E − (red) due to a "phonon-kick" mechanism. The other three conversion processes in (c) and (b) are also enhanced by the recombination because of the vibrational excitations of the spring-like chemical bonds.

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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.

Point defect chemistry strongly affects the fundamental properties of materials and has a decisive impact on device performance. The Group-V dopant is prominent acceptor species with high hole concentration in CdTe; however, its local atomic structure is still not clear owing to difficulties in definitive measurements and discrepancies between experimental observations and theoretical models. Herein, we report on direct observation of the local structure for the As dopant in CdTe single crystals by the X-ray fluorescence holography (XFH) technique, which is a powerful tool to visualize three-dimensional atomic configurations around a specific element. The XFH result shows the As substituting on both Cd (As Cd ) and Te (As Te ) sites. Although As Te has been well known as a shallow acceptor, As Cd has not attracted much attention and been discussed so far. Our results provide new insights into point defects by expanding the experimental XFH study in combination with theoretical first-principles studies in II−VI semiconductors.