Electron spin resonance study of Si/SiGe quantum dots

In this work, we present systematic electron spin resonance (ESR) experiments on SiGe quantum-dot structures. A series of samples with different sizes of quantum dots is prepared by varying growth temperature and spacing between quantum-dot layers. At a frequency of about 9.5 GHz, two ESR signals with g factors around 1.9992 and 1.9994 are observed with magnetic field in growth direction. The signals shift and broaden with magnetic field in the in-plane direction. The estimated dephasing time T₂* amounts up to 500 ns. The saturation behavior yields relaxation time T₁ of about 10 μs. The relative intensity between the two peaks can be changed with illumination with subband-gap light. The two peaks are interpreted as s- and p-like states of electrons confined in the strained Si around the SiGe nanostructures.