| Research Abstract |
We study molecular beam epitaxial (MBE) growth, structural and electrical properties of novel epitaxial metal/semiconductor heterostructures (MSHs), consisting of monocrystalline CoAl, an intermetallic compound, and AlAs/GaAs III-V semiconductors. The CoAl with stoichiometric composition has a CsCl-type crystal structure whose lattice constant is very close to half the lattice constant of GaAs and AlAs, hence, it is a good candidate as a constituent metal in epitaxial monocrystalline metal/semiconductor heterostructures. We explore MBE growth of CoAl thin films on AlAs/GaAs, and also semiconductor overgrowth on ultrathin CoAl films, together with structural characterizations by in-situ reflection high energy electron diffractions, ex-situ X-ray diffractions and cross sectional transmission electron microscopy. By optimizing the growth parameters and procedures, high quality monocrystalline CoAl/AlAs/GaAs heterostructures with atomically abrupt interfaces have been successfully grown. Furthermore, we describe the electrical properties of such novel heterostructures, including Schottky barrier heights of CoAl/AlAs/GaAs MSHs and transport properties in ultrathin buried CoAl films.
We have fabricated resonant tunneling structures having a buried ErAs semimetallic quantum well and AlAs double barriers, on (001) GaAs substrates. In order to suppress three dimensional island growth of GaAs and AlAs on ErAs and to obtain flat interfaces, we adopted a template approach, in which one monolayr of Mn was deposited on ErAs prior to the growth of AlAs, in molecular beam epitaxy. In the current-voltage characteristics at room temperature, negative differential resistance was clearly observed in a significant number of diodes with the ErAs thickness ranging from 2.6 nm to 5.0 nm. This room temperature device operation on (001) substrates is, we believe, an important step towards the realization of semimetal/semiconductor hybrid quantum devices.
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