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Information × Registration Number 0209U001992, 0107U007850 , R & D reports Title Optimization of heat regimes of high-power SHF and light emitting devices based on nanostructures popup.stage_title Head Malyutenko V.K., Registration Date 13-04-2009 Organization Institute of Semiconductor Physics of NAS of Ukraine popup.description2 It is investigated the current crowding effect in visible (ІnGaN/GaN) and near (AlGaAs/GaAs) infrared multilayer light emitting diodes (LED). By means of local temperature measurements it is shown considerable overheating nonunifotmity caused by current crowding in ІnGaN/GaN multiple quantum well LEDs (L=460-470 nm). Combined influence of electrical and thermal effects results in "heat traps" - small high temperature zones (diameter 20 µm) inside active region. The temperature gradients in such local zones reach up to 104 °С/cm. Dangerous temperature gradients cause elastic mechanical stress and generation of active nonradiative energy levels in multilayer structures. It is shown both experimentally and theoretically that current crowding effect depend on energy band gap of active layer (LEDs emitting wavelength). At identical bias current, more long-wave LEDs show more nonuniform electroluminescence distribution in comparison with short-wave once. Besides, the increasing of nonradiative recombination impact also caused the highest temperature overheating of long-wave LEDs. The influence of current crowding on local overheating in LEDs (AlGaAs/GaAs flip-chip mesastructures, L=0.87-0.88 mm) with 98 % internal quantum yield is investigated. It is shown that despite of a high internal quantum yield and favorable for current spreading two-sided mesastructure in the series with considerable overheating (dT=50 °C), AlGaAs/GaAs LEDs demonstrate nonuniformity of active region excess temperature distribution (temperature gradient >950 °С/cm) which is responsible of devices catastrophic degradation. It is theoretically predicted two types of current crowding effect in mesastructures: contact current crowding at the contact metal surface and current crowding in active region. Product Description popup.authors popup.nrat_date 2020-04-02 Close