Terahertz Spectroscopic Analysis and Multispectral Imaging of Epitaxially Grown Semiconductors with Nanometer Resolution

Terahertz spectral analysis has been conducted on epitaxially grown semiconductor structures. Epitaxially grown semiconductors are important for microelectronic and optoelectronic devices and also for integrated circuits fabricated using semiconductors. In this paper, we report results of terahertz time-domain spectroscopy of grown SiGe layers on Ge buffer and separately a Ge buffer that was grown on a Si wafer. In particular, evolution of the time-domain spectra as a function of thickness of both samples was investigated by the terahertz pump-probe technique. Representative spectra were analyzed to determine the respective layers’ spectral signatures. It was found that the spectroscopic analysis uniquely identified different layers by characteristic absorbance peaks. In addition, terahertz imaging was conducted in a non-destructive, non-contact mode for detecting lattice stacking fault and dislocations. Sub-surface imaging of grown SiGe layers on Ge buffer and that of the Ge buffer grown on a Si wafer reveals interesting lattice features in both samples. A comparison with TEM images of the samples exhibits that the terahertz image reproduces the dimensions found from TEM images within the experimental error limits. In particular, 3D images of both samples were generated by the terahertz reconstructive technique. The images were analyzed by graphical means to determine the respective layer thicknesses. Thus, this technique offers a versatile tool for both semiconductor research and in-line inspections.