LED

A light-emitting diode (LED) is a semiconductor light source used as indicator lamps in many devices. LED can emit low-intensity red light, but also the visible, ultraviolet and infrared wavelengths, with very high brightness. When a light-emitting diode is forward biased (switched on), electron are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light corresponds to the energy of the photon and is determined by the energy gap of the semiconductor.

LED development began with infrared and red devices made with gallium arsenide. LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate. Most materials used for LED production reflect much light back into the material at the material/air surface interface which is an important aspect of LED production and a subject of much research and development.

Nano-LED

Physicists from Taiwan have designed and fabricated nano-sized light-emitting diodes (LEDs) that emit light spanning the entire visible spectrum. The nano-LED has a unique structure consisting of 40-nm-thick nanodisks kept between two layers of nanorods, to form a nanodisk-in-nanorod geometry. The nanodisks are made of indium gallium nitride (InGaN) which is a semiconductor widely used in LEDs and solar cells. The nanorods are made of gallium nitride (GaN). The InGaN/GaN nanodisk/nanorod structure is similar to a quantum well structure with a reduction in lateral sizes. The InGaN nanodisks sandwiched between the p- and n-GaN regions act as the full-color visible-light emitters when electrons and holes are injected across the p-n junction at a forward bias voltage. The electroluminescent light comes from the electron-hole recombination within the InGaN nanodisks. According to researchers, full-color LEDs can be achieved by overcoming large lattice strains, which degrade long-wavelength emissions. The InGaN/GaN nanorod system overcomes this problem due to the strain relaxation in the nanostructured geometry.

These full-color nano-LEDs cannot be used now for commercial lighting applications, but can be used in high-resolution imaging techniques that can resolve ultra small sub wavelength photolithography to get features of objects after carrying out research to overcome the diffraction limit, which is a fundamental limit on imaging resolution caused by the diffraction of waves.