Influence Of Strain On Group-Ⅳ Nanomembranes

For the group-Ⅵ nanomembranes materials, the light weight, high integration, low prices, mature manufacturing make it suitable for industrial and commercial productions. Moreover, we have a great sense of anticipation that the group-Ⅵ semiconductor monocrystalline nanomembranes integration into device and potential application could lessen the ardent challenges designers face. Especially, with the thickness less than 300 nm the membranes causing lots of new mechanical properties, that is unprecedented never seen before. Moreover, because the thickness is very thin, unbalanced stress is produced, and the strain release can create band offset in group-Ⅵ semiconductor hetero-structures, then to change the carrier mobility and the membranes material characteristics. Strain-engineered silicon nanomembrane has significant technological value,because the ultra-compliant monocrystalline group-Ⅵsemiconductor substrates has developed into a new platform for device integration and rapidly expanding the frontier in nanoscience and technology.Especially, based on the experimental results achieving, show the growth of Ge Quantum Dots on freestanding Silicon nanoribbon portrays the formation of anti-correlated pyramid-shaped nanocrystals（hut, QDs） strained on the two sides of the ribbons. In the dissertation, the questions that need to be addressed are, i. how is strain distributed on the freestanding Silicon nanoribbon. ii. what causes the anti-correlated ordering. And iii. what is the range of the largest ordering growth. This dissertation seeks to present the theory that strain effect is the driving force of this anti-correlation. Firstly, using the finite element method calculate the nanomembrane strain distributed. Then level set method and simulation results by the Finite element, statistics compiled quantum dots biggest orderly growth range related to the film thickness and growth rate. One theoretical calculation will help obtain the result by factors affecting the anti-symmetric growth.The main results are as follows:1. When the anti-correlation Ge QDs grown on two sides of the freestanding Si nanomembranes, quantum dots and the membranes inside emerge the uneven stress, and membrane surface stress reaches a maximum beneath the quantum dot; strain change with a corresponding membrane thickness variation.2. When these quantum dots on the both of nanomembranes were anti-correlated, the strain energy reaches a minimum value, in line with the principle of minimum energy.3. Discusses the strain is related to the thickness of thin film. With the increase of film thickness, film and the link between the two interfaces are getting smaller, symmetry and order of materials of epitaxial growth will be lower.4. Level set method is applied to calculate the nucleation rate and growth on the quantum dots. Analysis nucleation mechanism of the island by the dynamic formation process island. Then, calculate the 2 D model of the quantum dot epitaxial growth by the different growth way. Finally, make the 3D verification corresponding with 2 D growth model.5. Calculate the maximum range of highly orderly quantum dots in the best nucleation position of the quantum dot growth. For a uniformly grown surface, anti-correlated domain size is proportional to （?）(n_start is the nucleation density).6. Calculate the composition profiles of alloy quantum dots by MC and Finite element. In the different modes, the influence of substrate on plase separated. Finally, calculate phase separation critical value of miscibility gap surface diffusion depth（SDD） on the quantum dots and nanowires.