SOLITON PROPAGATION AND DIFFUSION OF OPTICALLY-EXCITED CARRIERS IN BETA-RHOMBOHEDRAL BORON

Drift experiments on optically excited electrons and holes in beta-rho mbohedral boron in drift of fields up to 146 V cm(-1) at room temperat ure show that the propagation of both carriers is of the soliton type. The velocities tend to saturate even at the rather low drift fields u sed. Characteristic mobilities are mu(e) = 0.11 and mu(h) = 0.076 cm(2 ) V-1 s(-1). Different ratios of the retrapping to the recombination r ate, 15 for electrons and 1.2 for holes, are explained by the differen t modes of action of the electronic states involved. For electrons the mean drift distance between generation and recombination exceeds 3 cm . The representative diffusion constant of electrons and holes D = 6 x 10(2) to 7 x 10(3) cm(2) s(-1) depends on the specific conditions. Th e diffusion covers carrier velocities between 10(-5) and 10(2) cm s(-1 ). The decay of photoconduction can be exactly described by the re-exc itation of trapped electrons and their subsequent recombination.