History
The diode has an unusually rich history because its one-way behavior was discovered independently in very different technologies: hot electrodes in a vacuum and contacts between semiconductor crystals and metal.
- 1879 — Practical incandescent lamp. Edison's carbon-filament lamp demonstrated practical electric lighting. The hot filament and evacuated glass envelope later provided the physical setting in which thermionic one-way conduction would be noticed.
- 1883 — The Edison effect. While studying lamp blackening, an extra metal plate was installed inside an incandescent lamp. Experiments showed that current could pass through the vacuum between the hot filament and the plate in a polarity-dependent way. Edison patented an application of the effect as a meter, but it was not yet understood as modern electron physics.
- 1890s — Crystal rectification emerges. Experimenters working with radio waves found that contacts involving crystals such as galena could conduct asymmetrically and detect high-frequency signals. Jagadish Chandra Bose experimented with galena and other detector materials during pioneering millimeter-wave work.
- 1897 — The electron identified. J. J. Thomson's cathode-ray experiments established the electron as a subatomic particle. Electron physics provided the missing framework for understanding thermionic emission and vacuum-tube conduction.
- 1904 — Fleming valve. John Ambrose Fleming turned the Edison effect into a two-electrode thermionic radio detector. The valve rectified high-frequency oscillations and became the first practical vacuum-tube diode.
- 1906 onward — Control grid and amplification. Adding a grid between cathode and plate produced the triode, which could amplify. Vacuum-tube electronics then supported radio, telephone repeaters, radar, sound systems, instruments, and early computers.
- Crystal detectors in early radio. “Cat's-whisker” detectors used a fine wire contact against a crystal. Finding a sensitive spot could be tedious, but these solid-state detectors made simple radio reception possible without a heated tube.
- 1940 — Silicon PN junction. Bell Labs researcher Russell Ohl found that a silicon sample with regions containing different impurities created a junction that rectified and responded strongly to light. The PN junction became one of the fundamental structures of semiconductor electronics.
- 1947 — Transistor. Bell Labs demonstrated the first transistor. The new solid-state amplifier eliminated the heater, glass envelope, and much of the power and size associated with vacuum tubes.
- 1950s — Semiconductor rectifiers expand. Germanium and especially silicon diodes increasingly replaced selenium and vacuum rectifiers in power supplies, radios, televisions, automobiles, and industrial equipment.
- 1960s — Practical visible LEDs. Semiconductor light emission developed into practical red indicators and later expanded across the visible spectrum. LEDs eventually replaced many incandescent indicators and displays.
- Modern era. Diode families now include ultrafast power rectifiers, Schottky devices, laser diodes, photodiodes, avalanche devices, TVS protectors, RF PIN diodes, varactors, silicon-carbide rectifiers, and high-power LEDs.
Two roads to the same circuit function
The vacuum diode and semiconductor diode are physically very different. The vacuum diode uses electrons emitted from a heated cathode and traveling through empty space. The semiconductor diode uses carrier motion through a solid junction. Yet both became valuable for the same circuit property: rectification.
The diode as a bridge in electronics history
The sequence from lamp to thermionic diode to triode is echoed, in a different physics, by the sequence from crystal detector to semiconductor diode to transistor. In both stories, mastering one-way carrier motion came before mastering controlled amplification.