Electron-hole drops in Ge-Si alloys

We present luminescence data in Ge0.85{Si}0.15$ showing that electron-hole drops (EHD) can exist in this material at low temperature. From our results we determine the EHD binding energy ${Φ}$ with respect to free excitons (3 meV) and we deduce the EHD critical density ${n}c(5 ×{10}¹⁷$ ${cm}^{{-}3}$). We have also measured at 2 K the EHD radiative efficiency ${η}$ (4.5%) and total lifetime ${τ}(4.4 μsec). From{η}$ and ${τ}$ we get the nonradiative lifetime ${{τ}}NR$ of EHD which is thought to be due to an Auger recombination process. This study shows that the EHD parameters investigated here (${n}c$, ${Φ}$, and ${{τ}}NR$) are really sensitive to the band structure.