Effects of growth temperature and oxygen pressure on the properties of heteroepitaxial ZnO thin films on sapphire (0001) substrates by pulsed laser deposition

Abstract

We report a systematic study on the effect of growth temperature and O 2 pressure on the structural, optical, and electrical properties of heteroepitaxial ZnO thin films prepared by pulsed laser deposition on sapphire (0001) substrates. The combination of high growth temperature and low O 2 pressure was found to improve the crystalline quality of initial heteroepitaxial ZnO films, which can be attributed to the enhanced surface migration of adatoms and thermal energy. The low-temperature photoluminescence spectra from ZnO films were dominated by donor-bound exciton emission with very weak deep level emission. The temperature dependent Hall measurement showed that the films are highly degenerated, mainly due to the high defect density near the interface region.

Stacking fault related3.31−eVluminescence at130−meVacceptors in zinc oxide

“…6 It is also frequently observed in epitaxial layers grown by different growth methods, especially after intentional p-type doping with various dopant species, preferentially group V elements. [7][8][9] This omnipresent luminescence band has been interpreted controversially, ascribing it, e.g., to donor-valence band transitions ͑D 0 , h͒, 1 electron-hole recombination from donoracceptor pairs ͑D 0 , A 0 ͒, 4 electron-acceptor transitions ͑e , A 0 ͒, 5 recombination of excitons bound to deep neutral acceptors ͑A 0 , X͒, 10 two-electron satellites of donor-bound excitons, 11,12 LO replicas of donor-bound excitons, 2 exciton recombination at silicon impurities, 13 or a "rotation domain structure-induced localized state bound exciton." 14 In the majority of the pertinent works, it has been ascribed to transitions of free electrons to neutral acceptor states ͑e , A 0 ͒ with ionization energy close to 130 meV as deduced from the spectral position of the band.…”