. This study is of great significance for understanding the electron transport mechanisms of AlGaN/GaN HEMTs with special gate metals such as Hf and W, and for further improving the electrical performance and stability of the devices.