Low-temperature photoluminescence spectra of doped Ge

Abstract

We report on an investigation of the photoluminescence spectra of Li-, As-, Ga-, and Sb-doped Ge crystals with impurity concentrations between ${10}^{15}$ and ${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. Extensive data on the temperature, time, and pump power dependences of these spectra are presented for the spectral ranges where the no-phonon (NP line) and the longitudinal-acoustic-phonon assisted (LA line) edge emissions from the electron-hole droplet (EHD) are expected to occur. The spectral ranges covered are 730-740 meV and 705-720 meV. The LA line of Ge:As is observed to have the properties of the EHD for $T\ensuremath{\lesssim}4.2$ K. On the other hand, time-resolved spectra show that different parts of the NP line of Ge:As decay at different rates. We conclude that the NP line has a contribution of impurity-induced emission from states other than the EHD. The LA lines of Ge:Li, Ge:Ga, and Ge:Sb are observed to possess pump power and time dependences similar to those observed for the NP line of Ge:As. The properties of these LA lines are interpreted in terms of impurity-induced emissions along with emission from the EHD. Comparison of the doped Ge spectra with those from doped Si suggest that the impurity-induced emission may be due largely to broadened "multiexciton complex" lines.