Bismuth based nanoelectronic devices

Bismuth (Bi) is a unique electronic material with small effective mass (∼0.001me) and long carrier mean free path (100 nm at 300K). It is particularly suitable for studying nano scale related phenomena such as size effect and energy level spacing. In this thesis work, bismuth based nanoelectronic devices were studied. Devices were fabricated using a combination of electron beam (e-beam) writing and thermal evaporation techniques. Dimensions of the fabricated devices were in the order of 100 rim. All structures were optimized for individual electrical characterization. Three types of devices were studied: Bi nanowires, Bi nanowires with dual side-gate structures and Bi nanodot structures. In the study of Bi nanowires, metal-to-semiconductor transition phenomenon and size effect were observed. The conduction behavior of Bi nanowires changed from metallic to semiconductor when the device's critical dimension was reduced to below 50 nm. It is a solid experimental evidence of the quantum confinement-induced bandgap theory. Additionally, it has been found in the present work that resistivity of individual Bi nanowire increased as linewidth decreased indicating size effect occurred in the Bi nanowires. Dual side-gate structures were formed adjacent to the Bi nanowires in an attempt to modulate the current. Measurements showed a 7% of current modulation. The small current modulation suggested the high carrier density in the nanowire which has prevented the full depletion of free carriers. 100 nm-diameter Bi nanodot structures were fabricated utilizing proximity effect of e-beam writing. Precise control of electron doses and process conditions led to the successful fabrication of sub-nanometer tunneling junctions to the nanodots. Significant non-linear current-voltage (I-V) characteristic was observed at low temperatures. The step like I-V characteristic was a strong indication of energy level spacing in the zero-dimensional nanodot structure. The successful observation of energy level spacing in a relatively large nanodot is due to the small effective mass of bismuth material which leads to a measurable energy level spacing