Local modes of bond-centered hydrogen in Si:Ge and Ge:Si

Abstract

Local vibrational modes of bond-centered hydrogen have been identified in Ge-doped Si (Si:Ge) and Si-doped Ge (Ge:Si) with in-situ-type infrared absorption spectroscopy. The infrared absorbance spectra recorded at $8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ immediately after implantation of the very dilute Si:Ge and Ge:Si alloys with protons reveal in each case four lines located at $\ensuremath{\sim}2000$ and $\ensuremath{\sim}1800\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, respectively. The dominating band in all spectra arises from quasi-isolated positively charged bond-centered hydrogen $({\mathrm{H}}_{\mathrm{BC}}^{+})$ centers, whereas the remaining features originate from different ${\mathrm{H}}_{\mathrm{BC}}^{+}$ defects perturbed locally by a nearby Ge in Si:Ge or Si in Ge:Si located in the first-, second- and third-nearest neighbor sites. These assignments are based on the analysis of the local mode frequencies and their absorption intensities, together with the isotopic shifts observed when hydrogen is replaced by deuterium, and the thermal stability of the modes. Our results are compared with previous experimental and ab-initio theory investigations.