Nanostructures and optical properties of self-assembled Ge quantum dots grown in a hot wall UHV/CVD system

Self-assembled Ge quantum dots (QDs) grown in a commercial ultra-high-vacuum chemical vapor deposition (UHV/CVD) reactor were demonstrated in this work. The Ge QD morphology, size distribution and uniformity depend on the amount of Ge flux, growth temperature and deposition rate. With precise control of deposition rate, a layer by layer growth or island formation can be achieved at 550°C. At this growth temperature, the 6.8 eq-ML Ge hut cluster has a density of ∼1×10¹¹ cm^-2 with a broadening distribution. With increasing the growth temperature to 600°C, the uniformity of Ge QDs distribution is improved, but its density decreases to 4×10⁹∼1.1×10¹⁰ cm^-2(at 12 eq-ML Ge QDs, we found that the mean size of dome-shaped QDs is ∼45 nm). Optical transition from Ge QDs with a Si cap was also analyzed from photoluminescence spectra. With a growth interrupt before Ge deposition at 600°C, the size uniformity and density of QDs could be further improved. Partial hydrogen-coverage in the front of epitaxial growth would be responsible for these homogeneous Ge QDs grown at 600°C in this isothermal reactor.