Volume 86, Issue 3, 01 August 1999
Index of content:
- DEVICE PHYSICS (PACS 85)
Design of a emitter-base junction in a Pnp heterojunction bipolar transistor for increased hole injection efficiency86(1999); http://dx.doi.org/10.1063/1.370945View Description Hide Description
Starting with Burt’s envelope functiontheory, we calculate the transmission coefficients of holes across an heterointerface while varying the width and gallium and arsenic fractions of the InP lattice-matched quaternary compound While comparing our results to the case of an abrupt interface, we find that the transmission coefficients of both heavy- and light-holes can be enhanced significantly for a 60-Å-wide quaternary layer with an arsenic fraction This should lead to an enhanced hole injection efficiency of Pnpheterojunctionbipolar transistors using the heterointerface analyzed here as an improved design of the emitter-base junction.
86(1999); http://dx.doi.org/10.1063/1.370946View Description Hide Description
Nanoscale titaniumstructures are fabricated on a patternedsurface using an atomic hydrogen resist. The patterning is achieved by removing small areas of hydrogen with a scanning tunneling microscope. The large chemical reactivity of the bare Si surface compared to the hydrogen passivated surface provides selective area growth of titaniumclusters grown by chemical vapor deposition using Titanium growth by chemical vapor deposition is normally limited by chlorine passivation of the bare Si surface. However, by removing the chlorine with the scanning tunneling microscope, the growth can be resumed.
Charge carrier trapping effect by luminescent dopant molecules in single-layer organic light emitting diodes86(1999); http://dx.doi.org/10.1063/1.370947View Description Hide Description
We investigated electroluminescent (EL)characteristics of single-layer organic light emitting diodes (SOLEDs). Our SOLED devices are composed of an inert polymer as a binder, in which hole transport molecules, emissive electron transport molecules (ETMs), and highly fluorescent dopants as luminescent centers are dispersed. We examined two typical dopants: rubrene and coumarin 6. These exhibited different charge carrier recombination and emission mechanisms. The dopant concentration dependence of the current density–voltage–luminance relationships clearly showed the importance of carrier trapping by dopant molecules for obtaining high luminance. When the dopant was rubrene, we observed that charge carriers were well trapped by the dopant molecule. This means that direct recombination of holes and electrons occurred on the dopant molecules and trapping significantly enhanced the external EL quantum efficiency For coumarin 6, on the other hand, we observed that charge carriers primarily recombined at the emissive ETMs and that the energy transfer from the host to the guest coumarin 6 molecule dominated the EL process. A comparison of these distinct processes revealed that carrier trapping by dopant molecules was necessary to enhance in SOLED devices. In our best SOLED device with rubrene as a dopant, we measured luminance of 2800 at which corresponds to
86(1999); http://dx.doi.org/10.1063/1.370948View Description Hide Description
The influence of oxidative and reductive treatments of indium–tin–oxide (ITO) on the performance of electroluminescent devices is presented. The improvement in device performance is correlated with the surfacechemical composition and work function. The work function is shown to be largely determined by the surface oxygen concentration. Oxygen-glow discharge or ultraviolet–ozone treatments increase the surface oxygen concentration and work function in a strongly correlated manner. High temperature, vacuum annealing reduces both the surface oxygen and work function. With oxidation the occupied, density of states (DOS) at the Fermi level is also greatly reduced. This process is reversible by vacuum annealing and it appears that the oxygen concentration, work function, and DOS can be cycled by repeated oxygen treatments and annealing. These observations are interpreted in terms of the well-known, bulk properties of ITO.