Lithium-related states as deep electron traps in ZnO

Carrier trapping in Li-doped ZnO was studied using Electron Beam Induced Current technique, as well as cathodoluminescence spectroscopy and persistent photoconductivity measurements. Under electron beam excitation, the minority carrier diffusion length underwent a significant increase, which was correlated with growing carrier lifetime, as demonstrated by the irradiation-induced decay of CL intensity of the near-band-edge transition. Variable-temperature cathodoluminescence and photoconductivity experiments showed evidence of carrier trapping and yielded activation energies of 280 and 245 meV, respectively. These observations are attributed to the presence of a deep, Li-related acceptor state.