Two-Electron Band-to-Band Transitions in Solids

Abstract

In highly excited Si and Ge there appears an emission band at about $h\nu =2\mathrm{}{E}_g$, which is explained by two-electron radiative transitions across the band gap. The dependence on energy, temperature, and excitation intensity is measured and compared with theoretical calculations. The weak temperature dependence, the quadratic dependence on the injection current, and the energy dependence agree with the theoretical consideration. A transition coefficient of about ${10}^{-61\mathrm{}}$ ${\mathrm{cm}}^9$ ${\sec }^{-1\mathrm{}}$ is found, in agreement with a rough theoretical estimate. The line shape indicates that, at least at room temperature, the two-electron transitions are phonon assisted. This leads also to the conclusion that the Auger recombination in Si must be phonon assisted, in contradiction to former considerations.