Optical Properties and Energy Band Structure of Zn3P2and Cd3P2 Crystals

Abstract

Edge absorption, photoconductivity, and reflectivity spectra are investigated of Zn3P2 crystals in the range from 1 to 12.5 eV and reflectivity spectra of Cd3P2 crystals in the range from 1 to 12.5 eV. The Eg value of Zn3P2 has been experimentally determined at 293 and 77 OK. Its nature has been found to be due to direct transitions. Three peaks of exciton and interband character have been observed in the photoconductivity spectrum of Zn3P2 single crystals. Complex structures (about 12 peaks) have been observed in the reflectivity spectra of both compounds. Most of these structures may be accounted for in terms of the well-known theoretical calculations of their bands. Several peaks have been observed in the most thoroughly studied spectrum of Zn3P2. These peaks cannot be explained by the theoretical band scheme and are probably caused by the peculiarities of the bands of real crystals of the Zn3P2 type, which have been lost in the well-known theoretical model because of the accepted simplifications of the crystal lattice.