Solid State Optical Detector.

The purpose of this project is to design and fabricate photo detectors which have an active cross-sectional area of 1 sq. mm and which will demodulate two laser beams leaving a frequency difference from low frequencies up to 11 GHz. In this report, the design of the detector is discussed. The only types of solid state devices which can satisfy the requirements are either p-i-n diodes or Schottky barrier diodes fabricated on semiconductor chips on which a thin 5.5 to 9.0 micrometer depending on the material epitaxial layer has been grown. Because of the high frequency involved, carrier transit times limit the thickness of the depletion region in the device. This, together with the area requirement, gives the device a capacitance between 12 and 23 pF which is large at 11 GHz. A sufficiently high cutoff frequency for the device can be obtained only if the series resistance is sufficiently low. Specific designs using silicon and GaAs are discussed, and the critical parts of the design identified. Author