KEYWORDS: Diffusion, Solids, Electrodes, Polymers, Information operations, Photorefractive polymers, Monte Carlo methods, Protactinium, Time metrology, Molecules
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.
KEYWORDS: Code division multiplexing, Polymers, 3D modeling, Molecules, Gadolinium, Statistical analysis, Instrument modeling, Information operations, Dielectrics, Monte Carlo methods
The proportionality of the logarithm of the mobility to the square root of the electric field is most likely caused by the broadening of the density of states according to both the Gaussian disorder model and the 3D correlated disorder model (CDM). Using these models, the relation between the slope of the mobility against the electric field and the dipolar component of the width of the density of states ((sigma) d) is analyzed. The (sigma) d for the donor and the host polymer are calculated using the dipolar disorder model in which a random distribution of permanent dipoles generates fluctuation in electric potential. A successful interpretation of the relation between (beta) and (sigma) d has been achieved using the formula based on the CDM. Assuming that all components of the density of states are described using Gaussian statistics, the van der Waals component is evaluated to be negligibly small from analyses of temperature dependence of the relation between (beta) and (sigma) d. The experimental results also shows that the value of the DOS width that is derived from the analysis of the temperature dependence of the zero-field mobility is different for the value of the DOS width that is derived from the analysis of the electric field dependence.
Saiwai-ku, Kawasaki 210-8582, JAPAN The drift mobility and the diffusion coefficient of molecularly doped polymers (MDPs) are measured by fitting the theoretical equation to the observed time—of—flight photocurrent transient. The 70% mobility enhancement is observed when 0.2 wt.% fullerene C70 is added to the diphenylamino— benzaldehyde diphenyl hydrazone (DPH) doped polystyrene. We consider this is due to the interaction between C0 and DPH which form the charge transfer complex.
Writing a refractive index grating by anomalous carrier diffusion without applying an external electric field has been achieved in a photorefractive polymer whose D/μ value is larger than that derived from Einstein's law. A grating was written in a photorefractive polymer by anomalous diffusion.
The efficiency of carrier generation by the zerographic discharge technique has been measured on four films; a molecularly C60-doped polymer film, a molecularly C70-doped polymer film, an aggregate C60 film, and an aggregate C70 film. The yield for molecularly C70-doped polymer was three orders of magnitude larger than that for the film of molecularly C60-doped polymer. The photon energy dependence of efficiency for the aggregate films differed from that for the molecularly doped polymer films. The carrier generation efficiency spectrum for the aggregate films showed peaks corresponding to the Frenkel type excitons. The sensitivity of a photoreceptor fabricated with C70 was 0.5(cm2/(mu) J) at wavelengths in the 420nm-670nm region.
A transport equation has been fitted to time-of-flight transient photocurrent signals of molecularly doped polymers in order to obtain both diffusion coefficient (D) and drift mobility ((mu) ) simultaneously. The logarithm of (mu) increased linearly with the square root of the electric field. The negative field dependence on the square root of the electric field at a low electric field that had been reported appeared to superimposing of drift and diffusion. The logarithm of D increased linearly with the square root of the electric field. The logarithm of D decreased linearly with T-2.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.