Effect of powder packing method on thermal field of SiC crystal grown by PVT method

Silicon carbide (SiC) polycrystalline powder. As the raw material for SiC single-crystal growth through the physical vapor transport (PVT) method, its surface size and shape have a great influence on growth of crystal. The surface size and shape of the evaporation area filled with polycrystalline powder were investigated by numerical simulation in this study. Firstly, the temperature distribution and deposition rate distribution for the PVT system were calculated by global numerical simulation, and the optimal ratio of polycrystalline powder surface diameter to seed crystal diameter was determined to be 1.6. Secondly, the surface of the evaporation area filled with polycrystalline powder was covered by a graphite ring and a graphite disc, respectively, to change its surface shape. The results show that adjusting the surface size and shape of the evaporation area filled with polycrystalline powder is an effective method to control the growth rate, growth stability, and growth surface shape of the single crystal. Finally, the result obtained by selecting appropriate covered structures for actual growth indicates that this process can act as a reference for improving the quality of single crystals.

Basal plane slip is most frequently observed deformation mechanism in 4H type silicon carbon (4H-SiC) single crystals grown by physical vapor transport (PVT) method. It has recently been reported, however, dislocations in such crystals can also glide in the prismatic slip systems. In our study, we have observed non-uniform distributions of three sets of prismatic dislocations in a commercial 4H-SiC substrate wafer. The non-uniformity is likely a result of the distribution of resolved shear stress on each prismatic slip system caused by the radial thermal gradients in the growing crystal boule. A radial thermal model during PVT growth has been developed to estimate the thermal stress across the entire area of the crystal boule. The model makes an excellent agreement with the actual observation, confirming that radial thermal gradients play a key role in activating prismatic slip in 4H-SiC during bulk growth.

Aluminum nitride (AlN) bulk crystals, approximately 50.8mm in diameter and up to 5mm thickness, were grown by a physical vapor transport (PVT) method in a tantalum crucible. To investigate the effect of crucible materials, various crucible materials, a graphite and TaC-coated graphite and tantalum crucible were used for the AlN growth. XRD pattern of AlN crystal grown on SiC seed in the Ta-crucible exhibited only (00l) peaks, indicating that AlN single crystal was successfully grown on SiC seed. The interface structure between AlN and SiC crystals was observed by a high resolution TEM.

Based on the physical vapor transport (PVT) method, the growth of large-size CdS crystals inside a vertical semi-closed tube is studied. Firstly, in order to ensure 1D diffusion-advection transport, multi-thin tubes are used in the growth tube. The XRD spectra of the CdS crystal grown in this configuration indicates that the crystal quality has clearly been improved, where the FWHM is 58.5 arcsec. Secondly, theoretical and experimental growth rates under different total pressures are compared; the results show that the experiential growth rate equation is valid for our semi-tube growth, and it could be used to estimate the growth rate and maximum growth time under different total pressures.

The physical vapor transport (PVT) method has been widely used in the growth of silicon carbide single crystals. In designing the growth system, effective thermal management is crucial, particularly regarding the temperature of the growth surface and the horizontal and vertical temperature gradients. In this paper, an inner rod positioned along the central axis of the crucible to optimize thermal field through numerical simulations. The results show that the introduction of the inner rod reduces the horizontal temperature difference of the growth surface from nearly 80 °C to less than 10 °C, significantly minimizing the bulging of the growth crystals. Additionally, simulations were performed to examine the effects of varying the radius and height of the inner rod, as well as the radius of the bottom graphite holder, with findings discussed in detail. This study provides a theoretical method for the growth of high-quality, low-stress 4H-SiC crystals with smooth surfaces. It also provides a reference for the growth of 3C-SiC from small distance of material source to seed by sublimation epitaxy.

SiC single crystal ingots grown by sublimation physical vapor transport (PVT) technique were prepared and then the SiC crystal quality with varying crucible design employing a guide tube and tantalum foil was systematically investigated. The growth rate of 2-inch SiC crystal grown by these crucible designs was about 0.3 mm/hr. The n-type and p-type 2”-SiC single crystals exhibiting the polytype of 6H-SiC were successfully fabricated. The doping concentration level of below ~1017/cm3 was extracted from the absorption spectrum and Hall measurement. The densities of micropipes and inclusions in SiC crystal boules grown using the graphite/Ta foil double layer guide tube were significantly decreased. Finally we improved crystal quality through the introduction of new crucible design.

The surface morphologies and structural information of several slice crystals grown by the physical vapor transport (PVT) method were investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis. Step-like structures were observed by AFM, corresponding with XRD results and the characteristics of layer-plus-island growth mode has been determined on the surface of a crystal grown from PVT, which is different from that of crystal thin film growth by molecular beam epitaxy (MBE) and physical vapor deposition (PVD) in that the driving force depends mainly on the velocity of evaporating source materials, the temperature of the substrate and interactions between molecules. However, the main driving force for the formation of a slice crystal hanging inside the growth tubes from PVT without the influence of substrate depends solely on the interactions between the molecules in the crystal.

Growth of SiC by PVT method with different sources for doping by a cerium impurity, CeO2 or CeSi2

In this report, the development of physical vapor transport (PVT) methods for bulk aluminum nitride (AlN) crystal growth is reviewed. Three modified PVT methods with different features including selected growth at a conical zone, freestanding growth on a perforated sheet, and nucleation control with an inverse temperature gradient are discussed and compared in terms of the size and quality of the bulk AlN crystals they can produce as well as the process complexity. The PVT method with an inverse temperature gradient is able to significantly reduce the nucleation rate and realize the dominant growth of only one bulk AlN single crystal, and thus grow centimeter-sized bulk AlN single crystals. X-ray rocking curve (XRC) and Raman spectroscopy measurements showed a high crystalline quality of the prepared AlN crystals. The inverse temperature gradient provides an efficient and relatively low-cost method for the preparation of large-sized and high-quality AlN seed crystals used for seeded growth, devoted to the diameter enlargement and quality improvement of bulk AlN single crystals.

Optimization of the thermal field of 8-inch SiC crystal growth by PVT method with “3 separation heater method”

The growth of p-type SiC crystals with low resistivities should be investigated due to its application inn-channel Insulated Gate Bipolar Transistor (IGBT) fabrication. In this paper, the growth of 2 inch p-type 4H-SiC single crystals was carried out by conventional physical vapor transport (PVT) method with Al 4 C 3 as Al dopant source. Results showed that the aluminum atoms can be effectively incorporated into SiC crystals and the color of Al-doped 4H-SiCcrystals was blue. With the increase of aluminum content in SiC crystals, the color of Al-doped SiC became darker and eventually opaque. At heavy Al doping condition, the polytype of 4H-SiC was not stable and the grown crystals easily turned to 6H-SiC polytype. In addition, by adopting Al-N co-doping technique, p-type SiC single crystals with stable 4H-SiC polytype were grown. However, due to the difficulty in controlling the release of Al, Al-N co-doped single crystals turned to n-p-n type conduction crystals. Noncontact resistivity measurement showed the minimum resistivity of p-type 4H-SiC wafers was about 4149 mfi-cm.

AlN is a kind of promising semiconductor material for high‐efficiency optoelectronic devices and high‐power high‐frequency electronic devices. In this work, high‐quality c‐plane AlN single crystal with low‐stress is grown on tungsten (W) substrate using a spontaneous nucleation physical vapor transport (PVT) method. Temperature field simulation and theoretical analysis provide a theoretical guide for the AlN crystals growth experiment. The hexagonal appearance c‐plane AlN crystal is obtained with a size up to 3 mm × 3 mm. A large radial temperature gradient and suitable supersaturation lead to a low nucleation density and the growth of AlN crystal with large size, which can be used to regulate nucleation density and size of AlN crystals on W substrate. X‐ray diffraction (XRD), Raman and electron backscatter diffraction (EBSD) results confirm that the crystal is grown along the c‐axis direction with hexagonal wurtzite structure and high crystalline quality. The Raman micro‐mapping results indicate that the grown AlN crystal has small tensile stress, close to free‐stress, and the biaxial stress decreases from interface to surface along with the increasing of crystal thickness. This work will greatly contribute to the research of AlN crystal growth on W substrate.

Evaluation of the change in properties caused by axial and radial temperature gradients in silicon carbide crystal growth using the physical vapor transport method

The quality of SiC crystals grown by the physical vapour transport (PVT) method wasstudied by means of optical microscopy and scanning electron microscopy (SEM)observations with the aid of etching by molten KOH. New types of defects were found,including triangular etching pits, shallow hexagonal etching pits and dendritic siliconinclusions in 4H-SiC. The triangular etching pits usually appear on the C face with a sizecomparable with the irregular dark etching pits due to the micropipes, while the shallowhexagonal etching pits were observed on the Si face with a size comparable with that due tothe micropipes. The silicon inclusions exhibit dendritic shape up to several microns likethose usually observed in metal alloys. In addition, 4H-SiC and 6H-SiC domains withdifferent polarities in the growth surface were found to develop from the same seed. Theinterface of 4H-SiC and 6H-SiC was one of the sources for inducing the micropipes.

In the conventional crucible structure for AlN crystal growth by physical vapor transport, owing to the long molecular transport path of Al vapor and the disruption of the gas flow by the presence of a deflector, the Al vapor easily forms polycrystals in the growth domain. The result is increased internal stress in the crystals and increased difficulty in growing large-sized crystals. On this basis, with the help of finite element simulations, a novel crucible structure is designed. This crucible not only optimizes the gas transport but also increases the radial gradient of the AlN crystal surface, making the enhanced growth rate in the central region more obvious. The thermal stresses between the deflector and the crystal are also reduced. High-quality AlN crystals with an FWHM of 79 arcsec were successfully grown with this structure, verifying the accuracy of finite element simulation of the growth of AlN crystals. Our work has important guiding significance for the growth of high-quality AlN crystals.