ANALYSIS OF RANDOM TELEGRAPH NOISE IN LARGE-AREA AMORPHOUS DOUBLE-BARRIER STRUCTURES

We have measured the temporal behavior of the perpendicular current through large-area (almost-equal-to 0.25 mm2) double-barrier structures fabricated from n+-type a-Si:H and quasistoichiometric a-SiN(x):H. The current switches randomly between distinct values with an amplitude between 0.5% and 10% of the total current. This behavior is reminiscent of random telegraph noise (RTN) observed in small-area (< 1 mum2) devices. The power spectra of the RTN can be fitted by a superposition of Lorentzians from which effective switching rates can be deduced. They are thermally activated and exhibit a dependence on the voltage applied to the sample. The RTN switching can be influenced optically by illuminating the sample surface with a He-Ne laser. While scanning the device area with the focused laser the RTN is influenced at one well-defined spot only. We associate this spot with a filament of less than 1 mum2 in size that carries a large fraction of the current through the device and argue that the current is controlled by the charging and discharging of a single defect in proximity to this filament via Coulomb blocking resulting in the observed RTN. In different samples distributions of switching times for capture and emission of electrons at a single defect are measured as a function of applied voltage and temperature. Based on these data different configurations of the defect located in the nitride barrier are discussed within a model of an acceptorlike trap with a strong electron-lattice coupling which exchanges charge with the adjacent n+-type a-Si:H layers.