Carrier transport in porous silicon

Abstract

Carrier transport in porous silicon layers has been studied by the time-of-flight method in the strong injection mode at temperatures T=290–350 K and electric field strengths F=(1.5–7)×104 V cm−1. The electron and hole drift mobilities μe≈2×10−3 cm2 V−1 s−1 and μh≈6×10−4 cm2 V−1 s−1 were obtained at T=292 K and F=4×104 V cm−1. An exponential temperature dependence of drift mobility with activation energy of ∼0.38 and ∼0.41 eV for, respectively, electrons and holes was established. It is shown that the type of time dependences of the photocurrent associated with carrier drift and the superlinear dependence of the transit time on the reciprocal of the voltage applied to a sample allow use of the concept of space-charge-limited currents under the conditions of anomalous dispersive transport. The experimental data are accounted for in terms of the model of transport controlled by carrier trapping into localized states with energy distribution near the conduction and valence band edges described by an exponential function with a characteristic energy of ∼0.03 eV.