Determination of Transition Mechanism and Polarity of a c-Plane ZnO Bulk by Using Contactless Electroreflectance Spectrum

Abstract

Contactless electroreflectance（CER）spectra of Zn and O-polarity faces of a c-plane ZnO bulk were measured at room temperature. Besides a depletion electric field existing in the sample, it is known that there is a polarization electric field due to nonzero spontaneous polarization. In this work, a mercury lamp was focused on the ZnO sample in the CER measurements to provide a photo-biased voltage to reduce strength of electric field of the sample. It was found that the spectrum with Hg lamp being on is more blue-shifted and its amplitude is smaller than that without Hg lamp. Thus the type of transition was attributed to excitonic transition. The shift of the excitonic transition-energies of the Zn- and O-faces were obtained by fitting experimental CER spectra by using Lorenzian line-shapes. In addition, the polarity of faces can be determined by the amount of shift with Hg lamp being on.