| Summary: | 博士 === 國立中央大學 === 電機工程學系 === 103 === This thesis demonstrates a novel migration phenomenon of Ge quantum dot (QD), which catalytically enhances the local oxidation of underlying silicon-containing layers during the planar oxidation of poly-Si1-xGex/Si3N4 heterostructures over the Si substrate. The internal structure, crystal morphology, and chemical composition of Ge QDs formed in this manner are systematically investigated, and consequently a two-step mechanism has been proposed to explain the unique migration behavior of Ge QDs in Si-containing layers. First, the Ge QD enhances the decomposition of Si-containing layers to release Si interstitials. Subsequently, released Si interstitials diffuse through the Ge QD or its surface and eventually get oxidized beyond the Ge QD, leading to the movement of Ge QD. Accordingly, the size, morphology, and spatial distribution of the Ge QDs are significantly influenced by the oxidation conditions and the underlying silicon-containing layers. Temperature- and power-dependent photoluminescence (PL) analysis suggested that the PL emission on the visible wavelength of Ge QDs embedded in SiO2/Si3N4 matrices is a consequence of exciton recombination of Ge QDs thanks to combined effects of strain and quantum confinement.
Based on this approach, this thesis further proposes a simple and controllable growth method for placing dense 3D Ge QD arrays in a uniform or a graded distribution by thermally oxidizing stacked poly-SiGe/Si3N4 in a layer-cake technique. Moreover, Ge-QD metal-oxide-semiconductor (MOS) photodetectors were fabricated and featured low dark current density (1.5×10-3 mA/cm2), superior photo-current-to-dark-current ratio (13 500), high photoresponsivity (2.2 A/W), and fast response time (5 ns), showing a great promise for direct integration with prevailing Si complementary metal-oxide-semiconductor (CMOS) electronic circuits. It is also worth to point out that the photo-current-to-dark-current ratio exhibits a strong dependence on the volume of Ge QD in the gate dielectrics and effective gate dielectric thickness.
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