Transport and optical properties of the Cd3-xZnxAs2 alloy system

Abstract

Measurements of thermoelectric power, isothermal transverse-Nernst coefficient and Hall mobility from 100 to 400 K on `as-grown' and doped poly-crystalline Cd3-xZnxAs2 alloys, with x=0, 0·6, 1·2, 1·8 and 3, together with transmission and reflectivity spectra from 1-15 μm for the bulk alloys and thin evaporated films are reported. It is believed that the principal valence band of Cd3-xZnxAs2 is a heavy-mass band possibly displaced in k-space with respect to the conduction band, the latter being highly nonparabolic and located at the centre of the reduced zone. The energy separation between the principal valence and conduction bands is zero in Cd3As2, but quickly becomes positive and large with the addition of Zn. The smallest direct energy gap has also been found to increase steadily with alloying, resulting in a more parabolic conduction band. The carrier scattering in the Cd-rich alloys was found to be by a mixture of acoustical and optical phonons, the magnitude of the relative contributions depending on the carrier density. The scattering of the heavy-mass holes in the Zn-rich alloys is believed to be by acoustical phonons.