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-μm line of an $ABC-\mathrm{YAG}$ (yttrium aluminum garnet doped with various concentrations of Er, Tm, Ho, and Yb) laser. At $T=7\mathrm{}$ K the zone-center-phonon linewidth is 1.8 ± 0.3 ${\mathrm{cm}}^{-1\mathrm{}}$. 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 $p=2.5\mathrm{}\times {10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$. 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.