Bismuth-containing semiconductors GaAs1−xBix for energy conversion: Thermoelectric properties

Abstract

The electronic transport properties of GaAs1−xBix alloys, are obtained using the semi-classical Boltzmann theory as incorporated in BoltzTraP code. The thermoelectric properties as a function of temperature at a constant value of chemical potential (μ) were calculated for the GaAs1−xBix alloys at x = 0.0–1.0 with stepsize of 0.25. GaAs1−xBix alloys are modeled using special quasi-random structures’ (SQS) Zunger approach. The GaAs1−xBix alloys have a direct band gap of 1.42 eV, 0.449 eV, 0.052 eV, 0.016 eV and −0.0056 eV for x = 0.0, 0.25, 0.50, 0.75 and 1.0, respectively. It is clearly seen that the energy gap decreases with increasing Bi concentration. The electronic band structures of GaAs1−xBix alloys show that the bands are less dispersive for all high symmetry directions, suggesting that these alloys possess large effective mass for the carriers and hence a high thermopower. Calculation show that GaAs0.75Bi0.25 exhibits high carrier concentration and hence high electronic conductivity and power factor, whereas GaAs shows the highest value for Seebeck coefficient. GaBi exhibits the lowest values for most of the transport properties. The GaAs1-xBix (x = 0.0, 0.25, 0.5, 0.75) alloys represents the p-type carrier except GaBi represent n-type at low temperate till 300 K then above this temperature it represents the p-type carrier. We should mention here the fluctuation in the values of σ/τ with changing the content of Bi atoms is attributed to the mobility and the concentration of the charge carrier. Finally substituting all As atoms by Bi atoms (GaBi) leads to reduce ke/τ to lower than that of GaAs. GaAs1−xBix alloys could be promising materials for thermoelectric applications due to the decrease in thermal conductivity with increasing x because bismuth is a heavy atom (better phonon scattering).