n-type conduction in Ge-doped CuGaSe2

In order to prepare n-type ${\mathrm{CuGaSe}}_{\mathrm{2}}$ as-grown, p-type ${\mathrm{CuGaSe}}_{\mathrm{2}}$ single crystals were at first doped by Ge implantation. Thermal healing of the implantation damage in vacuum resulted in strong electrical compensation of the material, but not in n-type conduction. This limitation was overcome by annealing of implanted samples in Zn atmosphere, resulting in n-type conduction of ${\mathrm{CuGaSe}}_{\mathrm{2}}$ with a carrier concentration at room temperature of up to ${10}^{16} {\mathrm{cm}}^{\mathrm{-3}}.$ The samples were analyzed by photoluminescence, resistivity, and Hall effect measurements. It was found that the Zn–Ge codoping minimizes the formation of Cu vacancies, which act as acceptor levels and lead to self-compensation, by the formation of ${\mathrm{Zn}}_{\mathrm{Cu}}$ defects. Furthermore, the number of electrically active Ge dopants is increased by a rise of the ${\mathrm{Ge}}_{\mathrm{Ga}}$ concentration compared to the ${\mathrm{Ge}}_{\mathrm{Cu}}$ defect density. The possibility of n-type conduction in Ga-rich ${\mathrm{CuIn}}_{\text{1−x}}{\mathrm{Ga}}_x{\mathrm{Se}}_{\mathrm{2}}$ compounds opens the possibility of the preparation of homojunction photovoltaic devices and might lead to improved solar cell performance of large band-gap chalcopyrites.