We report density-dependent effective hole mass measurements in undoped germanium quantum wells. We are able to span a large range of densities (2.0-11×1011cm-2) in top-gated field effect transistors by positioning the strained buried Ge channel at different depths of 12 and 44 nm from the surface. From the thermal damping of the amplitude of Shubnikov-de Haas oscillations, we measure a light mass of 0.061me at a density of 2.2×1011cm-2. We confirm the theoretically predicted dependence of increasing mass with density and by extrapolation we find an effective mass of ∼0.05me at zero density, the lightest effective mass for a planar platform that demonstrated spin qubits in quantum dots.

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The influence of dense vertical tube bundles in a batch bubble column reactor (BCR) of 100 mm diameter and 1100 mm clear liquid height on liquid dispersion and gas-liquid mass transfer was studied. In particular, the effects of different tube patterns (triangular and square pitch), tube diameters (8 and 13 mm) and bottom end designs (flat and U-tube) having a tube diameter-to-pitch ratio of approx. 1.3 were investigated. Dispersion coefficients were determined based on conductive tracer experiments recorded via wire-mesh sensors (WMS) with up to 90 measurement points distributed in the column's cross-section in between the tubes. The gas-liquid mass transfer coefficient was determined via fast-responding oxygen needle probes. Tube pitch and pattern were identified as the most crucial design parameters for the extent of liquid dispersion. We found that particularly the U-tube bottom end design induces large liquid circulation patterns, which enhance dispersion. The presence of internals decreases the kla value as a consequence of turbulence damping, which is also confirmed by lower kl values (e.g. 0.6 × 10−3 m s−1 for the empty BCR and 0.25 × 10−3 m s−1 for the square pitch with 8 mm tubes at 0.05 m s−1 superficial gas velocity), whereas the pitch is the most decisive design parameter. The U-tube bottom end design was identified as the most beneficial configuration with respect to liquid mixing and gas-liquid mass transfer.@en

Improvement of the photoluminescence (PL) of Phosphorus (P) doped Ge by P atomic layer doping (ALD) is investigated. Fifty P delta layers of 8 ×10¹³ cm^-2 separated by 4 nm Ge spacer are selectively deposited at 300 °C on a 700 nm thick P-doped Ge buffer layer of 1.4 × 10¹⁹ cm^-3 on SiO₂ structured Si (100) substrate. A high P concentration region of 1.6 × 10²⁰ cm^-3 with abrupt P delta profiles is formed by the P-ALD process. Compared to the P-doped Ge buffer layer, a reduced PL intensity is observed, which might be caused by a higher density of point defects in the P delta doped Ge layer. The peak position is shifted by ∼0.1 eV towards lower energy, indicating an increased active carrier concentration in the P-delta doped Ge layer. By introducing annealing at 400 °C to 500 °C after each Ge spacer deposition, P desorption and diffusion is observed resulting in relatively uniform P profiles of ∼2 × 10¹⁹ cm^-3. Increased PL intensity and red shift of the PL peak are observed due to improved crystallinity and higher active P concentration.

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