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 ${\mathrm{Al}}_{\mathrm{Zn}}^{+}$-${\mathrm{Li}}_{\mathrm{Zn}}^{\ensuremath{-}}$. We have associated the DAP band ${P}_{0}$ due to transitions involving ${\mathrm{Al}}_{\mathrm{Zn}}^{+}$ donor and ${\mathrm{Na}}_{\mathrm{Zn}}^{\ensuremath{-}}$ acceptor and the DAP band ${R}_{0}$ due to transitions involving a shallow donor and ${\mathrm{Li}}_{\mathrm{Zn}}^{\ensuremath{-}}$ 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\ifmmode\pm\else\textpm\fi{}2 meV, and the shallow donor associated with ${\mathrm{Li}}_{\mathrm{int}}$ as \ensuremath{\approx} 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.