LED.pdf

Light Emitting Diodes (LEDs) are essentially pn junction diodes that emit incoherent light when carriers are injected across a forward-biased junction. The history of LEDs dates back to 1907, with significant developments in the 1950s and 1960s, including the creation of the first practical visible-spectrum LED by Nick Holonyak Jr. in 1962. The theory behind LEDs involves minority carrier injection, where electrons from the n-side are injected into the p-side, recombining with holes and resulting in spontaneous emission of photons. The recombination can be direct or indirect, depending on the material's band gap. The wavelength of the emitted light depends on the band gap energy of the materials forming the p-n junction, with semiconductors having a 2 eV band-gap emitting light at about 620 nm (red) and a 3 eV band-gap material emitting at 414 nm (violet). Commercial LEDs often use III-V ternary alloys, such as GaAs1-yPy, and can be classified as homojunction or heterostructure devices, with heterostructure LEDs being brighter.