Transport drift length

The large transport efficiencies through the capillary for the aerosol gas-jet technique can be explained in terms of the laminar flow profile of the gas inside the capillary [32], According to Bernoulli s law, the gas pressure at the center of the capillary, where the velocity is highest, is lower than near the capillary walls. Thus, when the sub pm-sized aerosol particles drift away from the center of the capillary, they are subject to a restoring force toward the center of the capillary. Transport efficiencies of over 50% have routinely been achieved for transport capillary lengths over 20 meters. 

In most a-Si H solar cells, a built-in electric field (F) assists in the collection of photogenerated carriers, and efficient collection occurs as long as the drift length (/itF) is significantly larger than the film thickness. Crandall (1982) has shown that the transport in p-i-n cells can be charac-... 

If diffusion or drift lengths are low, the only way out is to change the layout of the cell in such a way that the local distance to the collecting contact falls within the possible transport path length. This guideline was followed in the CdTe-based ETA cell, where the local absorber thickness corresponded quite accurately to the estimated diffusion length. 

Global AMI.5 sun illumination of intensity 100 mW/cm ). The DOS (or defect) is found to be low with a dangling bond (DB) density, as measured by electron spin resonance (esr) of - 10 cm . The inherent disorder possessed by these materials manifests itself as band tails which emanate from the conduction and valence bands and are characterized by exponential tails with an energy of 25 and 45 meV, respectively the broader tail from the valence band provides for dispersive transport (shallow defect controlled) for holes with alow drift mobiUty of 10 cm /(s-V), whereas electrons exhibit nondispersive transport behavior with a higher mobiUty of - 1 cm /(s-V). Hence the material exhibits poor minority (hole) carrier transport with a diffusion length <0.5 //m, which puts a design limitation on electronic devices such as solar cells. 

Atoms taking part in diffusive transport perform more or less random thermal motions superposed on a drift resulting from field forces (V//,-, Vrj VT, etc.). Since these forces are small on the atomic length scale, kinetic parameters established under equilibrium conditions (i.e., vanishing forces) can be used to describe the atomic drift and transport, The movements of atomic particles under equilibrium conditions are Brownian motions. We can measure them by mean square displacements of tagged atoms (often radioactive isotopes) which are chemically identical but different in mass. If this difference is relatively small, the kinetic behavior is... 

More recent work [221-225] has not yet resolved the puzzle. It seems, however, that the small mobilities obtained initially were influenced by trapping, and the intrinsic value should be larger. Evidence for a sublinear increase in drift velocity with electric field and a tendency toward saturation has been found [224], but at a much higher field than proposed earlier. The lower limit of the low-field mobility would be about 103 cm2/V s. But since the chain length in the PDAs investigated to date is not known, the relative influence of intrachain transport and interchain hopping in this value is uncertain. It will be some time before values to be compared to a theory of transport in a CP are available. The high electron mobilities... 

The examination of several individual cut-and-paste cycles gives a drift corrected accuracy of about 11 nm, which is due to the length of the involved spacers (see reference [39]). Besides these small structures, large arrays of molecules can be created. In reference [26], we assembled 10 p sized structures with more than 5000 units and with a loss in transport efficiency of less than 10%. 

Fig. 9.19. Schematic of a typical drift test . A low-resistance metal stripe is patterned, over a length L, on top of a higher-resistance stripe through which an electric current is applied. As the current shunts through the lower-electrical-resistance metal, current-induced atomic drift leads to the formation of a depleted zone in the wake of electron transport at one end of the stripe and hillocks and extrusions at the other end.

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