Photoluminescence and excitation spectroscopy in heavily dopedn- andp-type silicon

Low-temperature photoluminescence and excitation spectroscopy measurements on heavily doped (up to 4×${10}^{20}$ ${\mathrm{cm}}^{-3\mathrm{}}$) $n$- and $p$-type silicon are reported. From the luminescence spectra values for the optical and the reduced band gap are deduced and compared with theoretical calculations. The shrinkage of the reduced band gap follows an $n^{\frac{1}{3}}$ law for carrier concentrations $n$ above the critical Mott density. Both $n$- and $p$-type samples show an identical shift of the reduced gap, whereas the shift of the optical gap is different due to the different density-of-states masses for electrons and holes. From photoluminescence excitation spectra the position of the optical gap is determined independently. A good agreement of the data obtained by these selective absorption measurements with the results from conventional luminescence spectra is found.