Index of content:
Volume 86, Issue 5, 01 September 1999
- DEVICE PHYSICS (PACS 85)
86(1999); http://dx.doi.org/10.1063/1.371123View Description Hide Description
Trends in the efficiency and small signal modulation behavior of porous siliconlight emitting diodes(LEDs) are reported for devices formed by the anodization of bulk silicon junctions. As the average size of the silicon skeleton is decreased, the external electroluminescence(EL) efficiency increases from 0.001% to 0.18% and there is a corresponding blue shift in the EL peak from 776 to 633 nm. An associated tenfold increase is observed in the photoluminescence efficiency while the diode resistance, at 2 V, increases from to Under small signal pulsed operation, the voltage dependence of the rising edge of the EL is well described by a carrier mobility of which is independent of the average size of the luminescent regions of the siliconnanostructure. The falling edge of the EL transient is dominated by radiative recombination of quantum confined excitons. The modulation speed is found to be limited by a combination of carrier mobility in the siliconwires and radiative recombination processes. Evidence of charge trapping and discharge is found in an EL overshoot phenomenon. The major application of this type of porous siliconLED, with modulation speeds below 1 MHz, appears to be for displays integrated with circuitry rather than for optical interconnection.
Surface energy and polarity of treated indium–tin–oxide anodes for polymer light-emitting diodes studied by contact-angle measurements86(1999); http://dx.doi.org/10.1063/1.371124View Description Hide Description
We present contact-angle hysteresis and surface energy of differently treated indium–tin–oxide (ITO) thin films obtained from contact angles for liquids with different polar character. We find that the hysteresis and the polar and dispersion component of the surface energy depend strongly on the surface treatments. Oxygen-plasma treatments induce the highest polarity and the highest total surface energy, and we suggest that this improves the interface formation with polymers, and therefore, the performance of light-emitting diodes. We discuss the results in relation to the ITO surface roughness and chemical heterogeneity modified by the different treatments.