An analytic model of the equilibrium hopping conductivity in a disordered organic semiconductor at large charge carrier densities is formulated. Calculated dependences of the equilibrium hopping mobility upon the carrier density are compared with recent experimental data obtained on doped poly(3-hexylthiophene) films. Doping is shown to create additional energy disorder due to potential fluctuations caused by the Coulomb field of randomly distributed dopant ions.
Optical experiments, involving photoluminescence (PL), the PL excitation and quenching spectra, as well as transmission and its quenching, were used to analyse the photochromic behaviour of some vacancy-related complexes in diamond. The 2.156 eV, 1.945 eV and 1.68 eV optical centres in CVD diamond are attributed to the neutral nitrogen-vacancy, negative nitrogenvacancy and neutral silicon-vacancy ([Si-V] 0) centres, respectively. Oscillatory behaviour in the excitation spectrum of the 1.68 eV luminescence is observed and from the threshold of the oscillations a position of E C − 2.05 eV is suggested for the ground state of the [Si-V] 0 centre.
An analytic model of the weak-field carrier transport in an
energetically disordered and positionally random hopping system
is formulated. Within the framework of this model, the carrier
mobility can be calculated by either direct averaging of carrier
hopping rates or by the use of the effective transport energy
concept. It is shown that multiple carrier jumps within pairs
of occasionally close hopping sites affect the position of the
effective transport level on the energy scale. In good
quantitative agreement with experimental data and results of
Monte Carlo simulation, the temperature and concentration
dependences of the mobility can be almost perfectly factorized,
i.e. represented as a product of two functions one of which
depends solely upon the temperature while the other governs the
dependence upon the density of localized states. The model is
also used for the calculation of trap-controlled hopping
mobility and for the analysis of hopping transport at high
charge-carrier densities.
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