Theoretical Defect Model for Synthesis Control of The Fermi Level Position in Cd₃As₂

Cd₃As₂ is a three-dimensional Dirac semimetal with sustained scientific interest. Intrinsic point defects, however, induce excess electron carriers that elevate the Fermi level <i>E</i>_F away from the Dirac point and limit accessibility to its topological features. By combining density functional theory (DFT) calculations of defect formation energies and quasiparticle self-consistent GW (QSGW) electronic structure calculations, we demonstrate an innate concentration dependence of defect formation energies, and we find that Cd interstitials are the primary source of this self-doping. We extrapolate formation energies to arbitrary electron concentrations, and we utilize a thermodynamic defect equilibria model to study how extrinsic electron accepting dopants (e.g. Si, Ge, Sn) and particular growth conditions can tune <i>E</i>_F closer to the Dirac point. Separately, Zn₃As₂ is a trivial semiconductor with a direct band gap of 1.0 eV that typically forms with intrinsic <i>p</i>-type doping, so the (Cd,Zn)₃As₂ alloy system is expected to undergo both a topological phase transition and a net doping crossover. Using Monte Carlo simulations, we determined representative alloy structures, which can serve as the basis for predicting electronic structure and defect properties of the alloy.