We present in-situ observations of the dynamical operation of multiple double-ended Frank-Read dislocation sources in a PVT-grown 4H-SiC wafer under thermal gradient stresses. The nucleation of these sources is facilitated by a specific configuration consisting of one basal plane dislocation (BPD) segment pinned by two threading edge dislocations (TEDs). This configuration is formed during PVT crystal growth by deflection of TEDs on to the basal planes by macrosteps and re-deflection of resulting BPDs back into TEDs. Under the influence of thermal gradient stresses induced by heating inside a double ellipsoidal mirror furnace, the pinned BPD segment glides and activates dislocation multiplication by the double Frank-Read source mechanism. A more intricate mechanism of swapping of TED pinning points between Frank-Read sources lying on same basal plane is identified, enabling one dislocation loop to effectively “pass through” the other dislocations on same basal plane.

Passivating contacts based on polycrystalline silicon (poly-Si) on an interfacial oxide are limited by parasitic absorption, which may be reduced by incorporation of foreign elements in the poly-Si layer. In this study, the influence of carbon incorporation in the concentration range of 6.9-21.5 at% on boron-doped polycrystalline silicon carbide (poly-SiC x ) layer properties is investigated and interpreted in the context of an application as full-area passivating contact on the front side of a solar cell. For constant annealing parameters, higher carbon concentrations reduce the crystallinity of the layers. A high crystallinity in turn is confirmed to be a key parameter for the application in a solar cell as it ensures both low resistivity as well as low parasitic absorption. Low recombination current densities in the range of 7.2-12.2 fA/cm 2 are determined for all layers on interfacial oxides on planar surfaces, whereas the differences are rather related to variations in the boron concentration than to the carbon concentration or the deposition parameters. A reduction of the (p) poly-SiC x layer thickness down to 10 nm would yield a parasitic absorption current density of 1.13 ± 0.13 mA/cm 2 . Using this value and the lowest measured recombination current density, a simple model predicts a theoretical solar cell efficiency limit of 26.7 ± 0.2%.

During 4H silicon carbide (4H-SiC) homoepitaxy and post-growth processes, the development of stress relaxation has been observed, in which interfacial dislocations (IDs) are formed at the epilayer/substrate interface, relaxing the misfit strain induced by the nitrogen doping concentration difference between the epilayer and substrate. It is widely believed that an interfacial dislocation is created by the glide of a mobile segment of a basal plane dislocation (BPD) in the substrate or epilayer towards the interface, leaving a trailing edge component right at the interface. However, direct observation of such mechanisms has not been made in SiC before. In this work, we present an in situ study of the stress relaxation process, in which a specimen cut from a commercial 4H-SiC homoepitaxial wafer undergoes the stress relaxation process during a high-temperature heat treatment while sequential synchrotron white beam X-ray topographs were recorded simultaneously. Based on the dynamic observation of this process, it can be concluded that thermal stress plays a role in the relaxation process while the increased misfit strain at elevated temperature most likely drives the formation of an interfacial dislocation.