We have synthesized high-quality gallium nitride ͑GaN͒ nanowires by a chemical-vapor-deposition method and studied the electrical transport properties. The electrical measurements on individual GaN nanowires show a pronounced n-type field effect due to nitrogen vacancies in the whole measured temperature ranges. The n-type gate response and the temperature dependence of the current-voltage characteristics could be understood by the band bending at the interface of the metal electrode and GaN wire. The estimated electron mobility from the gate modulation characteristics is about 2.15 cm 2 /V s at room temperature, suggesting the diffusive nature of electron transport in the nanowires.

On a single GaN nanowire, obtained by chemical vapour deposition, several Schottky-junction diodes were fabricated and their electrical transport properties were studied. Alternately attached metal electrodes of Al and Ti/Au formed a Schottky barrier junction (for Al) or an ohmic contact (for Ti/Au), resulting in several diodes on a single nanowire. The current-voltage measurements exhibited clear rectifying behaviour and no reverse-bias breakdown was observed up to the measured voltage, −5 V. The forward-bias threshold voltage was observed to decrease linearly with temperature, from 0.4 V at 280 K to 1 V at 10 K.

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Bismuth telluride (Bi 2 Te 3 ) and its alloys are some of the best available materials for near-room-temperature thermoelectric applications. [ 1 ] In particular, Bi 2 Te 3 nanowires have been studied extensively [3][4][5] because low-dimensional thermoelectric materials are expected to have a higher fi gure of merit due to quantum confi nement effects. [ 2 ] However, memory switching behavior has never been studied in Bi 2 Te 3 nanowires. Here, we report for the fi rst time reversible memory switching effects in Bi 2 Te 3 nanowires fabricated using anodized aluminum oxide (AAO) membranes. The fi ndings show that Bi 2 Te 3 nanowires display a reversible crystalline-amorphous phase change that is induced by a temperature, laser, or electric fi eld, similar to that reported for chalcogenide materials (Ge-Sb-Te alloys, GST). [6][7][8][9] We demonstrate that Bi 2 Te 3 nanowires show considerable promise as building blocks for phase-change random access memory (PRAM).Phase-change materials are used in nonvolatile optical memory (e.g., CDs and DVDs), and are being actively investigated as the media in universal solid-state memory devices that combine rapid read and write speeds, high storage density, and non-volatility. [ 10 ] The key feature of PRAM is the reversible phase transition of the phase-change material, caused by an electrical pulse, between the crystalline (low resistivity, SET) and amorphous (high resistivity, RESET) states.A major obstacle to achieving high-density PRAM devices is the large writing currents required to generate suffi cient thermal energy for a phase change, particularly during the crystal-to-amorphous phase transition, since a high current is required for melting. To reduce the writing currents, GST nanowires have been synthesized and were shown to satisfy many of the attributes of universal non-volatile memory devices. [ 12 , 13 ] However, GST nanowires are usually synthesized using vapor transport methods at high temperatures [11][12][13] and their large-scale assembly is not yet feasible. On the other hand, Bi 2 Te 3 nanowires exhibit memory switching characteristics that are comparable to GST nanowires [ 11 , 12 ] and they can be fabricated at room temperature using AAO membranes.Furthermore, the vertical growth of nanowires on a substrate permits a high-density assembly of Bi 2 Te 3 nanowires. Here, we describe in detail the memory switching properties of Bi 2 Te 3 nanowires.We fabricated Bi 2 Te 3 nanowires using electrodeposition within the nanopores of an AAO membrane made by anodizing Al plates. The nanowire structures were examined using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). An XRD pattern of the as-grown nanowires ( Figure 1 a) agreed with the rhombohedral crystal structure of Bi 2 Te 3 (JCPDS No. 15-0863) reported by others. [ 3 , 4 ] The spacing between adjacent planes in the HRTEM image (Figure 1 b) was 0.202 nm, which corresponded to the (110) lattice planes of the rhombohedral Bi 2 Te 3 crystal structure. In addition, the...

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