Spin transistor based on cadmium fluoride nanostructures
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DIMENSIONAL SYSTEMS
Spin Transistor Based on Cadmium Fluoride Nanostructures N. T. Bagraeva^, O. N. Gimbitskayaa, L. E. Klyachkina, A. M. Malyarenkoa, I. A. Shelykha, A. I. Ryskinb, and A. S. Shcheulinb aIoffe
Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia ^e-mail: [email protected] bSt. Petersburg State University of Information Technologies, Mechanics, and Optics, St. Petersburg, 197101 Russia Submitted July 8, 2008; accepted for publication July 10, 2008
Abstract—A study of CdBxF2 – x/p-CdF2/CdBxF2 – x planar sandwich structures fabricated on n-CdF2 crystal surface was carried out in order to obtain the spin-transistor effect at room temperature. Features related to the band gap of CdF2 (7.8 eV) along with those related to the spectrum for two-dimensional (2D) hole subbands in p-CdF2 quantum well (QW) were observed in the current–voltage characteristics for ultrashallow p+–n junctions. The results obtained demonstrate the important role for 2D hole subbands in the mechanism of the “proximity effect” that appears due to Andreev’s reflection in sandwich structures consisting of a narrow QW confined between superconducting barriers. Resonance behavior for the longitudinal voltage in a weak magnetic field normal to the plane of the p-CdF2 QW gives evidence for high degree of spin polarization for 2D holes. Analysis of the dependences for the 2D-hole-gas conductance on the magnitude and direction of the magnetic field normal to the plane of the p-CdF2 QW reveals anti-crossings for Zeeman sublevels in the singlet ground state and triplet excited state of boron dipole centers, responsible for the spin polarization of 2D holes in edge channels in the p-CdF2 QW. The high degree of spin polarization for 2D holes in edge channels in the p-CdF2 QW identifies the mechanism underlying spin-transistor I–V characteristics observed upon the variation of the gate voltage, which controls the magnitude of Bychkov–Rashba’s spin–orbit coupling. PACS numbers: 73.50.-h, 73.23.Ad DOI: 10.1134/S1063782609010163
conductors [4, 5]. Forward I–V characteristics for the p+–n junctions and p+-Si/n-CdF2 heterojunctions obtained reveal the band gap of CdF2 (7.8 eV). Furthermore, a study of the conductance along the p+–n junction plane identified the presence of a quantum well (QW) with type conductivity, containing degenerate two-dimensional (2D) high-mobility hole gas. In addition, analysis of the forward I–V curves for p+–n junctions and p+-Si/n-CdF2 heterojunctions provided for the identification of the valence-band structure for CdF2 crystals; apparently, the band structure is revealed as a result of ballistic transport for holes injected into the bulk of n-CdF2. Data from high-resolution I–V characteristics are in good agreement with the valence-band structure of CdF2 obtained by optical and photoelectron spectroscopy [6]. Thus, properties for CdF2-based lowdimensional structures make them rather promising for high-temperature nano- and optoelectronics, especially for implementation of electron-
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