1. Technical Field of the Invention
The present invention generally relates to the technical field of materials science, more specifically, it relates to the field of compound semiconductors, still more particularly to compound semiconductors with specific physical and chemical properties, and uses resulting from microgravity environment processing and methods of production.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
The following description of the art related to the present invention refers to a number of publications and other references. Discussion of such references herein is given to provide a more complete background of the principles related to the present invention and is not to be construed as an admission that such references are necessarily prior art for patentability determination purposes.
The invention described and claimed in the present application comprises the innovative combination of at least two technological areas: (1) the creation and management of microgravity environments; and (2) annealing, growth and processing of compound semiconductor materials. Combining those two areas as disclosed and claimed in this application results in the production of a compound semiconductor that has unique molecular structure resulting in physical characteristics not attainable using conventional production methods.
It is well-known and well-understood that gravity affects the structure of a material lattice in two distinct ways: (1) directly through deformation that it imposes on the lattice during formation; and (2) indirectly through convection which induces mixing of the material as a function of the mass of each element. NASA, ESA and other space agencies have sponsored numerous experiments that have shown that production of materials in microgravity suppresses the creation of inclusions, dislocations, and other defects.
In 1998, European researchers conducted a microgravity experiment on a sounding rocket to investigate the structure of SiC layers grown at microgravity conditions and to compare the microgravity results with SiC layers grown using an identical system on the ground. The researchers used Liquid Phase Epitaxy (LPE) to grow the SiC layers and introduced scandium into the silicon melt to increase the solubility of the carbon. A 4H polytype was grown on a 4H seed and a 6H polytype was grown on a 6H seed to determine the differing effect of microgravity on the polytype of SiC. The effect of adding scandium to the melt was to increase the solubility of Carbon in the melt resulting in growth rates increasing from a few μm per hour to as high as 350 μm per hour.
The sounding rocket spent 6 minutes in a microgravity environment (around 5×10−6 g) and they were able to grow 20 μm of SiC during that time. Control samples grown on-ground have a similar surface appearance to the microgravity grown samples but contain scandium carbide precipitates, nanopipes, micropipes and/or cavities as verified by TEM. However, none of the those defects were found in the sample grown in microgravity. So, they concluded that samples grown “in space microgravity conditions are superior in their defect structure to those ones grown on the ground.”
As previously, microgravity provides an environment that allows atoms in the material to arrange into their preferred, lowest energy state, free of irregularities and defects. The problem with the 1998 experiment described herein above was that the material had been doped with scandium to increase the solubility of the carbon. While this is a common process used on Earth to speed the growth of SiC layers it did add a new material to the structure of the resulting lattice. Scandium doesn't affect the electrical properties of the resulting SiC layers but the impact to the physical structure is not known, especially during formation in microgravity.
Additional research and experimentation is necessary to determine if silicon carbide grown in a microgravity environment without added Scandium would also be defect free. Further, since gravity is a physical effect on the lattice structure and formation, each dopant added to the silicon carbide melt has to be analyzed for its effect on the resulting structure during growth in microgravity. Therefore, the fact that researchers were able to grow defect-free silicon carbide with added scandium does not demonstrate that all silicon carbide produced in microgravity would be defect free.
The initial research conducted as a result of the 1998 experiment was useful, but it was far from teaching or suggesting methods to enable a person of ordinary skill in the art to develop our claimed invention without additional detailed research and experimentation.