Outdiffusion as a Technique for the Production of Diodes and Transistors

The outdiffusion process, which consists of the extraction of impurities from a semiconductor wafer by heating it to an elevated temperature in a high vacuum, is shown to be a practical method for the production of diodes and transistors. The usefulness of outdiffusion as a technique for device fabrication depends on how easily impurities can be evaporated from the crystal surface. The surface-evaporation velocity K which characterizes the ease of removal of impurities has been determined for the evaporation of antimony out of germanium at 700°C and is (1.5±0.5)×10-8 cm/sec. This value is large enough to indicate that it is definitely feasible to make high-frequency devices by outdiffusion. Narrow base germanium computer diodes have been fabricated that have a forward drop of 0.11 volt at 1 ma and that switch at speeds up to 5 mc. The operation of these graded base diodes is analyzed. Germanium n-p-n graded base transistors have also been fabricated which have grounded-emitter current gains, ß, of over 100 and alpha frequency cutoffs, f¿co, of above 200 mc.