Heteroepitaxial growth and luminescence properties of non-polar (1 1 0) orientation ZnO films on Si(0 0 1) substrates by pulsed laser deposition

Epitaxial growth of a ZnO(1 1 0)/STO(0 0 1)/TiN(0 0 1)/Si(0 0 1) heterostructure has first been demonstrated on a Si(0 0 1) substrate by pulsed laser deposition. The growth process was monitored in situ by reflection high-energy electron diffraction, and the epitaxial orientation relationship was further confirmed by ex situ x-ray diffraction analysis. Results show that the high (1 1 0) oriented ZnO films are in domain-growth mode, and composed of two kinds of domains with their c-axes perpendicular to each other along STO〈1 1 0〉. The excitation-density-dependent photoluminescence spectra analyses at 83 K indicate that the ZnO films have good optical quality with low defect density, and no significant deep-level emission is detected. The strong near-band-edge luminescence consists of several acceptor-related emissions such as the acceptor-bound exciton emission (3.352 eV), the free electron-acceptor emission (3.318 eV) and the donor-acceptor-pair emission (3.248 eV). The presence of these acceptor-related emissions in undoped ZnO films should be attributed to structural acceptor defects, which are mainly caused by the domain-growth mode in this case.