Transistors – From Point Contact to Single Electron

The first solid state electron device was the metal-semiconductor rectifier discovered by Ferdinand Braun in 1874 even before the discovery of the electron! He found that mercury metal contacts on copper or iron sulphide gave non-linear currentvoltage characteristics. In 1904 J C Bose obtained a U.S patent for point contact rectifiers on Galena (PbS). He found that the direction of rectification depended on the metal and also type of crystal. He thus called these positive or negative coherers. It is now known that these were due to n-type or p-type PbS. He also used these to detect microwave and optical radiation and proposed that the latter could form the basis of solar energy conversion – named Tejometer by him. No wonder Neville Mott said that J C Bose was sixty years ahead of his time!