Fermi-edge singularity in $p$-type modulation-doped SiGe quantum wells

A strong effect of $p$-type modulation doping on the radiative recombination in $\mathrm{Si}/{\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x/\mathrm{Si}$ quantum wells is observed by photoluminescence (PL) spectroscopy. The filling of the Si-Ge quantum wells due to the charge transfer of holes from the $B$ modulation doping in the adjacent Si layers causes an appearance of a broad asymmetric PL band with a characteristic sharp high-energy cutoff. A strong enhancement near the Fermi edge is shown, by varying structure parameters and experimental conditions, to correspond to the Fermi-edge singularity. Experimental evidence on the dominant mechanism responsible for the Fermi-edge singularity is given as due to a nearly resonant scattering between the electronic states near the Fermi energy and the next unoccupied subband of the two-dimensional hole gas.