Influence of oxygen pressure on elastic strain and excitonic transition energy of ZnO epilayers prepared by pulsed laser deposition

High quality ZnO epilayers (χmin ∼ 10%) were prepared on Al2O3 (0 0 0 1) substrates at a temperature of 750 °C by pulsed laser deposition (PLD) with oxygen pressure of 0.015, 0.15, 1.5, and 15 Pa. The best crystalline quality and strongest intensity of UV photoluminescence were observed on ZnO layer with oxygen pressure of 15 Pa. It is probable due to the higher oxygen pressure lessens oxygen deficiency in the film. The tetragonal distortion eT, which is caused by elastic strain in the epilayer, was determined by Rutherford backscattering/channeling. It reduces as a whole (from 0.93 to 0.65%) with the increase of oxygen pressure from 0.015 to 15 Pa and the excitonic transition energy simultaneously shows a weak blue shift.