Generation-Recombination Noise in a-Si:H Studied by Device Simulations
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Generation-Recombination Noise in a-Si:H Studied by Device Simulations J.P.R. Bakker1, P.J.S. van Capel1, B.V. Fine2 and J.I. Dijkhuis1 Debye Institute/Atom Optics and Ultrafast Dynamics, 2Spinoza Institute, Department of Physics and Astronomy, Utrecht University, P.O. Box 80000, 3508 TA Utrecht, the Netherlands
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Abstract An attempt is made to interpret low-frequency noise measured in a-Si:H n-i-n devices based on the assumption that the noise is due to generation-recombination (g-r) processes. The interpretation is based on a spatial distribution of recombination lifetimes of electrons obtained with the help from the AMPS-1D device simulation program. These lifetimes have the same order of magnitude as that of the noise observed. Further, a distribution of lifetimes naturally results from band bending. Simulations of noise spectra are obtained by multiplication of a phenomenological weight factor to the Lorentzian spectral contribution corresponding to the local electron lifetime. There are, however, two problems with this interpretation: (i) we were not able to come up with a reasonable noise description, where the relatively long electron lifetimes were not overshadowed by much shorter times (ii) the current description, where variance is included in a weight factor, is still incomplete, and therefore we can not explain the shape of the weight factor yet. I.
INTRODUCTION
Resistance fluctuations in the low-frequency (kHz) range in semiconductors with defects can have several sources. First, generation and recombination (g-r) of charge carriers generally lead to electrical fluctuations, characterized by one exponential lifetime and a Lorentzian noise spectrum [1,2]. A second noise source in an amorphous semiconductor may arise from fluctuating current filaments, producing 1/f noise, as found e.g. in doped hydrogenated amorphous silicon coplanar devices [3]. Noise spectra of n-in sandwich structures of a-Si:H show an intermediate spectral shape and allow for the determination of a characteristic frequency which is thermally activated [4]. Earlier, we interpreted the resistance noise measurements in terms of the carrier lifetime against recombination, using device simulations with input parameters such as to faithfully describe the time-averaged properties [5]. Typical features governing the electrical properties of an n-i-n device are (i) conduction by majority carriers (electrons) limited by the central part of the device (ii) band bending (iii) space-charge-limited conduction. One-dimensional device modeling of the amorphous semiconductor device is performed using the computer program AMPS-1D [6]. We demonstrated earlier that the kinetics of the electron recombination lifetime at a specific position in the device coincides with the kinetics of the experimentally determined characteristic noise frequency [5]. Therefore we assume the electron lifetime is the noise relaxation time. In this paper, we examine the cause of the position dependence of the resistance noise. We demonstrate that due to band bending a di
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