Photocurrent study on the splitting of the valence band and growth of MgGa₂Se₄ single crystal thin film by hot wall epitaxy

Abstract

A stoichiometric mixture of evaporating materials for MgGa 2 Se 4 single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, MgGa 2 Se 4 mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were 610 o C and 400 o C, respectively. The crystalline structure of the single crystal thin films was investigated by double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the MgGa 2 Se 4 obtained from the absorption spectra was well described by the Varshni's relation, E g (T) = 2.34 eV − (8.81 × 10 −4 eV/K)T 2 /(T + 251 K). The crystal field and the spin-orbit splitting energies for the valence band of the MgGa 2 Se 4 have been estimated to be 190.6 meV and 118.8 meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ∆so definitely exists in the Γ 5 states of the valence band of the MgGa 2 Se 4 /GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the A 1 -, B 1 -exciton for n = 1 and C 27 -exciton peaks for n = 27.