SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS — Physics STD 12 Science — Question

→The seed of the development of the modern solid-state semiconductor electronics goes back to 1930 's.
→Then it was realized that some solid state semiconductors and their junctions offer the possibility of controlling the number and the direction of flow of charge carriers through them.
→Simple excitations like light, heat or small applied voltage can change the number of mobile charges in a semiconductor, and hence can control the current. which means they act as a catalyst.
→Note that the supply and flow of charge carriers in the semiconductor devices are within the solid itself.
→Unlike the vacuum tubes/valves, no external heating or large evacuated space is required by the semi-conductor devices.
→They are small in size, consume low power, operate at low voltages and have long life and high reliability.
→Even the Cathode Ray Tubes (CRT) used in television and computer monitors which work on the principle of vacuum tubes are being replaced by Liquid Crystal Display (LCD) monitors with supporting solid state electronics.
→Much before the full implications of the semiconductor devices were formally understood, a naturally occurring crystal of galena (lead sulphide, PbS ) with a metal point contact attached to it was used as a detector of radio waves.