No abstract

As-grown 4H-SiC epitaxial layers were investigated by deep-level transient spectroscopy to study the formation of the well-known Z1,2 defect with energy levels normally detected at about EC−0.7 eV. Chemical vapor deposition, applying various nitrogen-doping concentrations and C/Si ratios (1.2–3) in the gas phase, was used to prepare the samples. The Z1,2 defect concentration was observed to increase with the incorporated nitrogen concentration. The dependence was linear for medium C/Si ratios (1.5–2.5). The highest and lowest applied C/Si ratios (3 and 1.2) enhanced and suppressed the Z1,2 defect formation, respectively. This behavior tentatively suggests a complex of nitrogen with interstitial carbon atoms or, less probably, silicon vacancies. In particular, the correlation between the Z1,2 defect formation and the nitrogen incorporation was clearly shown in the present investigation, in contradiction to conclusions of other authors. Previously reported negative-U properties of the Z1,2 deep-level defects could be confirmed. A 1:1 relation between the concentrations of Z1 and Z2 was obtained for the present as-grown epitaxial layers.

This paper describes the development of a scooter supporting the mobility of older people. The scooter is equipped with a drive assistance system and a special scooter navigation system. The drive assistance system consists of a velocity controller, a steering controller, and a collision avoidance system. In this paper it is demonstrated how the challenging control and steering tasks are modified to increase safety for older people. A special scooter navigation system is presented, to support elderly people in navigating on a safe route through the city using sidewalks, pedestrian lights and crosswalks. For extended positioning requirements a hybrid positioning system was developed combining GPS, WLAN, and inertial sensor data. By combination of these technical improvements it is demonstrated how older people are able to preserve their self-determined and independent life. Usability research was done with focus groups in order to become familiar with global user demands and expectations towards a mobility assistance system. Results show that the system components are expected to assist the user in navigation, steering and speed control rather than to take complete control on the driving situation.

No abstract

Basal Plane Dislocations (BPD) in SiC are thought to cause degradation of bipolar devices as they can trigger the formation and expansion of stacking faults during device operation. Therefore, epilayers without any BPD are strongly recommended for the achievement of long-term reliable bipolar devices. Such epilayers can be achieved by supporting the conversion of BPD into Threading Dislocations (TD), which depends on the epitaxial growth mode (as described in literature). In this work, the influence of several pre-treatments of the SiC substrate prior to epitaxial growth and different epitaxial growth parameters on the reduction of the BPDs in the SiC epilayers was investigated on 4° off-axis substrates. The dislocation content in substrates and epilayers was determined by Defect Selective Etching (DSE) in molten KOH. The averaged BPD density in epitaxial layers can be reduced to < 100 cm-2 for substrate preparation techniques and to < 30 cm-2 for well-suited epitaxial growth parameters. A certain combination of epitaxial growth parameters leads to < 3 BPD/cm2 in the epitaxial layer.

No abstract

No abstract

Nomarski optical microscopic, KOH etching and synchrotron topographic studies are presented of faint needle-like surface morphological features in 4H-SiC homoepitaxial layers. Grazing incidence synchrotron white beam x-ray topographs show V shaped features which transmission topographs reveal to enclose 1/4[0001] Frank-type stacking faults. Some of these V-shaped features have a tail associated with them and are referred to as Y-shaped defects. Geometric analysis of the size and shape of the V-shaped faults indicates that they are fully contained within the epilayer and appear to be nucleated at the substrate/epilayer interface. Detailed analysis shows that the positions of the V-shaped stacking faults match with the positions of c-axis threading dislocations with Burgers vectors of c or c+a in the substrate and thus appear to result from the deflection of these dislocations onto the basal plane during epilayer growth. Similarly, the Y-shaped defects match well with the substrate surface intersections of c-axis threading dislocations with Burgers vectors of c or c+a in the substrate which were deflected onto the basal plane during substrate growth. Based on the observed morphology of these defect configurations we propose a model for their formation mechanism.