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

Drift experiments on optically excited electrons and holes in beta-rhombohedral boron in drift of fields up to 146 V cm(-1) at room temperature show that the propagation of both carriers is of the soliton type. The velocities tend to saturate even at the rather low drift fields used. 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 rate, 15 for electrons and 1.2 for holes, are explained by the different 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. The diffusion covers carrier velocities between 10(-5) and 10(2) cm s(-1). The decay of photoconduction can be exactly described by the re-excitation of trapped electrons and their subsequent recombination.