On the nucleation, coalescence, and overgrowth of HVPE GaN on misoriented sapphire substrates and the origin of pinholes Tim Bohnen a,Ã , Aryan E.F. de Jong a , Willem J.P. van Enckevort a , Jan L. Weyher a,b , Gerbe W.G. van Dreumel a , Hina Ashraf a , Paul R. Hageman a , Elias Vlieg a a IMM, Radboud University, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands b Institute of High Pressure Physics, Polish Academy of Sciences, ul. Sokolowska 29/37, 01-142 Warsaw, Poland 1 article info Article history: Received 6 April 2009 Received in revised form 17 July 2009 Accepted 21 July 2009 Communicated by K.W. Benz Available online 26 September 2009 PACS: 61.72.Cc 61.72.Ff 61.72.uj 68.55.A 68.55.ag Keywords: A1. Nucleation A1. Defects A3. Hydride vapor phase epitaxy B1. Nitrides B2. Semiconducting gallium compounds abstract The nucleation of HVPE GaN on misoriented sapphire substrates and the transition from the nucleation layer to an epitaxial film were investigated. After a KOH/NaOH eutectic etch of the approximately 45 mm thick GaN layer, grown on sapphire using a low temperature nucleation, high temperature epitaxy process, the cross-sections revealed columnar structures, up to roughly 1 mm above the sapphire substrate. Photoetching of the thick GaN layers revealed inhomogeneous defect distributions along the cross-sections, which appeared to be related to the numerous pinholes originating at the GaN/sapphire interface. We present a model explaining the formation of pinholes by the coalescence of the GaN nuclei during the epitaxial overgrowth. & 2009 Elsevier B.V. All rights reserved. 1. Introduction Because of its excellent opto-electronic properties, GaN is widely implemented in the current generation of semiconductor opto-electronic devices, such as ‘‘Blu-ray’’ DVD players. Due to GaN’s wide bandgap of 3.4 eV, GaN-based devices can emit light with wavelengths around 365nm. This short wavelength lies in the UV region and utilizing it in data-storage devices increases the data capacity of a single DVD from 4 to 26 GB. Aside from its bandgap, GaN stands out favorably when compared to silicon and other conventional III–V semiconductors, such as GaAs, in terms of breakdown voltages, free carrier velocities, thermal conductiv- ity, and chemical inertness. Most commonly, the performance of GaN-based devices is limited by defects acting as electron–hole pair recombination centers or as scattering centers that limit thermal conductivity. In typical GaN devices one comes across a multitude of structural defects, such as dislocations and inclusions of cubic GaN. Most of these originate from the mismatch between the substrate, normally sapphire, and GaN. The mismatch between GaN and sapphire is large (  15% [1]) and a low temperature GaN nucleation layer or an AlN buffer layer is often applied to partially overcome this mismatch. Such a GaN nucleation layer is shown in Fig. 1 , where the individual GaN nuclei, which during overgrowth will coalesce into a smooth film, can be distinguished. Despite the introduction of a nucleation layer and an in-plane reorientation of the GaN lattice with respect to that of the sapphire, the strain in GaN layers on sapphire is still considerable. This results in the introduction of large numbers of defects, such as edge and screw dislocations, which can relax the strain in the GaN layer. Another common defect is the so-called pinhole, which is often found in large numbers in the first micrometer of the GaN layer [2–4]. These V-shaped defects consist of a void with an inverted pyramidal shape [5] and can introduce screw dislocations [5] or result in the formation of nanopipes in the crystal layers [3,6]. The ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2009.07.045 Ã Corresponding author. Tel.: +31 24 3653432; fax: +31 24 3652314. E-mail address: T.Bohnen@science.ru.nl (T. Bohnen). 1 Present address. Journal of Crystal Growth 311 (2009) 4685–4691