V-defects and dislocations in InGaN/GaN heterostructures A.M. Sa ´nchez a, * , M. Gass a , A.J. Papworth a , P.J. Goodhew a , P. Singh b , P. Ruterana b , H.K. Cho c , R.J. Choi d , H.J. Lee d a Department of Engineering, University of Liverpool, Liverpool L69 3GH, United Kingdom b LERMAT-FRE 2149 CNRS, ENSICAEN, 6 Boulevard du Mare ´chal Juin, 14050 Caen Cedex, France c Department of Metallurgical Engineering, Dong-A University, Hadan-2-Dong 840, Saha-gu, Busan 604-714, Korea d Department of Semiconductor Science and Technology, Semiconductor Physics Research Center, Chonbuk National University, Duckjin-Dong, Duckjin-ku, Chonju 561-756, Korea Received 25 November 2004; accepted in revised form 30 November 2004 Abstract In the growth of InGaN/GaN multi-quantum well (MQW) heterostructures by metal organic chemical vapor deposition, V-defects attached to threading dislocations have been observed and investigated. Energy-dispersive X-ray analysis and conventional transmission electron microscopy studies were carried out in order to determine the In composition and investigate the behavior of the dislocations. The V- defects are limited by {101 ¯ 1} lattice planes, they are attached to threading dislocations and may start at the third quantum well. The associated dislocation runs up into the overgrown GaN layer. Some (a+c ) dislocations were shown to decompose inside the multi-quantum well, giving rise to a misfit segment in the c -plane and a V-shape defect. D 2004 Elsevier B.V. All rights reserved. Keywords: 320; 496; 543 1. Introduction The outstandingly rapid progress in the field of III–V nitride semiconductor materials is due to their great importance for optoelectronic devices, particularly for short wavelengths, high power and high temperature electronic devices [1,2]. InGaN/GaN quantum wells are the active structures, which may cover the whole spectral range from near ultraviolet (3.4 eV) to near infrared (b0.7eV) applica- tions, such as light emitting diodes and laser diodes. Intensive research is being carried out to understand the effect of the structural defect on the properties of the material. Active III-N layers have a large density of defects that cross the epitaxial layer degrading the device perform- ance [3,4]. III-N epilayers are normally grown on a sapphire substrate. The large lattice mismatch and thermal coefficient differences between the GaN and the substrate lead to defective material, with huge densities of threading dis- locations and other structural defects such as stacking faults, inversion domains, etc. However, it was also recognized that GaN layers exhibit high efficiency even with this large density of extended defects [5]. The so-called V-defects have been frequently observed in the InGaN multi-quantum well (MQW) structures [6–9]. These defects have a hexagonal inverted pyramidal shape with {101 ¯ 1} walls and are limited by a hexagon in the basal plane [7]. Theoretical calculations have been carried out to understand the V-defect formation in GaN. Indium-induced changes in GaN(0001) surface morphology have been determined. Specifically, first-principles calculations revealed a substan- tial effect of In in the relative formation energies of {101 ¯ 1} and {0001} surface. The main In-induced change is the reduction of the surface energy in the former respect to the latter, promoting a V-defect or inverted hexagonal pyramid having {101 ¯ 1} facets [10]. The origin of the pyramid has 0040-6090/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2004.11.207 * Corresponding author. Tel.: +44 0 151 794 4704; fax: +44 0 151 794 4675. E-mail address: asf@liv.ac.uk (A.M. Sa ´nchez). Thin Solid Films 479 (2005) 316 – 320 www.elsevier.com/locate/tsf