Radiative recombination in heavily dopedp-type germanium

Abstract

Low-temperature photoluminescence studies on heavily doped $p$-type germanium are reported. In addition to the indirect-band-gap (0.75 eV) luminescence, direct recombination of nonthermalized minority carriers located at the conduction-band minimum at point $\ensuremath{\Gamma}$ is observed. The direct recombination occurs across the gaps ${E}_{0}$ and ${E}_{0}+{\ensuremath{\Delta}}_{0}$ (0.89 and 1.19 eV, respectively) and resonates strongly for exciting photon energies close to the energy gap ${E}_{0}$. The emission across the gap ${E}_{0}$ can be described as a mixture of band-to-band transitions with and without momentum conservation. From the luminescence spectra the shift of the indirect band gap as well as the direct band gap ${E}_{0}$ is determined as a function of carrier concentration and compared to full pseudopotential band-structure calculations.