Far-infrared spectroscopic identification of D^-states in GaAs, InP and InSb

Abstract

D- states (i.e. the states formed by a neutral donor, D0, binding an extra electron), D0 interexcited state transitions (i.e. n to m where the principal quantum numbers n, m are greater than 1) and cyclotron resonance are all observed simultaneously in the far-infrared spectrum of n-GaAs and n-InP. This observation constitutes the first unambiguous identification of D- states in a compound semiconductor. D- states have been observed in seven GaAs and two InP samples. A chemical shift is observed, but no central cell splitting is found even at the largest available fields (i.e. 24 T). D- states are studied under a variety of experimental conditions such as hydrostatic pressure, temperature and electric field bias. The application of hydrostatic pressure strongly enhances the D- intensity in VPE InP, but not in VPE GaAs. Effects attributable to the formation of D- complexes occur in GaAs when the temperature is reduced to 2 K. The intensity of the D- transition increases markedly with increasing electric field bias. Divergence between theory and experiment is evident when the dimensionless magnetic field parameter, gamma , exceeds unity, indicating the inadequacy of existing variational calculations in this regime. D- triplet and singlet transitions are tentatively identified in n-InSb.