One-Carrier and Two-Carrier Steady-State Space-Charge-Limited Currents in Amorphous Selenium Films

Steady-state one-carrier and two-carrier space-charge-limited currents (SCLC) and emission-limited currents were observed in amorphous selenium films ranging in thickness from 0.83 to 42 μm. Above a threshold $\frac{V}{L^2}\sim 1.5\times {10}^7$ V/${\mathrm{cm}}^2$ and below an upper limit of $\frac{V}{L^2}\sim 5\times {10}^8$ V/${\mathrm{cm}}^2$ relating the applied voltage $V$ and the film thickness $L$, the trap-free insulator model accounts for both the one-carrier and the two-carrier SCLC and yields the values ${\theta }_p=6.3\mathrm{}\times {10}^{-7\mathrm{}}$ and ${\theta }_n=2.5\mathrm{}\times {10}^{-6\mathrm{}}$ for the ratios of free to trapped holes and electrons, respectively, and $\tau \sim 1$ sec for the effective carrier recombination time.