Photoconductivity and Conductivity Processes in Si-Sn Films Grown on Si(100) Substrate at Room Temperature

Abstract

Photoresistors based on amorphous Si-Sn thin films (270-285 nm) with different concentration of tin were studied by spectral measurements of photoconductivity at room temperature and by low-temperature measurements of the Hall effect . Electrical contacts to the Si-Sn film was formed by aluminum layer deposition. When the Al contact is illuminated, the spectral sensitivity of the photoresistor with Sn consentration of 19% extends to 2060 nm due to Schottky barrier influence. It was proved that the Si-Sn alloy film provides photoresponse with cut-off energy of 0.98 eV that is close to the indirect band gap in the Si-Sn film. Three deep acceptor levels with activation energies of 90, 114, and 173 meV were found in the Si-Sn thin film (20% Sn) in the temperature range of 50 – 300 K. Sequential activation of the deep levels and their competition leads to a nonmonotonic change of the Si-Sn film conductivity (0.025 - 5.0 (Ω×cm)-1) and mobility of holes (100 – 500 cm2/(V·s)). The transition to the intrinsic conductivity region of the amorphous Si-Sn film was not observed up to room temperature.