Transport Properties and Observation of Semimetal-Semiconductor Transition in Bi-based Nanowires
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Transport Properties and Observation of Semimetal-Semiconductor Transition in Bi-based Nanowires Yu-Ming Lin,1 Stephen B. Cronin,2 Oded Rabin,3 Jackie Y. Ying,4 and Mildred S. Dresselhaus1,2 1 Department of Electrical Engineering and Computer Science, 2Department of Physics, 3 Department of Chemistry, 4Department of Chemical Engineering Massachusetts Institute of Technology, Cambridge, MA 02139 ABSTRACT Temperature-dependent resistance measurements of Bi-related nanowire arrays with different wire diameters and Sb concentrations are performed. The variation in the measured R(T) curves of these nanowires is closely related to the unique semimetal-semiconductor transition in Bi, and the results are explained by theoretical simulations. It is found that the special feature of the maximum in the resistance ratio R(10 K)/R(100 K) can be employed to experimentally identify the conditions for the semimetal-semiconductor transition. INTRODUCTION Nano-crystalline materials have received much attention recently because of their importance in fundamental studies and for potential applications in diverse fields. Various unusual phenomena and properties have been predicted and observed in nanoscale materials due to the enhanced finite-size effects when these materials are compared to their bulk counterparts. Among existing nanostructures, crystalline nano-sized materials with well-defined geometries comprise an important category for nanostructured materials, since their structural properties are usually more readily characterized, giving rise to better-defined attributes compared with other nano-structured materials. Thus, their physical properties may be predicted based on the wellestablished knowledge of their bulk counterparts, and models for various size effects can be developed to investigate the significance of their smallness. Bismuth (Bi) is a very attractive material for the study of low-dimensional systems due to its unique band structure and its very small electron effective masses [1]. Since quantum confinement effects are inversely proportional to the effective masses, these size effects are more readily observed in Bi than in other materials at a given size. Bulk bismuth is a group V semimetal, in which the electrons are distributed in three highly anisotropic carrier pockets at the
Figure 1. Schematic diagram showing an electronic phase transition (b) in Bi from a semimetal (a) to a semiconductor (c) as the size of the Bi crystal decreases. The transition is induced by a quantum confinement effect that causes the conduction and valence band energy extrema to rise and to decrease, respectively.
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L points of the Brillouin zone, and the holes are contained in one pocket at the T point [1]. It has long been expected that nanocrystalline bismuth may undergo a transition from a semimetal to a semiconductor as the size diminishes [2]. This unique semimetal-semiconductor transition occurs because, as the size of the Bi crystal decreases, the energy of the L-point conduction and the T-point valence ban
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