Structure and optical properties of non‐doped and N‐doped ZnO films with non‐polar surfaces grown homoepitaxially on single crystal ZnO (11$ \bar 2 $0) substrates

Abstract

Non‐doped ZnO films and nitrogen‐doped ZnO films (ZnO:N films) were grown epitaxially on non‐polar single crystal ZnO (11$ \bar 2 $0) substrates by using the plasma‐assisted reactive evaporation (PARE) method. The value of FWHM of the ω‐scan rocking curve of non‐doped ZnO (11$ \bar 2 $0) films were 26 to 62 arcseconds. Crystallinity of ZnO (11$ \bar 2 $0) films deteriorated with increase in N2 gas flow rate, but crystallinity of the films was better than that of ZnO (11$ \bar 2 $0) films grown on sapphire (11$ \bar 2 $0) substrates by the PARE method. Independently of N2 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 (D0X) at about 3.362 eV were clearly observed. PL intensity of D+X of non‐polar ZnO:N films was decreased but that of donor‐acceptor pairs (DAP) emission at around 3.308 eV of the films increased with an increase in N2 gas flow rate. It is thought that N atoms occupied oxygen sites and surface state density were decreased with increase in N2 gas flow rate and that N atoms act as acceptors in ZnO. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)