Hole ionization of Mn-doped GaAs: Photoluminescence versus space-charge techniques

The thermal quenching of the Mn-related emission in GaAs is studied by measuring both the drop in intensity and the reduction in the luminescence time decay as a function of temperature. It is shown that both these quantities are governed by a temperature-activated process with an activation energy equal to the hole-emission activation energy, which is, in turn, equal to the ground-state energy of the Mn acceptor level at $E_v$+0.11 eV. However, a large reduction is found in the thermal emission rates of holes in bulk material compared to thermal measurements made with deep-level transient spectroscopy in space-charge layers. This discrepancy is discussed in terms of a recapture mechanism which strongly affects measurements in neutral material. It is also demonstrated that great care has to be taken when the detailed-balance relationship is used for the determination of thermodynamic parameters.