High Efficiency GaN-based Light Emitting Diodes with Embedded Air Voids/SiO2 Nanomasks
ABSTRACT In this paper, the high performance GaN-based light-emitting diodes (LEDs) with embedded microscale air voids and an SiO(2) nanomask by metal-organic chemical vapor deposition (MOCVD) were demonstrated. Microscale air voids and an SiO(2) nanomask were clearly observed at the interface between GaN nanorods (NRs) and the overgrown GaN layer by scanning electron microscopy (SEM). From the reflectance spectra we show strong reflectance differences due to the different refractive index gradient between the GaN grown on the nanotemplate and sapphire. It can increase the light extraction efficiency due to additional light scattering. The transmission electron microscopy (TEM) images show the threading dislocations were suppressed by nanoscale epitaxial lateral overgrowth (NELOG). The LEDs with embedded microscale air voids and an SiO(2) nanomask exhibit smaller reverse-bias current and large enhancement of the light output (65% at 20 mA) compared with conventional LEDs.
IEEE Journal of Selected Topics in Quantum Electronics 07/2015; 21(4):1-1. DOI:10.1109/JSTQE.2015.2389529 · 3.47 Impact Factor
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ABSTRACT: InGaN light-emitting diodes (LEDs) embedded with air voids and a gallium oxide (Ga2O3) layer were fabricated through a photoelectrochemical (PEC) oxidation process. The epitaxial lateral overgrowth process occurred at the PEC oxidized nanorods to form the air-voids structure. The light output power of the treated LED with the air-voids structure had a 70% enhancement compared with a non-treated LED at a 20 mA operation current. High internal quantum efficiency and low piezoelectric field were measured in the treated LED structure through a bias-dependent micro-photoluminescence measurement. The strain-induced piezoelectric field in InGaN active layer was partially reduced by forming the Ga2O3 layer and the air-voids structure.01/2013; 2(4):R65-R69. DOI:10.1149/2.012304jss
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ABSTRACT: We investigate the structural properties of molecular-beam-epitaxy coalescence overgrowth of GaN columns at the nanoscale with transmission electron microscopy and other characterization techniques. Two samples grown over nanocolumns of different widths and spatial densities (columns/area) are compared. It is found that columns with a larger cross section (~500 nm) and correspondingly lower spatial density normally lead to un-coalesced overgrown domains ranging 5-8 μm in size. On the other hand, the overgrowth on the columns of a smaller cross section (~100 nm) and correspondingly higher density results in coalesced domains ranging from 1 to 5 μm in size. It is believed that among the smaller, more closely spaced columns the strain distribution resulting from overgrowth is more effective in leading to the uniformity of crystalline orientation, and hence successful coalescence. The optical characterization leads to the conclusion that the defect density in the sample grown on smaller columns is lower when compared with that grown on larger columns.Optical Materials Express 09/2013; 3(9). DOI:10.1364/OME.3.001450 · 2.92 Impact Factor