Large-area nanofabrication and applications in advanced nanoelectronic and nanophotonic devices

Abstract

The research work presented in this dissertation includes novel large area nanofabrication techniques and their applications in advanced nanoelectronic and nanophotonic devices. The fabrications and applications include: 1) high performance transparent electrodes, 2) a novel plasmonic nanocavity and its applications in organic solar cells and light emitting diodes, and 3) a bipolar plasmonic nonlinear optical device to enhance and tune second harmonic generation. Based upon these topics, the thesis is divided into the following parts.

First, a novel transparent electrode (TE), metallic deep subwavelength mesh electrode is developed and fabricated, showing better transmittance and conductance than previous TEs. Its performance dependence on nanostructure geometries and materials are investigated. The deep-subwavelength mesh electrode also has excellent antiglare properties. Such electrodes are fabricated on 4” wafer by nanoimprint, scalable to meter sizes.

Second, a novel plasmonic nanocavity from the MESH is developed, named "plasmonic cavity with subwavelength hole-array (PlaCSH)", consisting of a thin MESH as a transparent front electrode, a thin metal back electrode, and in-between layer of active material. This structure is used to create high performance solar cells and LEDs.

PlaCSH solar cell gives a solution to three central challenges in organic solar cells (light coupling into solar cell, light trapping in a sub-absorption-length-thick layer, and replacement of the indium-tin-oxide). Experimentally, the PlaCSH polymer SCs achieve high light coupling-efficiency/absorptance/power conversion efficiency, along with broad-band, Omni angle/polarization acceptance. In OLEDs, PlaCSH shows numerous benefits with both the small- molecule and polymer active materials. Enhanced light extraction, internal quantum efficiency, ambient light absorption, contrast, viewing angle, brightness, and decreased glare are all observed. The above experiments – along with simulations – confirm that PlaCSH can serve as an excellent optical antenna for both absorption and radiation.

In the last section, a new plasmonic nonlinear light generation (NLG) structure, termed “Plasmonic-enhanced, Charge-Assisted Second-Harmonic generator” (p-CASH), is developed, and shows high second-harmonic generation (SHG) enhancement, large SHG tunability by bias, wide tuning range, and high stability. A new SHG tuning mechanism for p-CASH is proposed. The new structure, new properties and new understanding should open up new designs and applications of NLG.