Vertical alignment control of self-ordered multilayered Ge nanodots on SiGe

Self-ordered multilayered Ge nanodots with SiGe spacers on a Si0.4Ge0.6 virtual substrate are fabricated using reduced-pressure chemical vapor deposition, and the mechanism of vertical ordering is investigated. The process conditions of Ge and SiGe layer deposition are H-2-GeH4 at 550 degrees C and H-2-SiH4-GeH4 at 500 degrees C-550 degrees C, respectively. By depositing the SiGe at 550 degrees C or increasing Ge content, the SiGe surface becomes smooth, resulting in vertically aligned Ge nanodots to reduce strain energy. Ge nanodots prefer to grow on the nanodot where the SiGe is relatively tensile strained due to the buried Ge nanodot underneath. By depositing at 500 degrees C and lowering Ge content, checkerboard-like surface forms, and the following Ge nanodots grow at staggered positions to reduce surface energy. The Ge nanodots are laterally aligned along the elastically soft 100 direction without pre-structuring resulting from the strain distribution.