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Abstract

An apparatus for making ac surface photovoltage (SPV) measurements of a specimen of semiconductor material under dc bias voltage conditions includes a light source whose output beam is intensity modulated, an adjustable dc bias voltage source, a conductive base for supporting the specimen and a novel capacitance type reference electrode assembly for sensing the SPV signals. The reference electrode assembly includes in one embodiment a transparent flexible sheet of insulating material having on one surface a first conductive coating which serves as a reference electrode and a second conductive coating which serves as a guard electrode, the first coating being transparent. The flexible sheet of insulating material is attached to a flat glass plate through an annular spacer. An elastomeric button is positioned between the sheet and the glass plate. When the SPV measurements are being taken the flexible sheet is pressed against the specimen with pressure sufficient to hold the reference electrode in close compliance with the specimen, with the pressure being applied to the glass plate and being transmitted from the glass plate to the flexible sheet of insulating material through the elastomeric button.

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First Claim