Diffused emitter and collector P-N-P and N-P-N silicon medium power transistors

Silicon p-n-p and n-p-n transistors for medium power audio use have been fabricated using diffusion of p or n-type doping elements into n or p-type silicon wafers to form emitter and collector regions. The wafers are prepared by etching flat circular depressions in silicon dice using a specially developed etchant. Diffused material surrounding the depressions is later removed to delineate the emitter. Dice must be proceased to recover minority carrier lifetime. A ring base contact and circular dot emitter and collector contacts are made to the wafer in a one-shot operation. The design permits simple self-jigging for mounting of the unit on the package. Collector to package mount gives efficient removal of heat.