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X-band microwave spectroscopy in a commercial EPR spectrometer at 1.5 K on modulation doped Si quantum well structures exhibits a relatively broad signal due to the coupled cyclotron-plasmon resonance, allowing to estimate both the carrier density and the electron mobility. After illumination above band gap, some of our heavily Sb-doped samples show a persistent splitting of this signal. Evaluation of the mobility yields a substantial increase of the mobility in the Si channel. Our results demonstrate that a major part of the scattering in the channel results from long range fluctuations of the Coulomb potential due to ionized donors in the doping channel. We attribute the substantial reduction in momentum scattering to screening of potential fluctuations within the doping layer by the additional carriers there. [ABSTRACT FROM AUTHOR] more...

We observe and investigate the cyclotron resonance (CR) of high mobility photo excited carriers in high resistivity (> 1000 Ωcm) bulk FZ-Si in a standard X-band electron paramagnetic resonance setup. At 2.5 K and low microwave (MW) power a series of very narrow CR lines is seen allowing for a very precise evaluation of the cyclotron masses. In addition, we make use of the narrow line-width to investigate electron heating caused by MW absorption. The minimum CR line-width of 1.2 mT implies an electron mobility of more than 7 · 106 cm2/Vs. Modelling the line-width we find that for a lattice temperature of 2 K, the electron temperature reaches 10 K at a MW power of 10 mW, and the temperature increases by 25 mK at 1 μW in spite of the fact that the sample is located in the MW cavity at the minimum of the electric field. At lower lattice temperature the electron heating is even bigger. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR] more...

The results of magnetic resonance investigation of GaMnAs samples prove that metal to insulator transition is accompanied by changing magnetic order from ferro- to ferrimagnetic. The observation of spin wave resonance (SWR) in ferrimagnetic samples let us to evaluate the range of exchange interaction, the range of spin correlations and the magnitude of local fluctuations. The observed range of exchange interaction is related to the length of hole localization. Dispersion dependence of spin waves (SW) in ferrimagnetic Ga1-xMnxAs qualitatively differs from the dispersion dependence of SW in classical ferromagnets. That difference is also explained. We relate the origin of uniaxial anisotropy field to the layer inhomogeneity. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR] more...