5 October 1999 New method for obtaining drift mobility and diffusion coefficient and their relation in photorefractive polymers
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Abstract
A new easy method for obtaining a drift mobility and a diffusion coefficient from a nondispersive time-of-flight transient has been developed. Nondispersive transients are described well in the theoretical photocurrent equation (PTE) based on the fact that a carrier packet drifts at a constant velocity and is spread by diffusion, the top electrode acts as a reflecting and partially absorbing wall, and the counter electrode acts as an absorbing wall. The fitting of the PTE to photocurrent transients gives the mobility and the diffusion coefficient (D) simultaneously. These are suitable characteristic values for descriptions of carriers transport because they do not show the thickness dependence and the negative field dependence in a low electric field. The mobility that sometimes shows the thickness dependence and the negative field dependence in a low electric field, however, has usually been measured from the time of the intersection of the asymptotes to the plateau and trailing edge of the transients. In order to obtain (mu) a from photocurrent transients by a simple method, we have tried to describe t0 and tail-broadening parameter W as functions of (mu) a and D, where W is defined as (t1/2 - t0)/t1/2 and t1/2 is the time at which the current is a half of that in the plateau region. The dependences of calculated (mu) k and W on the electric field and the sample thickness agreed well with those of the experimental data. These results verify the PTE and suggest that (mu) a and D can be calculated from t0 and W. We also report that the diffusion coefficient is proportional to the power of 2 of the mobility. This result agrees with a theory based on the Langevin equation which describes motions of carriers in a fluctuated field.
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Akiko Hirao, Hideyuki Nishizawa, Takayuki Tsukamoto, Kazuki Matsumoto, "New method for obtaining drift mobility and diffusion coefficient and their relation in photorefractive polymers", Proc. SPIE 3799, Organic Photorefractives, Photoreceptors, Waveguides, and Fibers, (5 October 1999); doi: 10.1117/12.363883; https://doi.org/10.1117/12.363883
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KEYWORDS
Diffusion

Solids

Electrodes

Information operations

Polymers

Photorefractive polymers

Monte Carlo methods

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