First-principles calculations of electronic structures and optical properties of group-IIIA elements doped wurtzite CdS

The electronic structures and optical properties of pure and group-IIIA elements doped wurtzite CdS are investigated using first-principles density-functional approach. The results indicate that when a group-IIIA element is introduced into CdS, the Fermi level moves upward into the conduction band from the band gap of undoped CdS, and the contributions of the s states of cations to the total density of states of CdS near the Fermi level are very large. The calculated optical properties show that absorption peaks located in the visible spectrum appear in group-IIIA doped CdS, but the intensities of the peaks are very weak, especially for the polarization vectors perpendicular to the c axis. Our calculations provide reasonable explanations to the experimental observations of the greatly decrease of resistivity of CdS while retaining high transparency with the doping of group-IIIA element.