A light-emitting diode (LED) is a semiconductor device that converts electric current into light. It works on the principle of electroluminescence in a p-n junction: when current passes through the semiconductor structure, electrons recombine with holes and emit photons. The Nizhny Novgorod connection to the LED is fundamental: the phenomenon of electroluminescence in a solid and the first device based on it were discovered and described in the 1920s by the Nizhny Novgorod physicist Oleg Vladimirovich Losev, who was working at the Nizhny Novgorod Radio Laboratory.
Discovery and the Nizhny Novgorod Connection
Oleg Losev, a researcher at the Nizhny Novgorod Radio Laboratory, discovered and systematically studied the glow of a carborundum (SiC) contact when an electric current was passed through it between 1923 and 1927. He called the phenomenon the "light relay" and published his results in Russian and foreign journals. It was the first documented case of controlled electroluminescence in a solid — in effect a demonstration of the principle on which, half a century later, the entire industrial LED technology was built. During Losev's lifetime, no practical application of the discovery was realized: semiconductor epitaxy technologies appeared considerably later.
History of the Technology's Development
The industrial LED in the modern sense appeared in the early 1960s: in 1962, the American engineer Nick Holonyak Jr. created the first visible red LED, based on gallium arsenide phosphide (GaAsP). Throughout the 1970s and 1980s, LEDs were used mainly in indicator devices — it was then that Soviet industry mastered its own series, including the AL307 series (red DIP LEDs based on gallium compounds), manufactured to technical specification aAO.336.076TU and intended for visual indication in general-purpose equipment. In the 1990s, the Japanese scientist Shuji Nakamura succeeded in producing a bright blue LED based on gallium nitride (GaN), which opened the way to white light and a revolution in lighting (Nobel Prize in Physics, 2014).
Operating Principle and Design
The basis of an LED is a semiconductor p-n junction made of Group III–V materials of the periodic table: gallium arsenide (GaAs), gallium phosphide (GaP), gallium nitride (GaN), silicon carbide (SiC), and their compounds. The wavelength of the emitted light, and therefore its color, is determined by the width of the material's band gap. For example, the AL307 series emits in the 650–675 nm range (red light) at a forward voltage of about 2 V and a current of 20 mA. Structurally, leaded (DIP) LEDs are housed in a plastic package with a hemispherical lens; surface-mount (SMD) versions have no leads and are soldered directly onto the board.
Applications
LEDs are used in visual indication, displays, street and household lighting, automotive optics, fiber-optic communication systems, and medical devices. In luminous efficacy, modern lighting LEDs surpass incandescent lamps by a factor of 10–15 and far exceed fluorescent sources in service life (typical operating life is tens of thousands of hours; the Soviet AL307-series indicator devices guaranteed at least 15,000 hours).