Mn concentration dependent structural and optical properties of a-plane Zn0.99-xMnxNa0.01O

Non-polar a-plane (112¯0) Zn0.99−xMnxNa0.01O (x = 0, 0.02, 0.03, 0.04, and 0.05) thin films have been prepared on r-plane (112¯0) sapphire substrates by pulsed laser deposition (PLD). The influences of Mn content on the structural and optical properties of the films have been studied. It is indicated that moderate Mn doping facilitates the non-polar growth of ZnO, and all the doped films are single phase with a hexagonal wurtzite structure. The transmittance spectra suggested that all films are transparent in the visible region exhibiting a transmittance above 80%. Mn2+ doped Zn0.99Na0.01O shows an initial decrease of optical band gap (OBG) for small concentration of Mn, followed by a monotonic increase. The anomalous decrease in OBG for low concentrations of Mn is attributed to the strong exchange interaction present between the sp electrons of the host matrix and d electrons of Mn. Emission studies were also performed showing suppressed blue-shifted ultraviolet band and dominant violet-blue bands, which might originate from the zinc vacancy (VZn) and zinc interstitial (Zni) defects. The intensity of defect-related emission peaks is Mn doping-level-dependent as well and the results coincide well with that from the structural analyses