Design, fabrication, and characterization of a germanium microwave transistor

This paper summarizes the design, fabrication, and characterization of a p-n-p planar epitaxial germanium transistor for use as an amplifier in the 1-to 4-GHz frequency range and as a high-speed switch. The analytical basis for the geometry and impurity profile arrived at in the development of this transistor is presented in conjunction with experimental measurements. It is shown that good agreement between experiment and theory can be achieved even in the 1-to 6-GHz frequency region when sufficient attention is given to the formulation of an adequate equivalent circuit. For example, the calculated fTof this germanium microwave transistor is 5.7 GHz, which compares to a typical measured value of 5.6 GHz. The measured maximum available gain of the better transistors is 13.4 dB at 1.3 GHz (the corresponding calculated value is 13.9 dB) with a 2.7-dB noise figure at the same frequency.