Extrinsic Doping Control in Cd₃As₂ Thin Films Grown via MBE

Cd₃As₂ is a prototypical Dirac semi-metal, a class of materials with gapless topologically protected electronic states. In this system, these topological electronic states are close to the intrinsic Fermi level and are well isolated from non-trivial bands. Additionally, this system is air stable and compatible with molecular beam epitaxy, including lattice matching to III-Sb and II-Te layers, and similar elements to conventional semiconductors. With applications including low-energy computing, optoelectronics, and themoelectrics, these materials have the capability to impact a variety of areas. To achieve this, however, more capabilities for tuning their properties need to be developed. In particular, strategies for changing the intrinsic n-type carrier concentration beyond electrostatic gating must be explored.<br/><br/>Here, attempts to dope Cd₃As₂further n-type, as well as p-type, are presented. First, Se and Te are introduced during growth, analogous to doping approaches in conventional semiconductors. This allows for films to be doped from 5e17 cm^-3 up to slightly over 3e18 cm^-3for [112] oriented films before compensation occurs [1]. Prior to compensation, mobility vs n_3d follows an expected trend, and fundamental parameters pulled from oscillation fitting are consistent with shifting the Fermi level without major changes in the band structure. Recent results reveal more sensitive doping in [001] oriented films, with higher achievable n-type carrier concentrations. For lowering the Fermi level, (Zn,Cd)₃As₂ is pursued. Similar attempts in bulk crystals and films grown via pulsed laser deposition achieve p-type films at &gt;20% Zn. Here, due to a lower starting n-type carrier concentration, multi carrier behavior is observed &lt;10%, with reduced n-type concentrations also possible. Combined, these efforts allow for significant control in the Fermi level position of a Dirac semimetal.<br/><br/>[1] A.D. Rice et al. Appl. Phys. Lett. 122, 061901 (2023)