Raman and photoluminescence analysis of stress state and impurity distribution in diamond thin films

Abstract

Photoluminescence (PL) and Raman spectroscopy were employed to investigate the nature and sources of stress and the type and distribution of impurities and defects in thin diamondfilmsgrown on silicon substrates. The types of impurities and defects which were detected in the diamondfilms are the nitrogen, silicon, and the sp 2‐type bonding of the graphitic phase. Our Raman analyses indicate that the diamondfilms exhibit a net compressive stress. After compensating for the thermal interfacial stress and for the stress due to grain boundaries it was found that the residual internal stress is compressive in nature. From Raman line‐shape analysis it was determined that the internal stress is due to the various impurities and defects present in the film. Moreover, the stress magnitude exhibits a strong correlation with the graphitic phase implying that the sp 2 bonding produces a dominant compressive stress field. The PL analytical line‐shape investigation of the nitrogen band at 2.154 eV indicates that the nitrogen centers are uniformly distributed in the film. The PL line shape exhibited a close fit to the Lorentzian–Gaussian convoluted line known as the Voit profile. The deconvolution of the line resulted in a dominant Gaussian component, corresponding to stress arising from line type defects, and a much smaller Lorentzian component corresponding to point defect stress. The Gaussian component was attributed to the graphitic phase implying that the sp 2 bonding is not in the form of a point defect but rather takes the form of a line or extended defect. The line‐shape investigation of the silicon band at 1.681 eV showed that the silicon centers are correlated with the silicon/diamond interfacial stress. Finally, the response of the nitrogen and siliconoptical centers to the internal stress, which is manifested via the PL linewidth, was also studied. The silicon band exhibits the narrower linewidth which may indicate that the silicon center complies less to the internal stress than the nitrogen center or that the two optical centers are interacting with different types of stress sources.