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.
Irradiation with 6 MeV electrons of near-UV (peak wavelength 385-390 nm) multi-quantum-well (MQW) GaN/InGaN light emitting diodes (LEDs) causes an increase in density of deep electron traps near E c À0.8 and E c À1 eV, and correlates to a 90% decrease of electroluminescence (EL) efficiency after a fluence of 1.1 Â 10 16 cm À2 . The likely origin of the EL efficiency decrease is this increase in concentration of the E c À0.8 eV and E c À1 eV traps.
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)
Study of the spectral noise density and its dependence on current density in as fabricated and degraded blue light emitting diodes (LEDs) based on InGaN/GaN quantum well structures are reported. It is shown that defects are generated nonuniformly in the course of degradation, being concentrated along extended defects penetrating into the active region of LEDs. It is demonstrated that the decrease in the exter nal quantum efficiency in the course of aging is due to the enhancement of charge transport uniformity, which leads to the formation of shunts and local overheating regions. Typically, in blue LEDs, these effects are responsible for the ambiguous development of the degradation process, which hinders prognostication of LED service life. The effect of noise suppression is observed in a narrow current density range (10 -2 to 10 -1 A cm -2 ) corresponding to the onset of radiative recombination.
In this study, we discuss the mechanisms behind changes in the conductivity, low-frequency noise, and surface morphology of biosensor chips based on graphene films on SiC substrates during the main stages of the creation of biosensors for detecting influenza viruses. The formation of phenylamine groups and a change in graphene nano-arrangement during functionalization causes an increase in defectiveness and conductivity. Functionalization leads to the formation of large hexagonal honeycomb-like defects up to 500 nm, the concentration of which is affected by the number of bilayer or multilayer inclusions in graphene. The chips fabricated allowed us to detect the influenza viruses in a concentration range of 10−16 g/mL to 10−10 g/mL in PBS (phosphate buffered saline). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed that these defects are responsible for the inhomogeneous aggregation of antibodies and influenza viruses over the functionalized graphene surface. Non-uniform aggregation is responsible for a weak non-linear logarithmic dependence of the biosensor response versus the virus concentration in PBS. This feature of graphene nano-arrangement affects the reliability of detection of extremely low virus concentrations at the early stages of disease.
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