A highly controllable doping technique via interdiffusion between epitaxial germanium layers and GaAs

Abstract

Interdiffusion between epitaxial Ge layers and GaAs substrates was used in this study to precisely control the doping concentration and doping type of the Ge layers. An extremely high n-type doping concentration (> 1020 cm−3) was achieved in a Ge layer grown at a low temperature of 300 °C; the layer exhibited a smooth surface morphology and excellent crystalline quality. Subsequent post-growth annealing processes led to a decrease of the n-type doping concentration followed by an n- to p-type transition because of the diffusivity difference between As and Ga atoms. Our experimental results indicated the preferential diffusion of As atoms and their consequent escape through the Ge top surface, resulting in the p-type transition via time-lagged Ga diffusion. We fabricated a Ge-on-insulator junctionless field-effect transistor using a heavily n-doped 10 nm-thick Ge channel, and the device demonstrated good performance.