E. Dobročka

Influence of barrier height distribution on the parameters of Schottky diodes

I‐V curves of Schottky diodes are simulated for a Gaussian type of the Schottky barrier height (SBH) distribution using the model of noninteracting parallel diodes. The mean value and the standard deviation of the distribution are supposed to be constant, i.e., not dependent on the voltage and the temperature. The influence of the distribution parameters and the temperature on the apparent barrier height and the ideality factor is analyzed. It is shown that the ideality factor increases and the apparent barrier height decreases with increasing standard deviation and decreasing temperature. The simulation also provides a rough estimate for the standard deviation. Values of ∼0.09 V can result in ideality factors up to 1.2. The importance of the effect of series resistance in the approach of noninteracting diodes is emphasized.

Growth of High-Dielectric-Constant TiO2 Films in Capacitors with RuO2 Electrodes

Titanium dioxide thin films were grown on RuO 2 layers by atomic layer deposition. The stabilizing effect of the bottom rutile-type RuO 2 layer resulted in growth of the TiO 2 rutile films at temperatures above 275°C. Stabilization of the TiO 2 rutile phase occurred due to local epitaxial growth of the polycrystalline RUO 2 /TiO 2 /RUO 2 structure, as revealed by transmission electron microscopy. A dielectric constant as high as 155 and equivalent oxide thickness (EOT) as low as 0.5 nm were determined from the capacitance-voltage measurements for the TiO 2 films grown above 275°C. A leakage current density of 10 -3 A/cm 2 at 1 V bias voltage was obtained for the films with EOT equal to 0.5 nm.

Influence of surface oxidation on plasmon resonance in monolayer of gold and silver nanoparticles

Surface plasmon resonance of gold and silver nanoparticle (NP) layers is investigated by the experiment as well as simulations. Although the good agreement was found for gold NP film, a significant mismatch in the resonance energy for silver NP film was observed. The deviation was assigned to the presence of silver oxide (Ag2O) in silver NPs. As an alternative to the NP size-dependent Drude model, the analysis based on effective medium approximation for refractive index of Ag-Ag2O material system is carried out and compared with the core-shell model. Both Mies model and numerical simulation results illustrate shift of the surface plasmon resonance due to silver NP surface oxidation.Surface plasmon resonance of gold and silver nanoparticle (NP) layers is investigated by the experiment as well as simulations. Although the good agreement was found for gold NP film, a significant mismatch in the resonance energy for silver NP film was observed. The deviation was assigned to the presence of silver oxide (Ag2O) in silver NPs. As an alternative to the NP size-dependent Drude model, the analysis based on effective medium approximation for refractive index of Ag-Ag2O material system is carried out and compared with the core-shell model. Both Mies model and numerical simulation results illustrate shift of the surface plasmon resonance due to silver NP surface oxidation.

AlGaN/GaN high electron mobility transistors with nickel oxide based gates formed by high temperature oxidation

We report on the design of gates of AlGaN/GaN high electron mobility transistors (HEMTs) to be predetermined for high temperature applications. In this design, nickel oxide (NiO) gate interfacial layer is formed by high temperature oxidation (T = 500–800 °C, for 1 min) of 15 nm thick Ni gate contact layer to provide a high temperature stable gate interface. AlGaN/GaN HEMTs with thermic NiO gate contact layer show excellent dc performance with higher peak transconductance, larger gate voltage swing, higher linearity, and thermal stability as compared to the reference device based on Ni gate contact layer.

High-permittivity metal-insulator-metal capacitors with TiO2 rutile dielectric and RuO2 bottom electrode

We describe properties of MIM capacitor structures with the RuO2 bottom electrode, TiO2 dielectric film and various top electrodes. The TiO2 films were grown by atomic layer deposition (ALD) at temperature 425 °C on metal organic chemical vapour deposited (MOCVD) RuO2 bottom electrodes grown at 300 °C. Due to local epitaxial growth on the RuO2 rutile structure, TiO2 films with the permittivity 135 and equivalent oxide thickness 0.58 nm were obtained. Capacitance density as high as 60 fF/μm2 was achieved. Au and Ni films for top electrodes were prepared by evaporation at room temperature. RuO2 films for top electrodes were grown by MOCVD. Strong effect of top electrode material on capacitance and leakage currents was observed. In addition, the stacks with TiO2 dielectric were found to be very sensitive to oxygen post-deposition treatment.

MgB2 tapes made of mechanically alloyed precursor powder in different metallic sheaths

MgB2 tapes have been made by the powder-in-tube technique using precursor powder prepared by mechanical alloying and deformed in Fe, Nb and Ti sheaths by two-axial and flat rolling. The best core uniformity and the highest core density were obtained for Ti sheathed tape. Different Jc values and current anisotropies were measured for applied sheath materials after the same deformation and heat treatment at 600 °C for 3 h or at 650 °C for 0.5 h, which is discussed and related to the interface reaction and to MgB2 core density and texture. The MgB2/Ti tape having the strongest sheath and the smoothest core/sheath interface has the best texture of MgB2 and consequently also the largest anisotropy ratio.

Atomic layer deposition grown metal-insulator-metal capacitors with RuO2 electrodes and Al-doped rutile TiO2 dielectric layer

Metal-insulator-metal structures for dynamic random access memory capacitor applications were prepared by atomic layer deposition. Rutile TiO2 dielectric layers were grown on top of RuO2 electrodes. TiO2 layers were doped in different ways by aluminum and these structures were compared to undoped ones. C-V and J-V measurements show that Al doping reduces the capacitance density of the stacks while reducing leakage current. Varying the initial Al doping profile did not change the electrical properties of the stacks. Leakage current analysis revealed that the current in the doped samples is controlled by Schottky emission.

Nanoscale Characterization of TiO2 Films Grown by Atomic Layer Deposition on RuO2 Electrodes

Topography and leakage current maps of TiO2 films grown by atomic layer deposition on RuO2 electrodes using either a TiCl4 or a Ti(O-i-C3H7)4 precursor were characterized at nanoscale by conductive atomic force microscopy (CAFM). For both films, the leakage current flows mainly through elevated grains and not along grain boundaries. The overall CAFM leakage current is larger and more localized for the TiCl4-based films (0.63 nm capacitance equivalent oxide thickness, CET) compared to the Ti(O-i-C3H7)4-based films (0.68 nm CET). Both films have a physical thickness of ∼20 nm. The nanoscale leakage currents are consistent with macroscopic leakage currents from capacitor structures and are correlated with grain characteristics observed by topography maps and transmission electron microscopy as well as with X-ray diffraction.

Potential use of V-channel Ge(220) monochromators in X-ray metrology and imaging

Several ways of tuning a higher asymmetry factor (>10) in V-channel X-ray monochromators, for metrological and imaging applications, were analysed. A more than sixfold intensity increase for compositionally and thermally tuned cases was achieved.

Low-temperature atomic layer deposition-grown Al2O3 gate dielectric for GaN/AlGaN/GaN MOS HEMTs: Impact of deposition conditions on interface state density

The oxide/semiconductor interface state density (Dit) in Al2O3/AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor (MOS-HEMT) structures with gate oxides grown by atomic layer deposition at low deposition temperature is analyzed in this work. MOS-HEMT structures with Al2O3 gate oxide were deposited at 100 and 300 °C using trimethylaluminum precursor and H2O and O3 oxidation agents. The structures were found to show negative net charge at oxide/barrier interface with density (Nint) of 1013 cm−2, which was attributed to the reduction of barrier surface donor density (NDS). Dit was determined using capacitance transient techniques, and the results were assessed by the simulations of the capacitance–voltage characteristics affected by interface traps. The results indicate a lower interface quality of the sample with Al2O3 grown using O3 agent compared to those with H2O, even though the former provided lowest gate leakage among the analyzed structures. Moreover, to uncover the NDS nature, Dit...