Doping Limits of Phosphorus, Arsenic, and Antimony in CdTe

Low p-type doping is a limiting factor to increase CdTe thin-film solar-cell efficiency toward the theoretical Shockley-Queisser limit of 33%. Previous calculations predict relatively high ionization energies for group-V acceptors (P, As, and Sb), and they are plagued by self-compensation, forming AX centers, severely limiting hole concentration. However, recent experiments on CdTe single crystals indicate a much more favorable scenario, where P, As, and Sb behave as shallow acceptors. Using hybrid functional calculations, we solve this puzzle by showing that the ionization energies significantly decrease with the supercell size. When including the effects of spin-orbit coupling and extrapolating the results to the dilute limit, we find these impurities behave as hydrogenic-like shallow acceptors, and AX centers are unstable and do not limit p-type doping. We address the differences between our results and previous theoretical predictions and show that our ionization energies predict hole concentrations that agree with recent temperature-dependent Hall measurements.

Automated summary

Low p-type doping is a challenge for increasing the efficiency of CdTe thin-film solar cells. Previous calculations suggested high ionization energies for group-V acceptors, which resulted in self-compensation and limited hole concentration. However, recent experiments on CdTe single crystals showed that P, As, and Sb behave as shallow acceptors. Through hybrid functional calculations, it was found that the ionization energies decrease significantly with the supercell size. Including the effects of spin-orbit coupling and extrapolating to the dilute limit, it was determined that these impurities act as hydrogenic-like shallow acceptors, and AX centers do not limit p-type doping. Comparison with previous theoretical predictions and agreement with temperature-dependent Hall measurements were also discussed.