Abstract
The photoluminescence (PT) properties of Al-doped ZnO thin films grown by the sol-gel dip-coating method have been investigated. At 12 K, nine distinct PL peaks were observed at 2.037, 2.592, 2.832, 3.027, 3.177, 3.216, 3.260, 3.303, and 3.354 eV. The deep-level emissions (2.037, 2.592, 2.832, and 3.027 eV) were attributed to native defects. The near-band-edge (NBE) emission peaks at 3.354, 3.303, 3.260, 3.216, and 3.177 eV were attributed to the emission of the neutral-donor-bound excitons (<TEX>$D^0X$</TEX>), two-electron satellite (TES), free-to-neutral-acceptors (e,<TEX>$A^0$</TEX>), donor-acceptor pairs (DAP), and second-order longitudinal optical (2LO) phonon replicas of the TES (TES-2LO), respectively. According to Haynes' empirical rule, we calculated the energy of a free exciton (FX) to be 3.374 eV. The thermal activation energy for <TEX>$D^0X$</TEX> in the nanocrystalline ZnO thin film was found to be ~25 meV, corresponding to the thermal dissociation energy required for <TEX>$D^0X$</TEX> transitions.
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