Defect-induced polytype transformations in LPE grown SiC epilayers on (111) 3C-SiC seeds grown by VLS on 6H-SiC Maya Marinova a,Ã , Georgios Zoulis b , Teddy Robert b , Frederic Mercier c , Alkioni Mantzari a , Irina Galben c , Olivier Kim-Hak d , Jean Lorenzzi d , Sandrine Juillaguet b , Didier Chaussende c , Gabriel Ferro d , Jean Camassel b , Efstathios K. Polychroniadis a a Department of Physics, Aristotle University of Thessaloniki, GR54124 Thessaloniki, Greece b Groupe d 0 Etude des Semiconducteurs, CNRS and Universit  e Montpellier 2, cc 074-GES, 34095 Montpellier cedex 5, France c Laboratoire des Mat  eriaux et du G enie Physique, Grenoble INP-CNRS, 3 parvis Louis N eel, BP257, 38016 Grenoble cedex 1, France d Laboratoire des Multimat  eriaux et Interfaces, UCB Lyon1-CNRS, 43 Bd du 11 nov.1918, 69622 Villeurbanne, France article info Keywords: SiC LPE TEM LTPL abstract The results of transmission electron microscopy (TEM) with low-temperature photoluminescence (LTPL) and Raman studies of liquid phase grown epilayers on top of a vapor liquid solid (VLS) grown 3C-SiC buffer layer are compared. While the 6H-SiC substrate was completely covered by the 3C-SiC seed after the first VLS process, degradation occurred during the early stage of the liquid phase epitaxy process. This resulted in polytype instabilities, such that several rhombohedral forms stabilized one after the other. These (21R-SiC, 57R-SiC) eventually led after few microns to a final transition back to 6H-SiC. This interplay of polytypes resulted in a complex optical signature, with specific LTPL and Raman features. & 2009 Elsevier B.V. All rights reserved. 1. Introduction Silicon carbide is a tetrahedrally coordinated wide band gap semiconductor. It is also one of the few compounds in nature distinguished by a strong polytypism. Today, a large number of short and long period unit cells have been identified and, since the difference in structural symmetry affects the physical properties, investigation of the conditions for polytype stabiliza- tion and/or transformation is important from fundamental and practical point of view. Among all polytypes, only one, 3C-SiC has the cubic symmetry ðF 43m Þ and the lowest band gap energy [1]. Other important short period polymorphs with non-cubic symmetry (P6 3 mc or R3m) and different degrees of hexagonality, and thus different band gap energies are 2H-, 4H-, 6H- and 15R-SiC. Special attention has been paid in the recent years to the growth of 3C-SiC crystals with appropriated structural quality for device applications. To this end, appropriate growth techni- ques have to be developed avoiding the polytype transformations. In the present work liquid phase grown epilayers are investigated by means of TEM, LTPL and Raman. The structural quality and the polytype instability, which resulted in complex optical signature, are discussed and possible reasons for the heteropolytypic growth outlined. The coincidence of the optical and TEM results is pointed out in an effort to understand the polytype alternation. 2. Experimental On-axis, Si face, 6H-SiC substrates were used as seeds for the first deposition of a 3C-SiC buffer layer with a thickness of few microns by the VLS mechanism in a Si (25 at%)–Ge(75 at%) melt [2]. A complementary LPE process was performed at a tempera- ture of 1650 1C and in pure Si solvent in order to increase the thickness [3]. The TEM observations were performed on a JEOL 100X conventional TEM operating at 100 kV and JEOL 2011 high resolution TEM operating at 200 kV. The LTPL spectra were collected at 5 K, using 20 mW of the 244 nm wavelength of a frequency doubled Ar + -ion laser as excitation source. A cooled charge-coupled device (CCD) camera completed the set-up. Micro-Raman spectra were collected at room temperature using a T64000 spectrometer from Jobin-Yvon Horiba fitted with a microscope and a cooled CCD camera. Using the 514.5nm line of Ar + for excitation, the focused spot diameter was 2 mm. ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physb Physica B 0921-4526/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2009.08.128 Ã Corresponding author. Tel.:+30 2310 998 146. E-mail address: marinova@physics.auth.gr (M. Marinova). Physica B 404 (2009) 4727–4730