Jingqi Li

Carbon Nanotube Driver Circuit for 6 × 6 Organic Light Emitting Diode Display

Single-walled carbon nanotube (SWNT) is expected to be a very promising material for flexible and transparent driver circuits for active matrix organic light emitting diode (AM OLED) displays due to its high field-effect mobility, excellent current carrying capacity, optical transparency and mechanical flexibility. Although there have been several publications about SWNT driver circuits, none of them have shown static and dynamic images with the AM OLED displays. Here we report on the first successful chemical vapor deposition (CVD)-grown SWNT network thin film transistor (TFT) driver circuits for static and dynamic AM OLED displays with 6u2009×u20096 pixels. The high device mobility of ~45u2009cm2V−1s−1 and the high channel current on/off ratio of ~105 of the SWNT-TFTs fully guarantee the control capability to the OLED pixels. Our results suggest that SWNT-TFTs are promising backplane building blocks for future OLED displays.

Influence of Triton X-100 on the characteristics of carbon nanotube field-effect transistors

Triton X-100 is used as a surfactant to disperse carbon nanotube (CNT) bundles. Its influence on the transfer characteristics of carbon nanotube field-effect transistors (CNTFETs) fabricated with the dispersed CNTs by the AC dielectrophoresis technique has been studied. We find that the surfactant at the interface between the CNTs and Au electrodes can change the work function of the electrodes and therefore convert the CNTFETs from typical p-type to having ambipolar characteristics. The adsorbed surfactant between the CNTs and SiO2 results in a significant hysteresis in the transfer characteristics of the CNTFETs.

Erosion resistance of polycrystalline diamond films to atomic oxygen

Abstract Polycrystalline diamond films deposited using hot filament chemical vapor deposition (CVD) technique have been investigated in atomic oxygen simulated as low earth orbit environment to examine their erosion resistance properties. After exposure to the atomic oxygen beam with a flux of 2.6×1016 atoms/cm2 s, the diamond films only show a small mass loss. The reaction efficiency is estimated to be between 6.35×10−26 and 8.28×10−26 cm3/atom. Oxidation mechanism is investigated through the reaction temperature influence on the reaction rate. We suggest that atomic oxygen reacts with diamond surface and forms ether (C–O–C) and carbonyl (>Cue605O) configurations besides eroding the surface.

Influence of contact height on the performance of vertically aligned carbon nanotube field-effect transistors

Vertically aligned carbon nanotube field-effect transistors (CNTFETs) have been experimentally demonstrated (J. Li et al., Carbon, 2012, 50, 4628-4632). The source and drain contact heights in vertical CNTFETs could be much higher than in flat CNTFETs if the fabrication process is not optimized. To understand the impact of contact height on transistor performance, we use a semi-classical method to calculate the characteristics of CNTFETs with different contact heights. The results show that the drain current decreases with increasing contact height and saturates at a value governed by the thickness of the oxide. The current reduction caused by the increased contact height becomes more significant when the gate oxide is thicker. The higher the drain voltage, the larger the current reduction. It becomes even worse when the band gap of the carbon nanotube is larger. The current can differ by a factor of more than five between the CNTEFTs with low and high contact heights when the oxide thickness is 50 nm. In addition, the influence of the contact height is limited by the channel length. The contact height plays a minor role when the channel length is less than 100 nm.

A high efficiency and cost effective Si thin film solar cell with novel periodic nanohole textured surface

Silicon thin film with nanohole array decorated surface is systematically studied via simulation for solar energy harvesting and compared with nanopillar array textured one. It is found that nanohole array structures can significantly improve the light absorption of the silicon thin film with optimized structural dimensions. Moreover, for the same thickness and optimized structure dimensions, the nanohole array shows better light-trapping than nanowire array. The electrical performance of the nanohole array textured silicon thin film solar cell is also optimized in terms of minority carrier diffusion length, emitter doping level, emitter junction depth after considering the impact of surface recombination velocity. The result provides a practical guideline to design and fabricate high efficiency nanohole textured Si thin film solar cell.

ANNEALING EFFECTS ON ELECTRIC CONTACTS BETWEEN CARBON NANOTUBES AND ELECTRODES

Single wall carbon nanotubes suspended in isopropyl alcohol are placed between two Au electrodes by ac dielectrophoresis method. Total resistance including the contact resistance and intrinsic tube resistance is found to decrease from 105–106 Ω for as-prepared samples to 104 Ω after annealing at 300°C in ambient environment. Measured I–V curves and Schottky barrier heights suggest that the electric contacts are changed from Schottky to Ohmic characteristics after annealing. These results demonstrate that annealing in ambient environment is a simple and efficient way to decrease the contact resistance.