Carrier - diffusion generation

The basic idea of most diffusion length measurement techniques is to generate a certain number of minority carriers inside the bulk Si, for example by illumination, and to measure the fraction of these carriers that diffuse to a collecting interface. This fraction can be determined capacitively [Bo6], as well as by measurements of the steady-state photocurrent [Dr2, Lei 1], The parameter obtained by these measurements is the minority carrier diffusion length ID of electrons in... 

By 7-irradiation, charge carriers are generated in the bulk of A1203 and Si02. By diffusion of the charge carriers to the surface of the solids, the decomposition of methanol is enhanced 63). 

The efficiency for backside illumination (bi-facial cells) is limited because the carriers are generated outside the field zone in proximity to the poorly passivated contact (poor blue response). Further optimization of absorber thickness, diffusion length, and contact passivation appears to be feasible. 

In most cases an external electric field is applied across the material with the result that the mobile carrier distribution will experience drift in the field toward a new position. Even in the absence of an applied field, the nonuniform distribution of the mobile charge carriers created will lead to their relocation due to diffusion. Although the free carriers are generated where the optical intensity is high, their recombination with counterions (in the case of hole transport these are anions) may occur anywhere in the medium. This includes recombination where the intensity is low, resulting in the separation of the charge distributions. Subsequent optical excitation is unlikely in these darker regions. We know that the counterions exist in... 

Good electrical properties of the epilayer (collection of the photogenerated carriers and generation of the current are linked to the diffusion length or lifetime of the minority carriers)... 

Sample introduction into a carrier stream generates a dispersing sample zone and each of its fluid elements is carried along at a velocity corresponding to its respective position in the stream. Convective mass transport is then a consequence of the parabolic distribution of the linear velocities of every fluid element (Fig. 3.1, upper). Diffusive mass transport is dependent mainly on the concentration differences between neighbouring fluid elements and their diffusion coefficients. Although diffusive mass transport occurs in an isotropic fashion, only its radial component is relevant as a factor influencing dispersion. 

Fig. 7. Electron-hole pair separation in a nanostructured semiconductor electrode (the darker area represents the nanocrystalline material). The charge carriers are generated within a distance from the internal surface that is comparable with the minority carrier diffusion length L. This leads to very efficient electron hole separation.

The experimental IMPS plot has the shape predicted for the case where charge carriers are generated at the electrolyte side and diffuse (or migrate) through the network to the substrate. The inverse of the characteristic frequency ojmm (measured with a given background light intensity) is plotted vs. in Fig. 44. 

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