Understanding the impact of Schottky barriers on the performance of narrow bandgap nanowire field effect transistors.

Semiconductor nanowires have been explored as alternative electronic materials for high performance device applications exhibiting low power consumption specs. Electrical transport in III-V nanowire (NW) field-effect transistors (FETs) is frequently governed by Schottky barriers between the source/drain and the NW channel. Consequently the device performance is greatly impacted by the contacts. Here we present a simple model that explains how ambipolar device characteristics of NW-FETs and in particular the achievable on/off current ratio can be analyzed to gain a detailed idea of (a) the bandgap of the synthesized NWs and (b) the potential performance of various NW materials. In particular, we compare the model with our own transport measurements on InSb and InAs NW-FETs as well as results published by other groups. The analysis confirms excellent agreement with the predictions of the model, highlighting the potential of our approach to understand novel NW based materials and devices and to bridge material development and device applications.

Oxygen plasma exposure effects on indium oxide nanowire transistors.

In(2)O(3) nanowire transistors are fabricated with and without oxygen plasma exposure of various regions of the nanowire. In two-terminal devices, exposure of the channel region results in an increased conductance of the channel region. For In(2)O(3) nanowire transistors in which the source/drain regions are exposed to oxygen plasma, the mobility, on-off current ratio and subthreshold slope, are improved with respect to those of non-exposed devices. Simulations using a two-dimensional device simulator (MEDICI) show that improved device performance can be quantified in terms of changes in interfacial trap, shifts in fixed charge densities and the corresponding reduction in Schottky barrier height at the contacts.

Nanoscale Carbon Modified α-MnO2 Nanowires: Highly Active and Stable Oxygen Reduction Electrocatalysts with Low Carbon Content.

Carbon-coated α-MnO2 nanowires (C-MnO2 NWs) were prepared from α-MnO2 NWs by a two-step sucrose coating and pyrolysis method. This method resulted in the formation of a thin, porous, low mass-percentage amorphous carbon coating (<5 nm, ≤1.2 wt % C) on the nanowire with an increase in single-nanowire electronic conductivity of roughly 5 orders of magnitude (α-MnO2, 3.2 × 10-6 S cm-1; C-MnO2, 0.52 S cm-1) and an increase in surface Mn3+ (average oxidation state: α-MnO2, 3.88; C-MnO2, 3.66) while suppressing a phase change to Mn3O4 at high temperature. The enhanced physical and electronic properties of the C-MnO2 NWs-enriched surface Mn3+ and high conductivity-are manifested in the electrocatalytic activity toward the oxygen reduction reaction (ORR), where a 13-fold increase in specific activity (α-MnO2, 0.13 A m-2; C-MnO2, 1.70 A m-2) and 6-fold decrease in charge transfer resistance (α-MnO2, 6.2 kΩ; C-MnO2, 0.9 kΩ) were observed relative to the precursor α-MnO2 NWs. The C-MnO2 NWs, composed of ∼99 wt % MnO2 and ∼1 wt % carbon coating, also demonstrated an ORR onset potential within 20 mV of commercial 20% Pt/C and a chronoamperometric current/stability equal to or greater than 20% Pt/C at high overpotential (0.4 V vs RHE) and high temperature (60 °C) with no additional conductive carbon.