뜨거운 곁쌓기법에 의해 성장된 MgGa2Se4 단결정 박막의 광전기적 특성

Abstract

A stoichiometric mixture of evaporating materials for MgGa2Se4 single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, MgGa2Se4 mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by hot wall epitaxy(HWE) system. The source and substrate temperatures were 610 ℃ and 400 ℃, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction(DCXD). The carrier density and mobility of MgGa2Se4 single crystal thin films measured from Hall effect by Van der Pauw method are 6.21×1017 cm-3 and 248 cm2/V․sec at 293 K, respectively. From the optical absorption measurement, the temperature dependence of energy band gap on MgGa2Se4 single crystal thin films was found to be Eg(T)=2.34 eV - (8.81×10-4 eV/K)T2/(T＋251 K). The crystal field and the spin-orbit splitting energies for the valence band of the MgGa2Se4 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 ΔSo definitely exists in the Γ5 states of the valence band of the MgGa2Se4/GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-, and C1-exciton peaks for n=1. After the as-grown MgGa2Se4 single crystal thin films was annealed in Mg-, Se-, and Ga-atmospheres, the origin of point defects of MgGa2Se4 single crystal thin films has been investigated by the photoluminescence(PL) at 10 K. The native defects of VMg, VSe obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Se-atmosphere converted MgGa2Se4 single crystal thin films to an optical n-type. Also, we confirmed that Ga in MgGa2Se4/GaAs did not form the native defects because Ga in MgGa2Se4 single crystal thin films existed in the form of stable bonds. In order to explore the applicability as a photoconductive cell, we measured the sensitivity(), the ratio of photocurrent to darkcurrent(pc/dc), maximum allowable power dissipation (MAPD) and response time. The results indicated that the photoconductive characteristic were the best for the samples annealed in Se vapour compare with in Mg, Ga, air and vacuum vapour. Then we obtained the sensitivity of 0.98, the value of pc/dc of 1.42×107, the MAPD of 331 mW, and the rise and decay time of 10 ms and 9.6 ms, respectively.