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LARGE AREA LATERAL PHOTOVOLTAIC EFFECTS IN HYDROGENATED AMORPHOUS SILICON FILMS KOJI OKUMURA Xerox Corporation, Webster Research Center, 800 Phillips Road, Webster, NY 14580 ABSTRACT Lateral photovoltages were measured in a 20 cm long strip of hydrogenated amorphous silicon deposited on a platinum foil. The position dependence was nonlinear. It was antisymmetric with respect to the center of the strip when the platinum substrate was electrically floating. If the platinum was grounded, the photovoltaic signal was zero at one end of the sample and increased monotonically to the other. The magnitude of the photovoltage was linearly dependent on the light intensity. The polarity of the photosignals when the sample was exposed to a flash of light at one position of its length was opposite to that of the semi-steady photovoltage when it was exposed to a steady light source. The phenomena can be explained on the basis of a model of charge carrier separation in the Schottky barrier junction at the point of illumination. Introduction Lateral photoeffects in the semiconductor p-n junctions were first reported by Wallmark [1] and confirmed and analyzed by Lucovsky [2], Niu [3], [4], Petersson [5] and others. More recently, Willens [61 and Levine et al [7] reported lateral photoeffects in the amorphous multilayers of Ti and Si deposited on a silicon wafer. In this paper an observations of lateral photovoltaic effects in a thin film of hydrogenated amorphous silicon (a-Si:H) deposited on a long strip of platinum foil over dimension of >10 cm are reported. Experimental A typical sample was a 0.5 pm to 1 pm film of uniform thickness n-type aSi:H deposited on a platinum strip of about 20 cm long by means of plasmaenhanced chemical vapor deposition (PECVD) of a silane and phosphine mixture (100 ppm) at 250 0 C. A pair of thin film aluminum electrodes were vacuum deposited on the surface of the a-Si:H film near the ends of the sample strip. The typical separation of the electrodes was 16 cm. To measure the transverse photovoltages at the interface of a-Si:H and platinum, a substrate consisting of a semitransparent film of platinum on Coming 7059 glass was used.

a-Si: H

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Figure 1. Sample configurations.

Mat. Res. Soc. Symp. Proc. Vol. 118. ' 1988 Materials Research Society

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The long foil strip sample was mounted on a holder along which the length of the sample could be slid in a long metal shielding box. A slit opening of 2 mm wide at the center of the chamber allowed illumination of the sample surface at various positions between the two end electrodes. The light source was either a Xenon flash lamp of about 10 ps duration or a incadescent lamp. Either one of the two electrodes on the a-Si:H film was grounded, and the other connected to a voltmeter or an oscilloscope (Figure 1). The platinum foil substrate was normally electrically floating, or connected to the circuit ground for some measurements. For the measurements2 of the transverse photovoltage, an aluminum film electrode o