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This dissertation, A Study of Gate Dielectrics for Wide-bandgap Semiconductors: GaN & SiC by Limin, Lin, 林立旻, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled A study of gate dielectrics for wide-bandgap semiconductors: A study of gate dielectrics for wide-bandgap semiconductors: G Ga aN N & & S SiiC C submitted by Lin Li Min Lin Li Min for the degree of Doctor of Philosophy at The University of Hong Kong in August 2007 Wide-bandgap semiconducting materials have many advantages over Si and are suitable for high-temperature and high-power applications. Dielectric quality is the most critical factor that affects the performance of MISFETs/MOSFETs. Unlike silicon, most wide-bandgap materials do not have high-quality thermally-grown oxide. In this thesis, the main work is focused on developing high-quality dielectrics for two wide-bandgap semiconductors: GaN and SiC. The electrical performance of the oxide formed with oxidation and annealing o o temperatures ranging from 750 C to 850 C is studied. The sample oxidized and annealed at 850 C has the best interface quality, but also rough surface morphology and high leakage. The samples oxidized at below 850 C have nitrogen atoms detected, which actually form a GaO N layer due to incomplete oxidation of GaN. x y The sample processed at 800 C has the smoothest surface morphology, best C-V curve and lowest leakage current, making it an optimal temperature for the growth of Ga O . 2 3 i Ga O can achieve low interface-trap density with GaN, but it is a leaky 2 3 dielectric. In order to suppress the leakage, a SiO /GaO N stack dielectric is 2 x y proposed. GaO N interlayer is thermally formed at 800 C. All the samples with or x y without interlayer are annealed in nitrogen or nitric oxide gas (NO) respectively. Inter-diffusion between the SiO layer and the GaN or GaO N layer introduces 2 x y + + positive Si or Ga ions, but these charges can be suppressed through NO annealing effectively. With preformed GaO N interlayer, the inter-diffusion under NO x y annealing ambient can be suppressed and thus leakage is reduced. The increase of leakage by adding GaO N layer can be minimized by increasing the thickness ratio x y of SiO to GaO N . 2 x y For SiC, the growth of SiO is much slower than that for Si and the existence of carbon atoms makes the SiO /SiC interface less satisfactory than the SiO /Si 2 2 interface. Trichloroethylene (TCE) oxidation is proposed for SiC to increase the oxidation rate, and also improve the dielectric quality. The increase of oxidation rate is calculated to be between 2.7% and 67 % for TCE ratios of 0.001 0.2 and temperatures of 1000 1150 C. At a TCE ratio of 0.05, a turnaround behavior is observed for the interface-trap density, oxide-charge density and flatband voltage. The TCE oxidation can also reduce the oxide damage induced by high-field stress. Based on the results of SiC MOS capacitor, nMOSFET is fabricated for SiC by using the TCE oxidation for the first time. Field-effect mobility, threshold voltage and sub- threshold slope are improved by the TCE oxidation due to gettering of impurities and removal of physical defects inside the oxide. ii Hf Ti O and Hf Ti ON are used as the high-k gate dielectrics for SiC for the x 1-x 2 x 1-x first time because adding titanium into hafnium-based oxide or oxynitride can enhance the dielectric constants and thereby reduce their electric field. For Hf Ti x 1- ON, the incorporation of nitrogen into the oxide not

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