Quantitative analytical spectroscopy of ultra-high purity germanium crystals

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High-purity and by design low-doped and co-doped semiconducting crystals are of great interest for material research. This includes techniques to produce such crystals as well as to characterize them. Such high quality crystals are important for both, fundamental and applied research and development. Undoped germanium (Ge) is widely used as optical windows, filters as well as detectors of ionizing radiation, particularly x-rays and gamma rays. Low-doped Ge crystals are excellent natural analogue of a single-electron conducting medium, where many physical models dealing with a single-electron approach can be experimentally verified. To date, mostly Ge-based low-dimensional materials (quantum dots and structures) are considered for single-electron systems and quantum technologies. Low-doped Ge or Ge with residual doping offers a unique possibility to experimentally access the theoretical single-electron model, which is a main approach for theoretical modelling energy spectra of electrically active impurities. The project is a joint effort of the research groups at the Leibniz-Institut für Kristallzüchtung (IKZ) and Humboldt-Universität zu Berlin (HUB). Both teams join in order to make the best use of their complementary expertise. The focus of the IKZ proposal is on making high-quality Ge crystals, with respect to the Ge host lattice, dopants and isotopic composition. The HUB team focusses on the spectroscopic characterization of the Ge crystals (e.g. optical constants, concentration of dopants). The goal of the HUB part of this cooperation project is to establish high-sensitivity analytical spectroscopy for characterization of ultra-pure, low-doped and undoped monocrystalline Ge. The project will deliver high-purity crystals with variable isotopic content. These crystals are precisely analyzed by measuring their energy spectra at ultra-low concentrations of electrically active impurities. Besides that, it will provide insights into impurity interactions with the host lattice, local modes, crystal defects and influence from isotope content.