Spin-orbit interaction and group-V donor lasing from silicon

Abstract

In this report we focus on the spin-orbit interaction which lifts the degeneracy of the 1s(T2) multiplet of bismuth (Bi) and antimony (Sb) donors in silicon. As experimentally shown it influences on THz laser spectrum of pointed impurity centers under their optical CO2 laser excitation. Note here that in unstressed silicon crystal stimulated emission is based on the 2p(+/-) -1s(T2) intracenter transitions in Bi donor and the 2p0-1s(T2) transitions in Sb. Special attention is paid to the influence of the axial compression stress applied along [100] and [110] crystallographic axes on the laser states and laser frequencies. As shown the axial stress in Si:Bi and Si:Sb shifts the laser lines that has not been observed for Si:P and Si:As where the spin-orbit effect is negligible. In addition in Si:Bi the [100] stress higher than 2kbar switches the upper laser state to the 2p0. Moreover spectrum measurements demonstrate that Bi donors in stressed silicon lase on the states bounded to the upper 4-delta valleys of the conduction band. The experimental data are discussed and the laser frequencies compared with theoretical calculations of donor energy levels.