Correlation of the Raman spectra with the thermal conductivity of a set of diamond wafers prepared by chemical vapor deposition

Abstract

Raman spectroscopy, at laser excitation wavelengths of 514.5, 785, and 1064 nm, is used to study a set of chemical-vapor-deposited (CVD) diamond wafers of known thermal conductivity κ. The in-plane thermal conductivity (at 25 °C) of the diamond wafers ranges from 4 to 22 W cm−1 K−1 and represents a wide range of diamond quality. The spectra were obtained from both macro/micro- sampling measurements, examining the top and bottom wafer surface, as well as wafer cross-sections. Discussed are the peak positions and linewidths of the Raman bands and their relation to sp3-bonded diamond and sp2-bonded carbon in the context of diamond quality and perfection, and the effects of wafer heterogeneities. The detailed analysis of the Raman spectra provides a robust correlation with the room-temperature bulk (or macroscopic) thermal conductivity of these samples. The correlation is made through the determination of the band area ratios of the diamond Raman line at 1333 cm−1 to that of the 1550 cm−1 band characteristic of nondiamond carbon impurities. This dependence is most pronounced for the Fourier-transform Raman data obtained with infrared excitation at 1064 nm, due to resonance enhancement, and therefore allows the detection of carbon impurities, especially for high-quality CVD diamond.