Hollow nanostructure-assisted growth of GaN by MOCVD and its applications

Jonghak Kim 1Heeju Woo 2Kisu Joo 3Sungwon Tae 1Daeyoung Moon 1Sunghyun Park 1Junghwan Jang 1Yigil Cho 4Jucheol Park 1Hwankuk Yuh 1Gun-Do Lee 1Jinsub Park 5In-Suk Choi 4Heung Nam Han 1Yasushi Nanishi 6Kookheon Char 2Euijoon Yoon 1,7

1. Seoul National University (SNU), School of Mat. Sci. Eng., Seoul 151742, Korea, South
2. Seoul National Unversity, School of Chemical and Biological Engineering (SNU), Seoul 151-744, Korea, South
3. Seoul National University, Graduate School of Convergence Science and Technology, Suwon 443270, Korea, South
4. Korea Institute of Science and Technology, High Temperature Energy Materials Research Center, Seoul 133791, Korea, South
5. Hanyang University, Department of Electronic Engineering, Seoul 133791, Korea, South
6. Department of Photonics, Ritsumeikan University, Kusatsu 525-8577, Japan
7. Advanced Institutes of Covergence Technology (AICT), Suwon 443270, Korea, South

Abstract

Light-emitting diodes (LEDs) become an attractive alternative to conventional light sources such as incandescent and fluorescent lamps due to their high energy efficiency, long device lifetime, and integration with other digital devices. However, different material properties between GaN and sapphire substrates cause several problems such as high dislocation density in GaN epitaxial layers, serious wafer bowing, particularly in large-area wafers due to thermal expansion mismatch, and poor light extraction efficiency of GaN-based LEDs due to total internal reflection. In this presentation, we propose a new growth strategy for the fabrication of high efficiency LEDs by incorporating artificial hollow nanospheres. In particular, polystyrene (PS)/silica core-shell nanospheres were synthesized and coated as a monolayer on a sapphire substrate by a modified dip coating technique. Sapphire substrates containing a monolayer of silica hollow nanosphere (S-HNS) could be prepared by the calcination of PS core and subsequent fixation to the substrate in a furnace. The subsequent growth of GaN by metalorganic chemical vapor deposition results in improved crystal quality due to nano-scale lateral epitaxial overgrowth. Moreover, well-defined voids embedded at the GaN/sapphire interface help scatter lights effectively with the maximum index contrast to increase the light extraction efficiency and reduced the wafer bowing due to partial alleviation of compressive stress in GaN. It was found that the GaN epilayer with embedded S-HNS had higher diffuse reflectance in all visible wavelength range, and reduced wafer bowing, and stronger integrated photoluminescence intensity. Detailed analyses of finite difference time domain (FDTD) simulation and finite element simulation were used to understand the effect of S-HNS on reflectance and structural properties, respectively. The blue LED with embedded S-HNS indeed had two-fold stronger light emission with respect to one without S-HNS, suggesting that the new GaN epitaxy scheme looks quite promising in achieving high external efficiency LEDs for solid-state lighting, particularly in the mass production of LEDs with large-area sapphire wafers.

 

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Presentation: Invited oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 10, by Euijoon Yoon
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-07 12:55
Revised:   2013-07-11 23:05