Analysis of the optical properties for Ga4P3Ti compound with a metallic intermediate band

An analysis of the optical properties from ab initio calculations of Ga4P3Ti system with a partially filled intermediate band is presented. This band is sandwiched between the valence and conduction band of the host semiconductor. This material, because of the intermediate band, have a technological application in solar cells. A study and comparison with different basis-set sizes, relaxation of the nuclear positions and contribution of the different bands is carried out for their electronic and optical properties. The results show that a sub-gap absorption of the host semiconductor takes place in this system as a consequence of the optical transitions between the partially filled intermediate band and the conduction band. Larger basis sets do not substantially improve the absorption coefficient results, although they modify the threshold of the absorption energies. In addition, the absorption coefficient profile is softer with the relaxation of the nuclear positions.