A Study of the Nucleation and Formation of Multi-functional Nanostructures using GaN-Based Materials for Device Applications
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Self-organized GaN nanostructures have been accomplished with lattice-(mis)matched using MOCVD. A lattice mismatched system (i.e. GaN nanostructure/ AlN) was utilized with S-K mode mechanism, whereas, metallic droplet method (i.e. Vapor-Liquid-Solid method) was employed in the lattice matched system (i.e. GaN nanostructure / AlGaN). The nanostructure size is adjustable by changing growth parameters (height: 2 ~ 15nm and diameter: 10 ~ 100nm). It has been found that the photon emission energy is tunable relative to the nanostructure size, and smaller nanostructures have larger photon energy. However, a numerical modeling was performed to investigate the relationship between quantum confinement (and/or piezoelectric polarization) and the dot size. For dot height < 4.1nm, the confinement effect is larger than the piezoelectric effect, otherwise the piezoelectric effect is more dominant. In addition, GaN nanostructures grown on Al0.15Ga0.85N have smaller lattice mismatch (less than 0.5%) than the GaN nanostructures grown on AlN. Therefore, the quantum confinement in a GaN/Al0.15Ga0.85N system is more dominant in determining photon emission energy than in a GaN/AlN system. The nanostructure advantages of quantum confinement and high thermal stability have been studied for the achievement of room temperature ferromagnetism using TM (transition metal; Mn or Fe). The transition metal (Mn or Fe) enhances nucleation of islands, resulting in size and density improvements. The magnetization measurements revealed magnetic properties of ferromagnetic nanostructure. Especially, room temperature ferromagnetism was observed in GaFeN nanostructures, which can contribute to ferromagnetic semiconductors operating above room temperature.