Electrical properties of uncontaminated PbTe films on mica substrates prepared by molecular beam deposition

Abstract

Uncontaminated PbTe films were prepared by molecular beam deposition under clean conditions in a uhv environment and the film properties were measured in situ. The carrier concentration was found to be determined by source conditions and values between 1016 cm−3 (intrinsic level) and n = 5 × 1018cm−3 could be obtained in a controllable manner. A low temperature anneal enabled bulk value Hall mobilities (1750 cm2 V−1 sec−1 at 300 K) to be obtained at room temperature and above which indicated that surface scattering in the films was predominantly specular. The mobility at low temperatures (down to 100 K) was limited by small potential barriers located at the double-positioned grain boundaries which were present in the film. Field effect measurements indicated the potential barriers arose from a continuous distribution of band gap states situated in the grain boundaries. These states had a fairly uniform density (⋍ 1012cm−2 (kT)−1) but there was some increase towards the conduction band edge. They also limited the field effect mobility (μFE) to ⋍0.5 bulk value, giving μFE ⋍ 800cm2 (volt sec)−1 for films with carr concentrations above 5 × 1017 cm−3. By exposure to low pressures of oxygen the carrier concentrations in annealed n-type films could be reduced to near intrinsic values with no associated degradation in the electrical properties. This indicated that the films were not compensated with the native p-type defect.