Single Crystal SiGe/Sapphire Epitaxy

Several of the patented methods included in this suite of technologies enable super-hetero-epitaxy of rhombohedral/cubic compound semiconductors on specially oriented trigonal (e.g. sapphire) or hexagonal (e.g. quartz) crystal wafer substrates. This includes alignment of the growth crystal lattice with the underlying substrate lattice to minimize misfit strain-induced dislocation defects in the growing crystal. Thus thicker, defect-free crystal layers can be made. Rhombohedral/Cubic crystal twin defects which is 60 degree rotated on [111] orientation in a rhombohedral/cubic SiGe layer structure can be reduced to well less than 1% by volume, essentially providing a defect-free semiconductor material. Alternately, engineered lattice structures with a high degree of twinning can provide SiGe with improved thermoelectric properties due to the phonon scattering that inhibits thermal conduction without compromising electrical conductivity. Additional patented technologies in this suite provide for physical vapor deposition (PVD) growth methods utilizing molten sputtering targets and thermal control of heated substrates, including electron beam heating, in order to give the atoms in the sputtered vapor or on the substrate surface the energy needed for the desired crystal growth. The remaining patented technologies enable x-ray diffraction methods for detecting and mapping crystal twin defects across the entire as-grown semiconductor layer. These defects are critical to the performance of any semiconductor device manufactured from such compound semiconductor materials.

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.

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.

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.

Additive manufacturing or 3-D printing is a rapidly growing field where solid, objects can be produced layer by layer. This technology will have a significant impact in many areas including industrial manufacturing, medical, architecture, aerospace, and automotive. The advantages of additive manufacturing are reduction in material costs due to near net shape part builds, minimal machining required, computer assisted builds for rapid prototyping, and mass production capability. Traditional thermal nondestructive evaluation (NDE) techniques typically use a stationary heat source such as flash or quartz lamp heating to induce a temperature rise. The defects such as cracks, delamination damage, or voids block the heat flow and therefore cause a change in the transient heat flow response. There are drawbacks to these methods.