Fabrication And Characterization Of Gan Grown On Cubic Si (100) And Gaas (001) Substrates
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Date
2015-09
Authors
Mohmad Zaini, Siti Nurul Waheeda
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Abstract
In general, this thesis presents the study of GaN layer grown on different cubic substrates. In the first part of this work, the properties of GaN film grown on (100)-oriented cubic Si substrate was investigated. Improvement in the properties of the GaN layer are observed by means of thermal annealing treatment. From the morphological, structural and optical measurements, the optimum annealing temperature was found to be around 800 ºC. Next, a photo-electrochemical etching technique was setup to fabricate a porous layer onto the GaN layer. The effect of thermal annealing at optimum annealing temperature is further studied on the properties of the porous GaN samples. The characteristics of the porous GaN were then investigated by observing its morphology, crystallography and optical properties. For comparison to the porous GaN, which was annealed prior to the etching (pre-annealed), another two porous GaN samples are also prepared, 1) without the annealing and 2) with the post-annealing. Based on the observations, it was found that the pre-annealing treatment results in a better formation of porous GaN while its crystalline quality is improved than its counterparts. Besides, from the optical point of view, the pre-annealed porous GaN still shows better luminescence properties among all. The outputs from the first part has been adopted in the second part of this work, which mainly focussed on investigating the presence of the hexagonal inclusions by detecting the evidence of stacking faults in the cubic GaN grown on (001)-oriented cubic GaAs substrate. Such faulty mechanism favored the growth of hexagonal phase materials, which in turn degrades the crystalline quality and purity of the cubic samples. The stacking faults and the hexagonal GaN inclusions increased as the thickness of the cubic GaN is
higher. It was found that the stacking faults disappeared in bulk cubic GaN sample (~50 μm) due to the annihilation factor and the percentage of hexagonal GaN was less than 22 %. However, the hexagonal inclusions was just few percent in the first ~10 μm layer of the cubic GaN. It appears to be a better surface for the subsequent cubic nitrides growth. Apart from that, it was revealed that the conductivity of cubic GaN samples varied with thickness as a result of different amount of hexagonal inclusions as well as defects and impurities level. Nonetheless, the electrical properties related to the Hall mobility and carrier concentration need to be improved to increase the performance of high power devices.
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Gan Grown