Masatoshi Kanaya

Structural defects in α-SiC single crystals grown by the modified-Lely method

Abstract Structural characterization of single crystalline α-SiC has been conducted by X-ray topography. Crystals were grown in the [0001¯] and the [11¯00] directions by the modified-Lely method, and wafers perpendicular and parallel to the growth directions sliced from the grown crystals were examined by transmission topographs of the Lang method. The crystals grown in the [0001¯] and the [11¯00] directions showed a significant difference in both types and densities of crystal defects. Each growth direction exhibited a peculiar defect formation, and the topography revealed that most of the defects were formed at the very initial stage of growth.

Mechanism of Molten KOH Etching of SiC Single Crystals : Comparative Study with Thermal Oxidation

The etching mechanism of SiC single crystals by molten KOH has been investigated. The etching process is significantly affected by the etching ambience: the etching rate is greatly reduced by a nitrogen gas purge. This result clearly suggests an essential role of dissolved oxygen in the melt. SiC{0001} surfaces show a large surface polarity dependence, where the etching rate of SiC(0001)C is about four times larger than that of SiC(0001)Si. The etching rate of SiC(0001)C exhibits an Arrhenius type temperature dependence with an activation energy of 15–20 kcal/mol. The obtained activation energy and selectivity between the (0001)C and the (0001)Si surfaces are quite similar to those for thermal oxidation, which implies that the surface oxidation process occurs during molten KOH etching of SiC and is the rate-limiting step for the etching. We have conducted a comparative study of molten KOH etching with thermal oxidation in regard to the crystal orientation, polytype and carrier concentration dependence.

Influence of the Seed Face Polarity on the Sublimation Growth of α-SiC

The influence of the face polarity of the seed crystal on the α-SiC sublimation growth has been investigated. Optical and electrical measurements were carried out for undoped and nitrogen-doped crystals grown on the (000)C and the (0001)Si faces. The undoped crystal grown on the (000)C face showed n-type conduction and high optical transmittance in the visible light region. In contract, the undoped crystal grown on the (0001)Si face was highly resistive p-type. It was dark in color and showed low optical transmittance. The differences between the two crystals are explained in terms of impurity incorporation during growth, which has different kinetics on the (000)C and the (0001)Si faces.

The Growth of Single Crystal of 3C-SiC on the Si Substrate by the MBE Method Using Multi Electron Beam Heating

The growth of a single crystal of 3C-SiC on a Si substrate by the MBE method has been performed. A single-crystal film can be grown at a substrate temperature Tsub=1150°C. This temperature is relatively low compared to that used in other methods. The diffused Si from a substrate plays an important part in the crystal growth of SiC, especially for a very thin film. The individual intensity of Si and C molecular beams (JSi and JC) and their intensity ratio JSi/JC should be selected with suitable values in accordance with the film thickness, considering the growth condition of the MBE method.

Impurity incorporation kinetics during modified-Lely growth of SiC

The impurity incorporation kinetics during modified-Lely growth of silicon carbide (SiC) have been studied in terms of several growth parameters. It was found that the nitrogen incorporation is well described by a Langmuir isotherm type equation, implying that dynamic equilibrium between the vapor phase and the adsorbed nitrogen is established. The polytype of grown crystal and the seed orientation influence the impurity incorporation. For growth on (0001)C, 6H-SiC crystals always incorporate more nitrogen and less boron than 4H-SiC crystals, while no clear polytypic dependence of impurity incorporation is observed for growth on (1100) and (1120). Atomic force microscope observations revealed that there is a marked difference in the growth morphology between 6H-SiC(0001)C and 4H-SiC(0001)C. The origin of the polytypic dependence of impurity incorporation during growth on (0001)C is discussed with reference to the growth surface morphology.

Nitrogen Incorporation Kinetics during the Sublimation Growth of 6H and 4H SiC

Nitrogen incorporation kinetics during the sublimation boule growth of SiC have been studied in terms of several growth parameters. 6H and 4H SiC crystals were heavily doped with nitrogen as a donor. It was found that the growth rate has little influence on the doping concentration, indicating that nitrogen incorporation is not kinetically limited at normal growth rates in the sublimation growth. On the other hand, surface polarity and polytype were found to influence the nitrogen incorporation kinetics at the growth front. By optimizing the growth conditions, bulk resistivities as low as 7.6×10-3 Ω cm and 5.3×10-3 Ω cm were obtained for 6H and 4H SiC, respectively.

Development of large single-crystal SiC substrates

This article reviews the recent development of large single-crystal silicon carbide (SIC) substrates. The technological potential of SiC for high-power, high-temperature, and high-frequency electronic devices has been recognized for several decades; however, such applications have been largely hindered by problems related to bulk crystal growth. The SiC bulk crystal growth technology has recently achieved drastic improvement and enabled the growth of large high-quality single crystals. Due to the availability of large high-quality substrates, progress in SiC thin-film epitaxy and devices has been rapid, and application of SiC to many fields is fast reaching its real potential.

Stepped structure on the {0001} facet plane of α-SiC

Abstract The surface topography of the {0001} facet of as-grown 6H and 4H SiC boules was observed ex-situ by atomic force microscopy (AFM). Peculiar stepped structures of SiC{0001} to the growth face polarity and the polytype were detected. Height steps equal to the c-lattice parameter (1.5 nm) were observed to be dominant on the 6H-SiC(0001)Si surface. They were very regularly arranged, i.e. straight and almost equally spaced. On the other hand, meandering macrosteps of height more than 10 nm were observed on the 6H-SiC(000 1 )C and the 4H-SiC(000 1 )C surfaces. Based on the results, the mechanism of formation of these surface morphologies is discussed.

Defect Formation During Sublimation Bulk Crystal Growth of Silicon Carbide

The defect formation during sublimation bulk crystal growth of silicon carbide (SiC) is discussed. SiC bulk crystals are produced by seeded sublimation growth (modified-Lely method), where SiC source powder sublimes and is recrystallized on a slightly cooled seed crystal at uncommonly high temperatures (≥2000°C). The crystals contain structural defects such as micropipes (hollow core dislocations), subgrain boundaries, stacking faults and glide dislocations in the basal plane. The type and density of the defects largely depend on the crystal growth direction, and many aspects are different between the growth parallel and perpendicular to the c-axis. Micropipes are characteristic defects to the c-axis growth, while a large number of stacking faults are introduced during growth perpendicular to the c-axis. We discuss the cause and mechanism of the defect formation

Nitrogen Incorporation Mechanism and Dependence of Site-Competition Epitaxy on the Total Gas Flow Rate for 6H-SiC Epitaxial Layers Grown by Chemical Vapor Deposition

The doping mechanism of nitrogen and the dependence of site-competition epitaxy on the flow rate of H2 carrier gas were studied for 6H-SiC epitaxial layers grown by chemical vapor deposition. The indication was that nitrogen, decomposed into a mono-atomic form (N) in the gas phase, participated in the doping process. The nitrogen decomposition and the reaction at SiC surfaces played an important role in the doping. Site-competition epitaxy for (0001)Si faces was not observed for the high flow rate of the H2 carrier gas because the nitrogen decomposition and the incorporation of the decomposed nitrogen into the epitaxial layers were suppressed by the high gas flow rate. As for (0001)C faces, neither site-competition epitaxy nor its dependence on the flow rate of the H2 carrier gas was observed. Based on the result on site-competition epitaxy, the high flow rate of the H2 carrier gas was applied to epitaxial growth on (0001)C faces in order to reduce the residual donor concentration and that as low as 1.5×1015 cm-3 was obtained for nondoped layers.