Bismuth Doping of CdTe: The Effect of Spin-Orbit Coupling

Using the Heyd, Scuseria, and Ernzerhof (HSE) hybrid functional, with the range-separation parameter modified to match the CdTe bandgap, the electronic structure and thermodynamic properties of bismuth-doped CdTe are calculated. The energy levels associated with bismuth in CdTe bandgap can be obtained only when the spin-orbit coupling (SOC) is included. Substitutional and interstitial Bi atom positions in CdTe lattice are investigated. Contrary to the outcome of calculations without SOC, these simple defects generate bands inside the CdTe bandgap. These bands can act as intermediate steps in two-step light absorption processes that lead to increasing the photocurrent in the solar cell.