| abstract |
A semiconductor substrate includes a first material layer made of a first material and including a plurality of protrusions, and a second material layer made of a second material different from the first material, filling spaces between the plurality of protrusions, and covering the plurality of protrusions. Each of the protrusions includes a tip and a plurality of facets converging at the tip, and adjacent facets of adjacent protrusions are in contact with each other. |