>"Philco used a patented process of applying two tiny electrochemical jet streams of liquid indium sulfate (electrolyte solution) on opposite sides of a thin st

>"Philco used a patented process of applying two tiny electrochemical jet streams of liquid indium sulfate (electrolyte solution) on opposite sides of a thin strip of N-type germanium base material. [...] The Philco surface-barrier transistor was the world's first high-frequency junction transistor, which was capable of obtaining frequencies up to 60 MHz. [...] [3]" Apparently (if this history is correct) -- this was the first metal to semiconductor junction transistor (earlier transistors apparently used semiconductor to semiconductor junctions). Germanium is a semiconductor, Indium is a metal (and a good conductor), and Indium Sulfate is apparently a salt of Indium...