High activation in arsenic doped single crystal CdTe thin film by molecular beam epitaxy

Single crystal model system is a valuable tool to investigate fundamental material properties. In this work, we use molecular beam epitaxy to deposit single crystal, in-situ arsenic (As) doped CdTe films on large area Si substrates to better understand As doping for photovoltaic applications. We found that As incorporation is highly temperature dependent: a substrate temperature difference of 50°C can lead to several orders of magnitude difference in As concentration. Cd overpressure during in-situ doping may limit out-diffusion of As but decrease As incorporation, especially at lower growth temperatures. Carrier concentrations greater than 1016 cm-3 can be achieved with or without Cd overpressure when annealed at temperatures above 500°C. However, to achieve greater than 50% activation (ratio of incorporated As to Hall p-type carrier concentration), higher annealing temperatures are required. Due to carrier concentration saturation, As incorporation also needs to be controlled to average levels of 1017 cm-3 to achieve high activation. These findings suggest that higher annealing temperature regimes may be beneficial to polycrystalline CdTe based PV devices.