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The chemical stability of La-containing passivating layers /high-k gate stacks on Ge substrates is investigated by x-ray photoelectron spectroscopy. It is found that upon exposure to oxygen, a La-covered Ge surface spontaneously converts to a stable LaGeOx passivating layer. However, in the presence of overlying metal layers such as Al and Hf or upon deposition of high-k metal oxide cap layers such as Al2O3 and HfO2, the LaGeOx layer strongly reacts with the overlayers forming LaAlOz and LaHfOz compounds. In the case of Al or Al2O3, the LaGeOx is completely dissociated, while in the case of Hf or HfO2, LaGeOx remains although with a change in composition. The results are interpreted in terms of oxygen densification according to which the strongly electropositive La drives the reaction toward the formation of oxides with the highest oxygen density. The results suggest that HfO2 has a better chemical compatibility with LaGeOx making it more suitable for the gate stack. [ABSTRACT FROM AUTHOR]

Ge-doped ZrO2 thin films are prepared on SiON/Si substrates by atomic oxygen beam deposition. It is shown that, at low growth temperatures (225–360 °C) and by using only a low amount of Ge (3–6.2 at. %), it is possible to develop a pure tetragonal zirconia phase, which remains stable after 1050 °C annealing in N2. The dielectric permittivity (k) shows pronounced correlation with the structural details of the oxide film and is increasing with Ge content to a maximum value of 37.7, which is obtained for a 6.2 at. % Ge-doped sample grown at 225 °C. The dielectric permittivity enhancement upon doping is attributed to the increase in the ZrO2 tetragonal distortion, as inferred from x-ray diffraction data. Obtaining tetragonal ZrO2 with very high k-values at low deposition temperatures and with excellent thermal stability could be beneficial for the integration of this dielectric in scaled devices requiring low equivalent oxide thickness. [ABSTRACT FROM AUTHOR]

Germanium metal-insulator-semiconductor capacitors with La2O3 dielectrics deposited at high temperature or subjected to post deposition annealing show good electrical characteristics, especially low density of interface states Dit in the 1011 eV-1 cm-2 range, which is an indication of good passivating properties. However, the κ value is estimated to be only about 9, while there is no evidence for an interfacial layer. This is explained in terms of a spontaneous and strong reaction between La2O3 and Ge substrate to form a low κ and leaky La–Ge–O germanate over the entire film thickness, which, however, raises concerns about gate scalability. Combining a thin (∼1 nm) La2O3 layer with thicker HfO2 degrades the electrical characteristics, including Dit, but improves gate leakage and equivalent oxide thickness, indicating a better potential for scaling. Identifying suitable gate dielectric stack which combines good passivating/interfacial properties with good scalability remains a challenge. [ABSTRACT FROM AUTHOR]

Carbon thin films were grown by magnetron sputtering at room temperature on silicon substrates, with the substrate bias voltage varying from +10 to -200 V. Transmission electron microscopy analysis has shown that films deposited at V[sub b]=+10 and -40 V are amorphous (α-C), while films deposited at V[sub b]=-200 V are nanocrystalline (nc-C). Temperature dependent conductivity measurements were carried out in the temperature range 300-77 K. With respect to conductivity, the results indicate that the investigated carbon films are classified in three groups: (i) In α-C films deposited at V[sub b]=+10 V (sp[sup 2] rich bonds), the variable range hopping (VRH) conduction dominates below 300 K. (ii) In α-C films deposited at negative V[sub b] up to -100 V (sp[sup 3] rich bonds), VRH conduction dominates at low temperatures (T<150 K) and a thermally activated process satisfying the Meyer-Neldel rule at higher temperatures (T>150 K). (iii) In nc-C film deposited at V[sub b]=-200 V, the conductivity is explained by a heteroquantum-dots model based on a thermal-assisted tunneling process. The earlier differentiation in the conductivity mechanisms may play a significant role in the field electron emission properties of the films. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The structural, electrical, and low-frequency-noise properties of heterojunctions of amor- phous-carbon (a-C) films grown on either n- or p-type single-crystal silicon are investigated. The a-C films were deposited by rf magnetron sputtering at room temperature with varying the substrate bias V[sub b], from +10 to -200 V. The study includes measurements of x-ray reflectivity (XRR), low-frequency noise at room temperature, and dark current-voltage (I-V) and capacitance-voltage (C-V) characteristics over a wide temperature range. Analysis of the XRR data indicates the presence of a thin SiC layer between a-C and Si, with thickness increasing up to about 1.8 nm for V[sub b]=-200 V. The results show that the noise properties of the devices are independent of the SiC interlayer and the a-C film deposition conditions, while the noise of the a-C/n-Si heterojunctions is about four orders of magnitude lower than that of the a-C/p-Si heterojunctions. Analysis of the I-V and C-V data shows that the rectification properties of the a-C/n-Si heterojunctions are governed by conventional heterojunction theory, while multistep tunneling is the current conduction mechanism in a-C/p-Si heterojunctions due to a high density of interface states. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Germanium is an important mainstream material for many nanoelectronic and sensor applications. The understanding of diffusion at an atomic level is important for fundamental and technological reasons. In the present review, we focus on the description of recent studies concerning n-type dopants, isovalent atoms, p-type dopants, and metallic and oxygen diffusion in germanium. Defect engineering strategies considered by the community over the past decade are discussed in view of their potential application to other systems. [ABSTRACT FROM AUTHOR]

Studies noise characterization of sputtered amorphous carbon film. Findings of Hall measurements performed at room temperature; Ohmic behavior for low applied voltages; Use of a noise model based on trapping-detrapping of holes of the valence band and gap states of exponential energy distribution.

Point defect properties including diffusion properties are technologically important in semiconductor materials particularly as the characteristic dimension of devices are a few nanometers. Tin is an isovalent dopant in germanium that is presently considered to form radiation tolerant devices and in defect engineering strategies aiming to contain the high n-type dopant diffusion. In the present investigation we show that the cBΩ thermodynamic model linking the defect Gibbs energy to the isothermal bulk modulus and the mean volume per atom, can describe tin diffusion in germanium. The model is used to calculate point defect thermodynamic parameters such as the activation entropy, activation enthalpy and activation volume of tin diffusion in germanium as a function of temperature. [ABSTRACT FROM AUTHOR]

In the present study we investigate the structural, Fermi surface and optical properties of the recently synthesized (ZrTi)AlC MAX phases using density functional theory. The inclusion of Ti in the M site causes a reduction of both the a and c lattice parameters. The reduction of the a lattice parameter with respect to Ti content is more significant and this is reflected in the increase of the c/ a ratio. The Fermi surfaces are formed mainly due to the low-dispersive transition metal d-like orbitals, which are responsible for the conductivity in the compounds. The energy loss spectra reveals that the two end members of (ZrTi)AlC ( x = 0 and 3) change from metallic to dielectric response at incident light energies 11.9, 13.4 and 10.8, 13.5 eV for [100] and [001] polarization directions, respectively. The reflectivity spectra indicate the ability of two end compounds ZrAlC and TiAlC to be candidate materials for coatings to reduce solar heating. The calculated optical functions show the dependence on the polarization directions. [ABSTRACT FROM AUTHOR]

Diffusion properties are technologically important in the understanding of semiconductors for the efficent formation of defined nanoelectronic devices. In the present study we employ experimental data to show that bulk materials properties (elastic and expansivity data) can be used to describe gold and silver diffusion in germanium for a wide temperature range (702-1177 K). Here we show that the so-called cBΩ model thermodynamic model, which assumes that the defect Gibbs energy is proportional to the isothermal bulk modulus and the mean volume per atom, adequately metallic diffusion in germanium. [ABSTRACT FROM AUTHOR]

Copper diffusion in germanium is fundamentally and technologically important as it has a very low activation energy and influences the precipitation and gettering of copper respectively. These constitute the understanding of copper's diffusion properties in germanium over a range of temperatures and pressures important. In the present study we use the cBΩ model in which the defect Gibbs energy is proportional to the isothermal bulk modulus (B) and the mean volume per atom (Ω). The elastic and expansivity data is used in the description of the cBΩ model to derive the copper interstitial diffusion coefficient in germanium in the temperature range 827-1,176 K. The calculated results are discussed in view of the available experimental data. [ABSTRACT FROM AUTHOR]

We report the results of total ionizing dose radiation tests on germanium-substrate MOS capacitors with HfO2/Dy2 O3 gate dielectrics with effective oxide thicknesses of ~1.9 and 1.1 nm. There are significant densities of border traps before irradiation, and no measurable changes in device response after 10 Mrad(SiO2) exposure. We attribute the lack of net oxide charge trapping to equal electron and hole trapping and/or charge neutralization via gate leakage current. The introduction of Dy2 O3 evidently leads to reduced charge trapping in these HfO2/Dy2 O3 dielectrics relative to devices with only HfO2. [ABSTRACT FROM AUTHOR]

Long-channel Ge pMOSFETs and nMOSFETs were fabricated with high-κ CeO2/HfO2/TiN gate stacks. CeO2 was found to provide effective passivation of the Ge surface, with low diode surface leakage currents. The pMOSFETs showed a large ION/IOFF ratio of 106, a subthreshold slope of 107 mV/dec, and a peak mobility of approximately 90 cm²/V · s at 0.25 MV/cm. The nMOSFET performance was compromised by poor junction formation and demonstrated a peak mobility of only ∼3 cm²/V . s but did show an encouraging ION/IOFF ratio of 105 and a subthreshold slope of 85 mV/dec. [ABSTRACT FROM AUTHOR]

The oxidation of a Ge surface by molecular oxygen in the presence of ultrathin La, Al, and Hf layers was examined by in situ x-ray photoelectron spectroscopy. Upon exposure to O2, clean bare Ge and Hf-covered or Al-covered Ge surfaces show no Ge–O bond formation. On the contrary, a La-covered Ge surface strongly reacts with O2 forming a stable germanate LaGeOx compound. This has a beneficial side effect for the interface because the formation of volatile GeO is suppressed, resulting in the good passivating properties of LaGeOx. The photoemission results are correlated with the oxygen density differences in the corresponding oxides. [ABSTRACT FROM AUTHOR]

In this work the authors investigate La2O3 and ZrO2/La2O3 high-k gate dielectrics on p-type Ge metal-insulator-semiconductor capacitors. La2O3 on Ge exhibits good electrical properties in terms of interface states density, but it may not be scalable yielding high equivalent oxide thickness (EOT) after annealing. By depositing a thin (2 nm) La2O3 passivating layer followed by a ZrO2 cap, a gate stack is obtained which is a very good insulator with improved EOT, retaining at the same time the good passivating properties of La2O3. This indicates that the ZrO2/La2O3 combination could be scalable gate stack to be considered as a candidate for Ge metal-oxide-semiconductor devices. [ABSTRACT FROM AUTHOR]

Thin La2O3 (LaGeOx) passivating layers combined with ZrO2 caps form a chemically stable bilayer gate stack on Ge with good electrical properties. The most important observation is that a higher-κ tetragonal zirconia phase coexists with the most commonly observed monoclinic, increasing the κ value of the oxide to about 32, thus benefiting the measured stack equivalent oxide thickness. This indicates that the ZrO2/La2O3 combination could be a promising candidate gate stack for Ge metal-oxide-semiconductor devices in terms of scalability. [ABSTRACT FROM AUTHOR]

Electrical data on ZrO2/GeO2 stacks prepared by atomic oxygen beam deposition on Ge at 225 °C reveal a relatively weak dependence of the stack equivalent oxide thickness upon the ZrO2 thickness. This trend points to a very high zirconia dielectric permittivity (k) value which is estimated to be around 44. This is indicative of zirconia crystallization into a tetragonal phase which is also supported by x-ray diffraction data. X-ray photoelectron spectroscopy analysis is in line with the assumption that due to a finite GeO2 decomposition, Ge is incorporated into the growing ZrO2, thus, stabilizing the high-k tetragonal phase. [ABSTRACT FROM AUTHOR]

Metal-oxide-semiconductor field effect transistors (MOSFET) with a thin high-k dielectric were fabricated on bulk n-type germanium substrates. Surface oxides were thermally desorbed in situ by heating the substrates under ultrahigh vacuum conditions. First an ultrathin passivating layer was formed by evaporating germanium in the presence of atomic oxygen and nitrogen supplied from a remote radio frequency plasma source. Subsequently, the HfO2 dielectric was deposited by evaporating hafnium in the presence of atomic oxygen. An in situ TaN metal gate was similarly deposited. Long channel devices were fabricated using a standard process flow. These devices exhibited a low equivalent oxide thickness (EOT) of 0.7 nm with gate leakage less than 15 mA/cm2 at VFB+1 V. Device mobility was extracted from Is-Vg and split C-V characteristics. Results indicate a 2× mobility enhancement in Ge p-MOSFET devices compared to Si control devices. The demonstration of subnanometer EOT suggests that high-k gate dielectrics on germanium are scalable to low EOT and suitable for use in ultrascaled MOSFET devices. [ABSTRACT FROM AUTHOR]

Energy diagrams of interfaces between (100)Ge and several rare-earth oxide insulators deposited from a molecular beam are determined using a combination of internal photoemission and photoconductivity measurements. For the wide band gap (5.9 eV) oxides Gd2O3 and LaHfOx, the band alignment at the interface is found to be close to that of HfO2 and is characterized by conduction/valence band offsets of ∼2/∼3 eV. In contrast, CeO2 which has a much narrower band gap (3.3 eV) does not provide a band alignment diagram corresponding to sufficient insulation. [ABSTRACT FROM AUTHOR]

The electrical properties of thick amorphous carbon (a-C) films with sequential sp[sup 3]-rich/sp[sup 2]-rich layered structure, grown by magnetron sputtering on Si substrates at room temperature, were investigated. At low electric fields, the conduction is due to the variable range hopping mechanism. At high electric fields, thermally assisted band-to-band indirect tunneling is the dominant conduction mechanism, while the Arrhenius plots of the current show a deviation from straight lines in the form of continuous bending satisfying the Meyer–Nelder rule. Comparative studies of low-frequency noise in sp[sup 2]-rich single layer and sp[sup 3]-rich/sp[sup 2]-rich layered a-C films indicate that the noise in the a-C layered originates from traps located mainly at the interfaces of the sp[sup 3]-rich/sp[sup 2]-rich bilayers. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Amorphous carbon (α-C) films were deposited on Si substrates by magnetron sputtering at room temperature, followed by a deposition of TiN on top of the carbon films to form heterojunction devices. The electrical properties of the TiN/α-C/Si devices were characterized by capacitance-voltage, conductance-voltage, and current-voltage measurements as a function of temperature. The results showed that the devices behaved like metal-insulator-semiconductor devices at low temperatures, while at higher temperatures, the carbon films exhibited a high internal conductivity and the overall performance was similar to that of heterojunction devices. The conductivity was adequately modeled and found to follow the thermionic field emission model. The TiN exhibited an excellent behavior as a metallic electrode of the devices. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Lithium aluminate, LiAlO2, is a material that is presently being considered as a tritium breeder material in fusion reactors and coating material in Li-conducting electrodes. Here, we employ atomistic simulation techniques to show that the lowest energy intrinsic defect process is the cation anti-site defect (1.10 eV per defect). This was followed closely by the lithium Frenkel defect (1.44 eV per defect), which ensures a high lithium content in the material and inclination for lithium diffusion from formation of vacancies. Li self-diffusion is three dimensional and exhibits a curved pathway with a migration barrier of 0.53 eV. We considered a variety of dopants with charges +1 (Na, K and Rb), +2 (Mg, Ca, Sr and Ba), +3 (Ga, Fe, Co, Ni, Mn, Sc, Y and La) and +4 (Si, Ge, Ti, Zr and Ce) on the Al site. Dopants Mg2+ and Ge4+ can facilitate the formation of Li interstitials and Li vacancies, respectively. Trivalent dopants Fe3+, Ni3+ and Mn3+ prefer to occupy the Al site with exoergic solution energies meaning that they are candidate dopants for the synthesis of Li (Al, M) O2 (M = Fe, Ni and Mn) compounds. [ABSTRACT FROM AUTHOR]