Analytical electron microscopy of (2 ¯ 01) β -Ga2O3/SiO2and (2 ¯ 01) β -Ga2O3/Al2O3interface structures in MOS capacitors

Abstract

Chemical and structural features of (2 ¯ 01) β-Ga 2O 3 interfaces with SiO 2 and Al 2O 3 gate oxides formed by low pressure chemical vapor deposition (SiO 2) and atomic layer deposition (Al 2O 3) 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 Ga 2O 3/SiO 2 interface revealed nanoscale interfacial roughness increasing with higher post-deposition annealing temperature. At the Ga 2O 3/Al 2O 3 interface, a few nanometers of epitaxial Al 2O 3 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-Ga 2O 3 metal-oxide-semiconductor devices.