The ability to integrate crystalline metal oxide dielectric barrier layers into silicon structures can open the way for a variety of novel applications which enhances the functionality and flexibility ranging from high‐K replacements in future MOS devices to oxide/silicon/oxide heterostructures for nanoelectronic application in quantum‐effect devices. We present results for crystalline gadolinium oxides on silicon in the cubic bixbyite structure grown by solid source molecular beam epitaxy. Additional oxygen supply during growth improves the dielectric properties significantly. Experimental results for Gd2O3‐based MOS capacitors grown under optimized conditions show that these layers are excellent candidates for application as very thin high‐K materials replacing SiO2 in future MOS devices. Epitaxial growth of lanthanide oxides on silicon without any interfacial layer has the advantage of enabling defined interfaces engineering. We will show that the electrical properties of epitaxial Gd2O3 thin films on Si substrates can further be improved significantly by an atomic control of interfacial structures. Finally, we will present a new approach for nanostructure formation which is based on solid‐phase epitaxy of the Si quantum‐well combined with simultaneous vapor‐phase epitaxy of the insulator on top of the quantum‐well. Ultra‐thin single‐crystalline Si buried in a single‐crystalline insulator matrix with sharp interfaces was obtained by this approach on Si(111). In addition, structures consisting of a single‐crystalline oxide layer with embedded Si nanoclusters for memory applications will also be demonstrated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The authors report on the impact of interface layer composition on electrical properties of epitaxial Gd2O3 thin films on Si(001) substrates. The electrical properties of epitaxial Gd2O3 thin films were improved significantly by controlled modification of interface layer composition. The minimum capacitance equivalent thickness estimated for Pt∕Gd2O3∕Si metal oxide semiconductor structures was as low as 0.76nm with leakage current density of 15mA∕cm2 at (Vg−VFB)=1V. The corresponding density of interface states was found to be 2.3×1012cm−2eV−1. The authors also find that a change in the interface layer composition significantly alters band alignment of Gd2O3 layer with respect to Si substrates.

Gd2O3 and Dy2O3 thin films were grown by atomic layer deposition (ALD) on Si(100) substrates using the homoleptic rare earth guanidinate based precursors, namely, tris(N,N'-diisopropy1-2-dimethylamido-guanidinato) gadolinium (III) [Gd(DPDMG)(3)] (1) and tris (N,N'-diisopropyl-2-dimethylamido-guanidinato)dysprosium (III) [Dy(DPDMG)(3)] (2), respectively. Both complexes are volatile and exhibit high reactivity and good thermal stability, which are ideal characteristics of a good ALD precursor. Thin Gd2O3 and Dy2O3 layers were grown by ALD, where the precursors were used in combination with water as a reactant at reduced pressure at the substrate temperature ranging from 150 degrees C to 350 degrees C. A constant growth per cycle (GPC) of 1.1 angstrom was obtained at deposition temperatures between 175 and 275 degrees C for Gd2O3, and in the case of Dy2O3, a GPC of 1.0 angstrom was obtained at 200-275 degrees C. The self-limiting ALD growth characteristics and the saturation behavior of the precursors were confirmed at substrate temperatures of 225 and 250 degrees C within the ALD window for both Gd2O3 and Dy2O3. Thin films were structurally characterized by grazing incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses for crystallinity and morphology. The chemical composition of the layer was examined by Rutherford backscattering (RBS) analysis and Auger electron spectroscopy (AES) depth profile measurements. The electrical properties of the ALD grown layers were analyzed by capacitance voltage (C-V) and current-voltage (I-V) measurements. Upon subjection to a forming gas treatment, the ALD grown layers show promising dielectric behavior, with no hysteresis and reduced interface trap densities, thus revealing the potential of these layers as high-k oxide for application in complementary metal oxide semiconductor based devices

This work documents the first example of deposition of high-quality Gd(2)O(3) thin films in a surface-controlled, self-limiting manner by a water-based atomic layer deposition (ALD) process using the engineered homoleptic gadolinium guanidinate precursor [Gd(DPDMG)(3)]. The potential of this class of compound is demonstrated in terms of a true ALD process, exhibiting pronounced growth rates, a high-quality interface between the film and the substrate without the need for any additional surface treatment prior to the film deposition, and most importantly, encouraging electrical properties.

The authors compare the properties of epitaxial Gd2O3 thin films grown on silicon substrates with three different orientations for high-K application. Pt∕Gd2O3∕Si(111) and Pt∕Gd2O3∕Si(110) metal oxide semiconductor heterostructures show promising electrical properties and hence, could be considered for future generation of complementary metal oxide semiconductor devices. Capacitance equivalent oxide thicknesses estimated from capacitance versus voltage characteristics are 0.97, 1.12, and 0.93nm for the films grown on Si(001), Si(111), and Si(110) substrates, respectively. The films exhibit good insulating property with leakage current densities of 0.4, 0.5, and 4.5mA∕cm2, respectively, at (Vg−VFBV)=−1V.