Electrically detected magnetic resonance of two-dimensional electron gases in Si/SiGe heterostructures

Strained ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}}_{0.75}{\mathrm{Ge}}_{0.25}$ heterostructures, grown by solid source e-beam evaporation molecular-beam epitaxy on Si(100) substrates, have been studied by electrically detected magnetic resonance. Samples with a low-temperature mobility of about ${10}^5{\mathrm{cm}}^2/\mathrm{V}\mathrm{}\mathrm{s}$ were used, some with Schottky gates enabling control of the electron density in the channel. For $T<\mathrm{}50\mathrm{}\mathrm{K},$ a conduction-band electron-spin-resonance signal caused by electron-electron scattering in the two-dimensional channel was observed in the dark. The signal intensity, g factor, and linewidth were observed to depend on electron density $n_e$ and magnetic-field orientation. For $n_e=4\mathrm{}\times {10}^{11}{\mathrm{cm}}^{\mathrm{-}2},$ $g_{\parallel }=2.0007\mathrm{}$ (H parallel to the major conduction-band valley axis), and $g_{\perp }=1.9999\mathrm{}$ (H perpendicular to major axis), which leads to an anisotropy of $g_{\parallel }-g_{\perp }=(8\mathrm{}\pm 2)\times {10}^{-4}.$ For $n_e<3\mathrm{}\times {10}^{11}{\mathrm{cm}}^{\mathrm{-}2},$ the anisotropy nearly disappears. For $H\parallel \left[100\right],$ resonance linewidths as low as 70 mG are observed. A model for the resonant change in the conductivity is developed and compared to experiment.