ab initio Energetics and Thermoelectric Profiles of Gallium Pnictide Polytypes.

The state-of-the-art Density Functional Theory (DFT) is utilized to investigate the structural, electronic, vibrational, thermal and thermoelectric properties of gallium pnictides GaX (X = P, As, Sb) in cubic zincblende (ZB) and hexagonal wurtzite (WZ) phases. The lattice parameters, bulk modulus, energy band nature and bandgap values, phonon, thermal and thermoelectric properties are revisited for ZB phase while for WZ phase they are predictive. Our results agree reasonably well with the experimental and theoretical data wherever they are available. The phonon dispersion curves are computed to validate the dynamic stability of these two polytypes and for further investigating the thermal and thermoelectric properties. Our computed thermoelectric figure of merit ZT gives consistent results with highest observed magnitude of 0.72 and 0.56 for GaSb compound in ZB and WZ phases respectively. The first time calculated temperature variation of lattice thermal conductivity for WZ phase shows lower value than ZB phase and hence an important factor to enhance the figure of merit of considered gallium pnictides in WZ phase. Present results validate the importance of GaX in high temperature thermoelectric applications as the figure of merit ZT shows enhancement with significant reduction in thermal conductivity at higher temperature values.