Growth and Hall-effect/photocurrent analysis on BaAl2Se4 layers grown by hot wall epitaxy method

Abstract

The epitaxial growth of photoconductive BaAl2Se4 layers, which have a tetragonal structure, was first achieved through the hot wall epitaxy method. From the Hall effect result, in the high temperature range of T>230K, the mobility decreased as a function of T−3/2 and its scattering was mainly due to the acoustic phonon mode of lattice vibrations through a deformation potential. Thus, at the intermediate temperature range (100<T<230K), the mobility gradually decreased as a function of T−1/2. This behavior was attributed to the piezoelectric potential scattering. In contrast, the mobility decreased in proportion to T1 in a low temperature range of T<100K and its decrease was caused by dislocation scattering. Through the relationship between the reciprocal temperature and the carrier concentration, three donor levels were found to be 0.3, 14.7, and 95.3meV below the conduction band. From the photocurrent (PC) spectra, three PC peaks A, B, and C corresponding to band-to-band transitions were observed at all temperatures. According to the selection rule, the crystal field and spin orbit splitting were found to be 0.2029 and 0.2154eV, respectively, through the direct use of PC spectroscopy. Based on the analysis of optical absorption and PC spectra, the optical band gap was well expressed by Eg(T)=Eg(0)−4.39×10−4T2/(T+250), where Eg(0) is estimated to be 3.4205, 3.6234, and 3.8388eV for the transitions corresponding to the valence band states Γ3(A), Γ4(B), and Γ5(C), respectively.