Abstract
A type of photoconductivity due to far-infrared light excitation is observed in n-channel inversion layers of Si MOS devices with high mobility. The photosignal is bipolar as a function of gate voltage and has little dependence upon the excitation light between the 337, 220 and 118 mu m laser lines. The photosignal is much stronger than that of inter-sub-band transitions. Shubnikov-de Haas oscillations are seen in the photosignals in a magnetic field and are found to be 180 degrees out of phase from the Shubnikov-de Haas oscillations in the conductivity. These characteristics can be understood in terms of heating of the inversion layer electrons. Photoconductivity due to cyclotron resonance is not observed in these samples.

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