Outdiffused junction diode

Narrow base diodes have been made by diffusing impurities out of compensated n-type germanium. If compensated n-type germanium is heated in high vacuum, the n-type impurities having a much higher diffusion constant diffuse out of the germanium more rapidly than the p-type impurities. If the initial donor and acceptor densities are properly chosen for a compensated n-type wafer, out-diffusion will produce a graded p-type skin which serves as the narrow base of the diode. The grading in the base region is such that fast operation can be obtained without either decreasing the punch-thru voltage or increasing the junction capacitance. The built-in field in the base region opposes the flow of minority carriers. However, since extremely narrow base widths can be obtained through the outdiffusion process, high-frequency diodes can be easily fabricated. For computer applications the built-in field helps to clear the stored charge when the diode is switched from forward to reverse bias. The effect of this field on the switching characteristics of the diode will be discussed. The characteristics of this diode which make it attractive for computer applications in the one to ten Mcs range as well as other applications will be indicated.