Structural investigation and lateral growth of silicon carbide crystals

Abstract: Today, most of the electronic device technology is based on Si as a semiconducting material. The demands from the industry of improved performance within smaller devices drives the silicon based devices to the limits imposed by nature and not by technology. To realize these demands new materials like silicon carbide (SiC) must be investigated. SiC is a 'wide bandgap' semiconductor material with several material properties far superior to Si. Unfortunatey, the material struggles with problems like structural defects within the material, which often have an adverse effect on device performance. A further need to investigate and understand the identity, properties and origin of these defects are crucial for realizing SiC devices in the future.For most applications the defect distribution in the material is an important parameter which will affect the performance of the final device. It is of crucial importance to know how the substrate dislocations evolve in respect to grown epilayers. In paper 1 4H-SiC commercial wafers and thick sublimation grown epitaxial layers have been studied concerning crystalline structure.One of the proposed main application for large area SiC devices is in high power systems such as voltage source converters in motors or HVDC transmission systems, where the stability during long term operation is critical. However, the electrical performance of some devices has been found to degrade during forward 2 current operation. The electrical degradation is a critical material problem for high power applications. In paper 2 the reason for this has been identified as generated stacking faults. In paper 3 a detailed study on the identity, properties and origins of different stacking faults causing degradation in 4H-SiC PiN diodes are presented.Large seeds with low defect density are important for bulk growth of SiC. At present, several kinds of crystallographic imperfections exist in SiC crystals. In paper 4 a new growth technique for lateral enlargement of SiC crystals is presented and evaluated.Liquid phase epitaxy (LPE) layers has been reported to reduce the micropipe density. In paper 5 the objective of the work was to study the structural impact in sublimation grown 4H-SiC epilayers in respect to nucleation on LPE buffer layers. A study of how the material is influenced by high doping is of major importance for understanding formation of misfit dislocations. In paper 6 stress in epitaxial layers due to N doping is investigated. A theoretical model for calculating the induced lattice compression and the critical thickness concerning formation of misfit dislocations in 4H-SiC layers with different N doping levels is presented.