Electroluminescence from ZnO nanowire-based heterojunction LED
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We have demonstrated that fabrication of the ZnO nanowire/GaN hetero-junction light emitting diode (LED) by contacting the tip of the ZnO nanowires with the GaN film, and UV electroluminescence from the p-n junction. In this study, we fabricated the heterojunction by directly-growth of the ZnO nanowires on the GaN film using nanoparticleassisted pulsed laser deposition. Photoluminescence spectrum of the ZnO nanowires showed a weak near-band-edge ultraviolet (UV) emission and a visible broad emission, which was related to transition by ZnO defect state. We applied a selective laser irradiation to the p-n junction of the ZnO-based LED. The UV emission was strongly enhanced from the laser-irradiated p-n junction.Keywords:
Ultraviolet
Pulsed Laser Deposition
Wide-bandgap semiconductor
p–n junction
We report enhanced light output of GaN-based light-emitting diodes (LEDs) with vertically aligned ZnO nanorod arrays. The ZnO nanorod arrays were prepared on the top layer of GaN LEDs using catalyst-free metalorganic vapor phase epitaxy. Compared to conventional GaN LEDs, light output of GaN LEDs with the ZnO nanorod arrays increased up to 50% and 100% at applied currents of 20 and 50mA, respectively. The source of the enhanced light output is also discussed.
Nanorod
Wide-bandgap semiconductor
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Commercially available GaN blue LEDs have been characterized for use as light sources for chemical sensors. These new LEDs are a double heterojunction structure of InGaN/AlGaN that have a peak output at 450 nm. Other groups have investigated these devices for full color displays. This investigation addresses parameters critical to chemical sensors. Several different paramters were characterized including spectra verses drive current, spectra before and after aging, output power verses drive current, and lifetime. The results of this characterization indicate that these devices perform well for some chemical sensors.
Characterization
Wide-bandgap semiconductor
Indium gallium nitride
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Short-wavelength, visible-light emitting optoelectronic devices are needed for a wide range of commercial applications, including high-density optical data storage, full-color displays, and underwater communications. In 1994, high-brightness blue LEDs based on gallium nitride and related compounds (InGaN/AlGaN) were introduced by Nichia Chemical Industries. The Nichia diodes are 100 times brighter than the previously available SiC blue LEDs. Group-III nitrides combine a wide, direct bandgap with refractory properties and high physical strength. So far, no studies of degradation of GaN based LEDs have been reported. Our study, reported in this paper, focuses on the performance of GaN LEDs under high electrical stress conditions. Our observations indicate that, in spite of a high defect density, which normally would have be fatal to other III-V devices, defects in group-III nitrides are not mobile even under high electrical stress. Defect tubes, however, can offer a preferential path for contact metals to electromigrate towards the p-n junction, eventually resulting in a short. The proposed mechanism of GaN diode degradation raises concern for prospects of reliable lasers in the group-III nitrides grown on sapphire.
Wide-bandgap semiconductor
Degradation
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Light emitting diodes (LEDs) on GaN templates with high-density V-shaped micropits have been grown and characterized by transmission electron microscopy, scanning electron microscopy, and photoluminescence. Higher emission efficiency has been obtained for the fabricated LEDs compared with those without V-shaped pits. The high efficiency of the LEDs is mainly attributed to the increase in light extraction efficiency due to the light extraction from the sidewalls of the V-shaped pits. The improved internal quantum efficiency of the device resulting from the reduction of the dislocation density in the light emitting area also contributes to the high efficiency of the LEDs.
Quantum Efficiency
Wide-bandgap semiconductor
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Wide-bandgap semiconductor
Indium nitride
Solid-State Lighting
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Indium gallium nitride
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Visible light emitting diodes (LEDs) using semipolar (11-22)-oriented InGaN/GaN quantum wells (QWs) were demonstrated. Three dimensional microfacet structures realized white/pastel emissions without phosphors, while planar structures led to LEDs with much less polarization-induced internal electric fields compared to the conventional LEDs on the (0001) plane, both of which cannot be realized without the (11-22) planes.
Wide-bandgap semiconductor
Indium gallium nitride
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We report on Mg doping in the barrier layers of InGaN/GaN multiple quantum wells (MQWs) and its effect on the properties of light-emitting diodes (LEDs). Mg doping in the barriers of MQWs enhances photoluminescence intensity, thermal stability, and internal quantum efficiency of LEDs. The light output power of LEDs with Mg-doped MQW barriers is higher by 19% and 27% at 20 and 200 mA, respectively, than that of LEDs with undoped MQW barriers. The improvement in output power is attributed to the enhanced hole injection to well layers in MQWs with Mg-doped barriers.
Wide-bandgap semiconductor
Quantum Efficiency
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The authors report on the enhancement of the light extraction efficiency of GaN-based light-emitting diodes (LEDs) via the texturing of n-type layers. Compared with standard LEDs, LED fabricated with the textured n-type layers produced a significant improvement in the output power, depending on the reflectivity of the n electrode, the etch-pit size, and the chip dimension. The textured LEDs were found to yield the output power enhancement as high as 54%. However, it was also found that the electrical property of the textured LEDs can be degraded when the size of the etch pits is too large, indicating that a well-controlled texturing process is required for the realization of high-efficiency LEDs.
Wide-bandgap semiconductor
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GaN nanorods and nanosheets with non-polar facets are used as templates to form InGaN QW active regions for LEDs on the nonpolar facets. Uniform, narrow spectra light emitting regions are formed on the nonpolar facets.
Nanorod
Wide-bandgap semiconductor
Template
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The effects of InGaN-based light-emitting diodes (LEDs) with Al composition increasing and decreasing GaN-AlGaN barriers along the growth direction are studied numerically. Simulation results suggest that the LEDs with GaN-AlGaN composition-decreased barriers show more significant enhancement of light-output power and internal quantum efficiency than LEDs with composition-increasing GaN-AlGaN barriers when compared with the conventional LED with GaN barriers, due to the improvement in hole injection efficiency and electron blocking capability. Moreover, the optical performance is further improved by replacing GaN-AlGaN barriers with AlGaN-GaN barriers of the same Al composition-decreasing range, which are mainly attributed to the modified band diagrams. In addition, the major causes of the different efficiency droop behaviors for all the designed structures are explained by the electron leakage current and the different increase rates of hole concentration with injection current.
Wide-bandgap semiconductor
Quantum Efficiency
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