High Efficiency GaN-based Light Emitting Diodes with Embedded Air Voids/SiO2 Nanomasks

Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of China.
Nanotechnology (Impact Factor: 3.82). 02/2012; 23(4):045303. DOI: 10.1088/0957-4484/23/4/045303
Source: PubMed


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.

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    • "It is well known that one of the methods to reduce TDs and enhance the internal quantum efficiency of GaN-based LEDs is epitaxial lateral overgrowth (ELO). Light output enhancement of GaN-based LEDs through microscale or nanoscale ELO (NELO) have been reported for sapphire substrates [5], [6]. However, there are few reported device results for LEDs on Si substrates through the NELO method [7], especially for Manuscript received March 26, 2013; accepted April 20, 2013. "
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    ABSTRACT: High-performance GaN-based green and yellow light-emitting diodes (LEDs) are grown on SiO2 nanorod patterned GaN/Si templates by metalorganic chemical vapor deposition. The high-density SiO2 nanorods are prepared by nonlithographic HCl-treated indium tin oxide and dry etching. The dislocation density of GaN is significantly reduced by nanoscale epitaxial lateral overgrowth. In addition to the much improved green LED (505 and 530 nm) results, the fabricated yellow (565 nm) InGaN/GaN-based multiquantum well (MQW) LEDs on Si substrates are demonstrated for the first time. High-quality GaN buffer and localized states in MQWs are correlated to obtaining high-efficiency long-wavelength emission in our devices.
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    ABSTRACT: A high-efficiency InGaN light-emitting diode (LED) structure was grown on a silane (SiH4)-treated undoped-GaN layer with a thin in situ grown SiN∞ layer and a 3-D island structure. A lateral one-step epitaxial growth process was performed on the SiH4-treated GaN island structure to form a series-of-embedded-air-void (SEAV) structure. The SEAV structure prevented the dislocation from propagating to the top LED epitaxial layer that reduced the leakage current and increased the internal quantum efficiency of the treated InGaN LED. The light output power of the treated LED had a 68% enhancement compared with that of the standard LED at 20 mA. The high output power and the narrow divergent angle of the treated LED structure were caused by the high light scattering process on the SEAV structure.
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    ABSTRACT: A relatively simple and easy and inexpensive liquid-phase deposition (LPD) method is employed to introduce nanoscale silica hemispheres on sapphire substrates for fabricating a nano-patterned sapphire substrate (NPSS). Compared with GaN grown on sapphire without any pattern, the NPSS-GaN film is of much better quality as observed by scanning electron microscopy, transmission electron-microscopy, X-ray diffraction, cathodoluminescence, and photoluminescence. This is because GaN is initiated from the c-plane instead of the LPD-silica surface. In addition, many dislocations within the NPSS-GaN bend toward the patterns, or end at the GaN/void interfaces.
    No preview · Article · Dec 2012 · IEEE Photonics Technology Letters
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