Epitaxial growth and electrical-optical characteristics of CaAl2Se4 layers by hot-wall deposition technique
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The epitaxial CaAl2Se4 (CAS) layers were first grown through the hot-wall deposition technique with an attached reservoirtail. The coincidence lattice mismatch between the CAS layer and the GaAs substrate was found to be -0.25% as a result ofthe compressive strain. From the relation between the reciprocal temperature and the carrier concentration, the donor leveloriginating 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 mobilityshowed a temperature dependence of two different types. One was T-1/2 at the temperature range of 90 < T < 220 K and theother was T-3/2 at the temperatures of T > 220 K. The former is the scattering due to the acoustic phonon mode of latticevibration, and the latter is due to the piezoelectric potential scattering. While, at the low temperatures below 90 K, the mobilitydecreased 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 temperaturedependentband-gap variation was well explained by Eg(T) = Eg(0) - 4.94 × 10−3T2/(T + 552), where Eg(0) is estimated to be3.8239, 3.8716, and 3.8801 eV. Consequently, low-temperature growth of the epitaxial CAS layers was successfully achieved byusing the hot-wall deposition technique.
Abstract
The epitaxial CaAl2Se4 (CAS) layers were first grown through the hot-wall deposition technique with an attached reservoirtail. The coincidence lattice mismatch between the CAS layer and the GaAs substrate was found to be -0.25% as a result ofthe compressive strain. From the relation between the reciprocal temperature and the carrier concentration, the donor leveloriginating 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 mobilityshowed a temperature dependence of two different types. One was T-1/2 at the temperature range of 90 < T < 220 K and theother was T-3/2 at the temperatures of T > 220 K. The former is the scattering due to the acoustic phonon mode of latticevibration, and the latter is due to the piezoelectric potential scattering. While, at the low temperatures below 90 K, the mobilitydecreased 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 temperaturedependentband-gap variation was well explained by Eg(T) = Eg(0) - 4.94 × 10−3T2/(T + 552), where Eg(0) is estimated to be3.8239, 3.8716, and 3.8801 eV. Consequently, low-temperature growth of the epitaxial CAS layers was successfully achieved byusing the hot-wall deposition technique.
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