Abstract

The use of interdigitated metal-semiconductor-metal contacts on semi-insulating GaAs enhances the responsivity of photoinduced-electromotive-force (photo-EMF) adaptive detectors by reducing the carrier transit time between electrical contacts. The unique polar character of the photo-EMF effect prevents the use of conventional interdigitated contact designs. For photo-EMF enhancement, the photoconductivity must be suppressed in every odd electrode pair. This is achieved through proton implantation to reduce the photocarrier lifetimes. The need to minimize the amount of area occupied by the back-action pairs while maintaining maximum collecting area between the active pairs is the source of the asymmetry. We present theoretical analysis of the scaling of the responsivity with the number of pairs. The theory is verified with experimental asymmetric interdigitated contact devices with 1, 2, 4, 8, 16, and 32 pairs of electrodes. The relative enhancement in responsivity is approximately equal to the number of pairs. The enhanced photo-EMF detectors have potential application to adaptive laser-based ultrasound detection.

© 2000 Optical Society of America

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