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 {μ}m. Above a threshold VL²~1.5×10⁷ V/cm² and below an upper limit of VL²~5×10⁸ V/cm² 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 θₚ=6.3×10^-7 and θₙ=2.5×10^-6 for the ratios of free to trapped holes and electrons, respectively, and τ~1 sec for the effective carrier recombination time.