Influence of the relative magnitude of the Jahn-Teller effect and level splitting in a cubic crystal field on the properties of the ground state of vacancy defects in semiconductors

The spatial structure of a vacancy and the properties of its electronic ene rgy levels in a semiconductor with a lattice possessing point symmetry T-d are considered for an arbitrary relationship between the Jahn-Teller stabil ization energy (associated with the F-2 vibrational mode) and the t(2)-a(1) splitting (Delta) caused by the cubic crystal field. The position of the m inimum of the adiabatic potential and the distortion of the electronic dens ity are calculated for the vacancy ground state for different relative valu es of Delta and coupling constants of the vacancy to the F-2 vibrational mo de. It is shown that, if the ground state of a carrier bound to a vacancy i s a t(2) state, the trigonal symmetry of the environment of the vacancy per sists for any values of Delta, but the amount of displacements of atoms nea r the vacancy and the localization of the wave function of the bound carrie r on the broken bond earmarked by the Jahn-Teller effect can depend heavily on Delta and are maximal at Delta --> 0. This is also the case when the gr ound state of the vacancy is the a(1) state, but the magnitude of Delta doe s not exceed a certain value, which is determined by the coupling constants and the elastic constant. The relation between Delta and the coupling cons tants is also shown to affect the properties of trigonal vacancy-shallow-do nor complexes. For these complexes, calculations are performed of the depen dence of the dipole direction determining the optical properties of the vac ancy defect on the distortion of vacancy orbitals caused by the donor enter ing into the complex. (C) 2000 MAIK "Nauka/Interperiodica".