Modern semiconductor physics has developed from the quantum mechanical work on energy band theory of charge carriers in semiconductors associated with the name of A. H. Wilson and his classic papers on the subject, and also with the name of Schottky who pioneered the atomistic approach to disorder phenomena in solids. This work dates from about 1930 and theoretical developments up to the beginning of the War were relatively slow. Semiconductor technology in the same period was represented by a few devices only. These included the copper oxide and selenium rectifiers which were in use in certain equipment and in the process of further development. The silicon whisker detector was being used for the detection and measurement of microwave power. It will be recalled that silicon carbide and galena had been used as detectors of radio waves before the common usage of the thermionic valve. The development of radar during the War, which required semiconductor devices for detecting and mixing microwaves meant that considerable work was carried out on silicon, and parallel work on germanium meant that by the end of the War high‐back voltage rectifiers, using germanium, were available in developmental quantities. Problems of thermal detection meant that photo‐conductive and photo‐voltaic cells were developed for this purpose based on the materials thallium sulphide and lead sulphide. Attention was also focussed on electronic processes in ionic crystals in terms of improving display screens for cathode ray and similar tubes.
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