Chalcogens in germanium.

Abstract

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 ${E}_{C}$-0.28 and ${E}_{C}$-0.59 eV for sulfur, ${E}_{C}$-0.268 and ${E}_{C}$-0.512 eV for selenium, and ${E}_{C}$-0.093 and ${E}_{C}$-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 ${\ensuremath{\Gamma}}_{0}$ intravalley phonon. The binding energy of the neutral 2s(${A}_{1}$) 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 ${E}_{C}$-0.268, ${E}_{C}$-0.28, and ${E}_{C}$-0.33 levels. The capture cross section of the latter shows a ${T}^{\mathrm{\ensuremath{-}}3.1}$ 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.