Why Te Doping Can Break the Traditional n-Type Doping Limit of Silicon

We report a theoretical investigation of the impact of hyperdoping with chalcogens (Se and Te) and pnictogens (P and As) on free-carrier concentrations of Si, employing density functional theory calculations. Our results illustrate that isolated substitutional chalcogens in moderately doped Si function as deep donors that are difficult to ionize at room temperature, unlike isolated substitutional pnictogens. The pairing of substitutional defects is found to be energetically favorable for every dopant element, implying that the concentration of substitutional pairs can be significant in hyperdoped Si. However, chalcogen-substitutional pairs have the capability to increase the carrier concentration, whereas pnictogen-substitutional pairs serve only as compensators for n-type doping. By evaluating the carrier concentrations for Te- and P-hyperdoped Si, we demonstrate the importance of substitutional Te pairs of Te-hyperdoped Si in breaking the traditional n-type doping limit observed in pnictogen-hyperdoped Si. Our work elucidates the underlying microscopic mechanisms that give rise to substantial carrier densities in chalcogen-hyperdoped Si, which will pave the way for the development of high-performance silicon-based devices.