Multiscale Modeling and Optimization of Group V Doping and Compensation in CdSe_xTe_1–x

This study investigates the defect properties and doping limitations of group V elements in CdSe_xTe_1–x. Group V acceptor dopants are able to increase hole concentrations and thereby enhance solar cell performance. However, their doping efficiency is limited by the formation of compensating donor defects with concentrations that depend on alloy composition, processing temperatures, and Cd segregation into grain boundaries. We use density functional theory (DFT) and lattice Monte Carlo (LMC) to identify the lowest-energy Se/Te alloy configurations and to understand the impact of temperature and local alloy configuration on As/P defect formation. Continuum simulations were then employed based on the results of the DFT and LMC calculations to explore As/P dopability in CdSeTe under various growth temperatures, initial chemical potentials, and alloy compositions. Moreover, the segregation of Cd at grain boundaries was investigated to understand its impact on compensating defects. The results of our LMC simulations suggest that P should be a more effective p-type dopant than As in CdSeTe, while both dopants become less effective as Se content increases. Additionally, the continuum simulations highlight that both As and P doping can enhance p-type conductivity, and both of them can reach hole density on the order of 10¹⁶ cm^–3 for 873 K initial growth temperature and 10¹⁷ cm^–3 for 1173 K initial growth temperature. We find that managing chemical potentials and the formation of compensating defects is crucial for optimizing carrier density and dopant activation efficiency and ensuring they remain stable.