The present work investigates the role of threading dislocation densities (TDD) in the low density regime on the vertical transport in Si 0.06 Ge 0.94 heterostructures integrated on Si(001). The use of unintentionally doped Si 0.06 Ge 0.94 layers enables the study of the impact of grown-in threading dislocations (TD) without interaction with processing-induced defects originating e.g. from dopant implantation. The studied heterolayers, while equal in composition, the degree of strain relaxation, and the thickness, feature three different values for the TDD: 3×10 6 , 9×10 6 and 2×10 7 cm -2 . Current-voltage measurements reveal that leakage currents do not scale linearly with TDD. The temperature dependence of the leakage currents suggests a strong contribution of field-enhanced carrier generation to the current transport, with the trap-assisted tunneling via TD-induced defect states identified as the dominant transport mechanism at room temperature. At lower temperature and at high electric fields, direct band-to-band tunneling without direct interaction with defect levels becomes the dominating type of transport. Leakage currents related to emission from mid-gap traps by the Shockley-Read-Hall (SRH) generation is observed at higher temperatures (>100 °C). Here, we see a reduced contribution coming from SRH in our material, featuring the minimal TDD (3×10 6 cm -2 ), which we attribute to a reduction in point defect clusters trapped in the TD strain fields.

We examine the Raman shift in silicon-germanium-tin alloys with high silicon content grown on a germanium virtual substrate by molecular beam epitaxy.The Raman shifts of the three most prominent modes, Si-Si, Si-Ge, and Ge-Ge, are measured and compared with results in previous literature. We analyze and fit the dependence of the three modes on the composition and strain of the semiconductor alloys. We also demonstrate the calculation of the composition and strain of Si x Ge 1 − x − y Sn y from the Raman shifts alone, based on the fitted relationships. Our analysis extends previous results to samples lattice matched on Ge and with higher Si content than in prior comprehensive Raman analyses, thus making Raman measurements as a local, fast, and nondestructive characterization technique accessible for a wider compositional range of these ternary alloys for silicon-based photonic and microelectronic devices.

The integration of GaN on Si as large scale substrates still faces many hurdles. Besides the large difference in the lattice constant and the high thermal mismatch existing between GaN and Si, spiral hillock growth phenomena are common problems in the development of thick GaN layers. In this work, hexagonal hillocks were observed on GaN/AlGaN high-electron-mobility transistor heterostructures grown on Si(111) by metal-organic chemical vapor deposition. The presence of these morphological and structural defects is attributed to the presence of localized contamination at the AlN/Si interface. These carbon-based defects cause highly defective regions in the AlN seed layer, which propagate through all the AlGaN buffer layers inducing the formation of V-shaped pits at the AlGaN interfaces. In hillock regions of the wafers, Raman spectroscopy indicates disturbed two-dimensional electron gas characteristics resulting from GaN/AlGaN interface roughness and a decreased amount of free carriers in the potential well. Energy-dispersive x-ray spectroscopy reveals Ga accumulation inside the V-pits and in nanopipes below, which is responsible for defective areas and the increased GaN growth rate resulting in hillock formation. Photoluminescence measurements confirm the presence of Ga-rich material reducing the inherent gallium vacancy concentration. Here, the reduced amount of Ga-vacancies acting as a shallow acceptor suppresses the ultraviolet luminescence band from donor–acceptor pair transition.

In this work, we investigate the effective background charge density in intrinsic Si0.06Ge0.94/Ge plastically relaxed heterostructures deposited on Si(001). Hall effect measurements and capacitance–voltage profiling reveal a p-type conductivity in the nominally intrinsic layer with a hole concentration in the mid 1015 cm−3 range at temperatures between 50 and 200 K. In view of the carrier freeze out that we observe below 50 K, we attribute the origin of these carriers to the ionization of shallow acceptor-like defect states above the valence band. In addition, one dominant hole trap located at mid-gap position is found by deep level transient spectroscopy. Carrier trapping kinetics measurements can be interpreted as due to a combination of point defects, likely trapped in the strain field of extended defects, i.e., the threading dislocation.

Growth mechanism of ScN on Sc2O3 for integration of Ga-polar GaN on Si(111) is investigated by in-situ X-ray photoemission spectroscopy, ex-situ time-of-flight secondary ion mass spectrometry, atomic force microscopy, and ab-initio density functional theory (DFT) calculations. The ScN films are grown by molecular beam epitaxy from e-beam evaporated Sc and N plasma. The films grow in a layer-by-layer (Frank–van der Merwe, FM) fashion. Diffusion of nitrogen into Sc2O3 and segregation of oxygen onto ScN are observed. The segregated O atoms are gradually removed from the surface by N atoms from the plasma. Experiment and theory show that nitrogen cannot be efficiently incorporated into Sc2O3 by exposing it to N plasma alone, and calculations indicate that anion intermixing between ScN and Sc2O3 should be weak. On the basis of ab-initio data, the in-diffusion of N into Sc2O3 is attributed mostly to the effect of interaction between ScN ad-dimers on the Sc2O3 surface in the initial stage of growth. The segregation of O to the ScN surface is understood as driven by the tendency to compensate build-up of the electric field in the polar ScN film. This segregation is computed to be energetically favorable (by 0.4 eV per O atom) already for a monolayer of ScN; the energy gain increases to 1.0 eV and 1.6 eV per O atom for two and three ScN layers, respectively. Finally, it is verified by DFT that the ScN deposition method in which Sc metallic film is deposited first and then nitridized would lead to strong incorporation of O into the grown film, accompanied by strong reduction of the Sc2O3 substrate.