Complete history of microwave technology (part 4). 1911 to 1921, notable discoveries made by Heike Kamerlingh-Onnes, Jan Czochralski (semiconducter crystals) and Walter Schottky.

In 1911, only three years after building the first helium liquefier, Heike Kamerlingh-Onnes discovered that mercury loses its electrical resistance entirely when cooled below 4.2 K in a liquid helium bath.

Jan Czochralski a scientist from Kcynia Poland was many years ahead of his time. In 1916, he developed a method for growing single crystals, which was almost forgotten until after World War II. Today the semiconductor industry depends on the Czochralski method for manufacturing billions of dollars worth of semiconductor materials. He was accused of being a Nazi sympathizer but was later acquitted. He died in Poland in 1953.

Walter Schottky. This German scientist's name is embedded in solid-state physics (Schottky effect, Schottky barrier, Schottky contact, Schottky diode). Born in 1878, he was a contemporary of Einstein and Max Planck. His work included super heterodyne receivers, noise theory, and radio tube work such as invention of the tetrode, but his most important contribution to microwaves is no doubt his investigation of metal-semiconductor rectifying junctions (published in 1938), which is the basis for the gate contact of all MESFETs. He died in 1976.

As radio applications grew more sophisticated (and popular), stations started broadcasting regular commercial programs. By 1920, the U.S. Department of Commerce


stepped in and began issuing radio licenses, and in 1921 formally declared a special service category (and corresponding transmission wavelength) for commercial stations.