Semiconductor Diode Gates

Semiconductor diodes are old from the viewpoint of communication engineering. The crystal detector was a fundamental part of the early radio receiver. It was also a troublesome part. The crystals were highly variable and unreliable and there was little theoretical understanding Of their physics which could be used as a basis for successfully exploring and controlling their characteristics. While the semiconductor continued to be useful in the field of power rectifiers and the copper oxide modulator later found extensive use in carrier telephone systems, the development of the vacuum tube into a relatively reliable device, with controlled characteristics, tended to eliminate the semiconductor from most of the communication field. The copper oxide modulator, in a carrier telephone system, is an early example of the type of application which could bring the semiconductor back into competition with the tube rectifier. In a radio receiver, the difference in unit cost, power consumption, space requirements, and maintenance expense, between a tube detector and a crystal, may be small compared with the engineering advantages; but in a telephone plant, with its multiplicity of units, each of these small increments of cost may be integrated up to a major item, and may determine the economic feasibility of the whole system. The need for better semiconductors than copper-oxide, when carrier frequencies moved up into the megacycle range, was a major stimulus to continue research in the semiconductor field.