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By analyzing the temperature ͑T͒ and density ͑n͒ dependence of the measured conductivity ͑͒ of twodimensional ͑2D͒ electrons in the low-density ͑ϳ10 11 cm −2 ͒ and temperature ͑0.02-10 K͒ regimes of highmobility ͑1.0 and 1.5ϫ 10 4 cm 2 / Vs͒ Si metal-oxide-semiconductor field-effect transistors, we establish that the putative 2D metal-insulator transition is a density-inhomogeneity-driven percolation transition where the density-dependent conductivity vanishes as ͑n͒ ϰ ͑n − n p ͒ p , with the exponent p ϳ 1.2 being consistent with a percolation transition. The "metallic" behavior of ͑T͒ for n Ͼ n p is shown to be well described by a semiclassical Boltzmann theory, and we observe the standard weak localization-induced negative magnetoresistance behavior, as expected in a normal Fermi liquid, in the metallic phase.The so-called two-dimensional ͑2D͒ metal-insulator transition ͑MIT͒ has been a subject 1,2 of intense activity and considerable controversy ever since the pioneering experimental discovery 3 of the 2D MIT phenomenon in Si metaloxide-semiconductor field-effect transistors ͑MOSFETs͒ by Kravchenko and Pudalov some 15 years ago. The apparent MIT has now been observed in almost all existing 2D semiconductor structures, including Si MOSFETs, 3,4 electrons, 5-7 and holes [8][9][10][11] in GaAs/AlGaAs, and electrons in Si/SiGe ͑Refs. 12 and 13͒ systems. The basic phenomenon refers to the observation of a carrier density-induced qualitative change in the temperature dependence of the resistivity ͑n , T͒, where n c is a critical density separating an effective "metallic" phase ͑n Ͼ n c ͒ from an "insulating" phase ͑n Ͻ n c ͒, exhibiting d / dT Ͼ 0͑Ͻ0͒ behavior typical of a metal ͑insulator͒.The high-density metallic behavior ͑n Ͼ n c ͒ often manifests in a large ͑by 25% for electrons in GaAs/AlGaAs heterostructures to factors of 2-3 in Si MOSFETs͒ increase in resistivity with increasing temperature in the lowtemperature ͑0.05-5 K͒ regime where phonons should not play much of a role in resistive scattering. The insulating regime, at least for very low ͑n Ӷ n c ͒ densities and temperatures, seems to be the conventional activated transport regime of a strongly localized system. The 2D MIT phenomenon occurs in relatively high-mobility systems, although the mobility values range from 10 4 cm 2 / Vs ͑Si MOSFET͒ to 10 7 cm 2 / Vs͑GaAs/ AlGaAs͒ depending on the 2D system under consideration. The 2D MIT phenomenon is also considered to be a low-density phenomenon although, depending on the 2D system under consideration, the critical density n c differs by 2 orders of magnitude ͑n c ϳ 10 11 cm −2 in 2D Si and ϳ10 9 cm −2 in high-mobility GaAs/AlGaAs heterostructures͒. The universal features of the 2D MIT phenomenon are ͑1͒ the existence of a critical density n c distinguishing an effective high-density metallic ͑d / dT Ͼ 0 for n Ͼ n c ͒ phase from an effective low-density insulating ͑d / dT Ͻ 0 for n Ͻ n c ͒ phase, and ͑2͒ while the insulating phase for n Ͻ n c seems mostly to manifest the conventional activated transport be...

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We present measurements of silicon ͑Si͒ metal-oxide-semiconductor ͑MOS͒ nanostructures that are fabricated using a process that facilitates essentially arbitrary gate geometries. Stable Coulomb-blockade behavior showing single-period conductance oscillations that are consistent with a lithographically defined quantum dot is exhibited in several MOS quantum dots with an open-lateral quantum-dot geometry. Decreases in mobility and increases in charge defect densities ͑i.e., interface traps and fixed-oxide charge͒ are measured for critical process steps, and we correlate low disorder behavior with a quantitative defect density. This work provides quantitative guidance that has not been previously established about defect densities and their role in gated Si quantum dots. These devices make use of a double-layer gate stack in which many regions, including the critical gate oxide, were fabricated in a fully qualified complementary metal-oxide semiconductor facility.