The system GeO2–TiO2 was studied experimentally at high pressure and temperature to measure the miscibility of the two components and to test its applicability as a temperature sensor in high-pressure experiments. Significant solubility between the two end-members was found, with two coexisting solid solutions at high pressure exhibiting mutual solubility that increases with temperature along a solvus. The two solid solution compositions at the solvus can be distinguished readily by X-ray diffraction. At higher temperatures, a complete solid solution exists between the two end-members. The complete solution occurs above a critical line in P–T space (a critical point at each pressure). The critical point is located near 1630 °C and mole fraction ${X_{{\rm{Ti}}{{\rm{O}}_{\rm{2}}}}} = 0.57$ at 6.6 GPa and changes by 60 ± 5° per GPa in the region from 4 to 7 GPa. A model for the shape of the solvus is developed using X-ray diffraction data points from a series of quench experiments and an in situ experiment, and the model is used to estimate the thermal gradients in a Kawai-type multianvil assembly.

The impact of the Al and Ge ratio in the Al-Ge pastes are investigated for fabricating the single crystalline Si1-xGex thick layers on large area Si substrates by screen-printing metallization process. From X-ray reciprocal space maps, Ge fraction in the fabricated Si1-xGex thick layers are found to increase up to 40% with increasing the Ge ratio in the Al-Ge pastes. On the other hand, the interface of the Si and Si1-xGex layers are getting winding with increasing the Ge ratio in the Al-Ge pastes. The Al-Si-Ge phase diagram indicated that uniform SiGe layer can be fabricated by adjusting the Al-Ge ratio in the pastes within the liquid phase region.

Pure and Nb-doped zirconium germanate materials of composition K2-xZr1-xNbxGe3O9.H2O where x = 0, 0.1, 0.2 and 0.25 with the structure of the mineral umbite have been successfully synthesised. The parent material displays negligible ion exchange of K+ for Cs+ but the doped materials shows much improved exchange. Synchrotron X-ray diffraction shows substantial peak splitting which varies with increasing niobium content. Preliminary Rietveld refinements suggest a two phase model with a caesium and potassium rich doped umbite phase.

Hydrogenated microcrystalline Silicon-Germanium (μc-SiGe:H) thin films were deposited using the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique from a gas mixture of SiH4, GeH4, H2 and Ar at a substrate temperature of 200 ° C. The films were deposited at a pressure of 1.5 Torr, while the RF power was varied in the range of 20 W to 35 W. Structural, optical and electrical characterization was performed in the films, Fourier Transform Infrared Spectroscopy (FTIR) was performed in order to analyze the hydrogen bonding of silicon and germanium, while Raman spectroscopy was used in order to analyze the crystallinity of the films. Through the optical and electrical characterization of the films, parameters such as the optical band gap (Eg) and the activation energy (EA) were obtained, respectively. The conductivity of the films changed up two to orders of magnitude from dark conditions to illumination AM 1.5. Finally, the correlation between deposition RF power and the film properties is presented.

GeTe/Sb2Te3 superlattices, also known as interfacial phase-change memory (iPCM), exhibit significantly faster switching and are characterized by much lower power consumption and longer data retention compared to devices based on alloyed materials. In early work, the superior performance of iPCM was linked to a crystal-crystal transition between the SET and RESET states. As the primary mechanism, a change in the stacking order of Ge and Te planes within a GeTe block was suggested. Subsequent STEM studies on epitaxial GeTe/Sb2Te3 superlattices demonstrated that the GeTe blocks were not located between Sb2Te3 quintuple layers but, were incorporated inside the latter, providing a serious challenge to the early explanation. In this work, we demonstrate that changes associated with the reconstruction of the SbTe terminating layers nearest to van der Waals gap leads to a pronounced change in the density of states and can serve as an alternative explanation for a large property contrast between the SET and RESET states in GeTe/Sb2Te3 superlattices.

As the scaling of the device dimensions in CMOS devices runs into physical limitations, new materials beyond Si with high electron and hole mobilities such as Ge, SiGe, and III-V materials are introduced. Challenges of CMP for these materials are reviewed in this paper. First we discussed the challenge of the new integration schemes to CMP. Loading effects can result in different growth rates for varying feature sizes, which results in a critical dimension dependent overburden. This makes it more difficult to meet the targets of the CMP process with respect to oxide loss and Ge/SiGe/III-V dishing. Secondly we discuss the challenge for the reduction of the defects during CMP for these new materials. Finally the challenge that is relevant especially for the introduction of III-V materials is studied. During the polishing of III-V materials, toxic gases as well as III-V containing liquid waste will be created. The chemical mechanism of the waste control is discussed.

We report on the formation of shallow junctions with high activation in both n+/p and p+/n Ge junctions using ion implantation and Flash Lamp Annealing (FLA). The shallowest junction depths (Xj) formed for the n+/p and p+/n junctions were 7.6 nm and 6.1 nm with sheet resistances (Rs) of 860 ohms/sq. and 704 ohms/sq., respectively. By reducing knocked-on oxygen during ion implantation in the n+/p junctions, Rs was decreased by between 5% and 15%. The lowest Rs observed was 235 ohms/sq. with a junction depth of 21.5 nm. Hall measurements clearly revealed that knocked-on oxygen degraded phosphorus activation (carrier concentration). In the p+/n Ge junctions, we show that ion implantation damage induced high boron activation. Using this technique, Rs can be reduced from 475 ohms/sq. to 349 ohms/sq. These results indicate that the potential for forming ultra-shallow n+/p and p+/n junctions in the nanometer range in Ge devices using FLA is very high, leading to realistic monolithically-integrated Ge CMOS devices that can take us beyond Si technology.

We present here a reactive ion etching recipe to fabricate germanium nanowires. We used a combination of Cl2, N2 and O2 and studied the influence of both the gas pressure and the O2 mass flow on the morphology of the nanowires. 5 µm long nanowires with an aspect ratio of 20 are demonstrated with smooth surfaces and a tapering below 20 nm/µm. We also show that both gold and aluminum can be used as hard mask; the latter achieving a selectivity with germanium above 100.

We present a review of our recent studies of Bias Temperature Instability (BTI) in Metal-Oxide-Semiconductor Field-Effect-Transistors (MOSFETs) fabricated with different material systems, highlighting the reliability opportunities and challenges of each novel device family. We discuss first the intrinsic reliability improvement offered by SiGe and Ge p-channel technologies, if a Si cap is used to passivate the channel, in order to fabricate a standard SiO2/HfO2 gate stack. We focus on SiGe gate stack optimizations for maximum BTI reliability, and on a simple physics-based model able to reproduce the experimental trends. This model framework is then used to understand the suboptimal BTI reliability and excessive time-dependent variability induced by oxide defect charging in different high-mobility channel gate stacks, such as Ge/GeOx/high-k and InGaAs/high-k. Finally we discuss how to pursue a reduction of charge trapping in alternative material systems in order to boost the device reliability and minimize time-dependent variability.

Germanene, the 2D graphene-like Ge nanosheet, has been recently the subject of many theoretical studies and experimental attempts to synthesize it on Ag(111), Au(111) and Pt(111) surfaces. The experimental and theoretical evidences of germanene show a 2D continuous honeycomb layer with a buckled conformation. Density functional theory (DFT) calculations have predicted a larger buckling for germanene than silicene whose origin is also associated with a pseudo Jahn–Teller (PJT) effect. In this work we show that despite the fact that both, silicene and germanene possess a buckled conformation with a PJT origin, their vibronic coupling have different origins. The analysis is based on the PJT puckering instability of the hexagermabenzene molecule, the single hexagonal unit of germanene. This is done through the linear vibronic coupling model between the ground and the lowest excited states, which leads to a puckering distortion of the more symmetric cluster. We study both, the multilevel superposition vibronic model and possible mixing of excited states of different irreducible representations, which have been used to show the origin of similar structural transitions in hexagonal silicon and gold ring systems respectively. We show that contrary to other cases with one six-member rings, for the hexagermabenzene molecule a mixture of both the multilevel PJT and a ground state coupling with two quasi-degenerate excited states is necessary for a satisfactory explanation of puckering. Our model allows a determination of the coupling constants and predicts simultaneously the Adiabatic Potential Energy Surface (APES) behavior for the ground and excited states around the maximum symmetry point. The analysis is based on a scalar relativistic DFT and time-dependent DFT (TD-DFT) calculations in the Zero Order Regular Approximation (ZORA) using the B3LYP hybrid functional.

Epitaxial Ge films are useful as a substrate for high-efficiency solar cell applications. It is possible to grow epitaxial Ge films on low cost, cube textured Ni(001) sheets using CaF2(001) as a buffer layer. Transmission electron microscopy (TEM) analysis indicates that the CaF2(001) lattice has a 45o in-plane rotation relative to the Ni(001) lattice. The in-plane epitaxy relationships are CaF2[110]//Ni[100] and CaF2[ $\bar 1$ 10]//Ni[010]. Energy dispersive spectroscopy (EDS) shows a sharp interface between Ge/CaF2 as well as between CaF2/Ni. Electron backscatter diffraction (EBSD) shows that the Ge(001) film has a large grain size (∼50 μm) with small angle grain boundaries (< 8o). The epitaxial Ge thin film has the potential to be used as a substrate to grow high quality III-V and II-VI semiconductors for optoelectronic applications.

The kinetics of Ge lateral overgrowth on SiO2 with line-shaped Si seeds is examined. The growth process is described by the difference between the growth rates of Ge on (100) planes (GR100) and <311> facets (GR311). The theoretical calculations well reproduce the growth kinetics. It is shown that narrowing the line-seeds helps Ge coalescence and flat film formation.

Silicon-germanium (SiGe) superlattices (SLs) have been proposed for application as efficient thermoelectrics because of their low thermal conductivity, below that of bulk SiGe alloys. However, the cost of growing SLs is prohibitive, so nanocomposites, made by a ball-milling and sintering, have been proposed as a cost-effective replacement with similar properties. Lattice thermal conductivity in SiGe SLs is reduced by scattering from the rough interfaces between layers. Therefore, it is expected that interface properties, such as roughness, orientation, and composition, will play a significant role in thermal transport in nanocomposites and offer many additional degrees of freedom to control the thermal conductivity in nanocomposites by tailoring grain size, shape, and crystal angle distributions. We previously demonstrated the sensitivity of the lattice thermal conductivity in SLs to the interface properties, based on solving the phonon Boltzmann transport equation under the relaxation time approximation. Here we adapt the model to a broad range of SiGe nanocomposites. We model nanocomposite structures using a Voronoi tessellation to mimic the grains and their distribution in the nanocomposite and show excellent agreement with experimentally observed structures, while for nanowires we use the Monte Carlo method to solve the phonon Boltzmann equation. In order to accurately treat phonon scattering from a series of atomically rough interfaces between the grains in the nanocomposite and at the boundaries of nanowires, we employ a momentum-dependent specularity parameter. Our results show thermal transport in SiGe nanocomposites and nanowires is reduced significantly below their bulk alloy counterparts.

Using our newly proposed interface conductance modal analysis (ICMA) formalism, we study the modal contributions to thermal interface conductance (G ) across the interface of crystalline silicon and crystalline germanium. We present the accumulation functions of G at different temperatures and predict G as a function of temperature after proper quantum-corrections have been applied. Different classes of vibration are identified across the interface, among which interfacial modes are determined to have the highest per mode contribution to G . The results demonstrate the ability of ICMA in not only calculating the spectral contributions to G but exactly pinpointing the shape of each vibrational eigen state.

The continuous trend of achieving more complex microelectronics with smaller nodes yet larger wafer sizes in microelectronics manufacturing lead to aggressive development requirements for chemical mechanical planarization (CMP) process. Particularly, beyond the 14 nm technology the development needs made it a must to introduce high mobility channel materials such as Ge. CMP is an enabler for integration of these new materials into future devices. In this study, we implemented a design of experiment (DOE) methodology in order to understand the optimized CMP slurry parameters such as optimal concentration of surface active agent (sodium dodecyl sulfate-SDS), concentration of abrasive particles and pH from the viewpoint of high removal rate and selectivity while maintaining a defect free surface finish. The responses examined were particle size distribution (slurry stability), zeta potential, material removal rate (MRR) and the surface defectivity as a function of the selected design variables. The impact of fumed silica particle loadings, oxidizer (H2O2) concentration, SDS surfactant concentration and pH were analyzed on Ge/silica selectivity through material removal rate (MRR) surface roughness and defectivity analyses.

Interest in next generation devices that integrate photonic and electronic functionality is focused on extending the capability of existing group IV material systems while maintaining compatibility with existing processing methods and procedures. One such class of materials which has been recently developed, Ge1-x-ySixSny ternary alloys, is being investigated for integrated Si photonics, solar cell materials, telecommunication applications, and for IR photodetectors. These alloys afford the opportunity to decouple the band gap energies and lattice constants over a wide range of values, potentially yielding direct and indirect character that can be coupled with a variety of different substrates dependent on composition.

In the present work, we report X-ray photoelectron spectroscopy (XPS) characterization of Ge1-x-ySixSny alloys grown by gas-source molecular beam epitaxy (GS-MBE) and investigate Ni- Ge1-x-ySiySny bilayer reactions with x-ray diffraction (XRD). The surface oxidation of samples stored in ambient conditions were measured with XPS. High resolution spectra showed chemical shifts of Ge, Si and Sn peaks consistent with Ge-O, Si-O and Sn-O bond formation. Depth profiling indicates a homogeneous composition throughout the bulk of the sample with surface oxidation confined to the top few nanometers. A highly tin-enriched layer was indicated at the surface of the material, while silicon was observed to be either enriched or depleted at the surface depending on the sample.

To study the interaction of the ternary with an ohmic contact commonly used in device fabrication processes today, nickel layers 30 nm thick were evaporated onto the alloys and were annealed in nitrogen up to 400 °C for periods as long as 1 hour. The XRD data show that the Ni2(Ge1-x-ySixSny) phase forms first followed by Ni(Ge1-x-ySixSny).

This article describes feasible and improved ways towards enhanced nanowire growth kinetics by reducing the equilibrium solute concentration in the liquid collector phase in a vapor-liquid-solid (VLS) like growth model. Use of bi-metallic alloy seeds (AuxAg1-x) influences the germanium supersaturation for a faster nucleation and growth kinetics. Nanowire growth with ternary eutectic alloys shows Gibbs-Thompson effect with diameter dependent growth rate. In-situ transmission electron microscopy (TEM) annealing experiments directly confirms the role of equilibrium concentration in nanowire growth kinetics and was used to correlate the equilibrium content of metastable alloys with the growth kinetics of Ge nanowires. The shape and geometry of the heterogeneous interfaces between the liquid eutectic and solid Ge nanowires were found to vary as a function of nanowire diameter and eutectic alloy composition.

Fundamental latency and energy limitations are driving major changes in communication and computation hardware. Parallel multicore and multiprocessor architectures are emerging as highly interconnected, communication-centric computation tools that at high node count will approach neural network connectivity and complexity. Monolithically integrated silicon photonics with electronics offers a promising platform for scaling functionality with high volume manufacturing and short design cycle times. The system parameters for this emerging “design for function” paradigm are cost, energy, and bandwidth density. The platform has been built on transmission of a λ ≈ 1550 nm photon wavelength; Si, Ge, Si3N4, and SiO2 materials; and standard complementary metal oxide semiconductor foundry processing. Dimensional shrink is achieved through strong signal confinement in high refractive index contrast material composites. Precision pattern transfer has enabled both photonic interconnect and signal processing functionality. New materials, process integration, and packaging are the keys to success.

As Si-transistor technology advances beyond the 10 nm node, the device research community is increasingly looking into the possibility of replacing Si with novel, high mobility materials as the transistor channel. Among several possible candidate materials, germanium and germanium-tin alloys (GeSn) have emerged as strong contenders for the next generation of complementary metal oxide semiconductor (CMOS) transistors. This article presents a comprehensive overview of the state of the art in Ge and GeSn transistor research. We address several key material challenges involved in fabricating high-performance Ge/GeSn-based CMOS transistors, such as gate stack formation and achieving low-resistance contacts to transistor source/drain regions. Using Ge/GeSn as channel materials, we present a FinFET-based, Si-compatible CMOS solution for device dimensions expected in the 7 nm technology node, discuss the practical challenges involved in realizing this design, and highlight directions for future research.