Effect of deposition rate on the characteristics of Ge quantum dots on Si (001) substrates

We have studied the effect of the deposition rate on the structural and optical characteristics of five-layer-stacked Ge self-assembled quantum dots (QDs) on a Si (001) substrate grown by molecular beam epitaxy. Ge QDs were formed using a pulse growth technique, which consists of high-rate Ge deposition and an interruption in growth. In this work, the deposition rate was varied from 1.1 Å/s to 2.8 Å/s. Pyramid-shaped QDs with a monomodal size distribution were obtained at 2.8 Å/s, while a bimodal size distribution including pyramid-shaped QDs and multifaceted dome-shaped QDs was observed between 1.1 Å/s and 2.2 Å/s. As a result, an improved size fluctuation of 11.1% and highest sheet density of 5.6 × 1010 cm− 2 were achieved for the QD sample grown at 2.8 Å/s. As for the optical characteristics, a single photoluminescence (PL) emission line at 0.825 eV with a width of 86.1 meV was observed at 12 K. Furthermore, we found that the PL emission from the Ge QDs shows type-II emission characteristics, i.e., the shift of the PL peak energy with respect to the PL excitation power (Pexc) was proportional to Pexc1/3.