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Efficient and green exfoliation of bulk MoS2 into few-layered nanosheets in the semiconducting hexagonal phase (2H-phase) remains a great challenge. Here, we developed a new method, water-assisted exfoliation (WAE), for the scalable synthesis of carboxylated chitosan (CC)/2H-MoS2 nanocomposites. With facile hand grinding of the CC powder, bulk MoS2 and water followed by conventional liquid-phase exfoliation in water, this method can not only efficiently exfoliate the 2H-MoS2 nanosheets, but also produce two-dimensional (2D) CC/2H-MoS2 nanocomposites. Interestingly, the intercalated CC in MoS2 nanosheets increases the interlayer spacing of 2H-MoS2 to serve as good candidates for the semiconductor devices. 2D CC/2H-MoS2 nanocomposites show superior electronic rectification effects in nonvolatile write-once-read-many-times memory (WORM) behavior with an ON/OFF ratio over 103, which can be rationally controlled by the weight ratios of CC and MoS2. These findings by the WAE method would open tremendous potential opportunities to prepare commercially available semiconducting 2D nanocomposites for promising high-performance device applications.

The buffer layer samples grown on the Si-face of the 4H- and 6H-SiC substrates were heated in a hydrogen flow at different temperatures (600–900 °C) and heating times (40–60 min) in order t...

This article introduces a programmable gas phase nanoparticle electrodeposition concept which enables the fabrication of multi-modal conductometric gas sensor arrays. The sensor application requires the deposition of more than one nanoparticle type to achieve orthogonal sensing capabilities and multi gas sensitivity and selectivity. The demonstrated “electronic nose” like array contains 1080 freeform point-to-point gas sensitive nanobridges of platinum, nickel oxide and gold based electrical connections on a single chip. The introduced architecture is different from previous reports; instead of two-dimensional thin metallic films, each gas sensitive bridge is a three-dimensional (3D) structure, which in turn, is composed of a porous but electrically conducting nanoparticle network. It was found that this architecture is unique since it does not require external heating to function. A multimodal sensor array will be demonstrated to detect various levels of Ammonia (NH3), Carbon Monoxide (CO) and Hydrogen Sulfide (H2S). Gas phase nanoparticle electrodeposition method uses a spark discharge-based nanoparticle source in combination with biased surface electrodes and charged photoresist patterns to accomplish the required programmable site selective deposition. The nanobridges form through nearest neighbor coulombic interaction.

To match the properties of a semiconductor to a desired application, it is crucial to control its crystal structure. Here, we show that, by implementing a corona discharge in a chemical vapor depos...

Ternary (Si1-xCy)Gex+y solid solutions were grown on Si-face 4H-SiC applying atomic layer molecular beam epitaxy at low temperatures. The grown layers consist of twinned 3C-SiC revealed by cross section electron microscopy. The germanium was incorporated on silicon lattice sites as revealed by atomic location by channeling enhanced microanalysis transmission electron microscopy studies. The Ge concentration of the grown 3C-(Si1-xCy)Gex+y heteroepitaxial layers decreases with increasing growth temperatures, but exceeds the solid solubility limit.

This article reports on the use of corona discharge to assist the vapor liquid solid growth of gallium oxide nanowires on silicon carbide substrates. The corona discharge increases the nucleation efficiency of the gold catalysts from 60% to 98% for 3C-SiC(1 1 1)/Si(1 1 1) Si-face substrates and from 15% to 80% for 6H-SiC(0001) substrates. The growth mode and crystal structure are not affected by the corona discharge. The gallium oxide growth starts with the formation of [ −3 1 1] oriented laterally overgrown terrace like nucleation zones with the gold catalyst particles floating on top. With evolving process time, the growth proceeds in the faster [0 1 0] direction, resulting in nanowires with an inclination angle of 51° towards the substrate surface. On silicon and sapphire substrates, the nucleation and growth of gallium oxide nanowires are suppressed.

This contribution shows self-aligning ruthenium interconnects. The underlying process is gas phase electrodeposition, which allows metallic particles to be deposited locally. This is performed with an adjustable airgap between the insulator and the deposited metallic structure. The size of the enclosed airgap can be adjusted directly. The deposition power has a direct influence on the growth rate and the morphology of the structure. With increasing deposition power, the resulting self-aligning nano-bridge becomes more compact.

Aluminium oxide was deposited on silicon, silicon carbide and epitaxial graphene grown on silicon carbide by atomic layer deposition using a standard MOCVD equipment. The morphology and the electrical properties of the aluminium oxide layers on both substrates were determined and compared to aluminium oxide layers deposited with a standard atomic layer deposition equipment. The high-k material fabricated with the developed MOCVD process show comparable or better properties compared to the standard atomic layer deposition process.

Epitaxial graphene on semiinsulating silicon carbide was grown using a high temperature method at atmospheric pressure in argon atmosphere. The temperature dependence of the layer quality was analysed using Raman and infrared spectroscopy. It is demonstrated that infrared spectroscopy can be used as a versatile tool to access the layer count and the quality of the epitaxial grown graphene on silicon carbide. The results obtained by infrared spectroscopy correlate with the Raman measurements.

Gallium oxide nanowires were grown on different substrates using a corona plasma assisted vapor phase epitaxy process and gold catalyst. It is shown that the silicon carbide pseudo substrate in combination with the plasma excitation of the gas phase supports the growth of the gallium oxide nanowires. Analyzing the orientation of the nanowires with respect to the growth surface, it is concluded that the nanowires growth proceed along the fast growth direction of gallium oxide.

Gallium nitride (GaN) is commonly used in high-power and high-frequency devices but one limiting factor for its wide application is the availability of cost-effective substrates. The approach of “engineered substrates” is consequently followed up in this work. Low temperature cofired ceramics are used as carrier substrates in this work. The flexible material system allows the creation of a thermo-mechanically compatible base for GaN components. Sputtered aluminum nitride (AlN) layer form the buffer layer for the GaN deposition. The surface quality of these buffer layers reaches an arithmetic mean height R of 10 nm after chemical mechanical polishing and forms thus a surface quality which is adequate for thin film processing. GaN layers grown on these substrates can have both, tensile and compressive stress levels, while such grown on (100) silicon for comparison purpose show exclusively tensile stress. The growth of the GaN layer and resulting morphology is assumed to be mainly influenced by the process conditions during molecular beam epitaxy. The polycrystalline GaN layers show pronounced c-axis orientation at deposition temperatures of 700°C and 800°C. These first results encourage a further development of this new substrate architecture for integrated GaN systems.

All carbon three terminal junctions were fabricated from epitaxial graphene grown on semiinsulating Si-face 4H-SiC. It is demonstrated that self-contained gate devices exhibit current modulation characteristics. The obtained current gain depends on the device design and is controlled by the applied gate voltage.

In this work, side gate transistors based on graphene and molybdenum disulfide in comparison to their respective top or back gated devices are presented. The graphene devices were fabricated based on an all carbon technology on silicon carbide substrates, whereas the molybdenum disulfide transistors were fabricated using the exfoliation technique. The output characteristics are analyzed in terms of transconductance in dependence on the geometrical device properties for each material. It is shown that side gate transistors are able to reach the transconductances of conventional top-gate MOSFETs and that this type of transistor can be used as a simple tool for material properties characterization.

An anisotropic etching process for mesa structures using fluorinated plasma with hydrogen addition was developed in an electon cyclotron resonance setup. The evolution of the mesa morphology was studied in dependence on the gas composition, the applied bias and the pressure. The achieved side wall slope approached 90° with a negligible trenching. The aspect ratios of the fabricated structure in the developed residue free ECR plasma etching process were between 5 and 20.

Graphene was grown on semiinsulating silicon carbide at 1800 °C and atmospheric argon pressure. The all carbon T- and Y-shape three terminal junction devices were fabricated using electron beam lithography. All devices featured the negative rectification effect. The exact properties of the devices like the curvature of the output voltage response can be tuned by changing the branch width in the T- and Y-shape devices. Beside the rectification a switching behavior is demonstrated with the same three terminal junctions.

AlGaN/GaN heterostructures were grown on sapphire and alternatively on silicon substrates covered with a thin SiC layer by MOCVD. The side gated transistors were fabricated using electron beam lithography. The conductivity of the drain-source branch could be tuned via the side gate formed by a two-dimensional electron gas directly connected to the source drain branch or separated by a trench. The electrical measurements of the fabricated in-plane-gated devices revealed unipolar transistor behavior for both types of substrates. The transconductance was 1 µA/V and the output conductance reached 1.9 µA/V for the side gate transisitor on sapphire. The transconductance and output conductance of the side gate device on silicon substrates were 6 and 18 µA/V, respectively. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

As an alternative to the standard Au-based ohmic contacts, in this letter, Ti/TiN contacts were used to fabricate GaN high-electron mobility transistors (HEMTs) with two barrier designs (Al0.2Ga0.8N/AlN and Al0.35wGa0.65N). The ohmic contact resistance for this Au-free metallization scheme with a very smooth surface morphology is $0.13~\Omega $ mm and the specific contact resistance is $\sim 10^{\mathrm {\mathbf {-6}}}~\Omega $ $\mathrm{cm}^{\mathrm {\mathbf {2}}}$ . Our best 100-nm gate transistors show a maximum drain current density of 1.13 A/mm and a peak extrinsic transconductance of 388 mS/mm. The fastest transistors with a gate length of 80-nm achieve cutoff frequencies of 176 GHz, rivaling the fastest GaN HEMTs on silicon and silicon carbide substrate with comparable gate length and Au-based ohmic contacts.

Al0.35Ga0.65N/GaN- and Al0.2Ga0.8N/AlN/GaN-heterostructures high electron mobility transistors (HEMTs) with a gate length (LG) varying from 1.2 to 0.08 µm were fabricated on silicon Si(111) substrates using a 3C-SiC transition layer. Metal organic chemical vapour deposition (MOCVD) was used to growth the AlGaN-heterostructures and a low pressure chemical vapour deposition (LPCVD) to create the 3C-SiC(111) transition layer preventing Ga-induced melt back etching and Si-out diffusion. Reduced Al content and an AlN interlayer improved the device performance. The HEMTs with LG=0.08µm had a maximum drain current density of 1.25 A/mm and a peak extrinsic transconductance of 400 mS/mm. A unity current gain cut-off frequency (ƒT) of 180 GHz and maximum frequency (ƒmax) of 70 GHz were measured on these devices.

Cubic polytypes of SiC, GaN and AlN were grown on silicon by molecular beam epitaxy. The mechanical properties of the epitaxial layers were investigated by nanoindentation. For 3C-SiC grown on Si(111) and Si(100) a dependence of the mechanical properties on the surface preparation with germanium prior to the carbonization was obtained.

Heteroepitaxial graphene on semiinsulating silicon carbide was used to fabricate nanoelectronic devices. T- and Y-branched graphene three-terminal junction devices were realized. Room temperature electrical measurements demonstrate pronounced nonlinear electrical properties of the devices. Voltage rectification at room temperature was observed. Increasing branch width reduces the curvature of the voltage rectification response curve of the three-terminal junc¬tions.

The dependence of the electrical properties of backgate graphene field effect transistor on the silicon surface preparation techniques prior to graphene exfoliation was studied. The influence of standard wet chemical cleaning, with and without a finishing step in an oxygen plasma are compared to a surface preparation finished by hexamethyldisilazane deposition. The carrier drift mobility of backgate p-channel graphene transistors was determined from the measured transconductance. The backgate graphene field effect transistor fabricated by bonding graphene on silicon dioxide modified with hexamethydisilazane showed an improved carrier drift mobility at low electric fields and higher transconductance.

We present the realization of high electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures, which were grown on silicon substrates using an ultrathin SiC transition layer. The growth of AlGaN/GaN heterostructures on 3C-SiC(111)/Si(111) was performed using metalorganic chemical vapour deposition (MOCVD). The 3C-SiC(111) transition layer was realized by low pressure CVD and prevented Ga-induced meltback etching and Si-outdiffusion in the subsequent MOCVD growth. The two-dimensional electron gas (2DEG) formed at the AlGaN/GaN interface showed an electron sheet density of 1.5 × 1013 cm− 3 and a mobility of 870 cm2/Vs. The HEMTs DC and RF characteristics were analysed and showed a peak cut-off frequency as high as 29 GHz for a 250 nm gate length.

To improve the quality of AlN layer deposit on SiC/Si, different Ge amounts (0.25, 0.5, 1, 2ML) were deposited before the carbonization process at the silicon substrate in order to reduce the lattice parameters mismatch between Si and SiC grown layers. The residual stress of the hexagonal AlN layers derives from the phonon frequency shifts of the E1(TO) phonon mode. The crystalline quality of the AlN layer is correlated to and investigated by the full width of the half maximum (FWHM) and the intensity of E1(TO) mode of the 2H-AlN. Best crystalline quality and lower stress value are found in the case where 1ML of Ge amount is predeposited. The E1(TO) mode phonon frequency shifts-down by 3 cm-1/GPa with respect to an unstrained layer.

Three-terminal junction devices were realized in graphene grown heteroepitaxially on semiinsulating silicon carbide as well as in AlGaN/GaN heterostructures grown by MOCVD on sapphire containing a two dimensional electron gas. These nanoelectronic devices were fabricated using electron beam lithography. In both types of heterostructures room temperature electrical measurements revealed a pronounced nonlinear electrical behavior of the fabricated nanoelectronic devices. The obtained voltage rectification at room temperature demonstrates the feasibility of func-tional three-terminal junctions in heterostructures consisting of types of high carrier mobility struc-tures than classical III-V semiconductor heterostructures.

Optical measurements are used to investigate the crystalline quality and the stress in thin AlN layers; these thin films are grown on cubic silicon carbide layers which are in turn grown on silicon (111) substrates. Different Ge amounts were deposited at the silicon substrate in order to reduce the lattice parameters mismatch between Si and SiC grown layers. The residual stress of the hexagonal AlN layers is derived from the phonon frequency shifts of the E 1 (TO) phonon mode. The crystalline quality of AlN films is investigated by considering the intensity of E 1 (TO) mode of the 2H-AlN and its full width of the half maximum (FWHM). Ge deposition at low temperature 325 °C, before the carbonization process leads to an improved crystalline quality and a reduced residual stress in the AlN/SiC/Si heterostructures. The best crystalline quality and the lowest stress value are found in the case where 1ML Ge amount was predeposited. The E 1 (TO) mode, phonon frequency shifts-down by 3 cm − 1 /GPa with respect to an unstrained layer. The obtained values for the phonon deformation are in reasonable agreement with theoretical calculations.

Epitaxial graphene was grown on Si-face 4H-SiC. A SiC pretreatment with a carbon cap¬ping technique was used as well as slow heating rates and a temperature of 1800 °C under atmos¬pheric argon pressure. The surface morphology was investigated by atomic force microscopy and Raman spectroscopy was performed for samples with different graphitization times.

XPD and XRD measurements revealed a difference in the crystallographic polarity of 3C-SiC(111) grown on Si(111) carbonized by ethene diluted in hydrogen at atmospheric pressure in a rapid thermal chemical vapour deposition reactor and the crystallographic polarity of 3C-SiC(111) formed in an ethene hydrogen gas mixture at low pressures. In the first case C-face polar material was formed, whereas in the second case the grown expitaxial layer exhibits Si-face surface polarity.

Black silicon is a fascinating multipurpose modification of bulk silicon which can be fabricated in a selforganized structure formation process during dry etching of bare silicon wafer leading to the formation of a high density of silicon needles. The smallest dimension of the tips approaches values between 1 and 2 nm. The silicon nanostructure exhibits an extremely low diffuse reflectivity. The nanosized tips and their coating with fluorine doped nonstoichiometric silicon dioxide are responsible for cathodoluminescence in the blue-green and red regions of the visible spectra (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An approach for the reconstruction of the composition profiles of heterostructures with chemically modified interfaces is presented. It is based on the comprehensive simulation of the heterostructure growth stages and the compositional changes occurring at the depth profiling stage during sputtering by secondary ion mass spectrometry. Combining simulation of the growth and the concentration measurement process allows the calculation of the real concentration depth profiles of the heterostructure components. Within the framework of the proposed approach, the composition of the SiC:Ge/Ge/Si:Ge/Si heterostructure is analyzed and the real depth profiles were calculated.

Structural evolution of indium oxide thin films deposited at room temperature by reactive magnetron sputtering and annealing in a reducing atmosphere were investigated. The as deposited indium oxide (In 2 O 3 ) films showed a dominating randomly oriented nanocrystalline structure of cubic In 2 O 3 . The grain size decreased with increasing oxygen concentration in the plasma. Annealing in reducing atmospheres (vacuum, nitrogen and argon), besides improving the crystallinity, led to a partial cubic to rhombohedral phase transition in the indium oxide films. Annealing improved the optical properties of the indium oxide film and shifted the absorption edge to higher energies.

In this work nanostructures based on a 30 nm thick 3C-SiC (100) heteroepitaxially grown on Si(100) are demonstrated. They consist of free standing nanoresonators with dimensions below 50 nm. The free standing nanostructures and resonators were defined by electron beam lithography using hydrogen silsesquioxane (HSQ) as a negative tone e-beam resist acting as a selective etching mask during the anisotropic and isotropic dry etching. The influences of the proximity effect, the crystallographic orientation, the angle of exposing on the feature size are highlighted.

Germanium modified silicon surfaces in combination with two step epitaxial growth technique consisting in conversion of the Si(100) substrate near surface region into 3C-SiC(100) followed by an epitaxial growth step allows the manipulation of the residual strain. The morphology and the residual strain in dependence on the Ge coverage are only affected by the Ge quantity and not by the growth technique. The positive effect of the Ge coverage is attributed to changes in the morphology during the conversion process, as well as to a reduced lattice and thermal mismatch between SiC and Si in consequence of alloying the near surface region of the Si substrate with Ge.

We present the realization of high electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures grown on silicon substrates using a SiC transition layer. The growth of AlGaN/GaN heterostructures on Si (111) was performed using metalorganic chemical vapour deposition (MOCVD). The (111) SiC transition layer was realized by low pressure CVD and prevented Ga-induced meltback etching and Si-outdiffusion in the subsequent MOCVD growth. The two-dimensional electron gas (2DEG) formed at the AlGaN/GaN interface showed an electron sheet density of 1.5x1013 cm-3 and a mobility of 870 cm²/Vs proving the high structural quality of the heterostructure. Device processing was done using electron beam lithography. DC and RF characteristics were analysed and showed a peak cut-off frequency as high as 6 GHz for a 1.2 µm gate HEMT.

A comprehensive characterization of the optical properties of wurtzite InN films grown by molecular beam epitaxy on Si(111) substrates is presented. Two types of films are investigated in this work: InN on AlN/Si(111) and InN on GaN/AlN/Si(111). Their properties are compared to a layer deposited on GaN/sapphire substrate. The dielectric function (DF) is obtained from spectroscopic ellipsometry (SE). The infrared studies yield the plasma frequency and thus the electron density, while the interband absorption is probed between 0.56 and 9.8 eV. For InN grown on Si(111) substrate, the absorption onset is slightly shifted to higher energies with respect to the InN film grown on GaN/sapphire which can be attributed to higher electron concentrations. Despite this, strongly pronounced optical transitions due to critical points of the band structure are found in the high-energy part of the DF. It emphasizes the already promising quality of the InN films on silicon. Band-gap renormalization (BGR), band filling, and strain are taken into account in order to estimate the intrinsic band gap of wurtzite InN. For the InN layers on silicon, we get a band gap between 0.66 and 0.685 eV.

The deposition of Germanium (Ge) prior to the conversion of Si(100) into 3C-SiC(100) results in changes of the structure and surface morphology of the formed silicon carbide layer. First of all it reduces the thickness of the 3C-SiC layer grown during the conversion process and therefore the probability of voids formation. Secondly, it increases the nucleation density of the formed 3C-SiC nuclei and therefore, decreases the grain size at Ge coverages below two monolayers. These affect the roughness of the SiC surface positively by modifying the width of the SiC-Si interface. If the Ge coverages exceed two monolayers the structural and morphological properties begin to degrade. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Structures grown using the technique of molecular-beam epitaxy during deposition of carbon and/or germanium atoms on an Si(111) surface were investigated experimentally and theoretically. Experimental profiles of in-depth component distribution were obtained using SIMS-profiling, whereas a complex technique of computer simulation taking into account diffusion and ballistic processes was applied for the calculated profiles.

The polarity of the 3C–SiC epitaxial layers grown on 3C–SiC(1 1 1)/Si(1 1 1) pseudosubstrates formed by carbonization using the deposition of elemental carbon under ultra-high vacuum conditions and alternatively at atmospheric pressure in a rapid thermal chemical vapour deposition reactor were studied with different diffraction and electron spectroscopy methods. It is unambiguously shown that the conversion under CVD conditions and the chosen heating-up rate led to the formation of C-face 3C – SiC ( 1 ¯ 1 ¯ 1 ¯ ) , where as for lower heating-up rates and carbon fluxes Si-face 3C–SiC(1 1 1) was obtained. The crystallographic polarity of the carbonized layers is then reproduced during epitaxial growth. Comparing the measurement results of different techniques available to detect the absolute crystallographic orientation it is shown that X-ray diffraction can be used routinely for the determination of the crystallographic polarity, even if the layers are much thinner then the penetration depth of the X-ray radiation. A model, which is based on the formation of energetically or kinetically favoured surface reconstructions at the early stages of the Si to SiC conversion process, is proposed to explain the formation of the different crystallographic polarities of 3C–SiC on a nonpolar Si(1 1 1) substrate.

The annealing of semiconductor surfaces via pulsed laser melting has been practised since the 70 ' s. During the process a thin surface layer is molten up to a depth of mkm and recrystallises, after the pulse is over, epitaxially on the non molten substrat. Depending on the segregation coefficient of additionally admixed atoms completely different doping profiles can be achieved. Typical for all pulse irradiation techniques is, that the melting process starts near the surface. The aim of the present work is to overcome this phenomen and to force a buried melting by large area flash lamp irradiation using an additional Ge admixture. The addition of Germanium locally leads to a reduction of the silicon melting temperature so that separated melting in the bulk of silicon can be observed. During cooling down of the sample the buried liquid layer recrystallises epitaxially on the non molten bulk material and for the case of additional doping of the layer special profiles can be observed. Ion implantation at high doses and high energies was used to produce structures with a buried germanium enriched layer. The pulse irradiation was performed at the Rossendorf flash lamp apparatus using intense light pulses with a duration of 20 ms from a field of Xe flash tubes. The energy density at the sample surface was varied within wide limits. For the determination of the Ge profiles after the flash lamp irradiation the RBS technique was used. The microstructure of the recrystallised films was observed by cross sectional TEM. It could be shown that buried melting takes place whereby the width of the molten zone depends on the energy density. Deep facetted melting, typical for virgin silicon material, was not observed.

A detailed investigation of the Ge concentration in implanted samples has been carried out by SIMS and the effects affecting the depth distribution and measurement results have been determined. It is found that the MCs+ SIMS technique is best suited to investigate Gex(4H-SiC)1-x solid solutions up to x=0.2, while the O2+ SIMS configuration is limited to x=0.1. The Ge concentrations obtained by SIMS are very close to the nominal values. On the opposite, performing a comparison with previous RBS data, we find that the RBS values are systematically underestimated by ~30%. Finally, at very high dose, we find that some of the implanted species are lost by recoil and sputtering effects.

Cubic gallium nitride epitaxial layers grown on differently carbonized silicon substrates were studied by high resolution X-ray diffraction. In the case of cubic GaN layers with equal layer thickness an improvement of the layer quality in terms of full width of the half maximum can be achieved by using higher carbonization temperatures. The higher crystalline quality led to an in¬crease of the residual stress in the grown layer. An increase in the thickness of the cubic Gallium Nitride allows to improve the crystallinity and to reduce the residual stress.

Carbon is able to crystallise in different allotrope modifications. They mainly differ in the dominating bindings formed in dependence on the hybridization sp, sp2 and sp3 of the carbon atoms. The present work demonstrates the formation of two different forms of car¬bon allotropes by heating both polar surfaces of on axis 6H-SiC(0001) and 6H-SiC(000 ) crystals to temperatures above 1600°C. In consequence of the structural evolution graphite-like (sp2-hybridised) and carbine-like (sp-hybridised) allotropic carbon modifications were obtained.

The influence of Ge deposition prior to carbon interaction with 3° off-axis Si(111) substrates on the structural and morphological properties of the formed silicon carbide (SiC) layer is studied. In situ reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) revealed the formation of the cubic silicon carbide (3C-SiC) modification. In situ spectroscopic ellipsometry measurements revealed a decreasing 3C-SiC thickness with increasing Ge predeposition. Atomic force microscopy (AFM) studies revealed that the surface overlayer morphology is mainly formed by periodic step arrangements whose relevant geometric parameters, i.e. lateral separation, height and terrace width, depend on the Ge content. Besides the changes of the step morphology, the surface roughness and the grain size and the strain of the formed 3C-SiC decreases with increasing germanium precoverage. Copyright © 2008 John Wiley & Sons, Ltd.

In this paper we present a methodology to affect the stability of polytypes formation during heteroepitaxial growth of SiC on Si. This methodology is based on the investigation of growth related parameters. These parameters involve substrate temperature, effect of impurities on surface diffusion, strain, and super-saturation conditions as solved by using SSMBE growth (Solid Source molecular beam epitaxy).

Infrared ellipsometry is a valuable tool to investigate the average stress and the stress distribution in thin silicon carbide layers grown on silicon as well as to monitor the changes in the stress state during device processing. It was obtained that low temperature carbonization in combination with low temperature epitaxial growth led to a compressive stress component in the SiC-Si interface region, whereas the aver'"' age stress state is tensile. Ge incorporation in the interface lowered the tensile residual stress component. Metallization of SiC increases the tensile stress in the SiC on Si.

The influence of Ge on the conversion process of Si to SiC was studied by depositing Ge and C on Si(111) followed by a stepwise annealing procedure. After the annealing step, the carbon deposited on the surface was completely converted into SiC. In the case of Ge predeposition, the SiC amount detected by XPS, AES and ellipsometry was lower compared to the reference sample in which no Ge was predeposited on the Si(111) surface. Therefore, Ge lowers the probability of SiC formation in the early stages. During the conversion process, Ge diffuses into the Si substrate and is mainly located near the SiC – Si interface with a concentration of around 2.5 – 3%. As a result of a complex alloying process promoted by interdiffusion of C and Ge as well as SiC nucleation, a thin 3C-SiC layer is formed on top of a Si1−xGex buffer layer. Copyright c � 2008 John Wiley & Sons, Ltd.

The influence of the growth conditions on the 3C-SiC layer quality in terms of crystallinity, morphology and residual strain was investigated. In dependence on the chosen growth conditions the stress state can be varied between inhomogeneous and homogeneous strain. For the reduction of the residual strain an alternative route for the improvement of the epitaxial growth of 3CSiC( 100) on Si(100) was developed. It consists in covering the silicon wafers with germanium prior to the carbonization step. The achieved improvement in the residual strain and crystalline quality of the grown 3C-SiC layers is comparable to SOI substrates. These beneficial effects were reached by using a Ge coverage in the range of 0.5 to 1 monolayer with respect to the silicon surface.

4H silicon carbide (Si 1-x C 1-y )Ge x+y solid solutions with an average Ge incorporation on lattice sites ranging from 0.7 to 2.5 percent were formed by ion beam synthesis. RBS and RBS/C investigations revealed a decreasing Ge lattice incorporation with increasing implantation dose above 10%. The carried out rapid thermal annealing at 1300 °C reduces the residual damage, increases the lattice site occupation and led to negligible change in the concentration profiles.

The effects of argon and nitrogen bombardment of 3C-SiC surfaces at acceleration voltages below 2 keV were studied by stylus profilometry, reflectometry, reflection high energy electron diffraction and Auger electron spectroscopy (AES). The erosion rate of the SiC surface was determined. It was found that the sputtering rate for argon was three times higher compared to nitrogen. AES measurements revealed argon and nitrogen incorporation at a depth of a few nanometers as well as stoichiometric changes at the same depth scale independent of the acceleration voltage. In the case of the interaction of nitrogen ions with the 3C-SiC surface the formation of a SiCNalloy was detected.

Flash lamp annealing of multilayer stack of the type SiC/Silicon overlayer(SOL)/SiC reduces the defect densities in the 3C-SiC/Si heteroepitaxial structure. Ge and C additions to the SOL lead to a substantial increase of the mass transfer from the upper layer to the lower SiC layer. If the Ge content of the SOL and the flash lamp annealing conditions are properly chosen a homogeneous layer with a 3C-SiC thickness between 150 and 200 nm can be achieved corresponding to a growth rate between 7.5 and 10.0 +m/s. The thickening of the lower layer depends on the SOL composition. Ge and/or C incorporation into the SOL and therefore into the Si melt enhances the mass transport from the upper SiC layer to the lower one.