A surface sensitive optical method for the evaluation of processed ZnO: exploitation of LO phonon interaction

We report on a surface property of bulk ZnO crystals and an optical method to evaluate it. Bulk ZnO crystals have a damaged surface layer due to chemomechanical polishing. We prepared the ZnO crystals by etching, and evaluated the improvement of the surface by high-resolution X-ray diffraction (XRD) and photoluminescence (PL). In PL measurements, the relative intensity of the first order longitudinal optical phonon replica of free exciton (FX-1LO) to second order process (FX-2LO) was compared. The relative intensity becomes weak with increasing etched depth and finally saturates at the etched depth of 5 μm. This result agrees well with XRD results.