Photo-Induced Electron Paramagnetic Resonance of Cr+ in ZnTe and Associated Photoconductivity Phenomena

Abstract

Optical excitation spectra and quenching spectra of the paramagnetic resonance of Cr ⁺ in ZnTe have been measured. Two different excitation bands are exhibited in the excitation spectra. One is a broad band corresponding to the excitation of holes from Cr acceptors to the valence band, and the other is that found at the high energy side of the spectra; this corresponds to the excitation of electrons from charged Zn vacancies to the conduction band. The latter is caused by the excess of Te used to lower the melting temperature of ZnTe. The quenching spectra correspond to the excitation of electrons from the charged Cr acceptors to the conduction band. From these data the energy levels of Cr acceptor and Zn vacancy were determined. Photoconductivity associated with the excitation of the paramagnetic resonance was also measured with a microwave absorption method. The negative photoconductivity was observed in the same wavelength region as the excitation band of the paramagnetic resonance. A resonance absorption mechanism of the microwave by hopping electrons among the Zn vacancies is proposed to explain this phenomenon.