Influence of AlGaN/GaN/InGaN superlattice on the characteristics of LEDs grown by metalorganic chemical vapor deposition Keun-Man Song a,c , Pil-Geun Kang a , Heung-Soo Shin a , Jong-Min Kim a , Won-Kyu Park a , Chul-Gi Ko a , Hyun-Wook Shim b , Dae Ho Yoon c,n a Korea Advanced Nano Fab Center (KANC), 906-10 Iui-dong, Suwon, Republic of Korea b Samsung LED, 314 Metan-dong, Suwon, Republic of Korea c School of Advanced Materials Science and Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Suwon, Republic of Korea article info Article history: Received 21 January 2010 Received in revised form 14 April 2010 Accepted 23 June 2010 Communicated by R. Bhat Available online 9 August 2010 Keywords: A1. X-ray diffraction A3. Metalorganic chemical vapor deposition B1. Nitrides B3. Light-emitting diodes abstract This study examined the influence of strain-compensated triple AlGaN/GaN/InGaN superlattice structures (SLs) in n-GaN on the structural, electrical and optical characteristics of LEDs by analyzing the etch pits density (EPD), stress measurement, high-resolution X-ray diffraction (HRXRD), sheet resistance, photoluminescence (PL) and light–current–voltage (L–I–V). EPD, stress measurement and HRXRD studies showed that the insertion of AlGaN/GaN/InGaN SLs during the growth of n-GaN effectively distributed and compensated for the strong compressive stress, and decreased the dislocation density in n-GaN. The operating voltage at 20 mA for the LEDs grown with SLs decreased to 3.18 V from 3.4 V for the LEDs grown without SLs. In addition, a decrease in the spectral blue shift compared to the LEDs grown without SLs was observed in the LEDs grown with the SLs. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Wide band gap GaN and its related alloys are promising materials for blue-UV optical devices, such as LEDs, LDs and photodetectors, on account of the variable direct band gaps ranging from 0.8 to 6.2 eV. Tremendous progress in III-nitride semiconductors has already led to commercial mass production of GaN-based LEDs and LDs [1–3]. In addition to the improved crystal quality, the epitaxial structure of LEDs is one of the key points for the high brightness of LEDs. It was reported that superlattice structures (SLs) play important roles in the perfor- mance of GaN-based optoelectronic devices. In particular, intro- ducing AlGaN/GaN strained SLs is a good method for suppressing the creation of defects due to strain relief in the AlGaN/GaN SLs [4]. Mg-doped AlGaN/GaN SLs yielded an increase in the hole concentration by increasing the ionization efficiency of acceptor energy level [5–7]. Mg-doped InGaN/GaN SLs showed a lower series resistance and turn on voltage by the polarization-induced field of the strained InGaN [8]. Highly Si-doped InGaN/GaN SLs grown on p-GaN effectively reduce the series resistance and turn on voltage of LEDs by the tunneling transport of carriers through electrically reversed p–n junction [9]. Therefore, the epitaxial structures of GaN-based LEDs for the next generation lighting sources have become more complicated with the development of III-nitride semiconductor technology and thicker using inserted functional interlayers, such as AlGaN/GaN SLs [5–7], InGaN/GaN SLs [8–9], InGaN electron reservoir layer [10]. Epilayers of III- nitride grown above a critical thickness induce the creation of strain related dislocation, cracking and bowing, which are the factors that limit the design possibilities of the epitaxial structure due to lattice mismatch and different thermal expansion coefficients between the substrate and epilayer. In particular, the evolution of strong stress during GaN growth leads to bending of the sapphire substrate on the macroscopic scale. This is considered to be a severe problem with increase in thickness of the epilayer and larger wafers in terms of mass production because the stress and large bowing of the epilayer can significantly affect the device process and parameters. Recently, Czernecki et al. suggested strain-compensated triple AlGaN/GaN/InGaN SLs to suppress the bowing and cracking in violet LDs [11]. These triple AlGaN/GaN/InGaN SLs were designed to compensate for the tensile stress of AlGaN caused by the compressive stress of InGaN with respect to GaN. However, there are no reports of detailed studies correlating the effect of AlGaN/ GaN/InGaN SLs on both the electrical and optical properties in LEDs. This paper reports a systematic study of the effect of Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2010.06.028 n Corresponding author. Tel.: + 82 31 290 7388; fax: + 82 31 290 7371. E-mail address: dhyoon@skku.edu (D. Ho Yoon). Journal of Crystal Growth 312 (2010) 2847–2851