Two-step lateral growth of GaN for improved emission from blue light-emitting diodes Young Jae Park a , Ji Hye Kang a , Hyun Kyu Kim a , Yashpal Singh Katharria a , Nam Han a , Min Han a , Beo Deul Ryu a , Eun-Kyung Suh a , Hyung Koun Cho b , Chang-Hee Hong a,n a School of Semiconductor and Chemical Engineering, Chonbuk National University, Chonju 561-756, Republic of Korea b Department of Material Science and Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea article info Article history: Received 1 February 2013 Received in revised form 28 February 2013 Accepted 18 March 2013 Communicated by R. Bhat Available online 4 April 2013 Keywords: A3. Metalorganic chemical vapor deposition A3. Selective epitaxy B1. Nitrides B1. Sapphire B2. Dielectric materials B3. Light emitting diodes abstract A two-step growth approach based on facet-controlled epitaxial lateral growth and the application of silica nanospheres was established to enhance the performance of GaN based light-emitting diodes (LEDs). In the first step, open inverted honeycomb cones (IHCs) were fabricated. These IHCs were filled with silica nanospheres and a second growth step was performed. As compared to LEDs fabricated on IHC templates, 2.7 fold electroluminescence (EL) intensity was obtained for silica nanospheres-stacked IHC due to improved crystal quality and light scattering at silica nanospheres. Simulation of emission intensity was carried out to determine the effect of dislocation density reduction on EL enhancement of the LEDs. & 2013 Elsevier B.V. All rights reserved. 1. Introduction GaN epilayers are ideal substrate materials for short-wavelength (visible and UV regions) light-emitting diodes (LEDs), laser diodes (LDs), and high power electronic devices [1]. The internal quantum efficiency (IQE) of GaN based LEDs is limited by the existence of high threading dislocation density (∼5 Â 10 8 cm -2 ) in heteroepitaxially grown GaN epilayers. The dislocations act as nonradiative recombi- nation center [2], scattering centers for carriers [3], reducing thereby the carrier mobility [2] and the thermal conductivity [4]. Achieving GaN films with low dislocation density is, therefore, crucial to improve emission efficiency of GaN LEDs. Epitaxial lateral over- growth (ELO) applied first by Kato et al. for GaN growth [5] has received considerable scientific attention as a way to efficiently reduce dislocation density which led to the demonstration of blue LD with lifetime of more than 10,000 h grown using ELO [6]. During the conventional ELO relying on a high ratio of lateral-to-vertical growth rates, propagation of dislocations in the laterally grown regions is normally blocked by thin SiO 2 or SiN x mask; however, the window regions retain the same dislocation density as that in the buffer layer [7]. Moreover, the coalescence of GaN growth fronts over the masked regions also leads to the generations of large number of threading dislocations [8]. A two step growth technique, known as facet-controlled ELO, exploits bending of vertically propagating dislocations in the lateral directions, and has shown promises for improving structural quality of ELO GaN [9,10]. It was shown that the mixed type dislocations are bent toward the mask areas and halted at the voids, while edge type dislocations are bent parallel to the mask stripe [10,11]. Although, this technique reduces dislocation density in the window regions, the coalescence boundaries remain highly defective, nevertheless [11]. Besides, the dislocation that does not encounter with a void over the mask may also be bent at the coalescence boundaries, and can thread up to the surface. Recently, Lee at el. [12] utilized self-assembled monolayers of silica micro- spheres to suppress dislocation in GaN epilayers. They obtained a dislocation density as low as 4 Â 10 7 cm -2 as the dislocations moving along the c-direction or those bent during the growth were blocked by the silica spheres. We have also reported that on one hand embedded self-assembled silica-nanospheres act as selective defect blocking masks and produce high quality GaN film with low dislocation density, while on the other they act as a scattering center of the emitted light and enhance the light extraction efficiency (LEE) [13,14]. It was found that the light emission improves with increasing amount of silica nanospheres in the LED. However, a few threading dislocations could still not be blocked and propagated to the top surface. Also, hexagonal etch pit could not provide enough space to confine a larger amount of silica nanospheres. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2013.03.026 n Corresponding author. E-mail address: chhong@jbnu.ac.kr (C.-H. Hong). Journal of Crystal Growth 372 (2013) 157–162