Binding energies of electrons by nitrogen pairs in GaP.

Abstract

Theoretical calculations of binding energies of electrons by nitrogen pairs in GaP are reported. The calculations are based on the Koster-Slater Green's-function equation and the central-cell defect-potential approximation of Hjalmarson et al. [Phys. Rev. Lett. 44, 810 (1980)]. The defect-potential parameters ${V}_{s}$ and ${V}_{p}$ are adjusted to fit the experimental binding energies of electrons by single N impurity and seven (NN${)}_{1}$ (x=1,2,...,7) pairs. The results are in general agreement for the first time with experiments for either range or ordering of binding energies, and thus strongly support the Hopfield-Thomas-Lynch model for isoelectronic traps. Besides, excited electronic states of (NN${)}_{1}$, (NN${)}_{3}$, (NN${)}_{5}$, and (NN${)}_{6}$ are reported. The energy value of the (NN${)}_{1}$ excited state supports the speculation of Cohen et al.