Germanium MOS technology for infra-red detectors

Fabrication of an electrically stable dielectric is a key enabling technology in the production of a Ge detector with enhanced response in the near infra-red spectrum. This work investigates the physical and electrical properties of silicon dioxide (SiO2) dielectrics deposited on Ge substrates. The deposited SiO2 (silox) layers have been densified at 600 and 800 °C. Significant Ge outdiffusion from the substrate into the densifying silox layer has been observed for the 800 °C process, and the diffusivity has been estimated as 1.5×10−4 μm2/min. The C–V characteristics of Ge MOS capacitors incorporating this silox dielectric display the onset of ‘low frequency’ operation at a relatively high frequency of 100 kHz, and the capacitor C–t response suggests that Ge carrier lifetime is much shorter than that measured for Si MOS capacitors. These phenomena are shown to result from the narrow band gap of Ge, and this work therefore emphasises that increased cooling will be required to exploit the infra-red detector properties of a practical Ge device.