Index of content:
Volume 86, Issue 7, 01 October 1999
- DEVICE PHYSICS (PACS 85)
86(1999); http://dx.doi.org/10.1063/1.371306View Description Hide Description
A one-dimensional numerical model for the quantitative simulation of multilayerorganic light emitting diodes(OLEDs) is presented. It encompasses bipolar charge carrier drift with field-dependent mobilities and space charge effects,charge carrierdiffusion, trapping, bulk and interface recombination, singlet exciton diffusion and quenching effects. Using field-dependent mobility data measured on unipolar single layer devices, reported energetic levels of highest occupied and lowest unoccupied molecular orbitals, and realistic assumptions for experimentally not direct accessible parameters, current density and luminance of state-of-the-art undoped vapor-deposited two- and three-layer OLEDs with maximum luminance exceeding were successfully simulated over 4 orders of magnitude. For an adequate description of these multilayerOLEDs with energetic barriers at interfaces between two adjacent organic layers, the model also includes a simple theory of charge carrier barrier crossing and recombination at organic–organic interfaces. The discrete nature of amorphous molecular organic solids is reflected in the model by a spatial discretization according to actual molecule monolayers, with hopping processes for charge carrier and energy transport between neighboring monolayers.
86(1999); http://dx.doi.org/10.1063/1.371307View Description Hide Description
We have investigated the lateral scalability limits of the conduction channels in several metal-oxide-semiconductor(MOS) structures, at room temperature, with the goal to understand for which geometries and under which operating conditions a narrow channel approaching the quantum-wire limit can maintain reasonable isolation. A wide range of calculations were carried out using an efficient two-dimensional self-consistent model based on the coupled Schrödinger and Poisson equations. We found that a good trade-off in performance and manufacturability is obtained with a T-shaped gate metallization. Our calculations show that if one uses a highly doped substrate for this system, a quasimonomode quantum wire can be realized at room temperature with a sufficiently high confining barrier. Because of random dopant fluctuations affecting reproducibility and threshold behavior, it would be desirable to eliminate doping in the channel when the width approaches nanometer scale. However, the same MOS structures implemented using an undoped substrate exhibits various problems, the most serious one being a very low confining potential. Considerable improvement is obtained if an undoped layer is grown on top of a highly doped substrate, leading to reasonable confinement and threshold control.