Abstract
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 1.1Å/s to 2.8Å/s. Pyramid-shaped QDs with a monomodal size distribution were obtained at 2.8Å/s, while a bimodal size distribution including pyramid-shaped QDs and multifaceted dome-shaped QDs was observed between 1.1Å/s and 2.2Å/s. As a result, an improved size fluctuation of 11.1% and highest sheet density of 5.6×1010cm−2 were achieved for the QD sample grown at 2.8Å/s. As for the optical characteristics, a single photoluminescence (PL) emission line at 0.825eV with a width of 86.1meV was observed at 12K. 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.
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