Enhanced overall efficiency of GaInN-based light-emitting diodes with reduced efficiency droop by Al-composition-graded AlGaN/GaN superlattice electron blocking layer

AlxGa1-xN/GaN superlattice electron blocking layers (EBLs) with gradually decreasing Al composition toward the p-type GaN layer are introduced to GaInN-based high-power light-emitting diodes (LEDs). GaInN/GaN multiple quantum well LEDs with 5- and 9-period Al-composition-graded AlxGa1-xN/GaN EBL show comparable operating voltage, higher efficiency as well as less efficiency droop than LEDs having conventional bulk AlGaN EBL, which is attributed to the superlattice doping effect, enhanced hole injection into the active region, and reduced potential drop in the EBL by grading Al compositions. Simulation results reveal a reduction in electron leakage for the superlattice EBL, in agreement with experimental results. (C) 2013 AIP Publishing LLC.open1133sciescopu

Polarization-engineered high efficiency GaInN light-emitting diodes optimized by genetic algorithm

A genetic algorithm is employed to find an optimum epitaxial structure of multiple quantum wells (MQWs) and electron-blocking layer (EBL) for a GaInN-based light-emitting diode (LED). The optimized LED is composed of locally Si-doped quantum barriers (QBs) in the MQWs and a quaternary heterostructured AlGaInN EBL having a polarization-induced electric field directed oppositely to that of a conventional AlGaN EBL. The optimized LED shows 15.6% higher internal quantum efficiency, 24.6% smaller efficiency droop, and 0.21 V lower forward voltage at 200 A/cm(2) comparing to the reference LED, which has fully Si-doped QB and 20-nm-thick Al0.19Ga0.81N EBL. We find that local Si doping near the QB/QW interface compensates the negative polarization-induced sheet charge at the interface and reduces electric field in the QWs, thereby enhancing electron-hole wave function overlap. In addition, the inverted polarization field in the quaternary EBL provides a high barrier for electrons but a low barrier for holes, resulting in enhanced electron-blocking and hole-injection characteristics.open1113sciescopu

Critical Loss of the Balance between Th17 and T Regulatory Cell Populations in Pathogenic SIV Infection

Chronic immune activation and progression to AIDS are observed after SIV infection in macaques but not in natural host primate species. To better understand this dichotomy, we compared acute pathogenic SIV infection in pigtailed macaques (PTs) to non-pathogenic infection in African green monkeys (AGMs). SIVagm-infected PTs, but not SIVagm-infected AGMs, rapidly developed systemic immune activation, marked and selective depletion of IL-17-secreting (Th17) cells, and loss of the balance between Th17 and T regulatory (Treg) cells in blood, lymphoid organs, and mucosal tissue. The loss of Th17 cells was found to be predictive of systemic and sustained T cell activation. Collectively, these data indicate that loss of the Th17 to Treg balance is related to SIV disease progression

Temperature-dependent efficiency droop in GaInN light-emitting diodes

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Temperature dependence of the efficiency droop in GaInN light-emitting diodes

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Enhanced overall efficiency of GaInN-based light-emitting diodes with reduced efficiency droop by Al-composition-graded AlGaN/GaN superlattice electron blocking layer

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Temperature dependence of efficiency in GaInN/GaN light-emitting diodes with a strain-control layer

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