Papers by Author: Emil Tymicki

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: A set of single crystal growth experiments was performed in the new resistively heated two-heater furnace, which plays the role of an induction furnace with a moving coil. In this new experimental setup we are able to control the shape of the crystallization front, from flat to extremely convex. The positive results of the experimental tests differ significantly from prior discouraging interpretation of computational modeling results obtained by a commonly used software, previously presented in the literature. The essence of a new regulation of the temperature field during the crystal growth is a displacement of the maximum of the temperature field, which at the beginning of the growth is located close to the seed and it moves towards the source material as the crystal length increases. In this way, the crystallization front is heated with a similar intensity regardless the increasing crystal length.

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: In this work we present the growth of 4H-SiC crystals (2 inch in diameter) on the 8° off- axis C-face 6H-SiC seeds, inclined toward [11-20] direction. The growth of crystals by physical vapour transport method (PVT) was realized with the open seed backside in the experimental setup with graphite resistive heater. Some of the crystals were doped with cerium in the purpose of the 4H polytype growth stabilization. For Ce-doped crystals the seed backside carbonization process was decreased in comparison with such effect observed in the undoped SiC crystals.

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: 4H-SiC single crystals grown by the seeded physical vapour transport method have been investigated. These crystals were grown on 6H-SiC seeds. The influence of the seed temperature, form and granulation of SiC source materials on the stability and efficiency of the 4H polytype growth have been investigated. A new way of the seed mounting - with an open backside - has been used. Crystals obtained were free of structural defects in the form of hexagonal voids. The crystalline structure of SiC crystals was investigated by EBSD (Electron Backscatter Diffraction) and X-Ray diffraction methods. Moreover, defects in crystals and wafers cut from these crystals were examined by optical, scanning electron and atomic force microscopy combined with KOH etching.

Abstract: Bulk crystals of 6H and 4H silicon carbide have been grown by PVT method. 6H-SiC were obtained in optimized near-to-equilibrium growth conditions in order to improve the crystal quality and to provide the 6H seeds for 6H to 4H-SiC conversion. In experiments of 6H to 4H polytype transformation a set of invariable growth conditions was applied: C-face seed, C-rich atmosphere, on-axis seed orientation, pre-heating of the source material, slightly convex crystallization front and optimized geometry of the growth system. Other growth parameters were varied to optimize the polytype conversion, e.g.: structural quality of the seed, intentionally added impurity (N and/or Sc), initial growth stage recipe, argon pressure and temperature gradient - resulting in variety of growth rates and temperatures of the seed. Special attention was paid to seed passivation and a scheme of temperature and inert gas pressure changes during growth. Crystals were characterized by KOH etching, X-ray diffraction, optical and AFM microscopy. A reproducible method of 75% efficient conversion was elaborated. A large central surface free of micropipes was observed with characteristic six symmetrical ridges as well as the increased concentration of nitrogen. The parasitic 15R-SiC polytype was nucleated on the vicinal part of the crystallization front of 6H-SiC and 4H-SiC crystals.

Abstract: Silicon carbide single crystals grown by the seeded physical vapour transport method have been investigated. These crystals were grown on the Si-face (0001) of 6H-SiC seeds. The growth proceeded under quasi-equilibrium conditions with the growth rate in the range 0.05-0.2 mm/h, that was extremely low as compared to used in standard growth processes. The shape and morphology of the crystallization fronts have been studied. Moreover, defects in crystals and wafers cut from these crystals were examined by optical and atomic force microscopy combined with KOH etching and X-Ray diffraction.

Abstract: Silicon carbide crystals were grown from the vapor. Improvement of the quality of the central part of the crystal was achieved by optimization of the geometry of the source material. Active thermal interaction of the source material and the crystallization front made possible an effective programming of the shape and morphology of the crystal. Termination of micropipes on microfacets formed on the crystallization front during growth was observed.