Fermi energy control of vacancy coalescence and dislocation density in melt-grown GaAs

Abstract

We have discovered a striking effect of the Fermi energy on the dislocation density in melt-grown GaAs. Thus, a shift of the Fermi energy from 0.1 eV above to 0.2 eV below its intrinsic value (at high temperature, i.e., near 1100 K) increases the dislocation density by as much as five orders of magnitude. Ther Fermi energy shift was brought about by n-type and p-type doping at a level of about 1017 cm−3 (under conditions of optimum partial pressure of As, i.e., under optimum melt stoichiometry). This effect must be associated with the fact that the Fermi energy controls the charge state of vacancies (i.e., the occupancy of the associated electronic states) which in turn must control their tendency to coalesce and thus the dislocation density. It appears most likely that gallium vacancies are the critical species.