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The structural and dielectric properties of gadolinium oxide (Gd 2O 3) grown on Si(001) depending on the epitaxial growth conditions were investigated. Gd 2O 3 layers were grown at temperatures between 250 ° C and 400 ° C with an oxygen partial pressure between 2 × 10 − 7 mbar and 5 × 10 − 7 mbar. The crystal structure of the Gd 2O 3 turns out to be monoclinic with rotational domains as revealed by x-ray diffraction measurements and transmission electron microscopy (TEM) investigations. The dielectric properties can be tuned with growth temperature, forming gas annealing, and an increase in oxygen partial pressure. Furthermore, the dielectric constant was found to increase with the layer thickness. This can be interpreted in terms of the presence of a two layer stack consisting an interfacial quasi-amorphous and monoclinic Gd 2O 3 on top, as confirmed by TEM. The value of around 33 was extracted for the dielectric constant of monoclinic Gd 2O 3, which is much higher than for cubic Gd 2O 3. The best Gd 2O 3 layers grown at 400 ° C and p O 2 = 5 × 10 − 7 mbar exhibit also a characteristic leakage current value J ( V fb − 1 V ) for a CET value of around 2 nm in the range of a few nA/cm 2, which enable the applicability in electronic devices.

X-ray photoelectron spectroscopy (XPS) was performed to study the formation process of Pr2O3/Si(001) interfaces and films during epitaxial growth and postgrowth annealing. A significant shift in the Pr and O core-level binding energy was found accompanied by an analogous shift in the Pr2O3 valence band maximum. This shift depends on the oxide layer thickness and interface structure, as indicated by ab initio pseudopotential calculations. It is caused by interface dipoles in the Si/Pr2O3 interface region due to the accumulation of oxygen. Besides providing a insight into the growth mechanism and interface properties of high-K dielectrics on Si, our results also demonstrate the usefulness of in vacuo XPS for investigating epitaxial growth processes.

We report about the influence of boron (B) on surface morphology of Si layers grown by molecular beam epitaxy on Si(111) mesas. Dimension of step-free mesa areas is reduced in comparison to pristine Si and scales with the B-coverage. This can be explained by a reduced mass transport on the Si surface in the presence of B-induced √3 × √3 surface structure which is due to a reduced Si equilibrium free adatom density. We demonstrate that a suitable combination of initial B coverage and Si layer thickness results in large step free areas and B doping concentration up to 4 × 1018 cm−3.

Undoped and boron-doped SiC layers are grown on hexagonal SiC(0001) substrates by means of solid-source molecular-beam epitaxy. Hexagonal 4H– and 6H–SiC layers are grown homoepitaxially via step-controlled epitaxy, whereas the cubic 3C–SiC is grown pseudomorphically via nucleation and subsequent step flow. The low-temperature photoluminescence spectra only show the well-known emission lines of the so-called D1 center. The line positions are compared with results of first-principles calculations. The growth conditions, the line shape, and the line shift with the polytype support an interpretation as bound-exciton recombination at a native-defect complex that contains a Si vacancy.

The controlled growth of SiC heteropolytypic structures consisting of hexagonal and cubic polytypes has been performed by solid-source molecular-beam epitaxy. On on-axis substrates, 4H/3C/4H–SiC(0001) and 6H/3C/6H–SiC(0001) structures were obtained by first growing the 3C–SiC layer some nanometer thick at lower substrate temperatures (T=1550 K) and Si-rich conditions and a subsequent growth of α-SiC on top of the 3C–SiC layer at higher T (1600 K) under more C-rich conditions. On off-axis substrates, multiheterostructures consisting of 4H/3C- or 6H/3C-stacking sequences were also obtained by first nucleating selectively one-dimensional wire-like 3C–SiC on the terraces of well-prepared off-axis α-SiC(0001) substrates at low T(

The growth kinetics of Si dots grown on 6H-SiC(0001) by molecular beam epitaxy were studied in real time by reflection high-energy electron diffraction. The critical thickness for the Stranski–Krastanov growth mode transition was found to be kinetically delayed leading to a gradual decrease of this thickness with increasing temperature (T). At T

Epitaxial growth of 6H–SiC on 6H–SiC(0001) via two‐dimensional nucleation was realized at 930 °C by solid‐source molecular beam epitaxy using the alternate supply of Si and C. The deposition was controlled to an atomic level by surface superstructures. The growth was started on the (√3×√3)R30° surface which turns into the (1×1) phase upon deposition of about 1 monolayer silicon and recurs after subsequent deposition of about 1 monolayer carbon. Deviations from the monolayer deposition and, moreover, growth around substrate related defects result in the deposition of 3C–SiC.

Epitaxial growth of stoichiometric SiC on Si(111) and 2°–5° off‐oriented 6H–SiC(0001) substrates was carried out at low temperatures (800–1000 °C) by means of solid‐source molecular beam epitaxy controlled by a quadrupole mass spectrometry based flux meter. The films were obtained on Si‐stabilized surfaces showing (3×3) and (2×2) superstructures in the case of SiC(0001). The reflection high‐energy diffraction (RHEED) patterns and damped RHEED‐oscillations during the growth on 6H–SiC(0001) at T≳900 °C indicate that two‐dimensional nucleation on terraces is the dominant growth process.

We report about the single crystalline growth and dielectric properties of Gd2O3(100) thin films on Si(100) surface. Using a two step molecular beam epitaxy growth process, we demonstrate that controlled engineering of the oxide/Si interface is a key step to achieve the atypical (100) oriented growth of Gd2O3. Unusually, high dielectric constant values (∼23–27) were extracted from capacitance voltage measurements. Such effect can be understood in terms of a two dimensional charge layer at the Gd2O3/Si interface (W. Sitaputra and R. Tsu, Appl. Phys. Lett. 101, 222903 (2012)) which can influence the dielectric properties of the oxide layer by forming an additional negative quantum capacitance.

Dielectric properties of epitaxial Gd2O3 thin films grown on Si have been found to improve significantly by incorporation of suitable dopants. However, in order to achieve optimum electrical properties from such doped oxides, it is important to understand the correlation between doping and the electronic structure of the material. In the present article, we report about the effect of nitrogen doping on the electronic structure and room temperature dc leakage properties of epitaxial Gd2O3 thin films. Epitaxial Gd2O3:N thin films were grown on p-type Si (111) substrates by solid source molecular beam epitaxy technique using molecular N2O as the nitridation agent. First investigations confirmed the presence of substitutional N in the Gd2O3:N layers. Incorporation of nitrogen did not affect the structural quality of the oxide layers. X ray photoelectron spectroscopy investigations revealed band gap narrowing in epitaxial Gd2O3 due to nitrogen doping, which leads to reduction in the valence band offset of the Gd2O3:N layers with Si. DC leakage current measured at room temperature revealed that despite reduction in the band gap and valence band offsets due to N doping, the Gd2O3:N layers remain sufficiently insulating. A significant reduction of the leakage current densities in the Gd2O3:N layers with increasing nitrogen content suggests that doping of epitaxial Gd2O3 thin films with nitrogen can be an effective route to eliminate the adverse effects of the oxygen vacancy induced defects in the oxide layers.

We report about the effect of nitrogen doping on the electrical properties of epitaxial Gd2O3 thin films. Epitaxial Gd2O3:N thin films were grown on Si (111) substrates by solid source molecular beam epitaxy using nitrous oxide as the nitridation agent. Substitutional nitrogen incorporation into the dielectric layer was confirmed by secondary ion mass spectroscopy and X-ray photoelectron spectroscopy analysis. Substantial reduction of the leakage current density and disappearance of hysteresis in capacitance-voltage characteristics observed in the Gd2O3:N layers indicate that nitrogen incorporation in Gd2O3 effectively eliminates the adverse effects of the oxygen vacancy induced defects in the oxide layer.

The electrical degradation of ultra low-k SiCOH dielectric before breakdown is investigated. A new technique to obtain information before breakdown has been developed to define stress conditions and observe degradation patterns before total destruction occurs. Electrical measurements and physical inspection in specifically designed test structures have been made to focus on intrinsic properties. A typical leakage current characteristic, voiding and tantalum transport have been observed. These observations have been interpreted by quantitatively adapting physical effects. This investigation provides a model that describes the observed phenomena in a qualitatively manner.

We report on the effect of carbon doping on electrical properties of epitaxial Gd2O3 grown on Si substrates. The incorporation of small amounts of carbon (0.2-0.5 vol. %) into epitaxial Gd2O3 has been found to be very useful in improving the electrical properties especially by reducing the leakage current behavior. The doping has a negligible impact on the structural quality of the oxide layer. We show that the very often found adverse effect of oxygen vacancy induced defects in oxides grown at higher temperature can be eliminated by moderate amount of carbon doping during growth.

The incorporation of few monolayers of Ge chemisorbed on Si surface has been found to have significant impact on the electrical properties of crystalline Gd2O3 grown epitaxially on Si substrates. Although the Ge coverage on Si surface does not show any influence on the epitaxial quality of Gd2O3 layers, however, it exhibits a strong impact on their electrical properties. We show that by incorporating few monolayers of Ge at the interface between Gd2O3 and Si, the capacitance-voltage characteristics, fixed charge and density of interface traps of Pt/Gd2O3/Si capacitor are much superior to those layers grown on clean Si surfaces.

Silicon nanocrystals embedded in a lattice-matched Gd2O3 matrix exhibit large size-dependent bandgap widening. Measurements of photocharging spectra of these crystals indicate only a marginal variation in the photoionization threshold energy. The latter suggests that most of the confinement-induced bandgap width variation is caused by the upward shift of the Si nanocrystal conduction band bottom.

Internal photoemission of electrons and holes into cubic Nd2O3 epitaxially grown on (100)Si reveals a significant contribution of Nd 4f states to the spectrum of the oxide gap states. In contrast to oxides of other rare earth (RE) elements (Gd, Lu) epitaxially grown in the same cubic polymorph, to hexagonal LaLuO3, and to polycrystalline HfO2, the occupied Nd 4f states produce an additional filled band 0.8eV above the O 2p derived valence band. The unoccupied portion of the Nd 4f shell leads to empty electron states in the energy range of 1eV below the RE 5d derived oxide conduction band. The exposed Nd 4f states suggest the possibility to use this metal and, possibly, other REs with low f-shell occupancy to control the interface band offsets by selective interface doping.

We report on the effect of domain boundaries on the electrical properties of epitaxial Gd2O3 thin films grown on Si(001) substrates with 4° miscut along [110] azimuth. Dedicated preparation of the substrate surfaces can lead to two different microstructures of epitaxial Gd2O3 layers when grown at identical growth conditions. A substrate surface with terraces of biatomic steps height is the key point to achieve single crystalline epitaxial Gd2O3 layer. Such epi-Gd2O3 layers exhibited significantly lower leakage currents compared with the commonly obtained epitaxial layers with two orthogonal domains. However, for capacitance equivalent thickness below 1 nm, this difference disappears, indicating that for ultrathin layers direct tunneling becomes dominating. Additionally, forming gas annealing can reduce the leakage current by a few orders of magnitude. Here, thinner layers of both structural types exhibited similar electrical properties.

Single crystalline Nd2O3 based capacitors with proper forming gas annealing treatment are fabricated. By elevating the temperature of substrate to 100°C, near interface oxide traps are observed according to the quasistatic C-V obtained at low frequency. Two types of traps, interface traps and near interface oxide traps, are demonstrated in this gate stack. Using the low-high frequency method, the interface trap density at flatband voltage condition and the near interface oxide trap density are estimated to be 5.17×1011eV−1cm−2 and 3.75×1012cm−2, respectively. The interface trap density is then further confirmed by the conductance method.

The as-grown single crystalline Gd2O3 thin film on Si(100) substrate suffers from flatband voltage instability and large hysteresis which are possibly due to the intrinsic dangling bonds induced by the existing binding mismatch at the Gd2O3∕Si(100) interface. The instability of flatband voltage and hysteresis of Pt∕Gd2O3∕Si and W∕Gd2O3∕Si structures can be fully eliminated by the introduction of traditional forming gas annealing with proper process optimization. Both optimized metal-oxide-semiconductor structures show negligible hysteresis with the interface state at the magnitude order of 1011∕cm2eV at the midgap of silicon and can be considered for the future of complementary metal oxide semiconductor devices.

Internal photoemission, photoconductivity, and spectroscopic ellipsometry experiments were carried out to characterize the electronic structure of interfaces of (001) and (111)-oriented Si with crystalline (epitaxially grown) and amorphous Gd2O3 insulators. The energy barriers for electrons and holes (3.2 and 3.9eV, respectively) appear to be sensitive neither to the orientation of the Si crystal surface nor to the oxide phase (crystalline or amorphous). This result indicates that despite the difference in Si–O bond density in going from (001) to (111)Si, the interface dipoles do not ensue any measurable effect on the electronic structure of the interface and the associated band offsets.

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.

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.

Ternary neodymium-gadolinium oxide (NGO) thin films were grown epitaxially on Si(001) substrates using modified molecular beam epitaxy. The electrical properties of NGO thin films demonstrate that this ternary oxide could be one of the most promising candidates to replace the conventionally used SiO2 or SiOxNy in complementary metal oxide semiconductor devices. The films were characterized with various methods. The capacitance equivalent oxide thickness of 4.5nm thin films extracted from capacitance-voltage (C-V) characteristics was 0.9nm. For such films, leakage current density and the density of interface traps were 2.6×10−4A∕cm2 at ∣Vg−VFBV∣=1V and 1.4×1012∕cm2eV−1, respectively.

We investigated the influence of additional oxygen supply and temperature during the growth of thin Gd2O3 layers on Si(001) with molecular beam epitaxy. Additional oxygen supply during growth improves the dielectric properties significantly; however, too high oxygen partial pressures lead to an increase in the lower permittivity interfacial layer thickness. The growth temperature mainly influences the dielectric gate stack properties due to changes of the Gd2O3∕Si interface structure. Optimized conditions (600°C and pO2=5×10−7mbar) were found to achieve equivalent oxide thickness values below 1nm accompanied by leakage current densities below 1mA∕cm2 at 1V.

We study the growth of insulator/Si/insulator nanostructures on Si(111) using molecular beam epitaxy. Based on different investigations, we develop an approach for the fabrication of a nanostructure with a continuous ultrathin single-crystalline silicon buried in a single-crystalline insulator matrix with sharp interfaces. This approach is based on an epitaxial encapsulated solid-phase epitaxy, in which the solid-phase epitaxy of silicon is accompanied by a vapor-phase epitaxy of the second insulator layer. We call this approach as cooperative solid-vapor-phase epitaxy. As an example we demonstrate the growth of buried epitaxial silicon in epitaxial Gd2O3.