Monocrystalline Structures Research Articles

Ultralow Resistivity Ge:Sb heterostructures on Si Using Hydride Epitaxy of Deuterated Stibine and Trigermane.

The nonconventional deuterated stibine (SbD3) compound has been used for the first time in combination with trigermane (Ge3H8) to produce hyper-doped Ge-on-Si films with carrier concentrations n > 10(20) cm(-3) and record-low resistivities ρ = 1.8 × 10(-4) Ω cm. The growth takes place on Ge and Ge1-xSix buffered Si(100) wafers at ultralow temperatures (∼330 °C) at which Sb diffusion is negligible, leading to extremely flat atomic profiles of the constituents. The Sb substitution in the Ge lattice is determined by RBS channeling and corroborated by high-resolution XRD, which also reveal a systematic increase in lattice constant vs concentration, as expected due to the incorporation of the larger Sb. High-resolution TEM illustrates defect-free monocrystalline structures with device-quality morphologies. The electrical characteristics of the samples are measured using Hall effect and resistivity measurements combined with contactless infrared ellipsometry and are found to be consistent with an extrapolation of the bulk Ge:Sb properties to the high carrier concentrations achieved in our films. The Sb/Ge ratio in the doped layers is approximately the same as that in the precursor reaction mixture, indicating a highly efficient Sb incorporation afforded by the compatible reactivity of the molecules employed in this study. The resultant films are attractive for next generation germanium technologies that require low-resistance n+ junctions or a Fermi level that approaches the direct gap minimum in the conduction band, which drastically enhances the optical emission efficiency of n-type Ge.

1/F α-Type Noise in Lead Sulfide-Based Photosensitive Elements

Of all the different types of infrared radiation photodetectors, only photoresistors based on lead sulfide PbS possess a variety of different methods and technologies of fabrication. This is because the first photoresistors were fabricated before the development of the theory of photoconductivity in monocrystals and, second, because of the failures which developers of photodetectors based on monocrystalline structures had experienced. The high absorption factor (10 4 cm ‐1 ) [1] suggested the use of thin (1‐2 µm) layers, whereas production of monocrystalline layers by an epitaxial method is possible only at high concentrations of the majority carriers (p ≥ 10 17 cm ‐3 ), which led to a decrease in the life of the carriers. Often, such films are considered to be nonphotosensitive, since the life of the carriers becomes less than their flight time to contact. Polycrystalline films that are suitable for the fabrication of photodetectors are one alternative. Methods of producing these types of films are provisionally divided into chemical methods based on reactions between acetic lead Pb(CH 3 COO) 2 , thiocarbamide (NH 2 ) 2 CS, caustic soda, and other reduction-oxidation agents, and physical methods, in which the primary PbS layer is deposited in a vacuum by means of thermal deposition. In most of the technologies employed, the layer is then annealed in a muffle furnace, oxygen (which is an acceptor impurity) then being introduced into the film. In certain cases, a technique of redeposition of layers in a vacuum with one photodetector layer on top of another is used, as a result of which a layer entraps only the limited number of molecules of oxygen necessary for increasing the life of the vacancies. Successes in the development of photodetectors based on polycrystalline films functioning at a frequency of 400‐1000 Hz have made it possible to solve urgent problems. In the transition from monocrystalline to polycrystalline layers, the mobility of the carriers falls 100-fold (with increasing dark resistance), with 1/F α -type noise becoming dominant over

Nanograin Effects on the Thermoelectric Properties of Poly-Si Nanowires

In this work we perform a theoretical analysis of the thermoelectric performance of polycrystalline Si nanowires (NWs) by considering both electron and phonon transport. The simulations are calibrated with experimental data from monocrystalline and polycrystalline structures. We show that heavily doped polycrystalline NW structures with grain size below 100 nm might offer an alternative approach to achieve simultaneous thermal conductivity reduction and power factor improvements through improvements in the Seebeck coefficient. We find that deviations from the homogeneity of the channel and/or reduction in the diameter may provide strong reduction in the thermal conductivity. Interestingly, our calculations show that the Seebeck coefficient and consequently the power factor can be improved significantly once the polycrystalline geometry is properly optimized, while avoiding strong reduction in the electrical conductivity. In such a way, ZT values even higher than the ones reported for monocrystalline Si NWs can be achieved.

Selenium Nanoparticles Synthesized via a Facile Hydrothermal Method

Crystalline selenium nanostructures were synthesized from the reaction of a GeSe3 glass with water at 85°C for 144 hours. The hydrolysis of the Ge-Se bonds releases Se fragments in the solution where they form a colloidal suspension of amorphous nanospheres. The later evolve toward a more stable hexagonal phase (trigonal) leading to the anisotropic growth of one-dimensional monocrystalline structures. Filaments, bars and tubes of monocrystalline trigonal selenium were obtained with diameters ranging from 10 nm to 1 µm and aspect ratio up to 180. This simple process in aqueous solution opens new perspectives for the synthesis of 1D nanoparticles of trigonal selenium at large scale.

Growth of heavily doped monocrystalline and polycrystalline SiGe-based quantum dot superlattices

Various SiGe-based Quantum Dot Superlattices (QDSLs) were grown using an industrial Chemical Vapor Deposition tool with the intent to develop efficient thermoelectric thin films at a large scale. We report first on the growth of monocrystalline SiGe-based QDSLs. We were able to control the SiGe spacer width and the sizes and densities of Ge dots. A vertical ordering behavior was observed for large dot structures, but not for those with the smallest dots (30–70nm wide, 3nm high). In situ B doping operated during growth led to hole densities of 5×1019 to 1×1020cm−3. We also report on the growth of polycrystalline SiGe-based QDSLs with the same equipment. We show in particular that vertically aligned Ge dots were formed in a similar way as in monocrystalline structures despite the presence of stacking faults and grain boundaries. A heavy p doping was also obtained on some of these structures.

Designer hydride routes to ‘Si–Ge’/(Gd,Er)2O3/Si(1 1 1) semiconductor-on-insulator heterostructures

We demonstrate Si–Ge integration on engineered M2O3/Si(1 1 1) (M = Gd,Er) dielectric buffer layers using non-traditional chemical precursors that provide new levels of functionality within the deposition process. Stoichiometric Si0.50Ge0.50 alloys and pure Si heterostructures are grown epitaxially via ultra-low-temperature chemical vapor deposition using SiH3GeH3 and Si3H8/Si4H10, respectively. In the case of Si on Gd2O3, an optimal growth processing window in the range of 500–600 °C was found to yield planar layers with monocrystalline structures via a proposed coincidence lattice matching mechanism (2aSi–aGd2O3), while for the SiGe system (2% lattice mismatch) comparable quality films with fully relaxed strain states are deposited at a lower temperature range of 420–450 °C. Extension of this growth process to Si on Er2O3 yields remarkably high-quality layers in spite of the even larger ∼3% lattice mismatch. In all cases, the Si–Ge overlayers are found to primarily adopt an A–B–A epitaxial alignment with respect to the M2O3 buffered Si(1 1 1). A comparative study of the Si growth using Si3H8 and Si4H10 indicates that both compounds provide an efficient and straightforward process for semiconductor growth on Gd2O3/Si(1 1 1), which appears to be more viable than conventional approaches from the point of view of scalability and volume.

Structural, electrical and optical properties of thermochromic VO2 thin films obtained by reactive electron beam evaporation

We present the structural and physical characterization of vanadium dioxide (VO2) thin films prepared by reactive electron beam evaporation from a vanadium target under oxygen atmosphere. We correlate the experimental parameters (substrate temperature, oxygen flow) with the films structural properties under a radiofrequency incident power fixed to 50W. Most of the obtained layers exhibit monocrystalline structures matching that of the monoclinic VO2 phase. The temperature dependence of the electrical resistivity and optical transmission for the obtained films show that they present thermoelectric and thermochromic properties, with a phase transition temperature around 68°C. The results show that for specific experimental conditions the VO2 layers exhibit sharp changes in electrical and optical properties across the phase transition.

Comparing Atomistic Machining of Monocrystalline and Polycrystalline Copper Structures

A molecular dynamic simulation study is presented to compare the machining of monocrystalline and polycrystalline copper structures with a rigid diamond tool at atomistic level. The equivalent grain size is 6 nm for the polycrystalline copper structure, which consists of 32 single crystals (i.e., grains) in total. Four cutting conditions of 3-D orthogonal machining are simulated for comparison. The results show that for both monocrystlline and polycrystalline machining, cutting forces increase with the increase of depth of cut, and the stress levels in primary and secondary shear zones increase with the increase of machining speed. More importantly, smaller cutting forces are required to machine the polycrystalline structure than the monocrystalline structure for all cutting conditions. This also leads to the lower stress levels in shear zones. In addition, in polycrystalline machining, the tangential forces are higher than the thrust forces, while the opposite is observed for monocrystalline machining. The results can be attributed to the grain boundary sliding mechanism in the nanostructured copper workpiece.

Polyphenylene Dendrimer‐Templated In Situ Construction of Inorganic–Organic Hybrid Rice‐Shaped Architectures

AbstractA novel dendrimer‐templating method for the synthesis of CuO nanoparticles and the in situ construction of ordered inorganic–organic CuO–G2Td(COOH)16rice‐shaped architectures (RSAs) with analogous monocrystalline structures are reported. The primary CuO nanoparticles are linked by the G2Td(COOH)16 dendrimer. This method provides a way to preserve the original properties of primary CuO nanoparticles in the ordered hybrid nanomaterials by using the 3D rigid polyphenylene dendrimer (G2Td(COOH)16) as a space isolation. The primary CuO nanoparticles with diameter of (6.3 ± 0.4) nm are synthesized via four successive reaction steps starting from the rapid reduction of Cu(NO3)2 by using NaBH4 as reducer and G2Td(COOH)16 as surfactant. The obtained hybrid CuO–G2Td(COOH)16 RSA, formed in the last reaction step, possesses a crystal structure analogous to a monocrystal as observed by transmission electron microscopy(TEM). In particular, the formation process of the RSA is monitored by UV–vis, TEM, and X‐ray diffraction. Small angle X‐ray scattering and Fourier transform infrared spectroscopy are used to investigate the role of the dendrimer in the RSA formation process. The obtained results illuminate that Cu2+COO− coordination bonds play an indispensable role in bridging and dispersing the primary CuO nanoparticles to induce and maintain the hybrid RSA. More importantly, the RSA is retained through the Cu2+COO−coordination bonds even with HCl treatment, suggesting that the dendrimers and Cu2+ ions may form rice‐shaped polymeric complexes which could template the assembly of CuO nanoparticles towards RSAs. This study highlights the feasibility and flexibility of employing the peculiar dendrimers to in‐situ build up hybrid architectures which could further serve as templates, containers or nanoreactors for the synthesis of other nanomaterials.

Highly strained metastable structures and selective area epitaxy of Ge-rich Ge 1− xSi x/Si(100) materials using nanoscale building blocks

Low-temperature heteroepitaxy (330 ∘C–430 ∘C) of Si 0.5Ge 0.5 and Si 0.25Ge 0.75 on Si(100) using single-source silyl-germanes [ SiH 3GeH 3,HSi(GeH 3) 3] produces monocrystalline structures, smooth and continuous surface morphologies and low defect densities. The metastable compressive strain in these films is dramatically enhanced relative to alternative growth methods. At such low temperatures the material grows seamlessly, conformally, and selectively in the “source/drain” regions of prototypical transistors. These results suggest that films grown via silyl-germanes could have applications in optoelectronics and as stressors for mobility enhancement in Si devices.

In situ diagnostics of the crystalline nature of single organic nanocrystals by nonlinear microscopy.

We elucidate the crystalline nature and the three-dimensional orientation of isolated organic nanocrystals embedded in a sol-gel matrix, using a polarized nonlinear microscopy technique that combines two-photon fluorescence and second harmonic generation. This technique allows the distinction between monocrystalline structures and nanoscale polycrystalline aggregates responsible for incoherent second harmonic signals.

Critère de fatigue polycyclique pour des matériaux anisotropes : application aux monocristaux

The high-cycle fatigue criteria based on a macroscopic–mesoscopic scale interpretation, initiated by Dang Van, were used essentially for polycrystalline materials. In the existing criteria the material isotropy at both mesoscopic and macroscopic scales plays a key role. The purpose of this paper is to revisit the macroscopic to mesoscopic fatigue approach taking into account the material anisotropy and some results obtained by Bui. The possible applications are some anisotropic steels or monocrystalline structures such as stitanium turbine blades. To cite this article: F. Cano et al., C. R. Mecanique 332 (2004).

Synthesis of ternary SiGeSn semiconductors on Si(100) via SnxGe1−x buffer layers

Single-phase Si1−x−yGexSny alloys with random diamond cubic structures are created on Si(100) via ultrahigh vacuum chemical vapor deposition reactions of SnD4 with SiH3GeH3 at 350 °C. Commensurate heteroepitaxy is facilitated by Ge1−xSnx buffer layers, which act as templates that can conform structurally and absorb the differential strain imposed by the more rigid Si and Si–Ge–Sn materials. The crystal structure, elemental distribution and morphological properties of the Si1−x−yGexSny/Ge1−xSnx heterostructures are characterized by high-resolution electron microscopy, including electron energy loss nanospectroscopy, x-ray diffraction (rocking curves) and atomic force microscopy. These techniques demonstrate growth of perfectly epitaxial, uniform and highly aligned layers with atomically smooth surfaces and monocrystalline structures that have lattice constants close to that of Ge. Rutherford backscattering ion channeling shows that the constituent elements occupy random substitutional sites in the same average diamond cubic lattice and the Raman shifts are consistent with the lattice expansion produced by the Sn incorporation into SiGe tetrahedral sites.

β-FeSi2 thin-films grown by a pulsed laser deposition

AbstractOrthorhombic β-FeSi2 thin-films were prepared on Si(100) and Si(111) substrates by a pulsed laser deposition method. When the substrate temperature was 500°C, β-FeSi2 thin-films were grown on Si(100) and Si(111) substrates. The thin-films grown on Si(100) and Si(111) substrates were polycrystalline and monocrystalline structures, respectively. The values of band-gap energy calculated from transmittance measurements were 0.71-0.72 eV. From Raman scattering measurements, it was found that the distortion due to the lattice mismatch between a β-FeSi2 thin-film and a Si substrate originates in the β-FeSi2/n-Si interface. Moreover, the fine crystals of β-FeSi2 existed in an amorphous thin-film which was grown on Si(111) substrate at room temperature (RT).From van der Pauw measurements, conduction type, carrier concentration and Hall mobility were p-type, 1018-1021 cm−3 and 200-500 cm2/Vsec, respectively. The p-n diode characteristics of these heterostructure diodes were investigated by I-V and C-V measurements. The results indicate that the carrier distribution agrees with an ideal one-sided slope junction.

P-n junction on monocrystalline structure of Sb2Te3 doped with Se or S

The aim of this letter is to report the preparation of Sb2Te3-Sb2Teg_xSx and Sb2Te3-Sb2Te3_xS~ monocrystalline structures. Contrary to all expectations, p -n junctions 'were observed on these structures. Similar problems were discussed previously [1] for Bi2Te3-Bi2Se3 system. Samples with a concentration gradient of Se and S, respectively, were prepared from Sb2Te3 single crystals. Sb2Te3 single crystals were grown using the Bridgman method in conical quartz ampoules. The starting elements of semiconductor purity (99.999%) in the stoichiometric ratio were synthesized at a temperature of 1073 K for 48 h. Ampoules charged with synthesized polycrystalline material were lowered into t]~e temperature gradient of 400 K (5 cm) -I at a rate of 1.3 mmh -t. Single crystals obtained, approximately 60 mm long and 10 mm in diameter, were used to prepare the samples of dimensions 10 mm x 10 mm x 2 ram. The cleavage planes of single crystals formed the larger-area sides of the samples. The samples prepared in this way were annealed in S and Se vapour, respectively, at 623 K for 50 h. After annealing, the samples were cleaved into halves along the {0 0 0 1) planes. The resultant samples in plate-like form were of dimensions 10 m m x 10 m m x 1 mm, having higher concentration of S and Se, respectively, in one side of the sample. The concentration profiles of the samples were measured perpendicularly to the {0 0 0 1 ) planes by means of an energy-dispersive X-ray (EDX) microanalyser (KEVEX; Fig. 1). It follows from Fig. 1 that Se atoms diffuse into Sb2Te3 crystals relatively easily and form there an area of mixed crystal. This is in agreement with the phase diagram of the Sb2Teg-Sb2Se3 system [2]. The Sb atoms needed for the formation of a compound is probably taken from SbTe point defects. Therefore, the crystal volume increases. The process can be expressed by the equation

Ion implantation distributions in crystalline multilayer targets

Range distributions of Bi in Si/Ge multilayer structures and N in Au/Si double-layer structures have been calculated using the computer simulation code COSIPO. Various combinations of amorphous, random, polycrystalline and monocrystalline structures were studied. Good agreement with existing experimental data was found. The crystalline structure is predicted to have measurable effect on the distributions, but in the case of N in Au/Si the discontinuity in the distribution is more sensitive on the layer thickness.

Cw infrared laser annealing of ion-implanted silicon

Solid phase epitaxial regrowth of ion-implanted Si was obtained with cw infrared radiation of CO2 (10.6 μm) and Nd : YAG lasers. Arsenic-implanted samples were analyzed by optical and electron transmission microscopy and by Rutherford backscattering with channeling. Dislocation-free monocrystalline structures were obtained on substrates which were preheated to 200–400 °C and then scanned with a laser beam of ∼25 W. There was no redistribution of the implanted As and the sample surface was free of any features which might indicate melting. A channeling angular scan showed that the As atoms were located exactly on the lattice sites. However, the relatively high values of sheet resistance suggest the presence of residual point defects.