Excited states at deep centers in Si:S and Si:Se

Abstract

The spectral distributions of the photoionization cross sections for the dominant sulfur- and selenium-related donor centers in silicon are presented. The measurements have been performed at different temperatures using junction space-charge techniques. The spectra of the electron transitions to the conduction band are best understood in terms of excited states. Two types of excited states are involved: those which are generally referred to as the Rydberg series and those which originate from the multivalley nature of the conduction band. The latter contain sharp peaks with half-widths of the order of 10 meV for the deeper donor levels and 2 meV for the shallower centers. The energy positions of these peaks are independent of temperature. The assignments of the ground states and the excited states are discussed and the results compared with previous data obtained from thermal measurements in Si:S and Si:Se.