Visible room-temperature photoluminescence from oxidized germanium

Strong visible photoluminescence (PL) has been observed at room temperature from oxidized amorphous hydrogenated germanium. Excitation by the 488 nm line from an argon ion laser yields a broad PL peak at 2.2 eV with a full-width-half-maximum (FWHM) of 0.5 eV. The luminescence intensity depends on the morphology of the untreated a-Ge:H film produced by plasma enhanced chemical vapor deposition (PECVD). Films ranging from ones with coarse columnar microstructure and poor photoelectronic properties to ones with microstructure similar to that of device-quality a-Si:H were intentionally chosen. After oxidation in air at 500°C for one hour, the films with coarse microstructure yield the highest luminescence intensity, comparable to that from porous silicon, while the best films with minimum microstructure yield orders of magnitude lower intensity. Removing the germanium oxide from the film reduces the luminescence intensity. Powder-like Ge was also produced by thermal evaporation in 0.3 Torr of argon. After annealing in air at 500°C for two hours strong PL is observed with peak position and spectral width similar to those from oxidized poor PECVD a-Ge:H and commercial GeO2.