The Studies Of The Solid-Liquid Interfacial Properties And Influences During The Vapor-Liquid-Solid Semiconductor Nanowire Growth

The researches of this thesis are supported by grants from The National Basic Research Program of China(No:2010CB327600)(Professor Xiaomin Ren is the chief scientist of this program), the National Natural Science Foundation of China (Grant No:61020106007and No:61077049)、New Century Excellent Talents of China (Grant No: NCET-08-0736) and the111Program in University (Grant No:B07005).The fabrication of novel opto-electronic devices based on the semiconcutor nanowire comes to reality because of the high crystal quanlity and compatability of the nanowire heterostuctures. The development of the nanowire growth theory is helpful for the understanding of the abnormal crystal phases and the unique morphologies appearance during the nanowire growth, and is helpful to the controllable nanowire growth and the nanowire devices fabrication exquisiteness. The thesis concentrates on the influences of the solid-liquid interface properties, such as the nucleation mode, atom diffusion pathway and the liquid stability, on the vapor-liquid-solid mode nanowire growth.The details are as follows:1. In the framework of triple-phase-line nucleation theory, the accurate droplet surface area variation is calculated for different nucleation sites at the VLS nanowire growth front. The nucleation site selection rules are obtained for nanowires with irregular liquid-solid interface. The experimental testification is performed with the assistance of GaAs/InGaAs/InAs nanowire heterostructure. The nucleation site selection phenomenon is obvserved at the transition section and the growth front of the nanowire heterostructure. 2. The nucleation center number at the nanowire growth front is studied by the fitting of the diameter-length relation by nanowire growth rate function; the conditional probability of new nucleus formation after the nucleation event is calculated with classical nucleation theory. The results reveal that the single nucleation center growth mode is prevailing for the nanowire growth.3. The triple-phase contact line of the droplets with small liquid surface tension at the nanowire top facet edge defect is readily to slip down to wet the nanowire sidewall. The latent reason is explored from the simulation of the wetting behavior by molecular dynamics. The mechanical equilibrium conditions are constructed by introducing the notion of contact line static friction. The results well explain the pinning energy barrier reduction caused by the wetting layer effect.4. The simulation of the Au/GaAs nanopillar system annealing process is performed by ab initio molecular dynamics. The real-time atom movement trajectories, site exchanging and the dissolving behavior are studied by the comparison of four different nanopillar structures. The results reveal the diffusion properties of the growth species which have low solubility in the eutectic alloy catalyst.5. The diffusion pathways of the dopant atom which has low solubility in the eutectic alloy droplet acting as the catalyst of the semiconductor nanowire growth are studied both experimentally and theoretically. The diffisivity enhancement at the nanoscale considering the liquid phase influences is explored with different diffusion modes.