ELSEVIER Physica B 219&220 (1996) 371 373 Raman scattering of disordered SiC S. Nakashima*, K. Kisoda, H. Niizuma, H. Harima Department of Applied Physics, Osaka University, 2-1 Yamadaoka , Suita, Osaka 565, Japan Abstract We have measured Raman scattering from SiC crystals containing stacking disorders. Raman intensity profiles are calculated for models of disordered structures and compared with the observed spectra. 1. Introduction It is well known that SiC shows polytypism, which is a phenomenon whereby a compound crystallizes in a variety of layered structures in the c-direction, namely polytypes. SiC polytypes which consist of a mixture of hexagonal and cubic stackings of Si-C double layers often contain random distribution of stacking faults of the atomic plains in the c-direction. The stacking dis- order in SiC crystals has been mainly investigated by X-ray diffraction and electron microscopy so far. Recently, Raman spectroscopic study has been made on SiC having disordered stackings [1]. Raman spectra of disordered SiC show broad bands at the frequencies corresponding to those of basic polytypes such as 6H, 15R, 4H, etc. These Raman spectra have been explained by a model taking account of the disorder in Raman bond polarizability only. A peculiar feature in disordered SiC is that long-range order in the stacking of the atomic layers is lost, but short-range order remains: It comprises small domains, each consisting of a basic polytype structure. Accord- ingly, Raman spectra of the disordered structures reflect the stacking structures of the domains. In the present work, phonon Raman spectra have been measured for various SiC crystals containing stacking * Corresponding author. disorders and compared with Raman intensity profiles calculated using a one-dimensional model considering disorder in the bond polarizability and force field. 2. Observed spectra of disordered SiC crystals 2.1. Weakly disordered SiC Raman spectra of disordered SiC crystals were meas- ured by use of a Raman microscope at room temper- ature. Samples used here were small flakes which were grown by the Acheson method. Fig. l(a) and (b) shows the Raman spectra taken at typical points in slightly disordered crystals in the fre- quency region of transverse acoustic modes. The folded transverse acoustic (FTA) modes corresponding to those of the 6H polytype appear with weak tail bands in the low- and high-frequency sides. Another interesting fea- ture of the spectra is the change in the intensity ratio of the FTA doublets. As the degree of the disorder is in- creased, the tails grow and the weak counterpart of the doublets becomes gradually buried in the tail bands. 2.2. Heavily disordered crystals" The FTA and FTO modes are broad and strongly distorted for heavily disordered SiC as shown in Fig. 2. 0921-4526/96/$15.00 :.~2"1996 Elsevier Science B.V. All rights reserved SSDI 0921-4526(95)00748-2