Current injection from a metal to a disordered hopping system. I. Monte Carlo simulation

Emission-limited charge-carrier injection in the dark from a metal into a r andom organic dielectric has been studied via Monte Carlo simulations. The dielectric has been modelled in terms of a regular lattice of point sites f eaturing a Gaussian distribution of energies to represent disorder. The ess ential input parameters are the zero-field energy barrier for injection (De lta), the variance (sigma) of the distribution of the hopping states, elect ric held, and temperature. By varying the jump distance the unimportance of long-range tunneling transitions has been established. Therefore, Fowler-N ordheim type j(F) charcteristics at high fields have to be considered accid ental. The dependence of the injection yield resembles that of Richardson-S chottky (RS) thermionic emission. Quantitative differences are noted, howev er, concerning the RS coefficient and the temperature dependence. The latte r tends to saturate at low temperatures, which is a signature of hopping am ong sites distributed in energy. [S0163-1829(99)08411-8].