Analytical electron microscopy of (2¯01) β-Ga2O3/SiO2 and (2¯01) β-Ga2O3/Al2O3 interface structures in MOS capacitors

Abstract

Chemical and structural features of (2¯01) β-Ga2O3 interfaces with SiO2 and Al2O3 gate oxides formed by low pressure chemical vapor deposition (SiO2) and atomic layer deposition (Al2O3) were investigated by analytical electron microscopy in order to identify features that may explain electrical properties recently observed in the same samples. Cross-sectional transmission electron microscopy at the Ga2O3/SiO2 interface revealed nanoscale interfacial roughness increasing with higher post-deposition annealing temperature. At the Ga2O3/Al2O3 interface, a few nanometers of epitaxial Al2O3 was seen prior to the complete crystallization of the gate oxide film after tens of seconds exposure to the electron beam. Multivariate statistical analysis of electron energy loss spectroscopy signals showed evidence of interdiffusion between Al and Ga into the substrate and gate oxide, respectively, which was more pronounced following post-deposition annealing at elevated temperatures. The interdiffusion provides an explanation for the increased interface trap density previously reported in these devices. These results identify issues with the processing methods of the gate oxide affecting the performance and reliability of β-Ga2O3 metal–oxide–semiconductor devices.