A microwave resonance investigation of quantum confined structures and defects in crystalline semiconductors

In this work, high frequency (W-band, 95 GHz) Electron Paramagnetic Resonance spectroscopy (EPR) and Optically Detected Magnetic Resonance (ODMR) have been used as the principal tools to investigate quantum confined structures and defects in crystalline semiconductors. The low dimensional structures discussed in this work could be successfully examined with magnetic resonance techniques thanks to the high sensitivity of ODMR in combination with the application of high microwave frequencies. The advantage of the latter, compared to more conventional frequencies, is the increased Zeeman resolution, the improved sensitivity and the relaxation of the life time requirements.; Our W-band setup was extended with a fiber bundle accessory to allow optical excitation of and light collection from a sample in the standard cylindrical cavity of a W-band spectrometer. This optical fiber bundle approach was shown to be efficient for ODMR experiments, even at low laser excitation powers.; Microwave resonance transitions have been observed in a thin In(Ga)As/GaAs layer with shallowly formed quantum dots. The optical detection technique, combined with the application of high microwave frequencies and a long exciton lifetime, allowed for the first observation of microwave resonances in semiconductor quantum dots grown with epitaxial techniques. The microwave resonances revealed the cyclotron resonance of the electrons in the two-dimensional wetting layer, corresponding to an effective mass of 0.053m0. Further magnetic resonance transitions between spin states of the holes confined in the shallow dots were observed and an inhomogeneity in the quantum dot plane, either in the shape of or in the strain on the shallow quantum dots was derived.; The W-band ODMR study of AgCl nanocrystals embedded in a crystalline KCl matrix, which was combined with atomic force microscopy (AFM) and continuous-wave and time-resolved photoluminescence measurements, revealed the high complexity of this system. In comparison with the PL band of bulk AgCl, the nanocrystal emission was broadened and its maximum was red-shifted. A dispersion of the decay kinetics was observed across the band: longer radiative lifetimes were observed for the low-energy part of the PL band. Whereas the ODMR spectrum of bulk AgCl is independent of the PL detection energy, a large dependence on the PL detection energy was observed for the nanocrystals. The spin resonances ascribed to the STH and SEC centers in the nanocrystals were observed only for detection in the extreme low-energy edge of the PL emission and their relative line intensities decreased substantially at higher temperature. Further, bulk-like STE centers and STE centers with nanocrystal character properties were observed.; Finally, an AgCl crystal that was intentionally doped with a high concentration of rhodium was studied with the conventional EPR technique. In addition to the known resonances from the RhCl3 complex, the EPR spectra reveal a new defect with axial symmetry around a [111] crystal axis. This center shows a highly temperature-dependent g-anisotropy: while at room temperature an isotropic line is observed at g = 1.987, this is continuously transforming into an axial spectrum with g⊥= 2.122 and g// = 1.727 at 2 K. Chemical analysis showed that high concentrations of rhodium and of iron are present in the crystal. Possible models for describing this center were discussed.