Silicon incorporation in LEC growth of single crystal gallium arsenide

Recent reports suggest that melt stoichiometry has a strong effect on silicon dopant incorporation in the LEC growth of GaAs single crystals. Our studies show that melt stoichiometry has no effect on silicon incorporation. Using a low pressure LEC process in a high volume manufacturing environment we routinely grow 2 inch or 3 inch diameter, up to 4 kg, single crystals of Si-doped GaAs with dislocation densities as low as 100 cm^-2. Crystals with Si concentrations ranging from 10¹⁶ to 10¹⁹ cm^-3, grown from melts having Ga/As ratios ranging from 0.75 to 1.4 and contained in quartz crucibles, all have a compensation ratio of about 0.5. Contamination of the melt by Si from the quartz crucible as well as removal of Si from the melt by the B₂O₃ encapsulant must be considered when interpreting Si segregation data. In the course of the work with As-rich melts, the excess As in the melt gave rise to constitutional supercooling resulting in interface breakdown similar to that observed for excess dopants. This is the first time that this phenomena has been reported for melt growth of GaAs single crystals.

Source: Journal of Crystal Growth

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Trapping of mobile Mu centers in single crystal AlN

We have investigated muonium (Mu) defect centers in single crystal AlN as an analog for atomic hydrogen impurities. A nitrogen-related muon level-crossing resonance is associated with a static center formed by trapping of a mobile Mu impurity at another defect. This trapped Mu is released above 800K.Muon spin depolarization data imply that both Mu0 and ground-state Mu+ centers are mobile. Strong correlations between growth of the trapped Mu resonance and Mu0 motion and transformation rates above 400K imply that Mu0 is the more likely precursor in that region.

Source: Physica B: Condensed Matter

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Experimental study of surface generation and force modeling in micro-grinding of single crystal silicon considering crystallographic effects

In this study, surface formation mechanism in micro-grinding of single crystal silicon is investigated based on analysis of undeformed chip thickness hm.A predicting model of grinding force considering crystallographic effects in micro-grinding of single crystal silicon is built. In this model, micro-grinding process of single crystal silicon is divided into two steps by one line on which hm of single grit equals to lattice constant. Two micro-grinding experiments with different ranges of cutting depths and feed rates have been designed and conducted on single crystal silicon to verify the model this paper proposes. The relationship between micro-grinding parameters and crack length lc is investigated and the empirical formula of lc is derived based on analysis of experiment results. Ductile-regime transitions in micro-grinding process of single crystal silicon have been revealed, 20 nm and 100 nm are turned out to be two critical conditions based on analysis of experiment results. It is found that the grinding force has a sudden change when micro-grinding process comes within material's crystal boundary in experiment. The force predicting model this paper proposes has well explained this phenomenon in micro-grinding of single cyrstal silicon. When micro-grinding undeformed chip thickness hm belows 0.5 nm, micro grinding force doesn't decrease with the decrease of cutting parameters but has a rising tendency, and these experimental measurements also provide a support to the result of model this paper proposes.

Highlights

• We build a predicting model of micro-grinding force considering crystallographic effects.

• We divide micro-grinding process of single crystal silicon into two steps by lattice constant.

• Two micro-grinding experiments with different cutting depths and feed rates are conducted.

• Empirical formula of lc in single silicon crystal micro-grinding is derived.

• Ductile-regime transitions in micro-grinding process of single crystal silicon are revealed.

Source: International Journal of Machine Tools and Manufacture

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Tensile measurement of single crystal gallium nitride nanowires on MEMS test stages

This paper reports direct tensile tests on n-type (Si-doped) gallium nitride single crystal nanowires that were grown by nitrogen plasma-assisted molecular beam epitaxy and which are essentially free of defects and residual strain. Nanowires were integrated with actuated, active microelectromechanical (MEMS) devices using dielectrophoresis-driven self-assembly and platinum-carbon clamps created using a gallium focused ion beam. For one nanowire, failure strain of 0.042 ± 0.011 was found. Most nanowire specimens appeared to demonstrate tensile strength in the range of 4.0 ± 1.7 GPa to 7.5 ± 3.4 GPa. Failure modes included clamp failure, transverse (nanowire c-plane) fractures, and insufficient force from the MEMS test actuator.

Source: Sensors and Actuators A: Physical

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Experimental Investigations into EDM Behaviors of Single Crystal Silicon Carbide

The present study aims to investigate the fundamental electrical discharge machining (EDM) characteristics of silicon carbide (SiC) single crystal material. The EDM machining performances of SiC are experimentally studied and compared to that of steel. Die-sinking EDM of SiC by utilizing copper foil electrodes was proposed and investigated. It was found that EDM characteristics of SiC have a big difference from those of steel. The EDM speed of SiC is higher and the tool wear ratio is lower compared to that of steel material, although SiC has a higher thermal conductivity and melting point. Thermal crack caused by the thermal shock of electrical discharges was found as another main factor contributing to the removal of the material in EDM of SiC material. Also it is concluded that the new foil EDM method for slicing SiC ingot has potential for slicing SiC wafers in the future.

Source:Procedia CIRP

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