Electro-optic and thermoelectric reponse of SiP and SiAs for solar and thermal applications

Based on first-principles calculations, we investigated the electro-optic and thermoelectric properties of SiX (X = P, As). We find that the SiP (-0.17 eV/atom) is more favorable than SiAs (-0.12 eV/atom) due to higher formation energies. The dynamical stability is calculated from the phonon spectra, and the non-negative frequencies confirms the stable nature of SiX. Our calculated electronic band gap shows the semiconductor nature of the SiP, and SiAs with the band gap values of 2.33 eV, and 2.04 eV, respectively. Interestingly, the SiP possesses a direct band gap, which could be promising for optoelectronic devices. Additionally, we performed calculations by replacing P/As with Se atom, and observed that the semiconducting nature is alter to metallic one. The sharp peaks in the optical spectra confirms the electron transition from valance band to conduction band. The SiX (X = P, As) compound strongly absorbed light of energy 4.0 eV, which suggests it a potential candidate for solar cell applications. Furthermore, the compound exhibited the strong absorption of whole sun spectrum (ultra-violet to infra-red wave length), makes it capable for the applications in optical devices. Additionally, we have computed the thermoelectric properties using Boltztrap code. We have estimated the zT value 0.67 and 0.76 for SiP and SiAs, respectively. Both the SiAs and SiP exhibits a high zT, which could be applicable in the thermoelectric devices. Based on our calculated results, we anticipate that our studied materials could be an encouraging candidate for optical devices and thermoelectric devices.