Fabrication and characterization of germanium n-MOS and n-MOSFET with thermally oxidized yttrium gate insulator: Formation of underlying germanium oxide and its electrical characteristics. (1st August 2023) - Wen, Wei-Chen
Abstract: A high-quality insulating film on germanium is essential for germanium applications. In this study, we oxidized metal yttrium at 500–550 °C to generate an yttrium oxide (Y-oxide) layer on germanium. According to transmission electron microscopy images, Y-oxide comprised three layers, which were Y2 O3, YGeO3, and GeOx from the top side. n-Type metal-oxide-semiconductor (n-MOS) capacitors and n-type MOS field-effect transistors (n-MOSFETs) with the Y-oxide gate insulator showed typical electrical characteristics. The n-MOS capacitor with the Y-oxide gate insulator had a lower interface state density ( D it ) and border trap density ( N bt ) than the n-MOS capacitor with a thermally oxidized GeOx insulator, suggesting that defects were terminated by Y atoms in the GeOx layer and GeOx /Ge interface. In contrast, the D it –energy distribution and N bt temperature dependence of the Y-oxide gate insulator were similar to those of the GeOx gate insulator, indicating that the defect signals originated in GeOx underlying YGeO3 . The structural analysis showed that the temperature of metal yttrium oxidation affected only the GeOx thickness. Therefore, adjusting the conditions of metal yttrium oxidation may produce Y-oxidized gate stacks with a thinner GeOx layer or even direct contact of YGeO3 and Ge, which may result in different D it values, N bt values, and N bt –temperature trends.