Temperature-depending Raman line-shift of silicon carbide

Silicon carbide (SiC) is often used for electronic devices operating at elevated temperatures. Spectroscopic temperature measurements are of high interest for device monitoring because confocal Raman microscopy provides a very high spatial resolution. To this end, calibration data are needed that relate Raman line-shift and temperature. The shift of the phonon wavenumbers of single crystal SIC was investigated by Raman spectroscopy in the temperature range from 3 to 112 degrees C. Spectra were obtained in undoped 6H-SiC as well as in undoped and nitrogen-doped 4H-SiC. All spectra were acquired with the incident laser beam oriented parallel as well as perpendicular to the c-axis to account for the anisotropy of the phonon dispersion. Nearly all individual peak centers were shifting linearly towards smaller wavenumbers with increasing temperature. Only the peak of the longitudinal optical phonon A(1)(LO) in nitrogen-doped 4H-SiC was shifting to larger wavenumbers. For all phonons, a linear dependence of the Raman peaks on both parameters, temperature and phonon frequency, was found in the given temperature range. The linearity of the temperature shift allows for precise spectroscopic temperature measurements. Temperature correction of Raman line-shifts also provides the ability to separate thermal shifts from mechanically induced ones. Copyright (C) 2009 John Wiley & Sons, Ltd.