Temperature‐depending Raman line‐shift of silicon carbide

Abstract

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 • 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.

Coordinated EDX and micro‐Raman analysis of presolar silicon carbide: A novel, nondestructive method to identify rare subgroup SiC

“…We also tested the heating effect of laser power on presolar SiC Raman features and found that the power needs to be increased by at least a factor of 10 before the TO peak starts to show a systematic downward shift of 1−2 cm −1 , which is in good agreement with the Bauer et al. () results. It is noteworthy to point out that the small heating effect of laser power on the SiC Raman signal is mainly the result of the small absorption coefficient of SiC at 532 nm so that only a very small fraction of the laser energy is absorbed in the material.…”

Effect of different current densities on optical properties of porous silicon carbide using photo-electrochemical etching

“…4 shows the Raman spectra of 6H-SiC and porous samples in the 940-990 cm -1 range. The peak at 965 cm À 1 is related to the longitudinal optic (LO) mode of the A 1 symmetry of SiC [6]. This peak exhibited a large change after etching under different current densities.…”

Raman measurements of substrate temperature in a molecular beam epitaxy growth chamber

“…14,15 Shifts are attributed to thermal expansion and the effect of phonon decay. For the zone-center E 2 vibration, a symmetric two-phonon decay has been applied to adequately describe the dependence from 20 to 350 K. 15 In this process, the initial phonon of energy ω 0 decays into two phonons each having energy ω 0 /2 and opposite momentum wavevectors…”

“…The full description in either Eq. (1) or (3) is necessary, although availability of the dependence across the low-temperature range 14,15 is helpful in determining the necessary constants. Better implementation of the linear model is expected when the k B T 0 > hcω 0 2 condition is met for the reference temperature.…”