ELECTRON-HOLE COLLISION CROSS-SECTION IN DISCRETE HOPPING SYSTEMS

Electron-hole collisions mediated by their Coulomb attraction are simu lated for discrete hopping systems in the presence of a high electric field E. The collision cross section S is found to be field-dependent and sensitive to transport anisotropy. For microscopically isotropic s ystems S is well represented by S-E = 4 pi e/epsilon E, following From the Langevin recombination theory, For anisotropic systems it is demo nstrated that S can be much larger or smaller than S-E for current flo w along the direction with the smaller or larger mobility, respectivel y. This effect is found to arise even in nominally isotropic systems b ecause of the field-induced mobility anisotropy. Disorder, however, te nds effectively to decrease the apparent degree of anisotropy.