Identifying spins states on self assembled Si/SiGe quantum dots by means of ESR

Self-assembled Si/SiGe quantum dots were systematically studied with ESR at 9.56 GHz. A set of multilayer structures were grown with molecular beam epitaxy with different vertical spacing between quantum dot layers and different dot sizes. An extensive characterization with transmission electron microscopy and atomic force microscopy provides good structural information of the ensembles of quantum dots. Furthermore the samples were characterized by photoluminescence. Two ESR signals were identified with g-factors around 1.9992 and 1.9994. Both signals show a small anisotropy in g-factors and linewidth with respect to the magnetic field along growth and in-plane directions. Spin-relaxation times T1 are determined with continuous wave ESR saturation measurements to be of the order of 10 μs. The spin dephasing times yield values up to 500 ns. Illumination with sub-bandgap light changes the relative intensity of the two signals. Based on calculations of the electronic structure of the heterostructures a qualitative model allows us to relate the two ESR signals to s- and p-like-states on the quantum dots.