A large area, high speed phototube employing a metal-semiconductor-metal anode

For free-space communication, inter-satellite communication and microwave modulated lidar-radar applications, a large area photodetector with low noise, high gain, and a bandwidth of a few gigahertz is needed. Commercially available avalanche photodiodes and photomultiplier tubes satisfy all the necessary requirements except bandwidth, limiting the free-space communication system data rate and underwater target detection sensitivity of microwave modulated lidar-radar applications. The work presented in this thesis is directed toward meeting the needs of these systems and involves the bandwidth extension of an existing vacuum phototube to 5 GHz to provide a large area, high speed and high gain photodetector for such applications. The approach taken in achieving this goal is to replace the currently used electron bombarded Schottky diode anode of the phototube with an interdigital metal-semiconductor-metal (MSM) device. The MSM device has been used primarily as a photodetector. This application is the first known use of an MSM device as an electron bombarded semiconductor device. The scope of this work includes the MSM device modeling, design, fabrication, optical characterization for functionality, and integration of the MSM anode in the phototube. A variety of devices were fabricated and characterized optically to prove functionality. Novel static and dynamic models are proposed for the electron bombarded MSM. Characterization of the experimental phototube showed the metal-semiconductor-metal device anode suffered damage during the fabrication process, causing a degradation in the overall performance of the anode and the phototube. The metal-semiconductor-metal device anode gain was limited to <2 and the bandwidth to 2.1 GHz, rather than a model predicted gain of 844 and bandwidth of 3 GHz. The overall responsivity of the phototube is 0.2 A/W, rather than a typical 100 A/W. Although the experimental phototube did not meet the design specifications, the results were not due to a design error, but rather to a manufacturing flaw. With a fine-tuned manufacturing process, the design and theory proposed in this work clearly indicates that the use of a metal-semiconductor-metal device as the anode of a phototube to be a viable and promising approach to increasing the phototube bandwidth while maintaining a large area and high gain.