Design, Modeling and Fabrication of Nanostructure Devices for Optoelectronic Applications

Abstract: The current research work encompasses design modelling and fabrication of vertically aligned nanowire metal oxide semiconductor based voltage tunable quantum dot devices for optoelectronic applications. A novel device scheme is proposed for developing such VTQDs by combining the effects of nanowire geometry dependent structural confinement in transverse directions and the voltage assisted surface quantization in longitudinal direction. The formation of VTQDs near oxide/semiconductor interface at room temperature is predicted by developing a self consistent quantum electrostatic simultaneous solver. The photogeneration phenomenon and carrier transport in nanowire MOS based VTQD devices is analytically modelled by adopting non equilibrium Greens formalism based on second quantization field operators for incident photons and generated photocarriers. Engineering the combined effects of structural and electrical quantization has enabled a route for developing wavelength selective direct colour sensors with high spectral resolution. The developed NEGF based analytical model is further extended to obtain photocurrent which can be utilized for harvesting solar energy. A design window is also proposed for obtaining the desired values of solar cell performance parameters with the optimized device parameters such as, the nanowire diameter and oxide thickness. Finally, a patterned array of such nanowire MOS based VTQD devices is fabricated by employing electron beam lithography. The step like behaviour in capacitance voltage characteristics of such devices measured in situ within the FESEM chamber confirms the formation of VTQDs at room temperature. Such patterned nanowire MOS based VTQD devices can be utilized for the advanced photosensing and solar energy harvesting applications.