Steven McGarry

Circuit-level transient simulation of configurable ring resonators using physical models

This paper presents a methodology for the incorporation of actively configurable interference-based optical elements into a circuit-level optoelectronic simulator. The self-consistent optoelectronic simulator is based on modified nodal analysis. The paper uses ring-resonator-based devices as examples of configurable devices. Construction of compact models of these devices from optical scattering and the waveguide elements using fundamental principles is presented in detail. In the results section, accuracy of the compact model of the ring resonator is first confirmed for static devices for steady-state and transient conditions. Last, the devices are placed in a complex optical circuit and used to modulate an optical carrier and select a particular channel from a multichannel optical signal. The modelling framework proposed proved to be robust and efficient for transient simulation of configurable elements in a self-consistent optoelectronic simulation engine.

Fabrication and modelling of screen-printed active electrolytic polymer devices

Active polymer materials allow the construction of cheap, flexible circuitry using simple printing techniques. A process and devices capable of performing a variety of circuit functions using electrolytic technology have been developed. The process is based on a simple screen printing system that allows the formation of multilayer circuitry with no active layer-to-layer alignment. Using this system, it has been possible to build a number of circuits utilizing transistor-like electrolytic devices and other active devices with novel topologies. Models have been developed that provide the ability to simulate arbitrary device geometries using a standard-cell approach for the basic elements required. These have allowed accurate simulation of the dynamic response of a number of device structures to be performed.

Ultrahigh-surface-area anatase thin films by direct oxidation of Ti film with hydrogen peroxide

Nanostructured titania films are formed by directly oxidizing titanium with hydrogen peroxide. A low-temperature anneal transforms the films from an amorphous phase to anatase crystal. Surface-area measurements of the annealed nanostructured titania using the Brunauer, Emmett, and Teller method reveal a specific surface area of 535 m 2 /g, the highest ever reported for a nanostructured titania film. The low-temperature anneal is compatible with heat-treated polyimide or polyester substrates for roll-to-roll processing of flexible electronics or solar cells.

Effect of PEDOT band structure on conductive polymer-insulator-silicon junctions

The effect of replacing a conventional metal with an organic conductive polymer in a metal-insulator-semiconductor (MIS) diode is examined theoretically and experimentally. Two sets of MIS diodes, one with gold and the other with poly(3,4-ethylenedioxythiophene) as the top “metal”, have been manufactured in parallel. Despite the two conductors having similar reported work functions of 5.1 eV to 5.2 eV, the hybrid devices exhibited far lower current densities as compared to their inorganic counterparts. Simulating the device behaviour reveals the limited width of the energy bands in the conductive polymer as the reason for low current density in the hybrid MIS.The effect of replacing a conventional metal with an organic conductive polymer in a metal-insulator-semiconductor (MIS) diode is examined theoretically and experimentally. Two sets of MIS diodes, one with gold and the other with poly(3,4-ethylenedioxythiophene) as the top “metal”, have been manufactured in parallel. Despite the two conductors having similar reported work functions of 5.1 eV to 5.2 eV, the hybrid devices exhibited far lower current densities as compared to their inorganic counterparts. Simulating the device behaviour reveals the limited width of the energy bands in the conductive polymer as the reason for low current density in the hybrid MIS.

Characterization and assessment of a novel hybrid organic/inorganic metal-insulator-semiconductor structure for photovoltaic applications

Hybrid organic/inorganic photovoltaic devices have recently emerged as a possible solution to the stability, charge transfer and mobility issues that have been limiting the lifetimes and efficiencies of the organic solar cells. The purpose of the project presented here is to assess the potential of a new hybrid metal-insulator-semiconductor (MIS) photovoltaic device design developed at Carleton University. The silicon substrate is nanostructured with a wet chemical etch resulting in about 1:1 aspect ratio structures of roughly 300nm in size. The interface is passivated with a thin dielectric tunnel barrier of alumina or silica. A layer of transparent conducting polymer, Poly(3,4-ethylenedioxythiophene) (PEDOT), is added through in-situ polymerization. The structure is then completed with a printed silver/polymer composite collection electrode. The electrical current-voltage (I-V) and capacitance-voltage(C-V) characteristics along with the effect of nanostructuring the substrate on the performance of such a solar cell is explored by comparison with unstructured devices. The C-V and I-V measurements are used to estimate changes in the effective device junction due to the structuring. The quality of the insulator layer as well as its optimal thickness are studied. The fabricated structures show photovoltaic behavior with the structuring yielding a significant increase in efficiency. The test structures show promise for the use in photovoltaics and further optimization of such a structure may yield fruitful results in solar applications.