Papers by Author: Rafał Jakieła

Abstract: In this work results of nitrogen doping in the amount of 0 vol.%, 3 vol.% and 10 vol.% on the growth of the 4H polytype on the 6H-SiC seed are presented. SiC crystals grown by PVT method on the (000-1) C-face of 6H seeds using the open seed backside design have been investigated. Structural and electrical properties of the crystals were studied by different experimental methods.

Abstract: Results of vanadium doping in PVT SiC bulk growth by the use of the seeding technique with an open seed backside are shown. Structural and electrical properties of 4H and 6H-SiC:V were investigated by a variety of experimental methods. In the crystal studied, the solubility limit of V in SiC was exceeded and structural defects consisting of V-rich precipitates occured. Electrical properties of this crystal were determined by the V3+/V4+ acceptor level. The V3+ charge state of vanadium was formed by compensating shallow donors (mainly nitrogen) and for both 4H and 6H polytypes it was detectable in optical absorption (in the near-IR range) and electron paramagnetic resonance.

Abstract: Presented are the results of studies on Ti-Al-N MAX phase formation in thin film multilayers of Ti, Al and TiN deposited on n-type GaN by magnetron sputtering. Two approaches to phase formation are shown, annealing Ti-Al-TiN multilayers at 600oC in argon and annealing Ti/Al multilayers at 600oC in nitrogen. Samples are characterized by means of High Resolution X-Ray Diffraction and Secondary Ion Mass Spectrometry profiling. As MAX phases are very stable at high temperatures the potential of their application as ohmic contacts to n-GaN devices is discussed.

Abstract: In this study, the formation of Ni, Ni-rich Ni2Si and Si-rich NiSi2 ohmic contacts to n-type 4H-SiC are investigated. The Ni/n-SiC ohmic contact with resistance rc ~ 4.2×10-4 Ω cm2 is formed after annealing at 1050oC. For Ni2Si/n-SiC, the contact resistances were rc ~ 4×10-4 Ωcm2 and rc ~ 3.5×10-4 Ωcm2 after annealing at 1000 and 1050oC, respectively. The non-ohmic I-V characteristics are observed for NiSi2/n-SiC contact even after annealing at 1050oC. The features of ohmic contact formation for Ni-based metallization to 4H n-SiC are discussed.

Abstract: n- and p-type 6H-SiC single crystals grown by PVT method using different charge materials – poly-SiC sinter or fresh SiC powder – have been studied. An open or closed seed backside during the growth processes have been applied. In the former, a distinct decrease backside etching of the seed was observed. Crystals have been extensively characterized with respect to their purity, quality and electrical properties using complex experimental methods. For the n-type boule an axially and radially homogeneous resistivity ~0.11 cm at 300 K was observed. Electrical properties of the p-type crystal, i.e., high room-temperature resistivity of 239 cm, were affected by compensation effects between residual donors (nitrogen and oxygen) and acceptors (mainly boron).

Abstract: The superplastic flow in tetragonal zirconia polycrystals stabilised 3mol% Y2O3 (3YTZP) is strongly affected by the dopant cations, which segregate at the grain boundary. It is proposed that this flow is controlled by grain boundary diffusion of Zr4+ ions and therefore the dopant cations should change the grain boundary diffusion. In order to prove this thesis the measurements of grain boundary diffusion coefficients were made using Hf4+ ions as tracer. Zirconia samples were doped with 1mol% of Al2O3, SiO2, MgO, MgAl2O4, GeO2 and TiO2. The tracer was deposited on the surface of the zirconia specimens by placing several drops of hafnium nitrate and then drying at 373 K. In this way, thin films of HfO 2 were obtained. The samples were heated in the range 1553 – 1773 K for 1 to 24 h. The concentration versus depth profiles were measured using secondary ion mass spectrometry (SIMS). Calculated hence grain boundary diffusion coefficients were several times bigger for doped samples than for pure 3Y-TZP samples.