Chapter V Investigation of Photoluminescence Spectra of Silicon at Different Optical Excitation Rates

Abstract

Silicon is a covalent semiconductor with noncoincident extrema in the k space. It is known that the edge of the valence band of Si is located at the center of the Brillouinzone and the corresponding edges of the conduction band are in six equivalent crystallographic positions along the <100> axis. In the case of semiconductors with extrema located at different points in the k space we can have optical transitions which create electron—hole pairs with zero or nonzero quasimomentum, the latter being governed by the structure of the semiconductor. The laws of conservation of energy and momentum determine the relationships revealed by experimental studies of absorption and luminescence processes. For example, indirect excitons may appear in the luminescence and absorption processes only in a dissipative system, such as a crystal containing imperfections and impurity centers or subject to lattice vibrations. Therefore, the positions of the exciton lines in the luminescence or absorption spectra are not simply governed by the binding energy but are subject to a shift in one or the other direction due to the presence of a third particle.