The epitaxial CaAl2Se4 (CAS) layers were first grown through the hot-wall deposition technique with an attached reservoir tail. The coincidence lattice mismatch between the CAS layer and the GaAs substrate was found to be -0.25% as a result of the compressive strain. From the relation between the reciprocal temperature and the carrier concentration, the donor level originating from slight stoichiometric deviations were extracted to be 1.77, 20.06, and 93.72 meV below the conduction band. Thus, from a log-log plot between the mobility and the temperature, at the high temperatures above 90 K, the electron mobility showed a temperature dependence of two different types. One was T-1/2 at the temperature range of 90 < T < 220 K and the other was T-3/2 at the temperatures of T > 220 K. The former is the scattering due to the acoustic phonon mode of lattice vibration, and the latter is due to the piezoelectric potential scattering. While, at the low temperatures below 90 K, the mobility decreased in proportion to T1. And its decrease is attributed to the dislocation scattering. From the photocurrent (PC) spectroscopy, we found that the characteristic PC peaks were originated by the band-to-band transitions. The temperaturedependent band-gap variation was well explained by E g(T) = E g(0) - 4.94 × 10−3T2/(T + 552), where E g(0) is estimated to be 3.8239, 3.8716, and 3.8801 eV. Consequently, low-temperature growth of the epitaxial CAS layers was successfully achieved by using the hot-wall deposition technique.

Keywords: Characterization, Hot wall epitaxy, Calcium compounds, Semiconducting ternary compounds