When you are talking about the history of some phenomenon, you will end up to the endless question where to start. So is also the case with LED components. As such, light emitting diode is the electrical component which conducts current to only one polarity of voltage, forward voltage, as told in an earlier blog. And this forward voltage applied into this diode produces electrical current that finally creates light. Not every diode produces light, the material has to be suitable in order to produce light. So in addition to having electrically PN diode characteristics, optically component’s material has to be capable of producing light.
This phenomenon, in which electrical current that is driven to the material induces material to emit light, is called electroluminescence. Light can be created also by heating, from chemical reactions, or even by sound, but these are not the topic of this post.
If electroluminescence phenomenon is considered, the first discoveries can be thought to be happened already in the beginning of the 20th century. In 1907 a British experimenter H. J. Round, who was assisting the famous Guglielmo Marconi, found electroluminescence phenomenon using silicon carbide, a compound of silicon and carbon, as light emitting material. He reported his observations to the editors of Electrical World in 1907. The name of the report was “A Note on Carborundum”. Carborundum is a synonym for silicon carbide (SiC). The first LED as such was reported by a Russian Oleg Losev in 1927 in the article “Injected light emission of silicon carbide crystals” in a Russian journal. At that time, no practical use for that kind of component was found. After that several decades passed without significant breakthroughs in LED development.
If LED development history is thought as the point of view of semiconductor materials, one significant material, or semiconductor alloy, was noticed throughout the years. It was gallium arsenide (GaAs) from which “light” emission could be noticed at infrared wavelengths. Bulk growth of a compound semiconductor GaAs commenced in 1954. Before GaAs, LEDs had been manufactured mainly from SiC. Infrared LEDs and lasers based on GaAs were first reported in 1962 by various groups working in such institutions as RCA, GE, IBM and MIT. By adding aluminium to GaAs, you can get the light output nearer to visible wavelengths; that is from infrared wavelengths to visible red wavelength. Aluminium brings along one problem: it is very susceptible to oxygen that decreases luminescence of the LED.
The decade of breakthrough for light-emitting diodes was definitely 1960’s. During 1961-1962, Texas Instrument workers James R. Biard and Gary Pittman reported GaAs emitting infrared light when electrical current was driven through it. The same men filed a patent in 1962 in which they described a zinc diffused PN-junction GaAs LED which emitted infrared light when the diode was forward biased. James Biard had patents also in many other significant discoveries in semiconductor technology, or microelectronic components, at that time. Several other institutions reported infrared LEDs after that as stated earlier.
Following issuance of Biard’s and Pittman’s patent, Texas Instruments started to develop infrared emitting diodes and finally informed about the commercial LED product, SNX-100, in 1962. But light emitting diode on visible spectrum was still waiting until 1962. Nick Holonyak from General Electric published his article in Applied Physics Letters in December 1962. He had developed red wavelength emitting LED based gallium arsenide phosphide (GaAsP). Thus an era of visible light LED components began. Later M. George Crawford invented the first yellow emitting LED and also improved the brightness of red LEDs remarkably. From those years LED development started from interesting scientific phenomenon and ending to commercial product. Still, there were many obstacles to beat over.
At first, LED were applied mainly in indicator lamps or seven segment displays. LEDs were very expensive at that time and usually they were used in expensive laboratory and electronic measurement equipment. In 1968 a company called Monsanto started to mass-produce visible spectrum LEDs, based on material gallium arsenide phosphide (GaAsP). With this semiconductor alloy, so-called ternary alloy consisted of three elements, red light could be generated. Still, there was enough light only for small indicator lamps. M. George Crawford mentioned earlier in the text was one key technical innovator and manager at Monsanto. Mr. Crawford joined Hewlett Packard after Monsanto and got 2002 National Medal of Technology together with Russell D. Dupuis and Nick Holonyak, for contributions to the development and commercialization of light-emitting diode (LED) technology.
During the 1970s prices of LED components started to come down. Dr. Jean Hoerni at Fairchild Semiconductor developed planar process for semiconductor chip fabrication and at the same time developed also packaging methods which jointly enabled to reduce costs to produce LED components. This was a very critical step forward in bringing LED also into other application domains than just pure indicator lights in expensive laboratory test equipment. Throughout the years light output increased gradually but there was still something missing that LED could have been thought as a general lighting component that eventually replaces traditional lighting, such as fluorescent tubes, incandescent or halogen lamps, and even high-pressure sodium or metal halide lamps.
How LEDs evolved from being simple indicator light into the lighting component that could be used in everyday general lighting? That you can read in two last parts of the LED history trilogy.