Observation of Phase-Filling Singularities in the Optical Dielectric Function of Highly Doped n -Type Ge

摘要: Phase-filling singularities in the optical response function of highly doped (>10^{19}  cm^{-3}) germanium are theoretically predicted and experimentally confirmed using spectroscopic ellipsometry. Contrary to direct-gap semiconductors, which display well-known Burstein-Moss phenomenology upon doping, critical point joint density electronic states associated with partially filled conduction band n-Ge corresponds so-called E_{1} E_{1}+Δ_{1} transitions, two-dimensional character. As a result this reduced dimensionality, there is no edge shift induced by Pauli blocking. Instead, one observes "original" (shifted only gap renormalization) an additional feature level occupation discontinuity at Fermi level. The experimental observation made possible recent development low-temperature, in situ doping techniques that allow fabrication films exceptionally flat profiles.