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Description: | INAs6A/4a (written on a label stuck to the glass phial). MANU Unsigned circa 1960 These are two crystals of indium arsenide in a cork stoppered glass phial. Indium arsenide, InAs, or indium monoarsenide crystals is a semi-conducting material that has a melting point of 942 degrees Celsius and a cubic crystal structure. It is used for making infrared detectors known as photovoltaic photodiodes and LED light emitting diodes. Indium arsenide detectors have the advantage that they can be used in higher-power applications at room temperature. It is also used for making diode lasers.
LEDs are made of crystals that allow electrical current to pass through in one direction only; the diode effect. In 1874, Karl Ferdinand Braun invented the first diode or point contact rectifier. Braun was studying the electrical properties of metal sulphides in solution and went on to examine the solid crystals. Braun noticed that certain sulphide crystals would allow an AC current to pass in one direction through the crystal but prevented its passage in the opposite direction thereby producing a DC current output.
In 1904 John Ambrose Fleming invented the thermionic or vacuum tube diode. His device consisted of two electrodes, a cathode (the filament) and an anode (the plate), encased within a glass tube under vacuum. When a current is applied to the cathode such that it is negatively charged, electrons flow to the anode and complete the circuit. However, if the current is reversed, no electrons flow. As in sulphide crystals the valve diode allows current to pass in one direction only.
The modern diode is essentially a modified transistor or point contact rectifier using a semi-conducting material (such as silicon or germanium. The material is coated at each end with two different substances, so that one end is positively charged and the other negatively charged. When a current is sent through the diode via the negative end, it is allowed to pass but if the current is applied to the positive end no current flows.
Henry Joseph Round (1881-1966) working for marconiat Babylon, Long Island, first observed the phenomenon of electro-luminescence in a semi-conducting material, silicon carbide, in 1907 but the yellow light it produced was too faint to be of any practical use. Several workers attempted to improve on Round's discovery and in 1936 George Destriau published a paper on the emission of light by zinc sulphide and is credited with having described the effect as "electro-luminescence".
A light-emitting diode (LED) is a semiconductor device that emits incoherent narrow-spectrum light when electrically biased or charges in the forward direction. Indium arsenide operates in the infrared spectral region at wavelengths between 1 and 4 µm. This effect is a form of electro-luminescence. The colour of the light emitted from an LED depends on the composition and condition of the semi-conducting material used, and can be infrared, visible, or near ultraviolet.
At Princeton, New Jersey, Rubin Braunstein (1922-f. 2006), working for RCA, the Radio Corporation of America, first published on infrared emissions from gallium arsenide and other semiconductor alloys in 1955. However, in 1961, Robert Biard (1921-f. 2006) and Gary E. Pittman, at Texas Instruments also found that gallium arsenide emitted infrared radiation under the influence of an electric current and it was Biard and Pittman who were awarded a patent for the infrared light-emitting diode.
The first commercial LEDs were only able to produce invisible, infrared light, but they were found to be very effective in sensing and photoelectric devices. Nick Holonyak Jr (1928-f. 2006) working as a consultant for the General Electric Company at Syracuse, New York developed the first practical visible-spectrum LED in 1962 and hand built devices were available from 1964. LEDs went into full-scale production for quartz watches in 1972. | License: | http://www.hmag.gla.ac.uk/spirit/rights/ | Publisher: | Hunterian Museum and Art Gallery, University of Glasgow | Rights holder: | Hunterian Museum and Art Gallery, University of Glasgow | Subjects: | SCIENTIFIC COLLECTION : | Source: | Hunterian Museum | Creator: | Hunterian Museum and Art Gallery, University of Glasgow | Identifier: | http://www.huntsearch.gla.ac.uk/cgi-bin/... | Language: | en-GB | Go to resource |
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