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 w ith boron concentration in the active layer similar to 10(18) cm(-3) h as been studied. Measurements were performed in the temperature range 4.2-10 K at different intensities of the exciting radiation 10(10)-10( 15) photons/cm(2) . s. Photoexcitation at 5.5 mu m 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 thr eshold-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. Thi s model can be used to numerically describe the current-voltage charac teristics with accuracy better than 5%, As a result, it is found that the photoconductivity rises and then reaches a plateau as the radiatio n intensity increases. Under these conditions, as under equilibrium co nditions (in darkness), the hopping conductivity also depends exponent ially on the electric field. This fact is explained in terms of the de struction by the electric field of (A(+) - A(-)) impurity complexes wh ich appear under nonequilibrium conditions. (C) 1998 American Institut e of Physics.