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Register a new userEnhancement of ultra-thin film emission using a waveguiding active layer
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Added by
Christophe Couteau Asst Prof
Publication date
2013
fields
Physics
and research's language is
English
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We present a theoretical study on the impact of an active optical layer on the emission properties of an ultrathin luminescent film. While the study can be generalized to any material, we focus here on a simple layered medium composed of a conjugated polymers (CPs) thin film, a zinc oxide layer (ZnO) and a sapphire substrate. The study spreads throughout variable aspects including the effect of the structure parameters on the CP luminescence and radiation pattern and more specifically the influence of the absorption and emission properties of the active layer. Comparing between the passive and active layer cases, the obtained results show that an enhancement of the CP luminescence of more than 20 times can be obtained by using an optically active underlying layer. The results can be explained in terms of photon recycling where the optically active layer acts as a photon reservoir and a secondary light source for the ultra thin film. This general concept is of a special interest for ultra-trace chemosensor.
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Zinc Oxide thin films were grown on c-sapphire substrates using pulsed laser deposition. Pump power dependence of surface emission spectra, acquired using a quadrupled 266 nm laser, revealed room temperature stimulated emission (threshold of 900 kW/cm2). Time dependent spectral analysis plus gain measurements of single-shot, side-emission, spectra pumped with a nitrogen laser revealed random lasing indicative of the presence of self-forming laser cavities. It is suggested that random lasing in an epitaxial system rather than a 3-dimensional configuration of disordered scattering elements, was due to waveguiding in the film. Waveguiding causes light to be amplified within randomly-formed closed-loops acting as lasing cavities.
We reported here a high-performance In2O3/InZnO bilayer metal-oxide (BMO) thin-film transistor (TFT) using ultra-thin solution-processed ZrOx dielectric. A thin layer of In2O3 offers a higher carrier concentration, thereby maximizing the charge accumulation and yielding high carrier mobility. A thick layer of InZnO controls the charge conductance resulting in low off-state current and suitable threshold voltage. As a consequence, the BMO TFT showed higher filed-effect mobility (37.9 cm2/V s) than single-layer InZnO TFT (7.6 cm2/V s). More importantly, an on/off current ratio of 109, a subthreshold swing voltage of 120 mV/decade, as well as a threshold voltage shift (less than 0.4 V) under bias stress for 2.5 hours were obtained simultaneously. These promising properties are obtained at a low operation voltage of 3 V. This work demonstrates that the BMO TFT has great potential applications as switching transistor and low-power devices.
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