Controlling SWIR photosensitivity limit by composition engineering: from Ge to GeSi nanocrystals embedded in TiO2

Abstract

The VIS-SWIR photosensing properties of Ge and GeSi NCs embedded in TiO2 films are investigated. For this, we deposit GeTiO2 and GeSiTiO2 films, respectively by magnetron sputtering and then we perform rapid thermal annealing (RTA) for Ge NCs and GeSi NCs formation, respectively. Raman studies and spectral photocurrent measurements were carried out. Ge NCs formation is evidenced in the Raman spectrum of GeTiO2 film annealed at 550 °C. The photocurrent spectra measured on the Ge NCs-TiO2 film present four peaks separated by deconvolution. The broad peaks at ~700, 890, 1010 nm are due to photo-effects in the Ge NCs-TiO2 film. More than that, the photocurrent increases exponentially with the increase of bias voltage. The cut-off wavelength is ~1240 nm. We achieve the extension of the photosensitivity limit to ~1310 nm in GeSi NCs-TiO2 films (800 °C RTA).