On the diffusion and activation of n-type dopants in Ge

Diffusion and activation of n-type dopants in Ge are discussed with particular emphasis on shallow junction formation. It is shown that both the increase of dopant diffusivity and the reduced fraction of substitutional dopant with increasing dopant concentration are determined by (double) negatively charged vacancies pairing with dopant atoms. The results show that P is the best choice donor atom in Ge as the achievable electron concentration is higher and the extrinsic diffusivity lower than that is the case for As and Sb. Possible ways to increase the dopant substitutional solubility and the degree of activation and to reduce extrinsic diffusivity by point defect engineering are also addressed. Co-doping with Sn seems a promising approach to increase the free carrier concentration and to suppress extrinsic donor diffusion.