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.

With the low-temperature halo-carbon epitaxial growth technique developed at MSU prior to this work, use of a halo-carbon growth precursor enabled low-temperature homoepitaxial process for 4H-SiC at temperatures below 1300 °C with good quality. Investigations of the nitrogen doping dependence are reported. It has been demonstrated that the efficiency of the nitrogen incorporation may be different for different substrate orientations, with the Cace showing the higher value of doping. The Si/C ratio is known to influence the doping during the epitaxial growth due to the site-competition mechanism. The doping on the Cace showed weak dependence on the Si/C ratio. On the Siace, the doping dependence follows the site-competition trend. At high Si/C ratio, the doping trend on Siace shows strong deviation. Both of the investigated trends are suggested for use as the main process dependencies for achieving a wide range of n type doping of SiC during the low-temperature halo-carbon homoepitaxial process.

Superior properties of Silicon Carbide (SiC), such as wide bandgap, high breakdown field and high thermal conductivity, have made it the frontrunner to replace Silicon for applications requiring high breakdown strength, mechanical and radiation hardness. Commercial SiC devices are already available, although their expected performance has not yet been realized due to a few problems related to device fabrication technologies, such as selective doping. This work explores non-traditional techniques for SiC doping (and selective doping in particular) based on previously unknown types of defect reactions in SiC and novel epitaxial growth techniques, which offer advantages over currently available technologies. Recent developments in SiC epitaxial growth techniques at MSU have enabled the growth of high quality SiC epitaxial layers at record low temperatures of 1,300°C. Lower growth temperatures have enabled highly doped epilayers for device applications. Prototypes of SiC PiN diodes fabricated, demonstrated low values of the series resistance associated with anodes grown by the low temperature epitaxial growth technique. At room temperature, 100 ìm-diameter diodes with a forward voltage of 3.75 V and 3.23V at 1,000 A/cm2 before and after annealing were achieved. The reverse breakdown voltage was more than 680 V on average, even without surface passivation or edge termination. Reduced growth temperatures also enabled the possibility of selective epitaxial growth (SEG) of SiC with traditional masks used in the SEG in Si technology. Previously, SEG of SiC was impossible without high temperature masks. Good quality, defect free, selectively grown 4H-SiC epilayers were obtained using SiO2 mask. Nitrogen doped selectively grown epilayers were also obtained, which were almost completely ohmic, indicating doping exceeding 1x1019 cm-3. Moreover, conductivity modulation via defect reactions in SiC has been reported as a part of this work for the first time. The approach is based on a new phenomenon in SiC, named Recombination Induced Passivation (RIP), which was observed when hydrogenated SiC epilayers were subjected to above bandgap optical excitation. Additional acceptor passivation, and thereby modification of the conductivity of the epilayer, was observed. Results of investigations of the RIP process are presented, and conductivity modulation techniques based on the RIP process are proposed.