Stacking rearrangement at 6H–SiC(0001) surfaces during thermal hydrogenation Th. Seyller a, * ,N.Sieber a ,T.Stark a ,L.Ley a ,C.A.Zorman b ,M.Mehregany b a Institute of Technical Physics, University of Erlangen-N€ urnberg, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany b Department of Electrical Engineering and Computer Science, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA Abstract We have investigated the Si–H stretch mode on 6H–SiC(0001) and 3C–SiC(111) after thermal hydrogenation by Fourier-transform infrared absorption spectroscopy. On 6H–SiC(0001) two Si–H stretch modes at ð2128:0  0:6Þ cm 1 and ð2133:5  0:6Þ cm 1 are observed. The intensity ratio of the two absorption lines varies with preparation temperature.On3C–SiC(111)essentiallyasolemodeisobservedat ð2128:4  1:0Þ cm 1 atalltemperatures.Thetwo modes observed on 6H–SiC(0001) are explained in terms of cubic and hexagonal stacking arrangements below the surface. The variation of the intensity ratio of the two modes on 6H–SiC(0001) indicates a temperature dependent preference for cubic or hexagonal termination. Possible mechanisms for the stacking rearrangement are discussed. Ó 2003 Elsevier Science B.V. All rights reserved. Keywords: Siliconcarbide;Hydrogenatom;Infraredabsorptionspectroscopy;Lowenergyelectrondiffraction(LEED);Ellipsometry; Etching; Surface structure, morphology, roughness, and topography 1. Introduction Hydrogen etching of SiC surfaces at tempera- tures around 1600 °C is a common technique to reduce surface roughness prior to homoepitaxial CVD growth [1,2]. Tsuchida and coworkers used Fourier-transform infrared absorption spectro- scopy in attenuated total reflection mode (FTIR– ATR) to show that 6H–SiC(0001) and (000  1) surfacesannealedinhydrogenaround1000 °Care coveredwithamonolayerofhydrogenintheform of Si–H and C–H entities, respectively [3,4]. In previous studies we have investigated the so-pre- pared surfaces using FTIR–ATR and additional probes such as low-energy electron diffraction (LEED) and photoelectron spectroscopy (XPS, SXPS,andUPS)[5–7].Thehydrogenatedsurfaces exhibita(1  1)periodicity(seeFig.1)andarefree ofunwantedcontamination.Theyaresurprisingly stable against oxidation in air and possess a low density of charged surface states. Interestingly, a splitting of the Si–H stretch modewasobservedonthehydrogenated6H–SiC- (0001)surfaceanddifferentmodelswereproposed inordertoaccountforthissplitting[3–6].Tsuchida et al. [3,4] suggested that the splitting is due to a microscopicallyroughsurface.Thiswassupported bythepresenceofSi–H 2 andSi–H 3 modesintheir * Corresponding author. Tel.: +49-9131-8527088; fax: +49- 9131-8527889. E-mail address: thomas.seyller@physik.uni-erlangen.de (Th. Seyller). 0039-6028/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0039-6028(03)00157-2 Surface Science 532–535 (2003) 698–704 www.elsevier.com/locate/susc