Arsenic Doped Heteroepitaxial CdTe by MBE for Applications in Thin-Film Photovoltaics

Open circuit voltages in CdTe based solar photovoltaics can be improved through increasing the acceptor carrier concentration in the absorber. Arsenic doped heteroepitaxial CdTe layers deposited by MBE are investigated as a means to understand the viability of arsenic as an alternative dopant source without the complication of polycrystalline grain boundaries or high temperature deposition processes. Crystal quality, thickness, and minority carrier lifetimes are correlated with arsenic incorporation and p-type carrier concentrations for both doped and undoped films. Films with carrier concentrations greater than 10¹⁵ cm^-3 have been produced using both an arsenic cracker source and a Cd3As2 effusion source though incorporation differs drastically between these two. As previous work has found, arsenic incorporation is shown to degrade crystal quality. Despite the lower crystal quality, minority carrier lifetimes greater than 1 ns have been achieved in samples with high carrier concentrations when the Cd₃As₂ source is used suggesting the benefit of cadmium overpressure. While the feasibility of arsenic doping during high temperature CdTe deposition processes is still not known, arsenic is shown to be a viable dopant source for continued investigation of heteroepitaxial model systems.