James P. McHugh

Growth of large SiC single crystals

We have grown 6H-polytype SiC single crystal boules up to 60 mm in diameter by the physical vapor transport process at 2300 o C. [0001] oriented substrate wafers prepared from these undoped crystals exhibit resistivities of up to 10 5 Ω cm and etch pit defect densities of 10 4 -10 5 cm -2 . Epitaxially-grown microwave MISFIT structures exhibit 5 GHz cutoff frequency; the highest reported to date

Large diameter 6H-SiC for microwave device applications

6H-polytype SiC single crystals with diameters up to 50 mm and lengths up to 75 mm have been grown in the c-and a-axis directions by physical vapor transport (PVT) at growth rates of 0.25 to 1 mm h -1 . Undoped crystals grown from purified source material reveal residual impurity concentrations in the 10 16 cm -3 range and resistivities up to 1000 Ω-cm. N + crystals with resistivities < 0.02 Ω-cm have been produced by controlled nitrogen doping. PVT-grown SiC crystals are characterized by dislocation densities of 10 4 to 10 5 cm -2 and can also exhibit micropipe defects in the 10 2 to 10 3 cm -2 range

Advancements in silicon web technology

Abstract Low defect density silicon web crystals up to 7 cm wide are produced from systems whose thermal environments are designed for low stress conditions using computer techniques. During growth, the average silicon melt temperature, the lateral melt temperature distribution and the melt level are each controlled by digital closed loop systems to maintain thermal steady state and to minimize the labor content of the process. Web solar cell efficiencies of 17.2% AM1 have been obtained in the laboratory while 15% efficiencies are common in pilot production.

Analysis of plastic deformation in silicon web crystals

Abstract Numerical calculation of {111}〈110〉 slip activity in silicon web crystals generated by thermal stresses is in good agreement with etch pit patterns and X-ray topographic data. The data suggest that stress redistribution effects are small and that a model, similar to that proposed by Penning and Jordan but modified to account for dislocation annihilation and egress, can be used to describe plastic flow effects during silicon web growth.

Advances in silicon carbide (SiC) device processing and substrate fabrication for high power microwave and high temperature electronics

High-power density, temperature tolerant silicon carbide (SiC) electronics offer an exceptional opportunity to increase the performance and lower the cost of many existing and emerging military and commercial products. Surveillance and tactical radar systems, compact electric tank and aircraft engine controls, high reliability aviation electronics, and radiation resistance satellite components are some examples. Recent technology advances have brought this potential payoff closer to reality. These include the fabrication of a record-setting MESFET device with 12 dB gain at 2 GHz and 2 W/mm of power at 1 GHz and the worlds first 2-inch diameter high-resistivity SiC wafers for planar devices and low resistivity substrates for power devices. Vertical transistor structures have also been fabricated using both Schottky barrier and MOS gates.<<ETX>>

CVD Diamond Coatings for the Infrared by Optical Brazing

Abstract Protective coatings of chemical vapor-deposited (CVD) diamond have been thermally bonded to soft infrared-transmitting optical windows of ZnSe and ZnS with chalcogenide glasses by the “optical brazing” process1. The diamond coatings were deposited on silicon by a microwave-excited plasma process, and transferred to the infrared optics. The silicon was subsequently removed, exposing the smooth nucleation surface. This approach to coating optical components accomplishes several purposes at once. The infrared optical components components are not subjected to the high temperature, reactive environment in which CVD diamond is deposited. Also, the rough diamond growth surface does not need to be polished because it is concealed in the chalcogenide bonding glass whose refractive index is made to closely match that of diamond. Measurements of reflectance and transmittance with a scanning infrared spectrophotometer confirmed that scatterering losses were greatly reduced, and were too small over most of the infrared spectrum to be detected by this technique. Windows as large as 3.8 cm have been diamond-coated by the optical brazing technique, and larger sizes are under development.