The effects of substrate temperature on the optical properties of Pb1–xSnxTe films formed by molecular beam epitaxy

Abstract

The optical properties are studied of Pb1–xSnxTe films grown using molecular beam epitaxy from a single source of Pb0.8Sn0.2Te on KCl (100) substrates in the temperature range 250 to 350 °C. Pb1–xSnxTe is found to be a direct band gap material with absorption coefficient of the order of 103 cm−1 near and above the fundamental absorption region. The energy gap Eg at room temperature is determined for these films from the IR transmittance and reflectance spectra. The refractive index nr is studied in the spectral range 7.3 to 25.6 μm and its value in the range 7.3 to 11.5 μm for one of the films grown at 325 °C is found to be close to the bulk value. The variation of nr with substrate temperature is reported.