Donor-acceptor pair bands in ZnSe

Abstract

The donor-acceptor pair (DAP) bands have been studied in single crystals of ZnSe grown by vapor-phase epitaxy, from solutions of Ga, and In, and also by liquid-phase epitaxy. The temperature dependence of both steady-state photoluminescence and time-resolved spectra was used to identify the DAP bands $R_0$, $Q_0$, $P_0$ associated with Li and Na dopants. The DAP band $Q_0$ at 2.695 eV was already identified by Merz et al. as due to ${\mathrm{Al}}_{\mathrm{Zn}}^{+}$-${\mathrm{Li}}_{\mathrm{Zn}}^{-}$. We have associated the DAP band $P_0$ due to transitions involving ${\mathrm{Al}}_{\mathrm{Zn}}^{+}$ donor and ${\mathrm{Na}}_{\mathrm{Zn}}^{-}$ acceptor and the DAP band $R_0$ due to transitions involving a shallow donor and ${\mathrm{Li}}_{\mathrm{Zn}}^{-}$ acceptor, respectively. This shallow donor level seems to be associated with the presence of Li in ZnSe and could be ${\mathrm{Li}}_{\mathrm{int}}^{+}$. From these studies we obtain the acceptor level due to ${\mathrm{Na}}_{\mathrm{Zn}}$, 124±2 meV, and the shallow donor associated with ${\mathrm{Li}}_{\mathrm{int}}$ as ≈ 26 meV, respectively. This study suggests that compensation in ZnSe may be related to background donor impurities such as ${\mathrm{Li}}_{\mathrm{int}}$ rather than native defects.