1 Scientific RepoRts | 7:45519 | DOI: 10.1038/srep45519 www.nature.com/scientificreports three dimensional characterization of GaN-based light emitting diode grown on patterned sapphire substrate by confocal Raman and photoluminescence spectromicroscopy Heng Li 1,* , Hui-Yu Cheng 2,* , Wei-Liang Chen 2,* , Yi-Hsin Huang 2 , Chi-Kang Li 3 , Chiao-Yun Chang 1 , Yuh-Renn Wu 3 , tien-Chang Lu 1 & Yu-Ming Chang 2 We performed depth-resolved pL and Raman spectral mappings of a GaN-based LeD structure grown on a patterned sapphire substrate (pss). our results showed that the Raman mapping in the pss-GaN heterointerface and the pL mapping in the In x Ga 1-x N/GaN MQWs active layer are spatially correlated. Based on the 3D construction of E 2 (high) Raman peak intensity and frequency shift, V-shaped pits in the MQWs can be traced down to the dislocations originated in the cone tip area of pss. Detail analysis of the pL peak distribution further revealed that the indium composition in the MQWs is related to the residual strain propagating from the pss-GaN heterointerface toward the LeD surface. Numerical simulation based on the indium composition distribution also led to a radiative recombination rate distribution that shows agreement with the experimental pL intensity distribution in the In x Ga 1-x N/ GaN MQWs active layer. In this century InGaN/GaN light emitting diodes (LEDs) have become the most widely used optoelectronic devices for solid-state lighting. Its advantages include a widely tunable range of emitting wavelengths from ultra- violet (UV) to near infrared (NIR) and a high electric-optical conversion efciency. Te material research in nitride semiconductors has also led to successful developments in optoelectronic device applications, such as laser diodes, photodetectors, solar cells, and power electronics 1–6 . Specifcally, InGaN compound semiconductors exhibit large oscillator strength, large exciton binding energy, high thermal conductivity, good mechanical stabil- ity, and intriguing optoelectronic properties, making it suitable for high power lighting applications 7 . However, due to the phenomenon of efciency droop, the efciency of GaN-based LEDs is suppressed with increasing injection current. Te large defect and dislocation density induced by the large lattice mismatch between GaN and hetero-substrates has also limited GaN-based light emitting devices for high current injection operations. It has become increasingly important to overcome the droop problem as LED devices are requested to maintain the same or even higher output power in decreased chip sizes 8,9 . Another important factor limiting the development of GaN-based devices is the lack of native substrates for GaN epitaxy. Commercial GaN-based LEDs are typically grown on c-plane sapphire substrate by hetero-epitaxy approach. Due to the mismatch between the sapphire and GaN lattices, this approach results in a large defect and dislocation density in the subsequently grown GaN epilayer 10,11 . Recently, one alternative and clever approach to suppress the defect and dislocation densities is the use of patterned sapphire substrate (PSS). Tis novel 1 Dept. of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 30050, taiwan. 2 Center for Condensed Matter Sciences, National Taiwan University, 10617, Taipei, Taiwan. 3 Graduate institute of Photonics and Optoelectronics and Department of electrical engineering, national taiwan University, Taipei, 10617, Taiwan. * these authors contributed equally to this work. correspondence and requests for materials should be addressed to t.-c.L. (email: timtclu@mail.nctu.edu.tw) or Y.-M.c. (email: ymchang@ntu.edu.tw) received: 04 November 2016 accepted: 27 February 2017 Published: 30 March 2017 opeN