LATTICE-MATCHED GROWTH OF TOPOLOGICAL SEMIMETAL CADMIUM ARSENIDE ON VIRTUAL TERNARY III-V SUBSTRATES

Abstract

Topological materials are a recently discovered electronic class which exhibits electronic band structures that deviate from the behavior of conventional electronic materials. These topological materials exhibit conical bands and host unique band elements such as Dirac and Weyl nodes through which phenomena such as the quantum Hall effect, quantum anomalous Hall effect, and the quantum spin Hall effect may be realized. These effects are protected against the destabilizing effects of thermal fluctuations through crystal symmetry-derived protection. The topological semimetal Cd3As2 is an excellent candidate for the realization of novel devices through magnetic alloying because of its demonstrated high electron mobility (>10,000 cm2/V•s). This dissertation details the molecular beam epitaxy growth and characterization of topological semimetal Cd3As2 thin films that are lattice-matched to ternary III-V alloy virtual substrates and optimized for high crystalline quality. This dissertation will first review the deposition of Cd3As2 and the relevant calculations made to determine the suitability of virtual substrates for its lattice matched-growth. Therefore, the stability of ternary III-V alloy buffers and their interfaces with Cd3As2 are discussed. Thermal and spinodal decomposition ranges for the ternary III-V alloys are also determined to fully understand them as virtual substrates for Cd3As2. Cd3As2 thin films are grown with thicknesses targeting 30-100 nm. Three ternary III-V alloy systems GaInSb, AlInSb, and InAsSb are grown on both GaAs and AlAs buffers, using GaAs (001) as a substrate. The structural properties of these high-quality, epitaxially grown single crystals are characterized using in situ pyrometry, reflection high-energy electron diffraction, high-resolution X-ray diffraction, X-ray reflectivity, atomic force microscopy, cross-sectional scanning electron microscopy, and tunneling electron microscopy. The optimal processing parameters for producing these Cd3As2 thin films and their virtual substrates are described in detail for easy application in future molecular beam epitaxy. Assessment of the electronic properties of Cd3As2 are conducted using Van der Pauw geometry Hall measurements at 2K with external magnetic fields ranging up to 14 T. The electronic attributes of resistivity, carrier density and mobility, and the presence of the quantum Hall effect are probed and reported. The potential epitaxy of different magnetic Cd3As2 alloys and proximal magnetic films are explored through calculations of Gibbs free energy. Sm is chosen as the candidate for future work seeking the quantum anomalous Hall effect in magnetic Cd3As2.