Electrical stressing of near-UV (peak wavelength 390–395 nm) multi-quantum-well GaN/InGaN light emitting diodes at a high drive current of 650 mA and elevated temperature of 110 °C causes a significant degradation in external quantum efficiency (EQE), correlated with the formation of nitrogen interstitial-related electron traps at Ec − 0.8 eV. The dependence of the spectral density of current noise SI on forward current If showed two regions prior to accelerated aging, with SI ∼ If due to the current flow via localized leakage channels (presumably dislocations) and SI ∼ If2 related to the generation-recombination noise caused by the Ec − 0.8 eV states and Ev + 0.75 eV hole traps in the space charge region. Electrical stress for <922 h did not change the EQE but gradually increased both reverse and forward leakage current. This was accompanied by a gradual increase in the density of the hole traps, but not the electron traps. The mechanism appears to be the displacement of Ga and In atoms, with the interstitials decorating dislocations and forming local leakage channels. For stress times >922 h, the peak EQE decreased from 26% to 15% and was accompanied by a further increase in the leakage current and density of both types of traps. One of the 20 studied diodes showed an anomalously high forward leakage current, and the noise spectrum in it was dominated by the SI ∼ If4 region typical for the presence of local overheated areas (presumably local In composition fluctuations). The EQE of this sample began to degrade after a much shorter stress time of 258 h.

Abstract. The first successful results of multifractal analysis application to a quantitative description of mosaic structure peculiarities, which are typical of GaN epitaxial layer with hexagonal modification grown on (0001) sapphire substrates, have been obtained. Characteristic size of the mosaic structure has been measured to be 200-800 nm. The direct dependence of mobility on the multifractal parameters (the Renyi dimension and the degree of the order index) of the surface topology of the mosaic structure has been observed for all GaN layers investigated.

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The degradation of blue light emitting diodes (LEDs) with different structural disorder based on MQW InGaN/GaN grown by MOCVD on sapphire has been investigated. New approach to analyze the degradation has been used. It takes into account the structural disorder determined by the extended defect system relaxation and related with poor coalescence of the mosaic structure domains. The results obtained leads to assumption that the migration and segregations of Ga on domain dislocation boundaries of the mosaic structure and the change of energy activation of Mg related centers are important reasons of degradation for all types of LEDs The fastest degradation for poor ordered LEDs was observed.

The results of low‐frequency noise study of three sets of LEDs classified for their low voltage leakage current (LC) values are reported. The LC values at 1‐2.5 V integrally characterize electrical properties of extended defect system (EDS) that is typical for InGaN/GaN structures. The lower LC value, the smaller concentration of extended defects is. It has been shown that low‐frequency noise peculiarities such as the shape of current dependences of the noise spectral density (SI) and increase in SI with an LC values growth are caused by EDS presence. The point defects (PD) contribution to non‐radiative recombination processes is observed in current density region 10‐2 – 10 A/cm2 where radiative recombination prevails. The non‐radiative caused by EDS at j < 10‐2 A/cm2 and at j > 10 A/cm2. The complicated behavior of EDS with an injection current change has been observed (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)