A new method for growing epitaxial films on foreign substrates − Bent epitaxy

In recent years, to mitigate the effects of climate change, countries’ transition to the green economy has accelerated, and thereby, the demand of semiconductor industry for wide-gap semiconductors such as SiC and GaN has increased dramatically. These semiconductors are expensive. To reduce the price of the final product, industrial production of thin epitaxial films of sought-after semiconductors on accessible and cheap substrates, such as Si and sapphire, is being developed. When growing epitaxial films on foreign substrates, the resulting heterostructure bends, becomes concave or convex, due to a mismatch between the coefficients of thermal expansion (CTE) of the substrate and the epitaxial film. As a result, the quality of the epitaxial film deteriorates and further processing of the resulting heterostructures in production lines becomes difficult or even impossible. The essence of the proposed new method is that the epitaxial film is grown not on a flat, but on a pre-curved substrate with the expectation that after cooling the fabricated heterostructure to room temperature, the heterostructure will take a flat shape due to the difference in the CTE of the epitaxial film and the substrate. A round bimetallic plate, located under the substrate, bends the substrate in the required direction to the desired value at the growth temperature, and gradually reduces the bend of the fabricated heterostructure during cooling, in proportion to the thermal contraction of the epitaxial film. This allows obtaining qualitative and flat epitaxial films, regardless of the material of the substrate or epitaxial film and the diameter of the substrate or thickness of the epitaxial film, without any buffer layers or carrying out any additional operations and costs.