A novel, fully automated, fabrication and characterization apparatus for polymer light-emitting diodes (PLEDs) was developed. This high throughput apparatus allows the fabrication of 49 devices with a controlled variation of essential parameters like material, material composition, blend concentration, layer thickness, and annealing temperature. Up to now, due to a lack of elaborate design tools, extensive experimental effort is required in order to optimize novel materials, material combinations and device structures for polymer based LEDs. Our novel apparatus provides an extensive dataset which can be used for device optimization and a profound device modeling offering a deeper theoretical understanding of underlying device physics in PLEDs.
With increasing demand for flat panel displays, which usually incorporate indium tin oxide (ITO) thin films, the price of
indium will rise dramatically in the future. For simple and cheap applications (such as LogoLED™, see
www.logoled.com) alternative anode materials have to be used. We will show that polymer-only anodes and wires are
sufficient to fabricate patterned polymer light-emitting devices (PLEDs), such as seven segmented displays. As another
approach to replace ITO we will present results from aluminum / PEDOT anodes devices with better stability and
bottom & top emission.
A polymer thin-film optical touch and proximity sensor is presented. The sensor is based on the monolithic integration of
polymer light emitting diodes, logos or displays, and polymer photodiodes on a common substrate. The main interest in this
new form of optical sensor lies in its potentially cost-effective manufacture on thin and flexible substrates. Potential
applications of such systems range from simple information displays with integrated touch-screen to biochemical sensors.
In this paper we present the theoretical analysis and the measurements of a quasi-optical band-pass filter, operating at 280 GHz. The filter consists of a metal screen, perforated periodically with cross-shaped apertures. The analysis is performed by the Method of the Moments (MoM), using entire domain basis functions. The Boundary Integral- Resonant Mode Expansion method is used in the calculation of the MoM matrices. The transmission and phase shifting characteristics of the band-pass filter were measured with a Terahertz Time-Domain Spectrometer and are compared with the theoretical results. The effects of the smoothness in the cross boundary, due to the fabrication process, are also discussed.
We have applied a newly developed transient terahertz time- domain spectrometer to study the temporal development of the dynamics of photogenerated carriers in semiconductor materials. The study presented here include semi-insulating (SI) and low-temperature-grown (LT) GaAs. By measuring the detailed shape of a subpicosecond electrical field pulse (THz pulse) transmitted through the sample at a time T after excitation with a femtosecond laser pulse, the absorption coefficient and refractive index in the region between 0.1 THz and 3 THz can be measured with high accuracy. By varying the time T, the transient absorption and index spectra can be measured with subpicosecond time resolution. Temporal and spectral behavior of the carrier dynamics in SI and LT GaAs, in dependence of intensity and wavelength of the excitation pulse, is measured. We directly observe carrier scattering to the sidevalleys and the subsequent return of the carriers to the central valley. The experimental data strongly suggest that the transmission of the THz pulse through the photoconducting surface layer of the semiconductor can be described as instantaneous tunneling of the electric field through a metal-like barrier.