Photoluminescence and Raman spectroscopic techniques were used to investigate sources of stress, and the type and distribution of impurities and defects, in thin films which had been grown onto Si substrates. The types of impurities and defects which were detected in the films were N, Si, and sp2-type bonding of the graphitic phase. The Raman analyses indicated that the films exhibited a net compressive stress. After allowing for thermal interfacial stresses, and the stresses which were due to grain boundaries, it was found that the residual internal stress was compressive in nature. On the basis of Raman line-shape analyses, it was determined that the internal stress was due to the various impurities and defects which were present in the film. Also, the magnitude of the stress exhibited a marked correlation with the graphitic phase; thus implying that the sp2 bonding produced a predominantly compressive stress field. A photoluminescence analytical line-shape investigation of the N band at 2.154eV indicated that the N centers were uniformly distributed in the film. The photoluminescence line-shape exhibited a close fit to the Lorentz-Gaussian convoluted line which was known as the Voit profile. Deconvolution of the line revealed a predominant Gaussian component, which corresponded to stresses which arose from line-type defects, and a much smaller Lorentzian component which corresponded to point defect stresses. The Gaussian component was attributed to the graphitic phase; thus implying that the sp2 bonding was not in the form of a point defect but rather took the form of a line or extended defect. A line-shape investigation of the Si band at 1.681eV showed that the Si centers were related to the Si/diamond interfacial stress. The response of the N and Si optical centers to the internal stress, which was reflected by the photoluminescence line-width, was also studied. The Si band exhibited a narrower line-width. This was suggested to indicate that the Si center complied less with the internal stress than with the N center, or that the 2 optical centers were interacting with different types of stress source.

L.Bergman, R.J.Nemanich: Journal of Applied Physics, 1995, 78[11], 6709-19