Investigation on low dimensional semiconductor systems carbon nanostructures and nanomaterials

Abstract

Semiconductors rule the electronics industry for the past several years due to their excellent electronic and transport properties. As the technology grows and moves towards miniaturization, low dimensional semiconductor systems (LDSS) such as quantum well (2D) and quantum wire (1D) finds its importance. Lot of research has already been carried out throughout the world that leads to the practical realization of novel devices such as quantum well lasers, quantum dot light emitting diodes with very high efficiency. Still the research is going on to explore the possibilities of technical devices. In the present work, the electrical property of both defect-free and defected carbon nanotubes due to applied perturbations like pressure, adsorption and doping have been explored and the results are compared with other materials. From the results, we could observe that the electrical conductivity change in defected tubes is drastic than in the defect-free tubes. From this study we observe that ammonia gas molecule exhibits drastic change in electrical conductivity than other gas molecules. The results show the semiconductor to metal transition (SMT) in donor doped CNTs while there is no feasibility of such a transition in 2D GaAs. For the first set, it is observed that the curvature effect is strong in chiral carbon nanotubes than in achiral tubes. Also, the energy required for an electron to jump into the conduction band is 0.25eV (approximately) for all the chiral tubes considered here and is less than 0.4eV, which falls in metallic region of CNTs. This indicates the strong effect of chirality on the n-type doped semiconducting SWNTs. As a second part of doping studies, (5,0) achiral and (4,2), (4,3) chiral CNTs of diameter ~0.4nm have been considered. For this case the effective mass values are estimated by including tube curvature. Future plan for further research includes i) confinement in small diameter CNTs ii) electrical property in doped nanotubes under pressure (iii) phase transition and hydrogen storage in graph