Volume 88, Issue 6, 15 September 2000
Index of content:
- DEVICE PHYSICS (PACS 85)
88(2000); http://dx.doi.org/10.1063/1.1289074View Description Hide Description
We studied the effect of photon recycling in double heterostructurelight emitting diodes(LEDs) with relatively small area contact providing nonuniform injection of electrons. A simple phenomenological model of the electron and photontransport in the LED is used to calculate the spatial distributions of electrons and output radiation as well as the external quantum efficiency as functions of device parameters. It is shown that photon recycling is the governing factor of the operation of LEDs with nonuniform injection.
Ultrathin layer alkaline earth metals as stable electron-injecting electrodes for polymer light emitting diodes88(2000); http://dx.doi.org/10.1063/1.1289518View Description Hide Description
Polymer light emitting diodes in which the cathode comprises an ultrathin layer of alkaline earth metal show much better operating lifetime, especially at high temperatures, in comparison with devices fabricated with cathodes from the same metals with thickness greater than 100 Å. The operating lifetime is dependent on the specific low work functionmetal used. Among the alkali and alkaline earth metals, devices with ∼30 Å Ba as cathode show the best half life during continuous operation. Using an ultrathin Ba cathode with an Al or Ag capping layer and poly[2-(3,7-dimethyloctyloxy)-5-methoxy-1,4-phenylenevinylene] as luminescent polymer, the half life reaches 400 h at and exceeds at room temperature when operated at a current density of with a luminance of
88(2000); http://dx.doi.org/10.1063/1.1289525View Description Hide Description
The instability of n-channel hydrogenated polycrystallinesiliconthin-film transistors has been investigated with respect to gate biasing. The hydrogenation was performed by hydrogen ion implantation through the gate oxide. The conduction mechanism in the gate oxide was studied for positive and negative gate bias, showing that the electron tunneling is much higher for positive gate bias. The oxide conduction follows the Fowler–Nordheim (FN)tunneling mechanism for electron tunneling from the channel and Poole–Frenkel for electron tunneling from the gate polysilicon. After constant FN stressing for short duration (<10 min), the evolution of the transfer characteristics with stress time indicate passivation of the grain boundarydangling bonds by the positive ions introduced into the gate during hydrogenation with simultaneous electron injection into the gate oxide and interface states generation. For longer FN stress duration, the transfer characteristics are degraded due to enhancement of the donor-like interface states generation.
88(2000); http://dx.doi.org/10.1063/1.1285957View Description Hide Description
A model for data retention in stacked gate structures has been formulated, considering that an alkali ion drift toward the negatively charged floating gate is a cause of degradation. A charge conservation law is obtained for the alkali ions, which reduces to a differential equation concerning the threshold voltage variation. A simple analytical expression for the threshold voltage variation has been obtained whose form is identical to the conventional model; however, the physical meaning is quite different. In the proposed model, the low activation energy is attributed to the potential barrier height formed by silicon dioxide atoms for alkali ions and the inconsistency in the conventional model can be solved.