Low-temperature formation of self-assembled Ge quantum dots on Si(100) under high carbon mediation via solid-phase epitaxy

CMOS-compatible low-temperature formation of self-assembled Ge quantum dots (QDs) by carbon (C) mediation via a solid-phase epitaxy (SPE) has been demonstrated. The samples were prepared by a solid-source molecular beam epitaxy (MBE) system. C and Ge were successively deposited on Si(100) at 200 °C and Ge/C/Si heterostructure was annealed in the MBE chamber. Sparse Volmer-Weber mode Ge dots without a wetting layer were formed for C coverage (θC) of 0.25 and 0.5 ML by lowering SPE temperature (TS) to 450 °C, but small and dense Stranski-Krastanov (SK)-mode Ge QDs with the wetting layer were obtained with increasing C coverage of 0.75 ML even at 450 °C. From the investigation of SPE temperature effect on Ge QD formation for θC of 0.75 ML, SK-mode Ge QDs of about 10 nm in diameter and of about 4.5×1011 cm−2 in density were formed at TS≥400 °C. The wetting layer of SK-mode QDs was almost constant 0.2-nm thick at TS≥450 °C. Measurements of chemical binding states of C in Ge QDs and at Ge/Si interface revealed that a large amount of C-Ge bonds were formed in the wetting layer for high C coverage, and the formation of C-Ge bonds, together with the formation of C-Si bonds, enabled the low-temperature formation of small and dense Ge QDs. These results suggest that the C-mediated solid-phase epitaxy is effective to form small and dense SK-mode QDs at low temperature.