Influence of stoichiometry and doping on vacancies in n-type GaAs

Native vacancies in n-type, Te-doped GaAs (n = 5 x 10(16)-5 x 10(18) cm(-3) ) were studied by means of positron annihilation. We investigated the influ ence of doping, thermal treatment, and stoichiometry adjusted by changing t he As pressure during annealing. Negatively charged monovacancies were foun d in all Te-doped samples under investigation. By using positron lifetime s pectroscopy in conjunction with measurements of the annihilation momentum d istribution and theoretical calculations, they can directly be identified t o be V-Ga-Te-As complexes. After thermal treatment at 1100 degrees C the de nsity of the vacancies c(v) increases with the As pressure (p(As)) like c(v ) = 0.1C(d)p(As)(1/4) where c(d) is the donor concentration. For such a tre atment, c(v) depends only on p(As) but not on the thermal history. The vaca ncy concentration was found to increase slightly with decreasing annealing temperature at a given p(As). This can be explained by the so-called Fermi level effect, i.e. the dependence of the equilibrium concentration of charg ed point defects on the position of the Fermi level. (C) 1999 Elsevier Scie nce B.V. All rights reserved.