PHOTOMIXING IN A BULK SEMICONDUCTOR PHOTODETECTOR.
STANFORD UNIV CALIF MICROWAVE LAB
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This study is concerned with bulk semiconductors as detectors of the difference frequency between two or more optical signals and as a demodulator of microwave AM modulated light. The basic experiment consisted of mounting single crystals of CdSe, Si, and GaAs in a coaxial mount and illuminating the crystals with the beam of single laser. A dc bias voltage was applied and the microwave and dc photocurrents were measured as a function of light intensity, bias voltage, temperature, microwave match, and the various crystal samples. Some of the experimental problems encountered are discussed. An outline of the pertinent, simplified photoconductor theory is presented along with an equivalent circuit for the photodetector device. Also, the semiconductor capture cross section, lifetime, and trap density is calculated from the measured values of photocurrent. The bulk semiconductor photodetector is shown to be a rugged, simple, and inexpensive device for detecting optical beat frequencies, particularly at high light levels and in the infrared. Author