Investigation of micropipe defect terminating during SiC crystal growth

Abstract

Micropipe is a vital defect for fabricating SiC based devices. In order to understand the evolution of micropipe during growth process, the authors studied axial cuts sliced from different parts of the sublimation grown SiC single crystals. The cuts have been characterised using optical microscopy, etching in molten mixed KOH and K₂CO₃, scanning electron microscope and X-ray photoelectron spectroscopy. It is found that second phase inclusion (silicon droplet) is contributing not only to the formation of micropipe defect but also to its termination during SiC growth process. And X-ray photoelectron spectroscopy measurement result shows that growth interface can be demarcated obviously without intentionally doping any other impurity, which offers a good and simple method for observing crystal growth process.     

Growth of low dislocation density single crystals of nickel

Low dislocation density single crystals of nickel have been grown at high ambient pressure by the Czochralski method. X-ray Laue picture shows that the crystals are strain-free. The dislocation density was determined to be <10³/cm² by the etching procedure. It was found that the necking and cone regions are very critical in the dislocation introduction in the crystals. An increase in the ambient pressure used during the growth seems to aid the crystal quality.     

Patterning SiC nanoprecipitate in Si single crystals by simultaneous dual- beam ion implantation

β–SiC nanoprecipitates can be patterned in crystalline silicon with an almost monomodal size distribution by simultaneous-dual-beam of C⁺ and Si⁺ ion implantations at 550 °C. Their shape appears as spherical (average diameter ~4–5 nm) ,and they are in epitaxial relationship with the crystalline silicon matrix. The narrow size distribution follows the left wing of the carbon distribution where the nuclear ion stopping, and thus the point defect generation rate is largest. This observation allows us to conclude that the induced damage act as sinks for C atoms leading to the SiC nanoprecipitates formation centered at the maximum of the simulated damage distribution. The nuclear reaction analysis, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy techniques were used to characterize the samples.     

Role of SiC substrate polarity on the growth and properties of bulk AlN single crystals

Two symmetrically nonequivalent silicon carbide (SiC) substrate orientations, (0001) Si-terminated and \((000\overline{1} )\) C-terminated, were used in the physical vapour transport growth of bulk aluminium nitride (AlN) single crystals. The crystals grown on Si-faces always exhibit an Al-polar growth surface. AlN growth on \((000\overline{1} )\) C-terminated surfaces of the SiC substrates was performed to obtain N-polar growth surfaces. An abrupt interface was observed between the AlN crystal and the C-face substrate which is in contrast to the growth on Si-faces where hexagonally shaped SiC hillocks are formed. The growth on C-faces is usually dominated by multi-site nucleation. Applying similar supersaturation conditions that led to step-flow growth on Si-faces to the C-faces resulted in a spiral growth mode, even on highly off-oriented substrates. The obtained broad X-ray diffraction rocking curves of such samples (full-width at half-maximum ≈380 arcsec) indicate the presence of more misfit dislocations and significant misfit stress. In addition, polarity inversion is observed in C-face grown crystals. Though the structural properties of the crystals grown on C-face are inferior to that of the crystals grown on Si-face, the incorporation of unintentional Si impurity was found to be lower (<2 wt%).     

Influence of reduction on the behavior kinetics of optical inhomogeneities in LiNbO3 single crystals

An investigation was made of the influence of high-temperature annealing in vacuum on the optical homogeneity of LiNbO₃ single crystals. It was observed that the residual light transmission decreased appreciably and the temperature dependence of this parameter almost completely disappeared. Pis’ma Zh. Tekh. Fiz. 24, 81–85 (November 26, 1998)     

超细SiC片晶的制备方法

超细SiC片晶由于其高强度、高弹性模量和高导热系数已成为替代价值昂贵、制备技术复杂的SiC晶须的理想的增韧材料SiC片晶的制备方法有化学制备法和机械制备法。本文中详细介绍了用机械方法制备SiC片晶的设备与工艺过程,阐述了各种制备方法的工作原理及其优缺点,通过对各种制备方法的比较得出采用气流磨与分级机结合工艺是目前制备系列超细SiC片晶有效的和最经济的生产工艺。     

The photoelastic constant and internal stress around micropipe defects of 6H-SiC single crystal

Hexagonal silicon carbide (6H-SiC) single crystals made by a modified Lely method contain a ‘micropipe’ which is one kind of serious defects degrading device performance. The micropipe accompanies strong internal stress around itself. We determined the photoelastic constant in the plane of (00·1) 6H-SiC and then estimated the magnitude of the internal stress around the micropipes. The photoelastic constant was 2.73 brewster at λ=546 nm. The internal stress around the micropipe was estimated to be 113∼166 MPa.     

MicroRaman study of bulk inclusions in SiC crystals

The growth of defect-free SiC substrates is of primary importance for the development of devices based on this material, since defects such as micropipes and crystalline inclusions limit the performance of SiC-based devices. The analysis of these defects is crucial for the improvement of these crystals. MicroRaman spectroscopy provides structural and electronic information with micrometric spatial resolution. We present herein a microRaman study of different solid inclusions in 4H-SiC; the results are discussed in terms of the polytype structure, crystal orientation in relation to the matrix, and local electron concentration and mobility around the solid inclusions.     

Model for kink-like deformation in CoTi single crystals

Single crystals of the B2 CoTi intermetallic compound were deformed in compression at temperatures between room temperature and 1000 K. The orientation was about 10° off the [001] cube axis. For B2 compounds with `strong’ AB bonding, the slip dislocations are often type gliding on planes although and slip cannot be ruled out especially when, as in this case, the Schmid factors for glide are very small. In the lower half of the temperature range, deformation progressed by a series of load drops which manifests itself as coarse bands formed at intervals along the gauge length. The bands are roughly parallel to the (001) plane but it is concluded that the slip planes are and that the kink-like behaviour is due to the formation of twist boundaries. A model for this behaviour is presented which is based on a pole mechanism and the glide of dislocations.     

On the identification of the polar surfaces of SiC crystals

The identification of the polar surfaces of silicon carbide with an alkaline solution was investigated by phase-contrast microscopy and two-beam interferometry. It is found that the alkaline solution produces growth patterns on the (0001) carbon surface, while the opposite (0001) silicon surface remains essentially unaffected. The merit of polarity determination by a growth method combined with phase-microscopy was proposed.     

Defects in polydiacetylene single crystals

The structure of single crystals of a substituted polydiacetylene (pTS) has been investigated using transmission electron microscopy. The structure of the perfect crystal has been examined and it has been shown that the molecules lie in the plane of the lamellar crystals in an extended-chain conformation. The formations of bend contour zone axis patterns has been analysed and they are found to be due to the crystal being deformed into the shapes of both cups (or domes) and saddles. A common defect in the crystals was a stacking fault; using dark-field microscopy it has been found to have a displacement vector of 1/2 [1¯21]. It has been shown that such a stacking fault can be accommodated without any disruption to either the molecular backbone or the relatively large sidegroups on the molecule. The significance of these stacking faults with regard to the structure of polymer crystals in general is discussed.     

Shape-controlled nanopores in single crystals

Nanometer length-scale holes (nanopores) are often formed in amorphous materials for fundamental studies of molecular mass transport. In the current study, electron beam irradiation in the transmission electron microscope was used to form nanopores in a crystalline material (Si). Analysis of the nanopores showed that they are formed by knock-on of atoms by the high energy incident electron beam, and surface diffusion is partially responsible for the hour-glass shapes that are found for some nanopores. Energetically favorable three-dimensional shapes of nanopores were simulated, and the nanopores simulated in the model crystalline material were found to be more stable than the nanopores simulated in the amorphous material. The nanopore shape was also found to depend on the nanopore diameter-to-length ratio. Based on the above, we demonstrate the advantage in using a crystalline material for nanopore formation and show that control of the three-dimensional shape of nanopores formed by electron beam irradiation is possible.     

Modified single crystals for high-power underwater projectors

Underwater electroacoustic projectors using single crystals based on the lead magnesium niobate-lead titanate (PMNT) composition were investigated. The large electromechanical coupling coefficient (k(33) > 0.90) and piezoelectric coefficient (d(33) > 1500 pC/N) of PMNT have been demonstrated to improve transducer bandwidth and source level relative to conventional piezoelectric ceramics. The low mechanical quality factor (Q(M) < 200) and low temperature stability (T(RT) < 95°C) of PMNT, however, limit its utility in high-power, high-duty-cycle applications. Use of modified single crystals was shown to result in transducers which exhibit up to 5 dB improvement in source level over PMNT when operated at resonance. Compared with a PZT4 transducer, these modified crystals offer similar source level and power handling capability at resonance, but the available bandwidth is doubled and a 6 dB improvement in maximum source level is achieved when driven off resonance.     

Dislocation density in electrolytically-coloured KCl crystals

Dislocation densities have been investigated in potassium chloride crystals, electrolytically coloured in the temperature range of 550–710°C. The results show an increase in the dislocation density with coloration temperature upto 650°C and decrease thereafter. This is attributed to the movement of dislocations and interactions between them during electrolytic coloration of the crystals.