Extrinsic Doping Control of the Topological Semimetal Cd₃As₂ from Defect Theory

The standard approach for studying defect concentrations in solid-state systems using first principles formation energies is to evaluate a thermodynamic equilibrium at a model growth temperature. For lower (room or operating) temperatures, these defect concentrations are then “frozen in”, and only the Fermi level E_F is re-equilibrated. However, this assumption overlooks the possibility of short-range diffusion and defect redistribution, even when the overall composition determined by the growth step remains fixed. To model this redistribution, we developed an approach to solve for the non-equilibrium chemical potentials as a function of temperature while maintaining the elemental stoichiometry. We then apply this approach to the Dirac semimetal Cd₃As₂ in the presence of external dopants. Our previous work (PRB 107, 224110, 2023) identified Cd interstitials and vacancies as the primary defects in self-doped Cd₃As₂, with excess interstitials leading to undesirable n-type doping that limits access to the Dirac point under most growth conditions. Here, we utilize the expanded defect equilibrium model to study extrinsic doping with the goal of introducing additional electron accepting defects (Group I on Cd and Group IV on As) and lowering E_F.