Electrical properties of (ZnTe) x(CdSe) 1− x single crystals

Abstract

Electrical properties of as-grown and annealed (ZnTe) x (CdSe) 1 − x single crystals, prepared by the vapour phase growth technique in the entire range of x in the temperature range 160–400 K are reported for the first time. The electrical conductivity and Hall measurements were carried out by the dc van der Pauw technique. The conductivities of as-grown crystals were very low but increased considerably after annealing in Zn Cd vapours. Crystals of ZnTe and CdSe were always p and n type respectively. However, in the mixed crystals of (ZnTe) x (CdSe) 1− x , n-type conductivity was observed for x ⩽ 0.4 and p-type conductivity was observed for x ⩾ 0.5. XRD studies showed that crystals with x ⩽ 0.4 had wurtzite structure, whereas crystals with x ⩾ 0.5 had zincblende structure. Hall mobilities increased with decrease of temperature in crystals of all compositions indicating the dominance of optical phonon scattering. The activation energies obtained from the carrier concentration data are also reported. According to the autocompensation theory, crystals with x ⩾ 0.5 which are in the vicinity of the structural transition range might have n-type conductivity whereas the observed conductivity is p-type. Though the autocompensation phenomenon of wide-gap semiconductors explains the resilience to conductivity-type change, recent studies have otherwise shown that the presence of D-A pairs and states independent of gap energy etc., might be responsible for compensation.