Hot Wall Epitaxy(HWE)법에 의해 성장된 ZnAl2Se4 단결정

Abstract

ABSTRACT Properties of photoconductivity for ZnAl2Se4 single crystal thin film grown by hot wall epitaxy

Lee Ki-Jung Adviser : Prof. Hpong Kwang-joon Ph.D Major in Physics Education Graduate School of Education, Chosun University

A stoichiometric mixture of evaporating materials for ZnAl2Se4 single crystal thin films was prepared from a horizontal electric furnace. These ZnAl2Se4 polycrystals had a defect chalcopyrite structure, and its lattice constants were a0= 5.5563 Å, c0= 10.8897 Å. To obtain a single crystal thin film, mixed ZnAl2Se4 crystal was deposited on the thoroughly etched semi-insulating GaAs(100) substrate by hot wall epitaxy (HWE) system. The source and the substrate temperatures were 620 ℃ and 400 ℃, respectively. The crystalline structure of the single crystal thin film was investigated by using a double crystal X-ray rocking curve and a X-ray diffraction scans. The carrier density and the mobility of the ZnAl2Se4 single crystal thin film are 8.23 ×1016 cm-3 and 287 m2/v․s at 293K, respectively. To identify a band gap energy, the optical absorption spectra of the ZnAl2Se4 single crystal thin film was investigated in the temperature region of 10-293 K. The temperature dependence of the direct optical energy gap is well presented by the Varshni's relation, . The constants of Varshni's equation had the values , , and for the ZnAl2Se4 single crystal thin film. The crystal field and the spin-orbit splitting energies for the valence band of the ZnAl2Se4 have been estimated to be 109.5 meV and 124.6 meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the Δso definitely exists in the Γ5 states of the valence band of the ZnAl2Se4/GaAs epilayer. The three photocurrent peaks observed at 10K are ascribed to the A1-, B1-exciton for n = 1 and C21-exciton peaks for n = 21.