High Mobility Transport Layer Structures for Rhombohedral Si/Ge/SiGe Devices

Performance of solar cells and other electronic devices such as transistors can be improved greatly if carrier mobility is increased. Si and Ge have Type-II bandgap alignment in cubically strained and relaxed layers. Quantum well and super lattice with Si, Ge, and SiGe have been good noble structures to build high electron mobility layer and high hole mobility layers. However, the atomic lattice constant of Ge is bigger than that of Si and direct epitaxial growth generates large density of misfit dislocations which decrease carrier mobility and shorten device life time. So it required special buffer layers such as super lattice or gradient indexed layers to grow Ge on Si wafers or Si on Ge wafers. The growth of these buffer layers takes extra effort and time such as post-annealing process to remove dislocations by dislocation gliding inside buffer layer. This invention is a fabrication method for high mobility layer structures of rhombohedrally aligned SiGe on a trigonal substrate. The invention utilizes C-plane (0001) Sapphire which has a triangle plane, and a Si (Ge) (C) (111) crystal or an alloy of group TV semiconductor (111) crystal grown on the Sapphire.