Optical functions of nanocrystalline ZnO containing voids and doped with Ga

摘要

The pulsed laser deposited nanocrystalline ZnO films doped by Ga up to six weight percent are studied by X-raydifraction and generalized spectro-ellipsometry. We report substantial atomic structure modification of heavyGa-doped ZnO resulted and a concentration dependent increase of inter-planar distance. Measured dielectricfunction spectra show strong blue-shift of the samples studied. Equilibrium atomic configurations and electronenergy structure of ZnO containing defects (voids and Ga impurities) are studied by the density functional theory(DFT) and generalized gradient approximation (GGA). Atomic geometries are obtained from the total energyminimization method. Optical functions are calculated within the random phase approximation including thequasi-particles corrections and plasma excitation effects. We report energetically favorable paths of the voidsgrowth and aggregation in ZnO. Comparative analysis of experimental and theoretical results indicate thatmeasured blue-shift in ZnO:Ga substantially exceeds the Burstein-Moss shift as used in many previous work tointerpret concentration dependence of optical functions in heavy doped ZnO. We demonstrate that additionalmechanisms, such as structural and alloying effect, should be involved for quantitative interpretation of opticsof the nano-crystalline heavy-doped ZnO films.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.