An unwanted green satellite emission in blue GaInN light emitting diodes (LEDs) has been investigated under various electrical bias conditions and temperatures. The dot-shaped green satellite emission appears only under electrically biased conditions of the LED (but not under photoluminescence excitation) and contributes directly to a high subthreshold leakage current of the LED. A weak temperature dependency of the green satellite emission intensity is observed indicating that tunneling-assisted radiative recombination involving Mg acceptors is the origin of the green emission.
A two-dimensional TiO₂ photonic crystal layer is fabricated on Y3Al5O12:Ce3+ (YAG:Ce) yellow ceramic plate phosphor (CPP) to enhance its forward emission. A triangle lattice pattern is defined by molecular transfer lithography with polyvinyl alcohol nanostructured templates. A 4.5 improvement in yellow emission is achieved from photonic-crystal-structure (PhC) patterned YAG:Ce CPP compared to a nonpatterned one. The PhC-patterned YAG:Ce CPP shows a collimated far-field intensity emission pattern compared to the random-patterned and nonpatterned one.
GaInN/GaN multiple-quantum-well light-emitting diodes (LEDs) with 0.4 µm-thick AlGaN cladding layers and two quantum wells (QWs), designed for investigating the origin of efficiency droop, are demonstrated to have a lower efficiency droop than typical GaInN/GaN LEDs with 5 QWs. Considering the much less electron leakage over the active region, and the larger carrier density due to the smaller active volume of the LED with AlGaN cladding layers than those of the typical LED, it is suggested that the dominant mechanism responsible for the efficiency droop is electron leakage rather than the Auger recombination which scales with the cubic power of the carrier density.
A simple and versatile method for fabricating nanopatterns by a lift-off procedure is demonstrated. The technique involves the use of molecular transfer lithography based on water-soluble templates to form a nanopatterned UV-curable material on a PMGI layer, which serves as an underlying resin suitable for lift-off processes. This bi-layer procedure is used for the fabrication of nickel patterns, which are subsequently used as a hard mask for plasma etch processing. Using this procedure, a two-dimensional TiO(2) photonic crystal layer with a 450 nm lattice constant is fabricated on Y(3)Al(5)O(12):Ce(3+) (YAG:Ce) yellow ceramic plate phosphor to enhance its forward emission. The yellow emission in the forward direction is improved by a factor of 3.5 compared to that of a conventional non-scattering YAG:Ce phosphor plate excited by a blue LED.
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