Low-Dispersion, High-Voltage, Low-Leakage GaN HEMTs on Native GaN Substrates

Abstract

In this paper, the advantages of GaN high electron mobility transistors (HEMTs) grown on native GaN over GaN/Si or GaN/sapphire substrates are investigated and correlated with epitaxial material quality. Transmission electron microscopy plan-view and cross-sectional analyses of GaN/GaN reveal dislocation densities below ${1} \times {10}^{{6}}$ cm−2, which is at least three orders of magnitude lower than that of GaN/Si or GaN/sapphire. In the case of GaN/Si, the dislocations not only originate from the substrate/nucleation layer interface, but also the strain relief and isolation buffer stacks are main contributors to the dislocation density. GaN/GaN HEMTs show superior electrical and thermal performance and feature three orders of magnitude lower OFF-state leakage. The current collapse (also referred to as current dispersion or $R_{ \mathrm{\scriptscriptstyle ON}}$ -increase) after stress bias is less than 15% compared with 50% in the case of GaN/Si. A 2% drop of the ON-state current due to self-heating in dc operation when compared with 13% and 16% for GaN/Si and GaN/sapphire, respectively. The GaN/Si thermal performance becomes comparable to that of GaN/GaN only after substrate removal. Therefore, GaN/GaN provides high ON-state current, low OFF-state leakage current, minimal current collapse, and enhanced thermal power dissipation capability at the same time, which can directly be correlated with the absence of high dislocation density.