Structure and optical properties of non-doped and N-doped ZnO films with non-polar surfaces grown homoepitaxially on single crystal ZnO (11(2)over-bar0) substrates

Non-doped ZnO films and nitrogen-doped ZnO films (ZnO:N films) were grown epitaxially on non-polar single crystal ZnO (11 (2) over bar0) substrates by using the plasma-assisted reactive evaporation (PARE) method. The value of FWHM of the scan rocking curve of non-doped ZnO (11 (2) over bar0) films were 26 to 62 arcseconds. Crystallinity of ZnO ( 11 (2) over bar0) films deteriorated with increase in N-2 gas flow rate, but crystallinity of the films was better than that of ZnO (11 (2) over bar0) films grown on sapphire (11 (2) over bar0) substrates by the PARE method. Independently of N-2 gas flow rate, AFM images of non-polar ZnO films showed a smooth surface with about 1 nm of root mean square roughness. In near band-edge PL spectra from these non-doped ZnO films measured at 5 K, free-exciton emission (FE) at about 3.378 eV, ionized-donor-bound excitons (D+X) at about 3.368 eV and neutral-donor-bound excitons ((DX)-X-0) at about 3.362 eV were clearly observed. PL intensity of D+X of non-polar ZnO: N films was decreased but that of donoracceptor pairs (DAP) emission at around 3.308 eV of the films increased with an increase in N-2 gas flow rate. It is thought that N atoms occupied oxygen sites and surface state density were decreased with increase in N-2 gas flow rate and that N atoms act as acceptors in ZnO. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim