Gaas Nanowires As Elementary Structures In Microsystems:Growth And Their Characteristics

The research in this doctoral thesis is supported by several grants as listed below. The National Basic Research Program of China (973Programs, Grant No:2010CB327600):"Compatible Heterogeneous Integration and Functional Microstructure Assemblage for the Development of Novel Optoelectronic Devices"、The National Natural Science Foundation of China (Grant No:61020106007and61376019).Ⅲ-Ⅴ semiconductor nanowires have attracted more attention in recent years due to their possibility to building blocks of the nanoelectronic and nanophotonic devices. In the past few years, group-Ⅲ-Ⅴ semiconductor nanowires have been synthesized by several different methods. Gallium arsenide nanowires (GaAs NWs) are one of the most important candidates for nanodevices. In this thesis, we investigated synthesize and characteristic of GaAs NWs in both experiment and theory. The mainly purpose of this research are fabricating GaAs nanowires and their heterostructures, understanding the micromechanism of GaAs nanowires. The main results of our research are listed as follows:1、We have investigated the catalyst-free selective-area growth of GaAs and GaAs/InxGa1-xAs/GaAs (0<x<1) radial heterostructure nanowires on GaAs(111)B substrate by MOCVD. Our results show that the selective-area growth of GaAs nanowires is strongly dependent on growth conditions such as growth temperature and the pressure of AsH3. GaAs nanowires length would become longer when reducing the mask opening size. Thus we can form the GaAs nanowires uniform arrays with appropriate length and width by control growth conditions and mask opening size. Then photoluminescence of GaAs/InxGa1-xAs/GaAs (0<x<1) core-shell nanowires was carried out. 2、We have investigated the preadsorption of gallium on GaAs(111)B surface during the self-catalyst growth of GaAs NWs by first-principles calculations. The result shows that the Ga adatoms dislike to incorporate into the GaAs(111)B surface. We found that the Ga adatoms stable on GaAs(111)B surface only at low coverages. These Ga adatoms have a tendency to form Ga droplets when the Ga coverage increased continuously. The micromechanism of Ga droplets formed on GaAs(111)B surface also have been revealed. And the As atoms prefer to adsorb on GaAs(111)B surface associated with the numbers of Ga adatoms increased. The Ga droplets can be used as collector of As atoms due to the As adatom can stabilize the GaAs(111)B surface with Ga preadsorption. Our results are useful to understand the self-catalyst growth of GaAs nanowires.3、We have investigated the effect of surface dangling bonds and molecular passivation on the doping of GaAs nanowires by the first-principles density functional calculations. Our results show that the positively charged surface dangling bonds on Ga atom is the most stable defect for both ultrathin and large size GaAs nanowires. It could formed the trap centers of holes and then prefer to capture the holes from p-type doping. Thus it could obviously reduce the efficiency of the p-type doping. Then we found that the NO2molecule is electronegative enough to capture the unpaired electrons of surface dangling bonds when it adsorbed at it. It can be used as the passivation material of the Zn-doped GaAs nanowires.4、We considered several different surface adsorption species to investigated the the band gap modification of GaAs nanowires. It is found that the band gap of GaAs nanowires can be tailoring by the surface passivating species. This phenomenon originated from the charge compesation between passivation atoms and surface atoms. Thus, the band gap of GaAs nanowires can be modified by both diameter and surface preparation. We can tailor the band structure of GaAs nanowires by choosing different passivation materials.