Chalcogens in germanium

The chalcogens S, Se, and Te have been introduced by diffusion into single-crystal germanium. Both thermal- and optical-junction space-charge techniques have been performed in parallel with photoconductivity studies using a Fourier-transform spectrometer. Electronic levels within the energy gap have been monitored from both valence and conduction bands using various techniques. The suggested double-donor states are found to be at EC-0.28 and EC-0.59 eV for sulfur, EC-0.268 and EC-0.512 eV for selenium, and EC-0.093 and EC-0.33 eV for tellurium. Evidence is found for excited states of S, Se, and Te. The neutral center of Se exhibits line spectra and corresponding Fano resonances due to a Γ₀ intravalley phonon. The binding energy of the neutral 2s(A₁) state of 7.4 meV is reported. A fitting of the spectra of deeper Se levels is in excellent agreement with a singly ionized center. Electron thermal-emission rates and capture cross sections are reported for the EC-0.268, EC-0.28, and EC-0.33 levels. The capture cross section of the latter shows a T^-3.1 temperature dependence. Furthermore, an unidentified double donor exhibiting excited states is found in several samples, having a binding energy of 207 meV. It is suggested to be oxygen related. Finally a comparison is made with data obtained from chalcogen-doped silicon.