An analysis of the shape of a luminescence band induced by transitions of free electrons to carbon atoms in semi-insulating undoped GaAs crystals

Abstract

The shape of a photoluminescence band observed due to recombination of free electrons at shallow-level acceptors (carbon atoms) in semi-insulating undoped GaAs crystals was analyzed at various temperatures (T=4.8–77 K). It is shown that at low temperatures the shape observed essentially differs from the theoretical one, while at high temperatures theory and experiment agree closely for radiative transitions of free electrons to isolated shallow-level acceptors. The difference between the experimental and theoretical shapes of the photoluminescence band is associated with the broadening of carbon-induced acceptor levels (i.e., with the formation of the acceptor impurity band), resulting from the effect of electric fields of randomly distributed ionized acceptors and donors on “isolated” carbon atoms. Coincidence of the shapes is associated with a considerable increase in the energy of free carriers (to values up to and above the width of the acceptor impurity band).