ИСТИНА

Semiconductor compounds GaN, InN, AlN and their alloys have hexagonal crystallografic lattice and energy gap from 0.7 to 5.6 eV. Their electrical and optical properties were initially studied in the middle of XX century, but a boom of their research began in the 90th years after inventions of superbright blue LEDs and lasers. Problems of technology of III-Nitrides. Molecular-beam and metallo – organic epitaxy. Substrates: Sapphire, Silicon Carbide, Silicon. Homo- epitaxial substrates: GaN, AlN - polar, semi- polar and non- polar crystal orientations. Dislocations during epitaxial growth: from 1010 cm-2 to 108 and to 104 cm-2. Nano- heterostructures for LEDs. Problems of p-type doping. First structures with one quantum well (QW), multiple quantum wells (MQWs); complicated structures with superlattices. Spontaneous and piezoelectric polarization; doping barriers. Quantum efficiency (QE) of LEDs: electrical efficiency (injection coefficient, series and parallel resistance), internal efficiency of radiative recombination, coefficient of optical extraction, external quantum efficiency, power efficiency. Spectral dependence of GaN- based LEDs. Maximum of QE for blue LEDs. Problem of QE at high currents (efficiency droop). Problems of QE for green and yellow LEDs, for UV LEDs. Constructions of chips and primary optics for LEDs. Simulation of LED's constructions. White LEDs. Spectral sensitivity of human eyes and luminous efficiency. Various types of white light LED emitters; “cold”, “natural” and “warm” light. Phosphors for white LEDs. Luminous efficiency, color indexes, color temperature. Luminous efficiency of white LEDs in perspective and predictions. LEDs for modern and future lighting. Energy economy, benefits of LEDs lighting. Problems of applications of LEDs lighting – standards, safety, concurrence with lamps, state politics, public opinion.