Helium-like impurity centers in silicon and germanium: Infrared light interaction, non-equilibrium distributions and optoelectronic applications

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The joint goal of the applicant groups is to investigate the potential of helium-like impurity centers in the elemental semiconductors silicon and germanium for optoelectronic applications in the mid-infrared wavelength range. The activation energies of such impurities fall into the infarred spectral region. In particular, we want to study optical, electro-optical and magneto-optical as well as non-equilibrium properties and dynamical processes of double donor centers in silicon and double and triple acceptors in germanium. The temporal and spectral characteristics of such materials depend on fundamental features such as the nature of the electrically active centers formed in the semiconductor after doping, the structure of the excited levels of all active impurities, including their spin-orbit and spin-triplet states, the capture and intracenter relaxation of non-equilibrium charge carriers. These are not all known or not completely understood for the materials. The largest intracenter transitions of helium-like impurity centers have energies exceeding the characteristic energy of the optical phonon of the host lattice. This is expected to slow down the intracenter relaxation and, therefore, the whole capture process. Additionally, the forbidden triplet-singlet decay may result in long relaxation times for those electrons ending in such triplet states. These features will be experimentally investigated by two-color time-resolved spectroscopy and theoretically modelled. A special focus is on the technological aspects of crystal growth and doping of the semiconductors.