Space-Charge-Limited Currents in Iodine Single Crystals

Transient and steady-state measurements of space-charge-limited hole photocurrents in iodine generated at one electrode are presented. The hole drift mobility perpendicular to the $\mathrm{ac}$ crystallographic plane is 0.7 ${\mathrm{cm}}^2$/v sec and varies with temperature approximately at $T^{-1.2\mathrm{}}$. The transient measurements are compared with the theory presented in the preceding paper and found to be in very good agreement with it in regard to both transport phenomena and trapping processes. This theory is employed in the analysis of the experimental data to characterize the hole trapping kinetics. Trapping times derived in this manner range from tens of microseconds to seconds, depending on the crystal-growth conditions and subsequent treatment. These conditions affect also the location of the dominant trapping levels above the valence-band edge and their density, which, for different samples, range from 0.45 to 0.6 ev and from ${10}^{11}$ to ${10}^{14}$ ${\mathrm{cm}}^{-3\mathrm{}}$, respectively. The hole capture cross sections are usually very small, of the order of ${10}^{-20\mathrm{}}$ ${\mathrm{cm}}^2$.