Index of content:
Volume 91, Issue 5, 01 March 2002
- DEVICE PHYSICS (PACS 85)
91(2002); http://dx.doi.org/10.1063/1.1445276View Description Hide Description
3 MeV proton irradiation effects on single junction and tandem solar cells have been investigated for the fluence range from to The overall radiation degradation of tandem cells was higher than single junction cells. It was observed that the spectral response of the GaAs bottom cell degrades more than the InGaP top cell. Proton irradiation decreases the longer wavelength spectral response more significantly than the shorter wavelength in both and cells. The difference in the degradation properties of and polarity InGaP solar cells is discussed. The radiation response of a tandem InGaP/GaAs cell is very nearly that which is predicted from the information of these two cells independently. The minority-carrier diffusion length in the base layer was determined from the spectral response data. The minority-carrier diffusion length damage coefficient was analyzed for and GaAs cells. The minority-carrier injection-enhanced annealing of radiation-induced defects in and cells were also observed.
91(2002); http://dx.doi.org/10.1063/1.1445283View Description Hide Description
In an effort to elucidate the mechanism of scallop formation during reflow of solder/Cu joints in flip-chip and ball-grid array technologies, a planar intermetallic compound layer (mostly was initially formed by solid-state annealing of SnPb/Cu joints at for ten days. Upon subsequent reflow, dissolution of the intermetallics and formation of scallops were observed. Detailed investigation has indicated that a thermal grooving process due to dissolution of the intermetallic compound during the initial reflow cycles contributes to the formation of scalloped structures, the morphology of which is dictated by the force equilibrium condition. Upon subjecting the solder joints to several reflows, the average intermetallic layer thickness was found to first decrease and then increase, which is shown to be in good agreement with the prediction made by a model based on simultaneous dissolution and growth of the intermetallic compound during reflow. The kinetics of dissolution-growth process during reflow has also been shown to depend on the initial intermetallic thickness and the shape of the solder cap.
Conduction and low frequency channel noise of GaAs based pseudomorphic high electron mobility transistors91(2002); http://dx.doi.org/10.1063/1.1445494View Description Hide Description
Conduction and low frequency channel noise of gallium–arsenide (GaAs) based pseudomorphic high electron mobility transistors are investigated. The following analysis takes into account both the noise source associated with the intrinsic part of the device and the sources located within the access path. In order to discriminate between these two noise origins, a model of the transistor conduction is proposed using only a few parameters which are easily extracted. It is shown that the intrinsic channel noise agrees with Hooge’s model with parameter about for the studied technology. Moreover, the values of the access resistances are an important parameter to describe correctly the conduction and the noise behaviors.
91(2002); http://dx.doi.org/10.1063/1.1435422View Description Hide Description
We demonstrate that ordered microlens arrays with 10 μm diam poly-dimethyl-siloxane lenses attached to glass substrates increase the light output of organic light emitting devices(OLED) by a factor of 1.5 over unlensed substrates. The lenses, which are considerably smaller than, and not aligned to the OLEDs, outcouple light that is emitted outside of the escape cone of the substrate. We show that an electrophosphorescent device based on a fac tris(2-phenylpyridine)Iridium doped emitting layer has its external quantum efficiency increased from 9.5% using a flat glass substrate, to 14.5% at low current densities using a substrate with microlenses. No change in the emission spectrum is observed for different viewing angles using the lens arrays.
91(2002); http://dx.doi.org/10.1063/1.1448868View Description Hide Description
Dose-rate calculations for intense electron-beam diodes using particle-in-cell(PIC) simulations along with Monte Carlo electron/photon transport calculations are presented. The electromagnetic PIC simulations are used to model the dynamic operation of the rod-pinch and immersed- diodes. These simulations include algorithms for tracking electron scattering and energy loss in dense materials. The positions and momenta of photons created in these materials are recorded and separate Monte Carlo calculations are used to transport the photons to determine the dose in far-field detectors. These combined calculations are used to determine radiographer equations (dose scaling as a function of diode current and voltage) that are compared directly with measured dose rates obtained on the SABRE generator at Sandia National Laboratories.