Effect of annealing on photoluminescence and Raman scattering of Sb-doped ZnO epitaxial layers grown on a-Al2O3

ZnO thin films have been realized via monodoping antimony (Sb) acceptor by Molecular Beam Epitaxy on a-Al2O3 substrates. The influence of annealing on photoluminescence (PL) and micro-Raman spectra of ZnO:Sb layers was analyzed. PL spectra recorded at 6 K are dominated by two peaks: at around 3.31 eV and 3.35 eV. First one is assigned to free electrons to neutral acceptors (FA) transition and the second peak corresponds to donor bound exciton (D0X). In order to properly identify and analyze Raman modes, the room temperature Stokes Raman spectra were compared with the spectra of similar ZnO:As/Al2O3 structures. In addition to regular ZnO and Al2O3 modes, recorded ZnO:Sb Raman spectra contain 3 additional modes at around 509, 532 and 575 cm−1 that are associated with antimony doping. The intensity of doping-related bands decreases with increasing annealing temperature, which indicates the improvement of crystalline quality of the structure. The spectra also reveal the presence of compressive in-plane strain that decreases in value with increasing annealing temperature and is due to thermal residual stress, resulting from differences in thermal expansion coefficients of ZnO and Al2O3