Nanomaterials, Devices and Interface Circuits: Applications for Optoelectronic and Energy Harvesting

In the first part of this dissertation, the effect of surface passivation on the near-band-edge emission (NBE) of as grown ZnO nanowires has been studied. It was shown that decorating the ZnO nanowires with sputtered metallic nano-particles can strongly enhance the NBE of as grown ZnO nanowires. Since the ZnO NWs have a weak NBE, numerous studies have been done to enhance the NBE and photoluminescence (PL) efficiency of ZnO NWs. Different methods such as polymer coating of ZnO NWs and hydrogen plasma treatment are seen to boost the NBE and photoluminescence efficiency of ZnO NWs. Recently, among the different passivation methods the effect of metallic nanoparticles (NPs) on PL properties of ZnO NWs have been the focus of much research. In most studies an enhancement of NBE was observed and the results were interpreted in terms of surface plasmons, unintentional hydrogen incorporation and the nature of the contact formed between the metal and ZnO NWs. Our study demonstrates that decorating the ZnO NWs with metal NPs in the presence of high energy Ar atoms cleans the surface of ZnO NWs from near surface traps and surface adsorbed species, thus it leads to a strong enhancement of NBE emission and a relative reduction of visible peak.;In the second part of this thesis, the piezoelectric properties of ZnO nanowires have been the focus of the study. Since demonstration of the first nano-scale energy harvester device based on one single ZnO NWs a comprehensive model which can explain the generation of strain induced piezoelectric field in the presence of free carriers has not been proposed. The piezoelectric constitutive equations, which are used to calculate the strain induced piezoelectric potential, can be applied in a medium with zero or negligible free carriers.;Therefore, in case of piezoelectric metal oxide semiconductor materials such as ZnO NWs with a free carrier density about 1018 cm-3 the constitutive equations cannot be applied directly. Here, we have developed a model which strongly conciliates some strongly divergent opinions behind operation of the semiconductor piezoelectric nano-generators. In order to develop such a physics-based model, first the electrostatic potential and depletion width in piezoelectric semiconductor NWs are derived by considering a non-depleted region and a surface depleted region and solving the Poisson equation. By determining the piezoelectric induced charge density, in terms of equivalent density of charges, the effect of piezoelectric charges on the surface depletion region and the distributed electric potential in NW have been investigated. The numerical results demonstrate that the ZnO NWs with smaller radii have a larger surface depletion region which results in a stronger surface potential and depletion region perturbation by induced piezoelectric charges.;In the last part of our study on piezoelectric energy harvesters the low power interface circuits which are one of the fundamental building blocks of any self-powered devices has been studied. Utilization of piezoelectric energy harvesters to power electronic devices has attracted significant attention recently. However, the power generated by a piezoelectric energy harvester is too small to power an electronic device directly. Hence, a low power, efficient interface circuit between the energy harvester and a storage unit is essential in any piezoelectric energy harvesting system. Here, a new interface circuit topology for piezoelectric energy harvesting applications is proposed and various design factors for circuit-level optimization are discussed. In the proposed interface circuit a peak detector circuit operating in the sub-threshold region with power dissipation around 160 nW together with a delay circuit form the control block, which is one of the more important units of the piezoelectric energy harvesting systems. (Abstract shortened by UMI.).