Current-voltage characteristics of Si:B blocked impurity-band structures under conditions of hopping-transport-limited photoresponse

The photoconductivity of Si:B blocked-impurity-band (BIB) structures with boron concentration in the active layer ∼1018 cm−3 has been studied. Measurements were performed in the temperature range 4.2–10 K at different intensities of the exciting radiation 1010–1015 photons/cm2·s. Photoexcitation at 5.5 µm was realized using a semiconductor laser. At temperatures below 6 K and low bias voltages (<0.5 V) the current-voltage characteristics were found to have a threshold-like character. The threshold voltage rises as the temperature is lowered and the radiation intensity is increased. A model based on the Frenkel’-Poole effect in the impurity band has been developed. This model can be used to numerically describe the current-voltage characteristics with accuracy better than 5%. As a result, it is found that the photoconductivity rises and then reaches a plateau as the radiation intensity increases. Under these conditions, as under equilibrium conditions (in darkness), the hopping conductivity also depends exponentially on the electric field. This fact is explained in terms of the destruction by the electric field of (A+-A−) impurity complexes which appear under nonequilibrium conditions.