Exploratory observations of random telegraphic signals and noise in homogeneous hydrogenated amorphous silicon

Abstract

Noise measurements on unhydrogenated and hydrogenated rf sputtered intrinsic amorphous silicon reported by D’Amico, Fortunato, and Van Vliet [Solid-State Electron. 28, 837 (1985)] have 1/f and Lorentzian spectra, respectively. Similar noise measurements on glow-discharge deposited hydrogenated amorphous intrinsic silicon reported by Bathaei and Anderson [Philos. Mag. B 55, 87 (1987)] gave a 1/f m spectrum with 0.7<m<1. Even more recently Ley and Arce [Proc. MRS Symposium, San Diego (1989)] have reported random telegraph signals in a-Si:H/a-Si1−xNx:H double barrier structures. The associated noise was a Lorentzian noise spectrum. In this paper the first observation of random telegraph signals in notionally homogeneous heavily doped (p+) glow-discharged-deposited amorphous silicon is reported. It was found that the current passing through the sample fluctuates between two easily identifiable levels with the periods of fluctuations separated by a quiescent period. The occurrence of these fluctuations is unpredictable but the current noise spectrum obtained during quiescent periods is Lorentzian, probably indicative of a generation-recombination process. Noise measurements are not possible at higher biases (>105 V/cm) as the current fluctuates chaotically and this is also the prebreakdown regime of the sample.