Theoretical And Experimental Research On Axial Double Heterostructure Nanowires

The research work is mainly supported by the grants from the National Basic Research Program of China (No.2010CB327600), the National Natural Science Foundation of China (No.61020106007and61077049), the111Program of China (No. B07005), and BUPT Excellent Ph.D. Students Foundation (No. CX201213).Compared with single heterostructure, double heterostructure nanowire has the obvious superiority to achieve high-performance optoelectronic device due to stronger carrier confinement. However, theoretical study on the critical dimensions of double heterostructure nanowires has not been reported to date. In addition, Experimental verification of theoretical predictions has been somewhat lacking, largely due to the arduous nature of investigations requiring the imaging of interface dislocations across a full range of nanowire radius, layer thickness and lattice mismatches. In this thesis, a great deal of work is demonstrated about theoretical and experimental research on axial double heterostructure nanowires. The main achievements are listed as follows:1. The stress and strain distributions of axial double heterostructure nanowires with different mediumlayer thickness are calculated by elastic mechanics model of low dimensional semiconductor material. It indicates that whether the stress of mediumlayer is released depends on the values of height and radius. When the stress in mediumlayer is not released completely, the interaction of the stress fields generated at two heterointerfaces must be considered.2. Critical dimensions for an axial double heterostructure nanowire are studied by using finite-element method based on the energy equilibrium criteria. Results show that the dislocations incline to emerge at higher interface when the lattice misfit is less than0.72%, while at lower interface when exceeds0.72%. Two critical radiuses are obtained: One is called dislocation-free critical radius, below which the structure is coherent regardless of the thickness. The other is named dislocation-unavoidable critical radius, above which dislocations are always energetically favored. The area between the two critical dimensions is the dislocation controllable region, in which double heterostucture nanowires can grow coherently by controlling the nanowire radius. The simulated results are in good agreement with the experimental data.3. Au-assistant GaAs/InxGa1-xAs/GaAs (x=0.15) double heterostructure NWs on GaAs (111) substrate are grown by using Low-Pressure Metalorganic Chemical Vapor Deposition (LP-MOCVD). The samples selected with different radius are tested by TEM. The results show that when the radius of nanowires is less than the critical radius, the heterointerfaces are almost coherent.