Boron mediation on the growth of Ge quantum dots on Si (1 0 0) by ultra high vacuum chemical vapor deposition system

Self-assembled Ge quantum dots (QDs) with boron mediation are grown on Si (1 0 0) by an industrial hot wall ultra-high-vacuum chemical vapor deposition (UHV/CVD) system with different growth temperatures and dopant gas flow rates. Diborane (B₂H₆) gas is applied as a surfactant on the Si (1 0 0) prior to the growth of Ge QDs. Small dome and pyramid shaped Ge QDs are observed after boron treatment as compared to the hut shaped Ge cluster without boron pre-treatment at 525 and 550 °C. The Ge QDs have a typical base width and height of about 30 and 6nm, respectively, and the density is about 2.5 × 10¹⁰cm^-2 for the growth temperature of 525 °C. Through weakening the Si-H bond during the epitaxy growth and changing the stress field on the surface of the Si (1 0 0) buffer, boron mediation can modify the growth mode of Ge QDs. When the growth temperature is low (525-550 °C), the former factor is dominate, as the growth temperature is raised (600 °C), the latter parameter may play an important role on the formation of Ge QDs. Optical transition from Ge QDs is demonstrated from photoluminescence (PL) spectra. Furthermore, multifold Ge/Si layers are also carried out to enhance the PL intensity with first Ge layer treated by B₂H₆ and avoid the generation of threading dislocations.