Photoluminescence and optically detected magnetic resonance of Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ strained-layer superlattices grown by molecular-beam epitaxy

Photoluminescence (PL) and optically detected magnetic-resonance (ODMR) experiments have been performed on a set of Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$ strained-layer superlattices grown by molecular-beam epitaxy. A variety of parameters was explored to expand on the results of an earlier investigation and to test models proposed for the origin of the broad emission bands. These include the dependences of the magnetic resonance on temperature, microwave power, and excitation power density. In addition, sets of samples were grown to study the PL and ODMR as a function of layer thickness, Ge composition, total superlattice thickness, and doping with group-V impurities. The results provide clear evidence that the recombining holes derive from the strain-split ${\mathit{M}}_{\mathit{J}}$=±3/2 valence band in the ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$ layers. Although the identification of the recombining electron is not as strong as that made for the hole, it can be associated with the valley-degenerate Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$ conduction band. When these conclusions from the ODMR are combined with results from the PL and other studies, the most appealing model for the origin of the broad emission bands is donor-acceptor pair recombination.