Search

Ge/SiGe heterostructures are promising in the view of silicon-foundry compatible THz optoelectronic applications. Here we present a structural and optical characterization of Ge/SiGe parabolic quantum wells that represent ideal systems for room-temperature THz emission and strong light-matter coupling investigation.

The realization of a Ge/SiGe THz emitter is of great interest since it can help to reach room-temperature operation due to the peculiar electron-phonon interaction in nonpolar crystals. Here we present Ge/SiGe quantum-well building blocks epitaxially grown on silicon wafers in order to understand limitations of this material platform in the perspective of realizing a Si-based laser.

Electron-optical phonon interaction is the dominant energy-loss mechanism in low-dimensional Ge/SiGe heterostructures and represents a key parameter for the design and realization of electronic and optoelectronic devices based on this material system compatible with the mainstream Si complementary metal-oxide semiconductor technology. Here we investigate the intersubband relaxation dynamics of $n$-type Ge/SiGe multiquantum wells with different symmetry and design by means of single-color pump-probe spectroscopy. By comparing the experimental differential transmittance data as a function of the pump-probe delay with numerical calculations based on an energy-balance rate-equation model, we could quantify an effective value for the optical phonon deformation potential describing the electron-phonon coupling in two-dimensional Ge-based systems. We found nonradiative relaxation times longer than 20 ps even in samples having intersubband energy separations larger than the optical phonon energy, evidencing the presence of a less effective electron-phonon coupling with respect to that estimated in bulk Ge.

Strain relaxed Si 1 − x Ge x buffer layers on Si(001) can be used as virtual substrates for the growth of both strained Si and strained SiGe, which are suitable materials for sub-7 nm CMOS devices due to their enhanced carrier mobility. For industrial applications, the threading dislocation density (TDD) has to be as low as possible. However, a reduction of the TDD is limited by the balance between dislocation glide and nucleation as well as dislocation blocking. The relaxation mechanism of low strain Si 0.98 Ge 0.02 layers on commercial substrates is compared to substrates with a predeposited SiGe backside layer, which provides threading dislocations at the edge of the wafer. It is shown that by the exploitation of this reservoir, the critical thickness for plastic relaxation is reduced and the formation of misfit dislocation bundles can be prevented. Instead, upon reaching the critical thickness, these preexisting dislocations simultaneously glide unhindered from the edge of the wafer toward the center. The resulting dislocation network is free of thick dislocation bundles that cause pileups, and the TDD can be reduced by one order of magnitude.

We develop a generalized theory for the scattering process produced by interface roughness on charge carriers and which is suitable for any semiconductor heterostructure. By exploiting our experimental insights into the three-dimensional atomic landscape obtained on Ge/GeSi heterointerfaces obtained by atom probe tomography, we have been able to define the full set of interface parameters relevant to the scattering potential, including both the in-plane and axial correlation inside real diffuse interfaces. Our experimental findings indicate a partial coherence of the interface roughness along the growth direction within the interfaces. We show that it is necessary to include this feature, previously neglected by theoretical models, when heterointerfaces characterized by finite interface widths are taken into consideration.

The waveguide losses from a range of surface plasmon and double metal waveguides for Ge/Si1−xGe x THz quantum cascade laser gain media are investigated at 4.79 THz (62.6 μm wavelength). Double metal waveguides demonstrate lower losses than surface plasmonic guiding with minimum losses for a 10 μm thick active gain region with silver metal of 21 cm−1 at 300 K reducing to 14.5 cm−1 at 10 K. Losses for silicon foundry compatible metals including Al and Cu are also provided for comparison and to provide a guide for gain requirements to enable lasers to be fabricated in commercial silicon foundries. To allow these losses to be calculated for a range of designs, the complex refractive index of a range of nominally undoped Si1−xGe x with x = 0.7, 0.8 and 0.9 and doped Ge heterolayers were extracted from Fourier transform infrared spectroscopy measurements between 0.1 and 10 THz and from 300 K down to 10 K. The results demonstrate losses comparable to similar designs of GaAs/AlGaAs quantum cascade laser plasmon waveguides indicating that a gain threshold of 15.1 cm−1 and 23.8 cm−1 are required to produce a 4.79 THz Ge/SiGe THz laser at 10 K and 300 K, respectively, for 2 mm long double metal waveguide quantum cascade lasers with facet coatings.

In this work we shed light on the early stage of the chemical vapor deposition of graphene on Ge(001) surfaces. By a combined use of m-Raman and x-ray photoelectron spectroscopies, and scanning tunneling microscopy and spectroscopy, we were able to individuate a carbon precursor phase to graphene nucleation which coexists with small graphene domains. This precursor phase is made of C aggregates with different size, shape and local ordering which are not fully sp(2) hybridized. In some atomic size regions these aggregates show a linear arrangement of atoms as well as the first signature of the hexagonal structure of graphene. The carbon precursor phase evolves in graphene domains through an ordering process, associated to a re-arrangement of the Ge surface morphology. This surface structuring represents the embryo stage of the hills-and-valleys faceting featured by the Ge(001) surface for longer deposition times, when the graphene domains coalesce to form a single layer graphene film. (C) 2018 Elsevier Ltd. All rights reserved.

We report on the formation of Zn nanoparticles induced by Ga+ focused ion beam on single crystal ZnO. The irradiated materials have been studied as a function of the ion dose by means of atomic force microscopy, scanning electron microscopy, Raman spectroscopy and transmission electron microscopy, evidencing the presence of Zn nanoparticles with size of the order of 5–30 nm. The nanoparticles are found to be embedded in a shallow amorphous ZnO matrix few tens of nanometers thick. Results reveal that ion beam induced Zn clustering occurs producing crystalline particles with the same hexagonal lattice and orientation of the substrate, and could explain the alteration of optical and electrical properties found for FIB fabricated and processed ZnO based devices.

We explore saturable absorption and terahertz photoluminescence emission in a set of n-doped Ge/SiGe asymmetric coupled quantum wells, designed as three-level systems (i.e., quantum fountain emitter). We generate a non-equilibrium population by optical pumping at the 1→3 transition energy using picosecond pulses from a free-electron laser and characterize this effect by measuring absorption as a function of the pump intensity. In the emission experiment we observe weak emission peaks in the 14–25 meV range (3–6 THz) corresponding to the two intermediate intersubband transition energies. The results represent a step towards silicon-based integrated terahertz emitters.

The exploitation of intersubband transitions in Ge/SiGe quantum cascade devices could pave the way towards the integration of THz light emitters into the silicon-based technology. Aiming at the realization of a Ge/SiGe Quantum Cascade Laser (QCL), we investigate optical and structural properties of n-type Ge/SiGe coupled quantum well systems. The samples have been investigated by means of X-ray diffraction, scanning transmission electron microscopy, atom probe tomography and Fourier Transform Infrared absorption spectroscopy to assess the growth capability with respect to QCL design requirements, carefully identified by means of modelling based on the non-equilibrium Green function formalism.

We systematically investigate the chemical vapor deposition growth of graphene on Ge(110) as a function of the deposition temperature close to the Ge melting point. By merging spectroscopic and morphological information, we find that the quality of graphene films depends critically on the growth temperature improving significantly by increasing this temperature in the 910–930 °C range. We correlate the abrupt improvement of the graphene quality to the formation of a quasi-liquid Ge surface occurring in the same temperature range, which determines increased atom diffusivity and sublimation rate. Being observed for diverse Ge orientations, this process is of general relevance for graphene synthesis on Ge.

Theoretical predictions indicate that the n-type Ge / Si − Ge multi-quantum-well system is the most promising material for the realization of a Si -compatible THz quantum cascade laser operating at room temperature. To advance in this direction, we study, both experimentally and theoretically, asymmetric coupled multi-quantum-well samples based on this material system, that can be considered as the basic building block of a cascade architecture. Extensive structural characterization shows the high material quality of strain-symmetrized structures grown by chemical vapor deposition, down to the ultrathin barrier limit. Moreover, THz absorption spectroscopy measurements supported by theoretical modeling unambiguously demonstrate inter-well coupling and wavefunction tunneling. The agreement between experimental data and simulations allows us to characterize the tunneling barrier parameters and, in turn, achieve highly controlled engineering of the electronic structure in forthcoming unipolar cascade systems based on n-type Ge / Si − Ge multi-quantum-wells.

n-type Ge/SiGe terahertz quantum cascade laser are investigated using non-equilibrium Green's functions calculations. We compare the temperature dependence of the terahertz gain properties with an equivalent GaAs/AlGaAs QCL design. In the Ge/SiGe case, the gain is found to be much more robust to temperature increase, enabling operation up to room temperature. The better temperature robustness with respect to III-V is attributed to the much weaker interaction with optical phonons. The effect of lower interface quality is investigated and can be partly overcome by engineering smoother quantum confinement via multiple barrier heights., 5 pages, 5 figures

With the aim of tuning the optical properties of SiC selective solar absorbers, we investigate the surface micro/nano-texturing of porous silicon carbide by using two approaches, namely i) the femtosecond laser treatment and ii) the fluorine based reactive ion etching. It is found that both the techniques are capable of inducing significant surface morphology modification inducing a substantial roughening. The surface features produced are found to be tunable by tailoring the main process parameters, i.e. translation speed and pulse repetition rate for laser treatment, and RF-power, gas pressure and gas mixture for the reactive ion etching process.

Tin doped indium oxide (ITO) coatings have been deposited on epoxy resin and glass substrates by low temperature (70 °C) RF magnetron sputtering. Influence of different process parameters on coating morphological and electrical properties has been studied. Epoxy resin surface roughness influence on coating microstructure was also investigated. We have found that: (i) deposition chamber oxygen content is the main parameter affecting surface electrical resistance, (ii) microstructure and electrical properties are similar in both glass and polymeric smooth substrates; in the latter the substrate stability (type of polymer and degree of cure) is important to prevent microcracks formation as a result of stress release after deposition, and (iii) rough substrates present a non-uniform microstructures with formation of clusters of crystallites with various orientation.

We report on the morphological investigation of nanoscale thick patterns obtained by the scanning probe assisted local oxidation technique on graphene layers grown directly on Ge (100) substrates using CVD technique. Protruding mounds and lines are produced by applying a negative voltage to the atomic force microscope probe while translating the probe tip across the sample surface. The main features of the local oxide produced and the differences with respect to similar experiments conducted on Ge or Si samples are presented.

An extended formation of faceted pit-like defects on Ge(001) and Ge(111) wafers was obtained by thermal cycles to T> 750 {\deg}C. This temperature range is relevant in many surface-preparation recipes of the Ge surface. The density of the defects depends on the temperature reached, the number of annealing cycles performed and correlates to the surface-energy stability of the specific crystal orientation. We propose that the pits were formed by preferential desorption from the strained regions around dislocation pile-ups. Indeed, the morphology of the pits was the same as that observed for preferential chemical etching of dislocations while the spatial distribution of the pits was clearly non-Poissonian in line with mutual interactions between the core dislocations., Comment: European Union (EU), Horizon 2020, Far-Infrared Lasers Assembled using Silicon Heterostructures,FLASH,Grant number: 766719

In this paper we investigate the structural and optical properties of few strain-unbalanced multiple Ge/GeSi quantum wells pseudomorphically grown on GeSi reverse-graded substrates. The obtained high epitaxial quality demonstrates that strain symmetrization is not a mandatory requirement for few quantum-well repetitions. Photoluminescence data, supported by a thorough theoretical modeling, allow us to unambiguously disentangle the spectral features of the quantum wells from those originating in the virtual substrate and to evaluate the impact on the optical properties of key parameters, such as quantum confinement, layer compositions, excess carrier density, and lattice strain. This detailed understanding of the radiative recombination processes is of paramount importance for the development of Ge/GeSi-based optical devices.

Display Omitted Focused ion beam and oxygen plasma etching are used for controlled disruption of ferritin.The detection gain of iron by EDX upon focused ion beam treatment increased by 300%.XPS detection of Fe in ferritin after oxygen plasma etching was enhanced by ~15. Ferritin is the main protein devoted to iron storage in living systems. Several evidences show that ferritin can bind in vivo metals other than iron, such as aluminium. Moreover, recent studies demonstrated that ferritin iron core composition differs between physiological and pathological brain ferritins. The precise evaluation of chemical species present within the ferritin mineral core and their chemical coordination is therefore of paramount importance. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy are powerful tools to perform this chemical analysis: however the protein shell surrounding the mineral core reduces significantly the amount of electrons/photons detected, thus reducing the potentiality of these techniques.In this framework we investigated the use of physical treatments, namely focused ion beam milling and oxygen plasma etching, in order to overcome the limitations imposed by the presence of the protein shell. We demonstrated that the combined use of focused ion beam milling and energy dispersive X-ray spectroscopy provides an enhancement of iron detection by a factor of about two. As for the X-ray photoelectron spectroscopy technique, it has an intrinsic low capability of probing the core metal in ferritin due to the electron escape depth value that is of the order of the protein shell thickness. Using a pre-treatment in oxygen plasma the detection of iron was enhanced by a factor of more than 15. Therefore, the disruption of the protein shell by plasma etching or ion milling emerges as a fundamental prerequisite to perform an accurate chemical characterization of the ferritin core.

The early stage of the growth of Ge planar films on a Si(001) surface is investigated in real-time by using the spectroscopic ellipsometric technique. We demonstrate the possibility to measure the deposition rate and follow its evolution during the growth. The use of spectroscopic ellipsometry in combination with atomic force microscopy and X-ray photoelectron spectroscopy demonstrates that the deposition rate evolution is related to the stress status of the growing film through the variation of its complex dielectric constant.

Germanium is emerging as the substrate of choice for the growth of graphene in CMOS-compatible processes. For future application in next generation devices the accurate control over the properties of high-quality graphene synthesized on Ge surfaces, such as number of layers and domain size, is of paramount importance. Here we investigate the role of the process gas flows on the CVD growth of graphene on Ge(100). The quality and morphology of the deposited material is assessed by using mu-Raman spectroscopy, X-ray photo emission spectroscopy, scanning electron microscopy, and atomic force microscopy. We find that by simply varying the carbon precursor flow different growth regimes yielding to graphene nanoribbons, graphene monolayer, and graphene multilayer are established. We identify the growth conditions yielding to a layer-by-layer growth regime and report on the achievement of homogeneous monolayer graphene with an average intensity ratio of 2D and G bands in the Raman map larger than 3.

We report on the realization of high-mobility two-dimensional electron gas based on modulation-doped Si/SiGe heterostructure grown directly on thin SiGe-On-Insulator (SGOI) substrate. The samples were grown by using low-pressure chemical vapor deposition. A pregrowth procedure for the cleaning of the SGOI surface that preserves the integrity and the composition of the substrate was developed. An electron mobility as high as 10(5)cm(2)V(-1) s(-1) at T = 0.4 K and 2000 cm(2)V(-1) s(-1) at T = 300 K was obtained. (C) 2007 Elsevier B.V. All rights reserved.

Display Omitted Argon and oxygen plasma processes are used for controlled disruption of ferritin.XPS detection of Fe in ferritin film after plasma process was enhanced by ~10.XPS reveals the oxidation state of Fe in the ferritin core after the plasma etching. Ferritin is the main iron storage protein in living systems. Recent studies demonstrated that the chemical species present in the ferritin core and their chemical coordination can be different between physiological and pathological ferritin proteins. Therefore it is of paramount importance revealing the presence of metals other than iron and their oxidation state in the protein core.In this work we investigated and compared the use of argon and oxygen plasma processes for the erosion of the protein shell surrounding the mineral core, which is necessary for the chemical analysis of the ferritin core by surface sensitive technique such as X-ray photoelectron spectroscopy. We find that both the proposed etching processes are effective in the disruption of the protein shell and in the exposure of the Fe inside the core of the molecules. Neither oxygen nor argon plasma induced significant artifacts in the samples nor produce dramatic roughening in the surface allowing for a controlled thinning of the ferritin film. In the plasma treated samples X-ray photoelectron spectroscopy detected the Fe(III) oxidation state of metal present inside the ferritin cavity.

We report on the electrical transport of wire-based devices fabricated on modulation-doped Si/SiGe two-dimensional electron gas. Two different geometries were investigated: straight and bended wires. In both cases, we found typical features of Coulomb blockade regime. Nevertheless, single electron transistor effects were found only on wires with bends. Reported data suggest that the insertion of bends is a suitable tool for obtaining single electron transistor behavior in Si/SiGe wires.

The conductance of strongly confined one-dimensional constrictions fabricated from Si/SiGe two-dimensional electron gases is investigated. Conductance measurements reveal conductance quantization in units of G(0)=2e(2)/h rather than 2G(0)=4e(2)/h, as expected in the presence of valley and spin degeneracy. Furthermore, at temperatures below T=400 mK, small steps and peaklike features, superimposed to the conductance plateaus, become visible. The conductance in the presence of parallel and perpendicular magnetic field shows that significant valley splitting is present even at zero magnetic field. The enhanced valley splitting observed in our etched devices is related to the strong in-plane confinement.

The process of capping Ge islands with Si overlayers is known to have a strong influence on their composition and shape. In this work we have investigated Ge islands on Si produced by chemical vapor deposition covered with Si layers of different thickness. The structural characterization was carried out by X-ray absorption spectroscopy at the Ge-K edge. A noticeable Si uptake by the islands is evident upon capping. Bond length for the first three shells have been analyzed by comparison with models based on the valence force field method. The results evidence that the islands have, on the average, a relaxed state with presumably strained parts in contact with the Si matrix. 2005 Elsevier B.V. All rights reserved.

We fabricated strongly confined Schottky-gated quantum point contacts by etching Si/SiGe heterostructures and observed intriguing conductance quantization in units of approximately 1e2/h. Non-linear conductance measurements were performed depleting the quantum point contacts at fixed mode-energy separation. We report evidences of the formation of a half 1e2/h plateau, supporting the speculation that adiabatic transmission occurs through 1D modes with complete removal of valley and spin degeneracies., Comment: to appear in Physical Review B

We discuss the effect of the deposition of a Si cap layer on the composition and morphological properties of Ge(Si)/Si(001) self-assembled islands deposited by chemical vapor deposition at 750 degrees C. The morphological evolution of the island shape was investigated by means of atomic force microscopy and the actual island composition has been measured by means of x-ray photoemission spectroscopy and x-ray absorption spectroscopy techniques. At an early stage of Si capping, Si atoms are incorporated in the island layer. As a consequence, we observe a reverse Stranski-Krastanov growth dynamics in agreement with the volume-composition stability diagram proposed for domes, pyramids, and prepyramids in the GexSi1-x/Si(100) system. We find that the island burying begins when the Ge average composition reaches the value x=0.28. Once the islands are buried under a thin silicon layer their composition is unaffected by subsequent silicon deposition. We conclude that strain relief, rather than thermal diffusion, is the main driving force for the observed Ge-Si alloying. (c) 2005 American Institute of Physics. (c) 2005 American Institute of Physics.

Low field magnetotransport revealing signatures of ballistic transport effects in strained Si/SiGe cavities is investigated. We fabricated strained Si/SiGe cavities by confining a high mobility Si/SiGe 2DEG in a bended nanowire geometry defined by electron-beam lithography and reactive ion etching. The main features observed in the low temperature magnetoresistance curves are the presence of a zero-field magnetoresistance peak and of an oscillatory structure at low fields. By adopting a simple geometrical model we explain the oscillatory structure in terms of electron magnetic focusing. A detailed examination of the zero-field peak lineshape clearly shows deviations from the predictions of ballistic weak localization theory., Comment: Submitted to Physical Review B, 25 pages, 7 figures

Highly efficient and transparent multicomponent catalysts for Dye Solar Cells (DSCs) were obtained by simultaneous electrodeposition of platinum and cobalt-sulfide (Pt:CoS) on conducting glass substrates from a mixture solution of both precursors. At equal charge transfer resistances (RCT), the superior transparency of electrodeposited (ED) Pt:CoS compared to ED Pt-only and ED CoS-only was attributed to the synergic combination of a very thin CoS layer and a fine dispersion of Pt nanoparticles. The highly catalytic properties of Pt:CoS with less electrodeposited material consumption, carried out at room temperature, can represent a fast and energy saving fabrication process, also compatible with flexible plastic substrates. In fact, DSCs with the ED Pt:CoS counterelectrodes showed the highest power conversion efficiency in back illumination, which is the configuration used for flexible metallic and bifacial DSCs during operation, gaining on average almost 14% and 7% in device efficiency with respect to ED CoS-only and ED Pt-only based cells. These results are important for all applications where transparency represents a key factor (e.g. BIPV, metal based devices) and may also point at blending different precursor solutions as a more general route for electrodeposition of layers with added functionality.

We apply a new experimental method for determining band lineups at the Ge Si (100) heterostructure. This method uses a modern version of an old spectroscopy: the photoelectric yield spectroscopy excited with photons in the near UV range. It is shown that both substrate and overlayer valence-band tops can be identified in the yield spectrum, thus allowing a direct and precise determination of the band lineup. We find an offset of 0.36 ± 0.02 eV for heterojunctions whose overlayers were grown according to the Stranski-Krastanov mechanism.

An X-ray scanning microscope study of self-organized morphological defects arising during the growth of thick SiGe virtual substrates grown on Si(001) surface is reported. The 200 nm microscope resolution permitted to probe the local alloy composition. The measured variations of the Ge content in the alloy demonstrate that defect formation and evolution represent a strain relief mechanism. The observed large stress concentration inside the defect and the absence of the cross-hatch pattern on its internal facets are findings in close analogy with the lateral strain relaxation of self-organized islands in heterostructures.

The growth of high-mobility modulation-doped Si/SiGe heterostructures on silicon-on-insulator (SOI) substrates is demonstrated. The structural and electrical properties of the samples are comparable with those of similar samples grown on standard Si substrates. Electron mobilities as high as 2800 cm 2 V −1 s −1 at room temperature and 8.2×10 4 cm 2 V −1 s −1 at 4 K are obtained.

In this letter, we report on the optical properties of multistacked Ge quantum dots grown on Si(001). We demonstrate that the two emission bands observed in the photoluminescence spectra are related to the presence of strained and relaxed islands. Within both types of islands, the experimental findings support the hypothesis of the presence of quantum confining regions whose dimensions are governed by the strain relaxation process.

We present a new experimental method for determining band lineups at the semiconductor heterojunctions and apply it to the $c\ensuremath{-}\mathrm{S}\mathrm{i}\left(100\right)/a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ heterostructure. This method uses a modern version of an old spectroscopy: the photoelectric yield spectroscopy excited with photons in the near UV range. It is shown that both substrate and overlayer valence-band tops can be identified in the yield spectrum due to the high escape depth and the high dynamical range of the technique, thus allowing a direct and precise determination of the band lineup. A value of $\ensuremath{\Delta}{E}_{V}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.44\ifmmode\pm\else\textpm\fi{}0.02\mathrm{eV}$ was found for the valence band discontinuity.

We have investigated the morphology defects, in particular, pits present in compositionally graded SiGe thick films heteroepitaxially grown on Si(001) surfaces. Besides the pits clearly related to impurities and interface defects, a class of pits intrinsic to the strained-layer growth has been found. Two stable and one metastable pit shapes have been identified that can be related to the alloy film thickness and pit dimension. The influence of the pits on the mobility of the two dimensional electron gas grown on these kinds of substrates has been also investigated.

We report the characterization of a single-electron transistor based on bended wires fabricated on modulation-doped SiGe two-dimensional electron gas. Electrical measurements show a diamond-shaped stability plot and a nonperiodic sequence of conductance peaks. The device behavior suggests the presence of disorder-induced multiple islands along the wire. Conductance oscillations remain well pronounced above liquid helium temperature.

We have investigated the weak antilocalization effect in a high-density two-dimensional electron gas (2DEG) in an AlGaN\\\/GaN heterostructure. The data were analyzed using the most representative theories on the weak antilocalization (WAL) correction to magnetoconductivity. The spin-orbit interaction (SOI) strength and the phase-coherence time were extracted from the fitting to the experimental data. We found that the use of the WAL peak analysis appears to be a reliable way of investigating the SOI strength and that the dependence on charge concentration revealed by the WAL data as reported in the literature can be considered a trustworthy experimental description of the SOI behavior in the AlGaN\\\/GaN 2DEG system.

We report on the use of a carbon-rich Pt-based material, obtained by electron and ion beam assisted deposition from metal-organic precursor, as a mask for pattern transfer processes. Thin and narrow mask patterns subjected to oxygen plasma and reactive ion etching (RIE) of silicon in SF(6) were investigated by atomic force microscopy and energy dispersive X-ray analysis. As for the masks obtained by electron beam assisted deposition, both the pattern and the surrounding halo were found to be etched in oxygen plasma. In contrast, the pattern deposited by assist of ion beam was basically unaffected, likely due to implanted Ga(+) ions during deposition, while the surrounding halo was found to be appreciably thinned. Masks having thickness as low as few nanometers sustained successfully a 200 nm RIE step, producing structures with sub-100 nm size. Mask stripping was achieved in Piranha bath. (C) 2011 Elsevier B.V. All rights reserved.

""We report on the fabrication process of suspended anodes implemented in Schottky-diode devices on epitaxial Ge. An air-bridge technique based on reactive ion etching in SF(6) was developed in order to release the Schottky contact bridge, ensuring higher control respect to wet etching. Metal-semiconductor junctions in the sub-micron range with rectifying behaviour have been obtained. The present fabrication process can be extended as is to the use of silicon on insulator substrates. (C) 2010 Elsevier B.V. All rights reserved.""

The beam of planar THz Schottky detectors is strongly concentrated in the dielectric half-space. With the goal of illuminating arrays from the free-space side, we started to investigate substrate removal from both GaAs and Ge-on-Si diode wafers. © 2011 IEEE.

Magnetotransport properties of a high-density AlGaN/AlN/GaN two-dimensional electron gas are reported. A quantitative model of amplitude and phase modulation of Shubnikov-de Haas oscillations was developed. This analysis allows the extraction of the spin splitting energy even if nodes and double peaks in the Fourier spectrum are not clearly observed. In this way the presence of two conducting channels was clearly identified. A spin splitting of 1.2 meV was found. © 2011 American Physical Society.

In this work, we investigated the magnetotransport properties of a two dimensional electron gas hosted in an AlGaN/AlN/GaN heterostructure and one-dimensional devices fabricated on it. At cryogenic temperature, high mobility and long mean free path is achieved, allowing ballistic transport experiments. Longitudinal resistivity measured in Hall bar geometry shows well-developed Shubnikov–de Haas oscillations with amplitude modulation. Amongst possible mechanisms, the zero-field spin splitting may be the origin of the observed effects. Split gate quantum point contacts were fabricated by electron beam lithography. Linear conductance measurements at zero magnetic field show clear quantized conductance plateaus at 2e 2/h and 4e 2/h. Non-perfectly quantized conductance values are found for higher plateaus, suggesting the presence of impurity scattering.