Daimler Chrysler Ag

Thomas Pearsall

Lorenzo Colace

Hartmut Presting

Gianlorenzo Masini

A voltage-controlled, wavelenght-selective photodetector includes comprising a double diode having a counter-polarized Si-Schottky diode and a SiGe PIN diode. The short-wave portion (&lgr;<0.9 &mgr;m) of the light entering the detector through a window generates electron-hole pairs in the Si-Schottky diode, while the longer-wave portion (1 &mgr;m<&lgr;<2 &mgr;m) passes through the substrate and is absorbed in the epitaxially deposited SiGe superlattice or the quantum well diode. The photocurrents of both detectors flow in physically opposite directions and subtract from each other, resulting in a wavelength-dependent operational sign of the photocurrent. The level of the bias voltage applied determines whether the photocurrent of the Si-Schottky diode or the photocurrent of the Si/Ge PIN diode determines the spectrum. This can be used, for example, in an application for decoding signals by transforming the light signal into an electrical output signal and subtracting the photocurrents of the two detectors which filters out the noise component and thus raises the signal/noise ratio of a light signal.

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Mercer Island, WA, United States of America

Thomas Pearsall