Excitonic phase diagram in unstressed Ge

Evidence is presented for a second condensed phase of excitons in unstressed, high-purity Ge, based on a simple plasma line-shape analysis. Above the critical temperature for electron-hole liquid condensation (Tc{}7 K), time-resolved photoluminescence spectra can be fit with an electron-hole plasma component with nondecaying density, implying spatial condensation into droplets. Shortly after the excitation source is switched off, all successive luminescence spectra are fit with a constant-density electron-hole plasma line shape plus contributions from free excitons and excitonic complexes. The spectral analysis is based on separate characterizations of electron-hole plasma and excitonic complexes from published experimental and theoretical work. The presence of a second condensed phase of excitons in unstressed Ge would be consistent with recent findings of a similar nature in stressed germanium and unstressed silicon. A possible phase diagram is suggested based on the present findings.