Applicability of the deformation-potential approximation to deep donors in silicon.

Abstract

Several deep double donors due to sulfur and selenium impurities, both isolated and in pairs, have been investigated in infrared-absorption and uniaxial-stress experiments. The study of several similar centers in their different charge states allows trends in parameters to be revealed. Particular attention is given to the applicability of effective-mass theory (EMT) and the deformation-potential approximation (DPA) to the various states studied. The np excited states are well described by EMT and hence their behavior under stress by the DPA. The deep 1s ground states do not follow DPA but shift linearly with respect to the center of gravity of the conduction bands with shift rates that increase with the ionization energy of the centers. Excited 1s states which are deeper than predicted by EMT are also observed to deviate from DPA. A perturbation approach beyond the DPA is developed to fit and compare data. For nontetrahedral centers the stress lifts their orientational degeneracy. The 1s(${A}_{1}^{+}$)\ensuremath{\rightarrow}ns transitions of chalcogen pairs are well described by DPA if matrix elements that couple the ns states are accounted for. For some centers, stress-induced crossings between allowed and forbidden states reveal information on states [1s(E) and spin-triplet states] that are not accessible by dipole transitions.