Theoretical investigation of the structural, electronic, and thermodynamic properties of CdS_(1-x)Se_x alloys

摘要

In this work, the structural, electronic, and thermodynamic properties of wurtzite (WZ) and zincblende (ZB) CdS1-xSex alloys are investigated using the density functional theory (DFT) and the cluster expansion method. A special quasirandom structure containing 16 atoms is constructed to calculate the band structures of random alloys. The band gaps of CdS1-xSex alloys are direct and decrease as the Se content increases. The delta self-consistent-field method is applied to correct band gaps that are underestimated by DFT. The band offsets clearly reflect the variation in valence band maxima and conduction band minima, thus providing information useful to the design of relevant quantum well structures. The positive formation enthalpies of both phases imply that CdS1-xSex is an immiscible system and tends to phase separate. The influence of lattice vibrations on the phase diagram is investigated by calculating the phonon density of states. Lattice vibration effects can reduce the critical temperature T-c and increase alloy solid solubilities. This influence is especially significant in the ZB structure. When only chemical interactions are present, the T-c values for WZ-and ZB-CdS1-xSex are 260K and 249 K, respectively. The lattice vibration enthalpy and entropy lower the T-c to 255K and 233 K, respectively. Published by AIP Publishing.