EFFECT OF SUBSTRATE TEMPERATURE ON THE GALVANOMAGNETIC, PHOTOELECTRICAL AND OPTICAL PROPERTIES OF Pb08Sn0.2Te THIN FILMS

The effect of substrate temperature on the electrical, photoconductivity, galvanomagnetic and optical properties of Pb0.8Sn0.2Te films was studied. The electrical resistivity decreases one order of magnitude as Ts increases and nearly unchanged with the temperature from 77-300 K. The carrier's concentration decreases by 2-3 orders of magnitude as Ts increases. It was observed that the carriers are p-type due to a slight excess Te in the films and nearly unchanged with temperature. The Hall mobility was observed to increase by 12 orders of magnitudes as Ts increases. The average optical transmittance was found to be 30 % for films deposited at room temperature and increases close to 90-100 % as Ts increases to 673 K. The optical band gap was calculated and was found to be quite higher than those for single crystal which decreases as Ts increases to be close to the band gap of the single crystal as films annealed at 673 K. The IR photoconductivity measurements shows that high photosensitivity at low temperature was observed while it was smaller at room temperature. The determined band gap from the photoconductivity measurements is similar to the obtained from the optical method while both of them are higher than the calculated from the semi-empirical formula of Pb0.8Sn0.2Te crystals. This difference was decreased as the substrate temperature increased and mainly depends upon the carrier's concentration. This was explained by the Burstein-Moss effect of low effective mass and/or high carriers concentration semiconductors.