Molecular Beam Epitaxy-grown Films Research Articles

Topological Phase Control of Surface States in Bi2Se3 via Spin-Orbit Coupling Modulation through Interface Engineering between HfO2-X.

The direct control of topological surface states in topological insulators is an important prerequisite for the application of these materials. Conventional attempts to utilize magnetic doping, mechanical tuning, structural engineering, external bias, and external magnetic fields suffer from a lack of reversible switching and have limited tunability. We demonstrate the direct control of topological phases in a bismuth selenide (Bi2Se3) topological insulator in 3 nm molecular beam epitaxy-grown films through the hybridization of the topological surface states with the hafnium (Hf) d-orbitals in the topmost layer of an underlying oxygen-deficient hafnium oxide (HfO2) substrate. The higher angular momentum of the d-orbitals of Hf is hybridized strongly by topological insulators, thereby enhancing the spin-orbit coupling and perturbing the topological surface states asymmetry in Bi2Se3. As the oxygen defect is cured or generated reversibly by external electric fields, our research facilitates the complete electrical control of the topological phases of topological insulators by controlling the defect density in the adjacent transition metal oxide. In addition, this mechanism can be applied in other related topological materials such as Weyl and Dirac semimetals in future endeavors to facilitate practical applications in unit-element devices for quantum computing and quantum communication.

Ion etching of HgCdTe: Properties, patterns and use as a method for defect studies

Abstract Analysis is performed of the contemporary views on the effect of ion etching (ion-beam milling and reactive ion etching) on physical properties of HgCdTe and on the mechanisms of the processes responsible for modification of these properties under the etching. Possibilities are discussed that ion etching opens for defect studies in HgCdTe, including detecting electrically neutral tellurium nanocomplexes, determining background donor concentration in the material of various origins, and understanding the mechanism of arsenic incorporation in molecular-beam epitaxy-grown films.

Ion implantation and ion milling in MBE Hg 1−xCd xTe films

Direct comparison of the effects of ion implantation with energy E = 20–150 keV (B + ions) and ion milling ( E = 0.5 keV, Ar + ions) on p-type HgCdTe (MCT) molecular-beam epitaxy-grown films with and without graded band-gap surface layers was performed. Both treatments were found resulting in formation of multi-layer n +–p or n +–n–p structures, comprising a radiation-damaged n + -layer with high electron concentration and, optionally, a deeper n-layer with low electron concentration. Basic processes, which occur in MCT under implantation and milling appear to be similar, and include formation of primary radiation defects, their interaction, and in-diffusion of interstitial mercury atoms with their interaction with defects already present in the crystal. The difference in energy and fluence typically used for ion implantation and ion milling in MCT results in different mechanisms of the formation of the n + - and n-layers. The presence of the graded band-gap surface layer was found to affect the thickness of the n-layer via internal electric field associated with the energy gap gradient.