High Quality Growth of Cd₃As₂ in (112), (001), and (110) Orientations Using Molecular Beam Epitaxy

The three-dimensional Dirac semimetal Cd₃As₂ has been shown to exhibit a variety of novel physics, providing a promising platform for their study. Thin film synthesis is enabling for scientific study as well as the realization of new devices, and growth has already been carried out on GaAs, GaSb, CdTe, SrTiO₃ and mica substrates. Due to its low energy (112) surface, however, the majority of thin film synthesis routes result in this orientation, while single crystals are limited by this cleave plane when performing studies requiring pristine surfaces. By expanding compatible substrate orientations, and ultimately the Cd₃As₂ orientation, much more of the band structure may be probed easily via photoemission, and a broader range of device structures may be integrated with it.<br/>Here, we present the design of II-VI buffer layers to template high quality Cd₃As₂in the (001) and (110) orientations on GaAs substrates. Lattice-matched Zn_xCd_1-xTe buffers are known to reduce defects in Cd₃As₂ epilayers grown on GaAs and improve their electron mobility [1]. We find that using ZnTe nucleation layers is critical for stabilizing Cd₃As₂(001) growth on GaAs (001) substrates, while Zn₃As₂ nucleation layers are required to remove tilt in the Zn_xCd_1-xTe buffer when growing on GaAs(110). These films have a much different morphology due to the higher surface energy, and also a much different dependence on arsenic incorporation compared to Cd₃As₂(112). However, we show that the Cd₃As₂ epilayers still exhibit room temperature electron mobilities greater than 18,000 cm²/V-s. Finally, we present a methodology for growing Cd₃As₂(112) epilayers on GaAs(001) substrates using an engineered CdTe interface to switch between orientations. Such schemes will allow for the design of Cd₃As₂ orientation for specific measurement and application needs.<br/>[1] A. D. Rice, K. Park, E. T. Hughes, K. Mukherjee, K. Alberi. Phys. Rev. Mat. <b>3</b>, 121201(R) (2019)