Optical detection of electron paramagnetic resonance for intrinsic defects produced in ZnO by 2.5-MeV electron irradiationin situat 4.2 K

Abstract

Intrinsic defects produced in ZnO by 2.5-MeV electron irradiation in situ at 4.2 K are studied by optical detection of electron paramagnetic resonance (ODEPR). Observed in the photoluminescence (PL) are ODEPR signals, which are identified with the oxygen vacancy, ${\mathrm{V}}_{\mathrm{O}}^{+}$, interstitial zinc, ${\mathrm{Zn}}_{i}^{+}$, and zinc-vacancy--zinc-interstitial Frenkel pairs. The Frenkel pairs are primarily observed in their $S=1$ exchange-coupled state, supplying strong evidence that interstitial zinc is a shallow effective mass double donor in ZnO. Annealing stages at $\ensuremath{\sim}65\text{--}119\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $\ensuremath{\sim}145\text{--}170\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ are observed for the defects associated with the zinc sublattice and are identified with the migration of interstitial zinc. Although interstitial oxygen is not observed in the ODEPR, a higher-temperature annealing stage observed in the PL at $\ensuremath{\sim}160\text{--}230\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is tentatively identified with the onset of its migration. The oxygen vacancy is stable to $\ensuremath{\sim}400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The relationship between the spin-dependent processes producing the ODEPR signals and the PL of the material remains unclear.