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Amorphous silicon pin solar cell with a twolayer back electrode Performance and analysis of amorphous silicon pin solar cells made by chemicalvapor deposition from disilane

A theory is presented for the transverse intensity distribution bistability of a Gaussian optical beam after its passage through a nonlinear thin film. The equations governing the intensity distribution are cast in the form analogous to optical bistability in a longitudinal cavity (a Fabry-Perot interferometer), i.e. , into two coupled transcendental equations from which multiple solutions are obtained. This formalism allows one to examine various physical approximations in obtaining the equations, and to improve on these approximations.It also lucidly illustrates the mechanisms of transverse intensity distribution bistability. The theoretical predictions are verified with quantitative experimental results on thin films of nematic liquid crystals.Optical bistability has been a subject of intensive investigation recently. ' Optical bistability in a system arises as a result of its nonlinear response to the input optical intensity, owing to some feedback from the output of the system. Intrinsic devices, where the feedback is purely optical, are usually based upon the Fabry-Perot cavities, ' where the transmission is governed by the Iongitudina/ intensity dependent phase shift. Depending on the relative magnitude of the optical input time, the material response time, and the cavity decay time, the behavior falls into a transient, quasisteady state and cw regimes.Optical bistability has been shown to be an interesting phenomenon for the study of chaos, and passage to chaos, and other fundamental as well as applied problems of optical switching and processing. A review of some of these processes has recently appeared.In this paper, we present the theory and experiment on a fundamentally different form of optical bistability, namely, bistability in the transuerse intensity distribution of a laser beam after its passage through a nonlinear thin (nematic) film. Feedback is provided by a partially transmitting mirror at the output end. The theory developed here is generally applicable to other thin films.Theory for this type of so-called "external" self-focusing bistability has been given before by Kaplan, who essentially treated the film as a nonlinear thin lens with a focal length that is dependent on the optical intensity. In the theory to be described below, we make a further refinement by taking into account the total phase shift due to the thin film, and compare and contrast the results with expressions obtained under the lens approximation. More interestingly, the transverse intensity distribution is described by the solution to transcendental equations in a manner analogous to the case involving longitudinal phase shift. The occurrence of bistability switching (in the onaxis power, e. g.) can then be clearly represented as some switching back and forth between the on-axis intensity and the intensity at the wing of the Gaussian beam.Theory and experiment on the so-called "strong selffocusing limit" bistability has been reported by Bjorkholm et al. In these studies, the nonlinear medium is rather thick so that ...

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We report a new effect, which we call photogating, that can be present in amorphous Si-based p-i-n structures under certain illumination conditions. This phenomenon feeds photogenerated carriers created by a bias light beam of one wavelength into the current response to a second probe light beam of a different wavelength. We demonstrate that this phenomena can lead to measured quantum efficiencies greater than unity. Our computer simulations show that this new effect owes its origins to trapped charge and to the condition that there is a low field region in the front of the structure in the presence of certain bias light.

Experimental results of very large, long-wavelength photocurrent gains in amorphous silicon-based Schottky barrier structures are reported. It is shown that these occur for devices in the space-charge current regime operated at forward bias voltages past the flatband condition. The analysis of microelectronic and photonic structures computer program is used to show that these high gains are due to hole trapping and the resulting modulation of the virtual cathode barrier potential at the ohmic contact. As demonstrated, these gains are bias voltage, bias light, monochromatic light intensity, material property, and device thickness dependent. This type of photocurrent gain is another photogating effect and is much different than the usual bulk photoconductive gain.