| Summary: | 碩士 === 國立彰化師範大學 === 光電科技研究所 === 96 === It has been well known that the high mismatch in lattice constant andthemal expansion coefficients between Si and GaN causes cracks andhigh density of dislocations when GaN is grown on Si substrate. Thesedefects deteriorate GaN film characteristics. In this thesis, the effect ofdifferent buffer-layers on GaN epilayer characteristics was investigated.
In chapter one, properties of GaN-based compound materials are firstintroduced. In chapter two, the operation principles of several instruments used for experiments as well as GaN crystal growth related papers were reviewed. In chapter three, the effects of AlN buffer thickness, III/V ratio of AlN nucleation layer, GaN/AlN superlattice structure and low-growth-rate GaN buffer layer on GaN epilayer characteristics were investigated. Experimental result indicates that GaN crystalline quality is enhanced using thinner AlN buffer thickness owing to dislocation density between GaN/AlN interface is reduced. The XRD -scan at GaN(0002) peak and the RT-PL FWHM are 0.35o and 78 meV, respectively. Moreover, AlN/GaN superlattice and low growth rate GaN buffer layer can also be used to reduce the dislocation densities. However, the epitaxial growth condition still needs to be optimized.
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