Self-compensation in PbSe : Tl thin films

Processes of defect formation are investigated in epitaxial PbSe: Tl films prepared by vacuum evaporation from molecular beams at various condensation temperatures from mixtures with a thallium content of 0-1.6 at. %. It is e stablished that an increase in the content of the acceptor impurity in the film is accompanied by a significant increase in the number of selenium don or vacancies through the self-compensation mechanism. The thallium concentr ations in the films are determined, along with the impurity transport coeff icients, which vary from 0.82 to 0.44 as the condensation temperature varie s from 250 degrees C to 350 degrees C. The carrier densities are calculated theoretically as a function of the thallium content in the films. The noti ceable discrepancy between theory and experiment for thallium concentration s in the film noticeable < 0.3 at. % is attributed to the presence of growt h-induced nonequilibrium donor defects in the sample, whose influence is ta ken into account by simply substituting their concentration into the electr oneutrality equation. Estimates based on self-compensation theory lead to t he conclusion that the films must be evaporated at T-K>400 degrees C to obt ain films having a low carrier density. (C) 1999 American Institute of Phys ics. [S1063-7826(99)00601-8].