Transmission Raman scattering from phonons and electronic impurity levels in Ge at 2 μm

Abstract

We have measured transmission Raman spectra of pure, arsenic-doped, and gallium-doped germanium using the 2.098-\ensuremath{\mu}m line of an $ABC\ensuremath{-}\mathrm{YAG}$ (yttrium aluminum garnet doped with various concentrations of Er, Tm, Ho, and Yb) laser. At $T=7$ K the zone-center-phonon linewidth is 1.8 \ifmmode\pm\else\textpm\fi{} 0.3 ${\mathrm{cm}}^{\ensuremath{-}1}$. The strength, position, and polarization properties of the valley-orbit electronic Raman line of Ge(As) have been measured and calculated. The electronic Raman spectrum of Ge(Ga) showed evidence of wave-function overlap at $p=2.5\ifmmode\times\else\texttimes\fi{}{10}^{16}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. Whereas Si and GaP exhibit a prominent acceptor electronic Raman line associated with a transition starting from the ${p}_{\frac{3}{2}}$ valence band and terminating on the ${p}_{\frac{1}{2}}$ valence band, Ge(Ga) shows no such Raman feature.