The effect of the electrical field enhancement at the junction discontinuities and its impact on the on-state resistance of power semiconductor devices was investigated. A systematic analysis of the mechanisms behind the techniques that can be used for the edge termination in power semiconductor devices was performed. The influence of the passivation layer properties, such as effective interface charge and dielectric permittivity, on the devices with different edge terminations was analyzed using numerical simulation. A compact analytical expression for the optimal JTE dose was proposed for the first time. This expression has been numerically evaluated for different targeted values of the blocking voltage and the maximum electric field, always resulting in the optimal field distribution that does not require further optimization with 2-D device simulator. A compact set of rules for the optimal design of super-junction power devices was developed. Compact analytical expressions for the optimal dopings and dimensions of the devices employed the field compensation technique are derived and validated with the results of numerical simulations on practical device structures. A comparative experimental study of several approaches used for the edge termination in SiC power diodes and transistors was performed. The investigated techniques included the mesa termination, high-k termination, JTE, and the combination of JTE and field plate edge termination. The mesa edge termination was found to be the most promising among the techniques investigated in this work. This stand-along technique satisfied all the imposed requirements for the ?ideal? edge termination: performance, reproducibility (scalability), and cost-efficiency. First of all, it resulted in the maximum one-dimensional electric field (E1DMAX) at the main device junction equal to 2.4 MV/cm or 93% of the theoretical value of critical electric field in 4H-SiC. Secondly, the measured E1DMAX was found to be independent of the voltage blocking layer parameters that demonstrate the scalability of this technique. Lastly, the implementation of this technique does not require expensive fabrication steps, and along with an efficient use of the die area results in the low cost and high yield.

New halo-carbon precursor, CH3Cl, is used in this work to replace the traditional C3H8 gas as a carbon precursor for the homoepitaxial growth of 4H-SiC. The traditional SiH4-C3H8-H2 systems require high growth temperatures to enable the desirable steplow growth for high-quality epilayers. A well known problem of the regular-temperature growth is the homogeneous gas-phase nucleation caused by SiH4 decomposition. However, the degree of Si cluster formation in the gas phase and its influence on our low-temperature epitaxial growth was unknown prior to this work. Growth at temperatures below 1400°C was demonstrated previously only for a limited range of substrate surface orientations and with poor quality. Mirror-like epilayer surface without foreign polytype inclusions and with rare surface defects was demonstrated at temperatures down to 1280-1300°C for our halo-carbon growth. Quantitatively different growth-rate dependences on the carbon-precursor flow rate suggested different precursor decomposition kinetics and different surface reactions in CH3Cl and C3H8 systems. Photoluminescence measurement indicated the high quality of the epilayers grown at 1300°C. A mirror-like surface morphology with rare surface defects was demonstrated for the growth on low off-axis substrates at 1380°C. The most critical growth-rate limiting mechanism during the low-temperature epitaxial growth is the formation of Si clusters, which depleted the Si supply to the growth surface, in the gas phase. Presence of chlorine in the CH3Cl precursor significantly reduces but does not completely eliminate this problem. The addition of HCl during growths improved the growth rate and surface morphology drastically but also brought up some complex results, suggesting more complex mechanisms of HCl interaction with the gas-phase clusters. These complicated results were explained partly by an additional mechanism of precursor depletion enhanced in presence of HCl. Complex changes in the effective silicon to carbon ratio in the growth zone indicated that the supply of carbon species may also be enhanced at least at low HCl flow rates. This fact allowed us to suggest that the gas-phase clusters may contain a significant amount of carbon. The new model assuming coexistence of the silicon and carbon in the gas-phase clusters enabled the explanation of the complex experimental trends reported in this work.

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Intermetallic composites of molybdenum disilicide reinforced with various amounts of silicon carbide particulate were produced by combustion synthesis from their elemental powders. Elemental powders were mixed stoichiometrically then ball-milled. The cold- pressed mixture was then chemically ignited at one end under vacuum at approximately 700°C. The combustion temperature of the process was approximately 1600°C which was lower than the melting point of molybdenum disilicide. This processing technique allowed the fabrication of the composites at 700°C within a few seconds, instead of sintering at temperatures greater than 1200°C for many hours. The end product was a porous composite, which was densified to >97% of the theoretical density by hot pressing. The grains of the matrix were 8-14 μm in size surrounded by SiC reinforcement of 1-5 μm. The morphology and structure of the products were studied by x-ray diffraction and scanning electron microscopy (SEM). Samples were prepared for hardness, fracture strength, and toughness testing at room temperature. There were improvements in the mechanical properties of the composites with increasing SiC reinforcement. The hardness of the materials increased from 10.1 ± 0.1 GPa (959 ± 13 kg/mm2) to 11.7 ± 0.6 GPa (1102 ± 52 kg/mm2) to 12.7 ± 0.4 GPa (1199 ± 36 kg/mm2) with the 10 vol% and 20 vol% SiC reinforcement, respectively. The strength increased from 195±39 MPa to 237±39 MPa with 10 vol% and to 299 ± 43.2 MPa with a 20 vol% SiC reinforcement. The fracture toughness increased from 2.79 ± 0.36 MPa.m1/2 to 3.31± 0.41 MPa.m1/2 with 10 vol% SiC and to 4.08± 0.30 MPa.m1/2 with 20 vol% SiC. The increase in hardness and flexural strength is due to the effective load transfer across the strong interface in the composites. The main toughening mechanism is crack deflection by the residual stress in the materials, induced by the differences in the thermal expansion coefficients and the elastic moduli of the matrix and reinforcement. / Thesis / Master of Engineering (ME)