Investigation On The Stress And Strain Distribution Of Ge/Si Semiconductor Self-Organized Quantum Dots

The nanoscale semiconductor materials have promisingtechnological applications in semiconductor industry because of itsspecial effects. The quantum dots (QDs) formation in lattice mismatchedsystems by self-assembled method now has attracted much attention.Strain distribution is important to nucleation. During the growth ofquantum dots, QDs nucleation on substrate is orderless, its shape and sizeare hardly to control. So, the stress and strain distribution of QDs systemsmust be studied, in order to control the growth process in experiments.In this paper, the stress and stress distributions of pyramidal Ge/SiQDs with a certain volume and different aspect ratios are firstly analysed.The stress and strain distributions of the QD in equilibrium state are given,and the hydrostatic strain and biaxial strain are similar in QDs withdifferent aspect ratio is found.Secondly, the stress and strain distributions of buried QDs are calculated. Compared with QDs without cap, we found the maximumstress (strain) just below the pyramid's edge.Lastly the strain energy of QDs are calculated, and the strain energyof QDs system is reduced with the increasing aspect ratio for a givenvolume are found. The free energy consisting of the strain energy andsurface energy is defined, and used to study the equilibrium shapes of thesystems. The results show that in order to minimize the total free energy',the quantum dot of a certain volume will adopt a particularheight-to-width aspect ratio- equilibrium aspect ratio. QDs of differentvolume will have different equilibrium aspect ratio, which are increasedwith volume.These can serve as a basis for interpretation of experiments onself-assembled QDs.