Doping dependence of the optical dielectric function in n-type germanium

Abstract

The doping dependence of the most important optical transitions in n-type Ge (E0, Eind, E1, E1 + Δ1, E0′, and E2) has been studied using photoluminescence and UV-Vis ellipsometry methods. By using high activity Ge sources, such as Ge3H8 and Ge4H10, and new-generation doping precursors, including P(GeH3)3, As(GeH3)3, and SbD3, doping levels approaching 1.5 × 1020 cm−3 have been achieved with flat dopant profiles, abrupt n/i interfaces, and close-to-unity dopant activation ratios. The excellent sample quality enabled measurements over sufficiently broad doping ranges to demonstrate, contrary to prior assumptions, that the electronic energy bands do not shift rigidly upon doping and that the different contributions to bandgap renormalization are donor-dependent. It is also shown that simple models of band filling effects provide a quantitative explanation of the doping dependence of critical point parameters such as amplitudes and phase angles. The analysis presented here yields new insights into the physics of highly-doped semiconductor and should facilitate the design of novel Ge-based group-IV microelectronic and photoelectronic devices.