Epitaxy of SiGe and Other Compound Semiconductors

III-nitride devices are commonly made on sapphire substrates today for various commercial electronic and optoelectronic applications. Thus, this innovation relates directly to the combination of devices on opposite sides of the sapphire substrate. One possible device combination is to have LEDs one side and solar cells on the other, such as for displays.

This innovation is based on a new fabrication method that alleviates the thermal loading requirement of the substrate, which previously required surface temperatures within the range of 850 to 900C. Our method employs a new thermal loading requirement of sapphire substrate for growing single crystal SiGe on sapphire substrate, in the range of 450 to 500C. SiGe/sapphire wafers produced via this process show a high reflectivity without the discoloration that appears in low quality films.

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.

Single Crystal SiGe semiconductors are viable via numerous advances patented by NASA. This includes the addition of a 1-2mm ring groove in the magnetron magnets which increases sputtering energy at 500C vs 800C, enabling thicker, faster deposition with better surface finish and consistent quality without heat soaking. The lack of thermal gradient removes inconsistencies in the product. SiGe can also utilize the CMOS manufacturing technique for additional cost savings and waste reduction. Further decreases to time investment for single crystal SiGe is made possible via reduced thermal load and soak temperatures, growing SiGe semiconductors on, conveniently, less expensive sapphire substrates. Crystal lattice matched growing methods to the sapphire substrate ensure defect-free SiGe production without interfacial dislocations. A graded indexed SiGe layer can be added to wafers grown in this lattice matched method, permitting thicker semiconductor growth without abrupt changes in strain build-up, carrier potential barrier, index of refraction change and bandgap at the interface. These advances provide improved semiconductor performance and quality with fewer defects in fabrication. The crystal alignment enables X-Ray diffraction identification of any defect location and density. It is also possible to also grow a Gallium Nitride or Indium Gallium Nitride layer on the opposite side of the Sapphire wafer, useful for solar capable LED display. A type II band-gap alignment of SiGe would result in highly efficient solar cells attaining 30% to 40% energy conversion efficiency. In addition to SiGe, the patented technology also covers these methodologies on tin-based or carbon-based semiconductors.

This technology is an integrated hybrid crystal LED display device that can emit red, green, and blue colors on one single wafer. Todays LEDs are built with many compound semiconductors with type-I direct bandgap energies of two different crystal structures. While Red, Orange, Yellow, Yellowish Green LEDs are commonly made with III-V semiconductor alloys of Aluminum Gallium Indium Phosphide (AlGaInP) and Aluminum Gallium Indium Arsenide (AlGaInAs) with cubic zinc blende crystal structures, the higher energy colors such as green, blue, purple, and Ultra-Violet(UV) LEDs are made with III-Nitride compound semiconductor of AlGaInN alloys with hexagonal wurtzite crystal structures. Because the atomic crystal structures are different for red LED and green/blue LEDs, the integration of these semiconductor LEDs as individual R, G, B pixels on one wafer was almost impossible or very difficult so far.