METAL-OXIDE-SEMICONDUCTOR STRUCTURES ON GERMANIUM BORON DOPED SILICON

Metal-oxide-semiconductor (MOS) capacitors were fabricated on germanium/boron (Ge/B) doped silicon substrates. Typical fixed charge and interface state densities were found to be 5×1010 cm -2 and 5×1010 eV-1 cm-2, respectively. Germanium counterdoping in the boron-doped silicon does not appear to degrade the interfacial properties of MOS structures. Avalanche electron injection produces a slight increase in interface state density, a reduction in inversion capacitance due to deactivation of boron, and a shift in flatband voltage. However, turnaround in flatband voltage shift is not observed due either to enhanced electron trapping or a reduction in donorlike interface state generation. Three different methods used to determine the electron barrier energy height at the silicon dioxide-Ge/B silicon interface yielded a value of 2.2 eV. This smaller barrier height is attributed to the smaller electron affinity of Ge/B-doped silicon.