The Physical Vapor Transport Method for Bulk AlN Crystal Growth.

Bulk aluminum nitride (AlN) crystals with different polarities were grown by physical vapor transport (PVT). The structural, surface, and optical properties of m-plane and c-plane AlN crystals were comparatively studied by using high-resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Temperature-dependent Raman measurements showed that the Raman shift and the full width at half maximum (FWHM) of the E2 (high) phonon mode of the m-plane AlN crystal were larger than those of the c-plane AlN crystal, which would be correlated with the residual stress and defects in the AlN samples, respectively. Moreover, the phonon lifetime of the Raman-active modes largely decayed and its line width gradually broadened with the increase in temperature. The phonon lifetime of the Raman TO-phonon mode was changed less than that of the LO-phonon mode with temperature in the two crystals. It should be noted that the influence of inhomogeneous impurity phonon scattering on the phonon lifetime and the contribution to the Raman shift came from thermal expansion at a higher temperature. In addition, the trend of stress with increasing 1000/temperature was similar for the two AlN samples. As the temperature increased from 80 K to ~870 K, there was a temperature at which the biaxial stress of the samples transformed from compressive to tensile stress, while their certain temperature was different.

High-aspect-ratio single-crystalline AlN nanowires: Free-catalytic PVT growth and field-emission studies

Hexagonal aluminium nitride (AIN) microrods with high crystalline quality were grown by physical vapor transport (PVT) method at low growth temperature between 1700 and 1850 degrees C. The length of as-grown microrod is around 1 cm, and the width between 200-400 mu m. The microrod exhibits typical hexagonal geometrical shape with pale yellow color under optical microscopy. Scanning electron microscope (SEM) and atomic force microscope (AFM) images show each microrod with closely arranged step waviness, of which the step interval is 2-4 mu m and the height several nanometers. Raman spectrum characterization showed characteristic peaks of high crystalline AlN. The rod-like structure is attributed to slow growth velocity at lower crystalline temperature, enabling Al and N atoms having enough time to move to the lower energy site and to form heiagonal microrod along direction. High quality hexagonal AlN microrod is an enrichment to one-dimensional semiconductor materials. Data from this study suggest that, by further study on size and impurity control, high performance miniaturized opto-electronic device is hopeful to be achieved.

Bulk crystal growth of aluminum nitride (AlN) comes into focus in order to provide substrates for deep-UV optoelectronics (LEDs, lasers, and sensors) which are typically based on Al-rich AlGaN epitaxial layers and structures. On AlN substrates, pseudomorphic AlGaN layers can be deposited with compressive strain and high structural quality [1, 2, 3]. In this context, the growth of AlN crystals by sublimation and recondensation (physical vapor transport method) at temperatures exceeding 2000 °C has proven to be the method of choice, as the boules and substrates show very high structural perfection at reasonable growth rates. Availability of AlN substrates as well as their useable area, structural quality, and electrical/optical properties are directly related to growth technology issues, including selection of set-up materials, seeding strategy, and pre-purification efforts. After a brief overview of history and applications of bulk AlN, the basic principles of AlN bulk growth by physical vapor transport (PVT) are reviewed. The formation of extended defects and the incorporation of impurities during growth as well as their impact on the material’s optical and electrical properties are discussed in detail. The main target of this chapter is to provide readers with enough information about AlN substrate preparation to understand and make informed decisions about employing AlN substrates for deep-UV optoelectronics.

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.

Control of powder recrystallization and crystallization interface shape for 8-inch SiC crystal growth by PVT method

Effects of growth direction and polarity on bulk aluminum nitride crystal properties

AlN 결정을 PVT(물리 기상 이동법, Physical Vapor Transport) 법으로 성장함에 있어 결정립의 성장 거동을 관찰하였다. 작은 AlN 결정립이 성장한 이후 결정립들은 이웃한 결정립과 합쳐지면서 성장하는 거동을 보였다. 이를 실체현미경을 이용하여 관찰한 결과를 보고하고자 한다. It was observed that the single grain of crystallite growth behavior in AlN (Aluminum Nitride) single crystal growth by PVT (Physical Vapor Transport) method. The single grain of AlN was grown in sequent experiments and adjacent crystallites were joined together after small grain was grown. The sequential results of those grains observed by stereoscopic microscope were reported.

PVT(물리 기상 이동법, Physical Vapor Transport) 법을 적용하여 질화알루미늄(AlN, Aluminum Nitride) 단결정을 성장하였으며, 성장된 결정의 결정성과 성장 온도에 따른 상에 대하여 고찰하였다. 성장된 단결정은 광학현미경을 이용하여 결정의 상을 관찰하였고, 관찰된 결과를 비교 분석하여 본 실험에 적용된 성장 장치에서의 최적의 성장 온도 조건을 설정할 수 있었다. 본 연구에서는 AlN 단결정 성장 결과를 비교 고찰하여 보고하고자 한다. AlN (Aluminum Nitride) crystals were grown by a PVT (Physical Vapor Transport) method and were characterized to phases on the growth temperature. The crystals phase and morphology were analyzed using an optical stereo-microscope and the optimum temperature for the growing was determined. In this report, the characteristics of the AlN crystals grown at various temperatures were reported.

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.

Purification of Cd0.9Zn0.1Te by physical vapor transport method

A recent study reported the rapid growth of SiC single crystals of ~1.5 mm/h using high-purity SiC sources obtained by recycling CVD-SiC blocks used as materials in semiconductor processes. This method has gained attention as a way to improve the productivity of the physical vapor transport (PVT) method, widely used for manufacturing single crystal substrates for power semiconductors. When recycling CVD-SiC blocks by crushing them for use as sources for growing SiC single crystals, the properties and the particle size distribution of the material differ from those of conventional commercial SiC powders, making it necessary to study their effects. Therefore, in this study, SiC single crystals were grown using the PVT method with crushed CVD-SiC blocks of various sizes as the source material, and the growth behavior was analyzed. Simulation results of the temperature distribution in the PVT system confirmed that using large, crushed blocks as the SiC source material generates a greater temperature gradient within the source compared to conventional commercial SiC powder, making it advantageous for rapid growth processes. Additionally, when the large, crushed blocks were vertically aligned, good crystal quality was experimentally achieved at high growth rates, even under non-optimized growth conditions.

The appropriate distribution of temperature in the growth system is critical for obtaining a large size high quality aluminum nitride (AlN) single crystal by the physical vapor transport (PVT) method. As the crystal size increases, the influence of the crucible on the temperature distribution inside the growth chamber becomes greater. In order to optimize the field of temperature and study the specific effects of various parts of the crucible on the large size AlN single crystal growth system, this study carried out a series of numerical simulations of the temperature field of two crucibles of different materials and put forward the concept of a composite crucible, which combines different materials in the crucible parts. Four composite crucible models were established with different proportions and positions of tantalum carbide (TaC) parts and graphite parts in the crucible. Calculations reveal that different parts of the crucible have different effects on the internal temperature distribution. The axial temperature gradient at the crystal was mainly governed by the crucible wall, whereas the temperature gradient was determined by the integrated effect of the crucible lid and the crucible wall in the radial direction. One type of composite crucible was chosen to minimize the thermal stress in grown AlN crystal, which is applicable to the growth of large sized AlN crystals in the future; it can also be used to grow AlN single crystals at present as well.

Basal plane slip is the most frequently observed deformation mechanism in hexagonal aluminum nitride (AlN) crystals grown by the physical vapor transport (PVT) method. However, prismatic slip can also take place in such crystals. In this study, slip in the three prismatic slip systems with nonuniform distributions, observed in a commercial 50 mm AlN substrate wafer, was investigated. The nonuniformity was attributed to the distribution of resolved shear stress in each prismatic slip system caused by radial thermal gradients in the growing crystal boule. A radial thermal model was established to quantitively estimate the thermal stress across the area of the crystal boule during PVT growth. The model results correlated well with both the experimental observations and theoretical calculations of the critical resolved shear stress, revealing that radial thermal gradients play a key role in activating prismatic slip during AlN bulk growth.

Enhanced synthesis of Sn nanowires with aid of Se atom via physical vapor transport