The long-standing problem of growing a commensurate crystalline oxide interface with silicon has been solved. Alkaline earth and perovskite oxides can be grown in perfect registry on the (001) face of silicon, totally avoiding the amorphous silica phase that ordinarily forms when silicon is exposed to an oxygen containing environment. The physics of the heteroepitaxy lies in establishing a sequenced transition that uniquely addresses the thermodynamics of a layer-by-layer energy minimization at the interface. A metal-oxide-semiconductor capacitor using SrTiO 3 as an alternative to SiO 2 yields the extraordinary result of t eq , 10 Å. [S0031-9007(98)07238-X] PACS numbers: 81.15. Hi, 73.40.Qv, 77.55. + f Since the advent of the integrated circuit in 1959 and the introduction of metal-oxide-semiconductor (MOS) capacitors in the early 1960s, electronic technology has relied on silica ͑SiO 2 ͒ as the gate dielectric in a field effect transistor. However, silica-based transistor technology is approaching fundamental limits. Feature-size reduction and the ever-demanding technology roadmaps have imposed scaling constraints on gate oxide thickness to the point where excessive tunneling currents make transistor design untenable; an alternative gate dielectric is needed [1].While now it is especially clear, with SiO 2 thicknesses in the sub-50-Å regime, the argument for alternative gate oxides is not new; it has been made from different perspectives for over 40 years [2][3][4][5]. Quite aside from the "physical" thickness limits that tunneling currents make obvious, the amorphous SiO 2 interface with silicon leaves dangling bonds as electronic defects disrupting translational symmetry at the interface. An alternative crystalline gate oxide would, in principle at least, uniquely maintain a one-to-one correspondence between physical and electrical structure preserving translational symmetry to atomic dimensions.Crystalline oxides on silicon (COS), simply by virtue of their high dielectric constants, could fundamentally change the scaling laws for silicon-based transistor technology. More importantly COS introduces the possibility for an entirely new device physics based on utilization of the anisotropic response of crystalline oxides grown commensurately on a semiconductor. In this Letter, we report that high dielectric constant alkaline earth and perovskite oxides can be grown in perfect registry with silicon. Commensurate heteroepitaxy between the semiconductor and the oxide is established via a sequenced transition that uniquely addresses the thermodynamics of a layer-by-layer energy minimization at the interface. The perfection of the physical structure couples directly to the electrical structure, and we thus obtain the unparalleled result of an equivalent oxide thickness of less than 10 Å in a MOS capacitor.An equivalent oxide thickness t eq can be defined for a MOS capacitor asin which´S iO 2 and´0 are the dielectric constants of silica and the permittivity of free space. ͑C͞A͒ ox is the specific capacitance of the...
We show that the physical and electrical structure and hence the inversion charge for crystalline oxides on semiconductors can be understood and systematically manipulated at the atomic level. Heterojunction band offset and alignment are adjusted by atomic-level structural and chemical changes, resulting in the demonstration of an electrical interface between a polar oxide and a semiconductor free of interface charge. In a broader sense, we take the metal oxide semiconductor device to a new and prominent position in the solid-state electronics timeline. It can now be extensively developed using an entirely new physical system: the crystalline oxides-on-semiconductors interface.
Thin-film epitaxial structures of BaSi2, BaO, and BaTiO3, have been grown on the (001) face of silicon using ultrahigh vacuum, molecular beam epitaxy (MBE) methods. Source shuttering for the metal species coordinated with a pulsed, or cyclic, oxygen arrival at the growing oxide surfaces significantly improves film quality. The epitaxial growth of BaO is accomplished without silica formation at the BaO/Si interface by stabilizing BaSi2 as a submonolayer template structure. In situ ellipsometric measurements of the indices of refraction for BaO and for BaTiO3 in a BaTiO3/BaO/Si multilayer gave n=1.96 for BaO and n=2.2 for the BaTiO3, within 10% of their bulk values. These values suggest that this structure can be developed as an optical waveguide. BaO is impermeable to silicon for films as thin as 10 nm at temperatures as high as 800 °C, and good epitaxy can be obtained from room temperature to 800 °C. The epitaxy is such that BaTiO3(001)∥BaO(001)∥Si(001) and BaTiO 3〈110〉∥BaO〈100〉∥Si〈100〉.
The barrier height for electron exchange at a dielectric-semiconductor interface has long been interpreted in terms of Schottky's theory with modifications from gap states induced in the semiconductor by the bulk termination. Rather, we show with the structure specifics of heteroepitaxy that the electrostatic boundary conditions can be set in a distinct interface phase that acts as a "Coulomb buffer." This Coulomb buffer is tunable and will functionalize the barrier-height concept itself.
Effect of interface defect formation on carrier diffusion and luminescence in In0.2Ga0.8As/Al x Ga1−x As quantum wells
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