Hole diffusion length

Jia,., Fujitani, Mv Yae, S., and Nakato, Y., Hole diffusion length and temperature dependence of photovoltages for n-Si electrodes modified with LB layers of ultrafine platinum particles, Electrochim. Acta, 42, 431,1997. 

Photocurrent measurements permit the determination of the hole diffusion length Lp. As was already noted, comparison of measured and calculated polarization curves allows Lp to be determined by a fitting procedure. For example, Butler (1977) and Wilson (1977) obtained for W03 and TiOz the values of Lp equal to 0.5 x 10-4 and 4 x 10-4 cm, respectively. 

Woodall et al.36 have analyzed the relationship between surface recombination velocity and the steady state band gap luminescence in GaAs. They calculate for 534nm excitation that a decrease in vs from 106cm/sec to 104cm/sec will triple the quantum efficiency at a 2.5Mm deep p-n junction if the hole diffusion length, Lp, is 3jim, and the electron diffusion length, L is 4/im. 

In the above, L is the hole diffusion length, t is the lifetime, p0 is the equilibrium hole density, and is the equilibrium band bending voltage. These equations are good approximations when 5 is not too small and are equivalent to that given in (2J where the exchange current parameter is used instead of the charge transfer rate constant. More accurate... 

In nanosized particle film electrodes, photogenerated holes can be rapidly transferred to the semiconductor/electrolyte interface and there be captured by the redox species in the electrolyte. In this way, the recombination losses can be diminished. This is of great importance for semiconductors like hematite with a very short hole diffusion length (2-4 nm). Another advantage is the large internal surface area, which characterize nanostructured semiconductor film electrodes. The latter decreases the current density per unit area of semiconductor / electrolyte interface. 

Fig. 8.4. Profile of light intensity at the semiconductor electrolyte junction. W is the width of the depletion layer and L, is the hole diffusion length. The penetration depth of the light...

Fig. 13. Spectral dependence of the normalized photocurrent as calculated from the surface recombination model of Schetzina (1979) (a) for several L, (the hole diffusion length) and (b) for several S (the surface recombination number) with 0.2 fira and film thickness 20 nm. [After Persans (1980).]...

G. S. Kousik and J. G. Fossum, P+-N-N+ Solar cells with hole diffusion lengths comparable with the base width A simple analytic model, Solar Cells 5 (1981-1982) 75-79. 

Here, O is the incident light flux, a is the absorption coefficient (assuming monochromatic illumination), W is the depletion layer width, Lp is the hole diffusion length, and jo is the saturation current density. The model assumes that there is no recombination in the SCR and at the interface. 

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