Theoretical Study Of Charge And Spin Resolved Quantum Transport In Iii V Semiconductor Nanostructures PDF Download

Electrons, the fundamental charge carriers in solid-state devices, possess three intrinsic properties: mass, charge and spin. Spin is a quantum mechanical property, but can be loosely visualized as a tiny "intrinsic" magnetic dipole moment attached to an electron. In conventional electron devices, spin magnetic moments point along random directions in space and play no significant role in device operation. In the emerging field of "spintronics" the central theme is to harness the spin degree of freedom of charge carriers to realize novel data storage and information processing technologies. Spintronic devices are already ubiquitous in state-of-the-art hard disks with large storage densities. A concerted global effort is underway to explore various spin-based information processing concepts, which can potentially be more energy-efficient than traditional charge-based electronics. In recent years, substantial research has been devoted to understanding carrier spin dynamics in metallic multilayers, tunnel junctions and inorganic semiconductors such as silicon, germanium and various III-V compounds. On the other hand, p-conjugated organic semiconductors that play a crucial role in organic electronics and displays are relatively new materials in the area of spintronics. Organic semiconductors offer several advantages (such as mechanical flexibility, chemical tunability of physical properties, low-cost and low-temperature processing) compared to their inorganic counterparts. The ability to control carrier spin dynamics in organic materials will open up possibility of new devices such as flexible non-volatile memories, spin-based organic light emitting diodes and spin filters. iii In this work, we have explored two key spin related phenomena in organic semiconductor nanostructures: (a) spin-polarized transport and (b) spin filtering. In the first sub-project, we explore spin transport in "nanowire" geometry instead of commonly studied thin film devices. Such experiments shed light on the spin relaxation mechanisms in organics and indicate ways to minimize such effects. Fabrication of organic nanowires with well-controlled geometry in the sub-100 nm range is a non-trivial task, and in this subproject we have developed a novel technique for this purpose. Spin transport in rubrene nanowires has been studied, which indicates significant suppression of spin relaxation in nanowire geometry compared to rubrene thin films. Our experimental data indicates that spin-orbit coupling is the dominant spin relaxation mechanism in rubrene nanowires. In the second sub-project, we explore spin filtering (transmission of one particular type of spin) through an organic nanostructure in which single wall carbon nanotubes (SWCNT) are wrapped with single stranded DNA (ssDNA) molecules. Efficient spin filtering has been observed in this system, which may enable magnetless spintronic devices in the future.