Application of photothermal ionization spectroscopy to the study of epitaxially grown germanium on silicon

We have applied the technique of photothermal ionization spectroscopy to the study of a 1-μm-thick p-Ge epilayer, grown by molecular beam epitaxy on a n-Si substrate, 500 μm in thickness. The spectra indicate that in the Ge layer there exists a series of charged acceptor defects with an ionization energy continuum starting at 15 meV, an ionization energy somewhat larger than those of the elemental substitutional acceptors. Our results show that photothermal ionization spectroscopy can be applied very advantageously to epitaxial layers of the Si1-xGex alloys that are Ge-like, i.e., for x≥0.85. For these layers, charged impurity centers and defects have their spectral features well separated from those of the Si substrate.

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