Analytical electron microscopy of (201) β-Ga_2O_3/SiO_2 and (201) β-Ga_2O_3/Al_2O_3 interface structures in MOS capacitors

摘要

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.