Enhanced Light Emission from N-Doped Ge Microdisks by Thermal Oxidation

Abstract

We have observed enhanced direct band-gap light emission from highly n-doped germanium microdisks on silicon by thermal oxidation. The microdisks are fabricated by electron beam lithography and dry etching. Thermal oxidation is found to be able to passivate the dry-etched sidewalls, thus efficiently suppress the nonradiative recombination related to the sidewalls and enhance the emission intensity. The enhancement factor increases as the disk size decreases, approaching about 3.42 for microdisks with radii of 0.8 µm. Investigation of light emission dependence on the thermal oxidation temperature from 100 to 550 °C show that there is a trade-off between reduction of doping concentration caused by dopant out-diffusion and surface passivation effect. These results indicate that thermal oxidation is a highly promising yet very simple way to fabricate high quality germanium microresonators, thus to realize low-threshold germanium lasers monolithically integrated on Si substrates.