Direct band gap narrowing in highly doped Ge

Direct band gap narrowing in highly doped n-type Ge is observed through photoluminescence measurements by determining the spectrum peak shift. A linear relationship between the direct band gap emission and carrier concentration is observed. We propose a first order phenomenological model for band gap narrowing based on two parameters whose values for Ge are EBGN = 0.013 eV and ΔBGN = 10−21 eV/cm−3. The application of these results to non-invasive determination of the active carrier concentration in submicron areas in n-type Ge structures is demonstrated.