Papers by Keyword: Sublimation

Abstract: The conditions to succeed in growing 3C-SiC single crystals are first, make available large 3C-SiC seeds and second, develop a suitable growth process. In this paper, we will address those two issues by reviewing the most recent results in the field. Nucleation, growth, structural quality and doping results will be presented. New insights on 3C bulk growth will be discussed with respect to a future development of real bulk 3C-SiC ingots.

Abstract: Two SiC single crystal ingots were prepared using sublimation PVT techniques through the different process procedure and then their crystal quality was systematically compared, because the present research was focused to improve the quality of SiC crystal by modifying the initial stage of the PVT growth. Before the main growth step for growing SiC bulk crystal, initial stage period where growth rate was kept to relatively low rate of <10μm/h was introduced to conventional process procedure. N-type 2”-SiC single crystals exhibiting the polytype of 6H-SiC was successfully fabricated. As compared to the characteristics of SiC crystal grown using the conventional schedule, the quality of SiC crystal grown with modifying the initial stage was significantly improved, exhibiting decrease of defect formation such as micropipe and polytype formation.

Abstract: The development of 3C-SiC crystals from <0001> oriented hexagonal seed has always suffered from the systematic twinning which appears during the nucleation step of the layer. Using the continuous feed – Physical Vapour Transport (CF-PVT) growth process, we succeeded in growing single domain 3C-SiC crystals. To explain that, we propose in this work, a model based on the interaction between the lateral expansion anisotropy of 3C-SiC nuclei and the step flow growth front. Depending on the step edges direction, we can obtain one 3C orientation developing simultaneously with the vanishing of the other one. This model is confirmed by cross sectional HRTEM observation of the α-β interface.

Abstract: We investigated the effects of hydrogen addition to the growth process of SiC single crystal using sublimation physical vapor transport (PVT) techniques. Hydrogen was periodically added to an inert gas for the growth ambient during the SiC bulk growth. Grown 2”-SiC single crystals were proven to be the polytype of 6H-SiC and carrier concentration levels of about 1017/cm3 was determined from Hall measurements. As compared to the characteristics of SiC crystal grown without using hydrogen addition, the SiC crystal grown with periodically modulated hydrogen addition definitely exhibited lower carrier concentration and lower micropipe density as well as reduced growth rate.

Abstract: SiC single crystal ingots were prepared onto different seed material using sublimation PVT techniques and then their crystal quality was systematically compared. In this study, the conventional SiC seed material and the new SiC seed material with an inserted SiC epitaxial layer on a seed surface were used as a seed for SiC bulk growth. The inserted epitaxial layer was grown by a sublimation epitaxy method called the CST with a low growth rate of 2μm/h. N-type 2”-SiC single crystals exhibiting the polytype of 6H-SiC were successfully fabricated and carrier concentration levels of below 1017/cm3 were determined from the absorption spectrum and Hall measurements. The slightly higher growth rate and carrier concentration were obtained in SiC single crystal ingot grown on new SiC seed materials with the inserted epitaxial layer on the seed surface, maintaining the high quality.

Abstract: AlN is considered as the most suitable substrate material for further development of high quality and high performance nitride-based micro- and opto-electronics. AlN ingots are often grown on SiC seeds. To solve the formation of cracks due to the difference in lattice parameters between seed and crystal we chose to “adapt” the lattice mismatch by a buffer layer of the (AlN)x(SiC)1-x solid solution. This paper gives some inputs on the growth of AlN and the solid solution by the sublimation technique, in terms of materials compatibility, hetero- and homo-epitaxial growth of AlN and on the preparation of crack-free solid solution single crystals.

Abstract: The benefits of depositing AlN-SiC alloy transition layers on SiC substrates before the seeded growth of bulk AlN crystals were determined. The presence of the AlN-SiC alloy layer helped to suppress the SiC decomposition by providing vapor sources of silicon and carbon. It enabled a higher growth temperature, and hence a higher growth rate. In addition, cracks in the final AlN crystals can be decreased because of the intermediate lattice constants and thermal expansion coefficient of AlN-SiC alloy. AlN-SiC alloys were first grown on off-axis SiC substrates by the sublimation-recondensation method. Then pure AlN crystals were grown upon those. For comparison, AlN crystals were directly grown on SiC substrates under similar conditions. X-ray diffraction (XRD) confirmed the formation of a pure single crystalline AlN layer upon the AlN-SiC alloy on SiC substrate. The presence of an AlN-SiC transition layer effectively inhibited the appearance of cracks in the resultant AlN crystals. X-ray topography (XRT) demonstrated that the thick AlN layer effectively released the strain present.

Abstract: A sublimation epitaxial method, referred to as the Closed Space Technique (CST) was adopted to produce thick SiC epitaxial layers for power device applications. We aimed to systematically investigate the dependence of SiC epilayer quality and growth rate during the sublimation growth using the CST method on various process parameters such as the growth temperature and working pressure. The etched surface of a SiC epitaxial layer grown with low growth rate (30 μm/h) exhibited a low etch pit density (EPD) of ~2000 /cm2 and a low micropipe density (MPD) of 2 /cm2. The etched surface of a SiC epitaxial layer grown with a high growth rate (above 100 μm/h) contained a high EPD of ~3500 /cm2 and a high MPD of ~500 /cm2, which indicates that high growth rate aids the formation of dislocations and micropipes in the epitaxial layer.

Abstract: We demonstrate high-speed and high-quality 6H-SiC homoepitaxial growth on a 1°-off c-plane SiC substrate by a closed-space sublimation method. By optimizing the size of single-crystal source materials in the growth system, a high-quality 6H-SiC epilayer with an X-ray diffraction rocking curve (0006) full-width at the half maximum (FWHM) of 38 arcsec was obtained. We also carried out doping of nitrogen and boron during the growth of the SiC epilayer. A strong donor-acceptor pair (DAP) emission at a peak wavelength of 570 nm under excitation by a 395 nm nitride-based light-emitting diode (LED) was observed. The 6H-SiC with DAP emission is promising for use as a phosphor in a nitride-based LED, because high-quality nitride layers can be grown on the SiC substrates with small off-oriented angles.

Abstract: High temperature chemical vapor deposition (HTCVD) simulations of silicon carbide (SiC) were demonstrated with experimental results. A vertical cylindrical reactor was used in an RF inductive heating furnace and the temperature was more than 2200
. SiH4 and C3H8 were used as source gases and H2 as carrier gas. A gas phase reaction model from the literature was used on the condition that the gas phase reaction is a quasi-equilibrium state. It was found that the major species were Si, Si2C, SiC2 and C2H2 in the gas phase reaction model as well as in the thermodynamic equilibrium calculation. Sublimation etching was considered in the surface reaction rates by modifying partial pressures of species with equilibrium vapor pressures. CFD-ACE+ and MALT2 software packages were used in the present calculation. The sticking coefficients were determined by fitting the calculated growth rates to the experimental ones. The simulated growth rate in a different reactor is in good agreement with the experimental value, using the same sticking coefficients. The present simulation could be useful to design a new reactor and to find optimum conditions.