Optical characterization of ZnMnO thin films on c-Al2O3

Abstract

Various optical measurement technologies have been used to characterize ZnMnO thin films with different Mn compositions grown by molecular beam epitaxy (MBE) on c-Al2O3 substrates. The lattice constant and the crystalization quality have been evaluated by using X-ray diffraction (XRD). Photoluminescence (PL) has been used to reveal the neutral-donor-bound exciton ((DX)-X-0) and to check the film's quality. Defect-related absorption signatures, in addition to near-band-edge absorption, due to the zinc vacancy and the donor-acceptor pair (DAP) have been found in the surface photovoltage spectra (SPS). Free excitonic transitions and their phonon-assisted replicas have been observed in the reflectance spectra. Our experimental results not only unveil specific optical transition energies but also indicate a rapid material deterioration when Mn incorporation goes beyond a certain amount to cause manganese segregation.