Quantum Transport in Silicon-On-Insulator Structures


Kei Takashina, Yukinori Ono, Akira Fujiwara, Yoshiro Hirayama*, and Toshimasa Fujisawa
Physical Science Laboratory

 Besides being of immense technological importance, electrons in silicon offer a number of unique possibilities for exploring new physical conditions and new phenomena. One of these arises due to their bulk dispersion relation where there are six, energetically degenerate conduction band valleys. In Si(100)-MOSFETs where electrons are two-dimensionally confined, this six-fold degeneracy is lifted, due to anisotropic effective mass, to leave only two low lying valleys available for occupation. 2-D electrons in such structures consequently have freedom as to how they occupy these degenerate valleys giving them a valley degree of freedom on top of in-plane motion and spin.
 In the present study, we have been able to show that valley-splitting, which lifts this remaining two-fold valley degeneracy can be enlarged and controlled over an unprecedented extent using SOI (Silicon-On-Insulator) MOSFETs [1] and that its effects can be observed clearly by direct transport measurements even without magnetic field (Figures) [2]. The results demonstrate considerable potential for exploring valley-related phenomena and new device possibilities.

[1] K. Takashina, A. Fujiwara, S. Horiguchi, Y. Takahashi, and Y. Hirayama, Phys. Rev. B 69 (2004) 161304(R).
[2] K. Takashina, Y. Ono, A. Fujiwara, Y. Takahashi, and Y. Hirayama, Phys. Rev. Lett. 96 (2006) 236801.
*Present address: Tohoku University

Fig. 1. Two-terminal conductance at 4.2K as a function of front-gate voltage VFG at various values of back-gate voltage VBG. The inset shows the experimental setup. A and B mark features associated with second-confinement-subband occupation and valley splitting respectively. Right: 2nd derivative of the data showing the evolution of the features. The white squares joined by lines mark self-consistently calculated positions of the onset of second-confinement-subband occupation using nominal parameters of the device. (The feature marked C is due to the onset of conduction.)

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