Oriented Si Substrates Research Articles

Synthesis of nanocrystalline In2O3 on different Si substrates at wet oxidation environment

Polycrystalline cubic indium oxide (In2O3) thin films were successfully grown without catalyst on the different orientation of Si substrates. In2O3 thin films have been synthesized by thermal evaporation of indium on unheated Si substrates, followed by wet oxidation process. The structural and optical properties of the In2O3 films were studied in terms of different substrates orientation. Through the Scherrer structural analysis revealed nanocrystalline structure for In2O3 films grown on Si (110), Si (100) and Si (111) orientations with crystallite size of 2.53, 3.36 and 3.43nm, respectively. Photoluminescence spectra showed a strong and broad emission at 570nm with two shoulders at 547nm and 604nm which related to oxygen vacancies. The band gap of polycrystalline In2O3 is determined as 2.15±0.15eV.

Synthesis of ZnO: Ge nanocomposite thin films by plasma gas condensation

In this work, we introduce a new method for the synthesis of Ge nanoparticles embedded ZnO thin films that are considered to be a potential candidate for photovoltaic applications. As opposed to current techniques, for the independent preparation of Ge nanoparticles, we propose using Cluster Deposition Source (CDS), which utilizes gas condensation of sputtered Ge atoms. For the synthesis of ZnO thin film host material conventional sputtering technique is employed. In the proposed technique independently synthesized Ge nanoparticles and ZnO thin films are combined into a composite structure on (100) oriented Si substrates. X-ray diffraction (XRD) patterns of the samples have revealed that Ge nanoparticles preferentially settle on (113) planes on top of the (002) oriented ZnO layer. It is realized that Ge nanoparticles with sizes ranging from 16nm to 20nm could be embedded into a well-defined ZnO matrix. In fact, transmission electron microscopy (TEM) studies performed on Ge nanoparticles captured on a Cu grids placed just above the substrate during deposition for about 60s have manifested that Ge nanoparticles reach to ZnO matrix as clusters composed of particles with sizes of about 7–8nm and then eventually grow larger due to substrate heating implemented during capping layer deposition. Optical absorption measurements have revealed that Ge nanoparticle inclusion lead to an additional absorption edge at about 2.75eV along with 3.17eV edge resulting from ZnO host.

X‐ray pole figure analysis of ZnTe layers grown on lattice mismatched substrates

AbstractThe electro‐optical effect of ZnTe is recently highlighted, and various device structures utilizing ZnTe are explored. ZnTe substrates are recently commercially available, and high quality homoepitaxial layers can be grown. On the other hand, the cost of the substrate could be a concern for the practical device application. In this study, Si and Al2O3 substrates were used since they are widely used for many kinds of device applications. The lattice mismatch between those substrate materials and ZnTe is above 10% and those mismatch strain should be carefully considered. ZnTe layers were nucleated on chemically treated substrate surfaces. (111), (110), (211) oriented Si substrates and (0001), (11‐20), and (10‐10) planes of Al2O3 were used. By taking the pole figure data and studying the crystal symmetry of the domain, detail information associated with the formation of domains in the layer was discussed. The pole figure analysis revealed that several kinds of (110) oriented ZnTe domains rotated 60 degrees each other were formed on (110) oriented Si surface. On the other hand, preferentially oriented single domain of (111) was confirmed for the layer grown on the (0001) plane of Al2O3. ZnTe layers grown on (10‐10) plane Al2O3exhibited a unique domain formation. Pole figure data combined with the conventional theta‐2theta measurement indicated that (211) oriented plane of ZnTe was a dominant domain formed on the (10‐10) plane Al2O3. These crystallographic features would be related to the interface valency as well as the interfacial bond structure. X‐ray pole figure method was a useful and powerful method to study the domain formation of the severely lattice mismatched structures. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Self-aggregated Si quantum dots in amorphous Si-rich SiC

Amorphous silicon quantum dots (Si-QDs) self-aggregated in silicon-rich silicon carbide are synthesized by growing with plasma-enhanced chemical vapor deposition on (100)-oriented Si substrate. Under the environment of Argon (Ar)-diluted Silane (SiH4) and pure methane (CH4), the substrate temperature and RF power are set as 350°C and 120W, respectively, to provide the Si-rich SiC with changing fluence ratio (R=[CH4 ]/[SiH4]+[CH4]). By tuning the fluence ratio from 50% to 70%, the composition ratio x of Si-rich Si1−xCx film is varied from 0.27 to 0.34 as characterized by X-ray photoelectron spectroscopy (XPS), which reveals the component of Si2p decreasing from 66.3 to 59.5%, and the component of C1s increasing from 23.9% to 31% to confirm the formation of Si-rich SiC matrix. Annealing of the SiC sample from 650°C to 1050°C at 200°C increment for 30min induces the very tiny shift on the wavenumber of the crystalline Si (c-Si) related peak due to the precipitation of Si-QDs within the SiC matrix, and the Raman scattering spectra indicate a broadened Raman peak ranging from 410 to 520cm−1 related to the amorphous Si accompanied with the significant enhancement for SiC bond related peak at 980cm−1. From the high resolution transmission electron microscopy images, the critical temperature for Si-QD precipitation is found to be 850°C. The self-assembly of the crystallized Si-QDs with the size of 3±0.5nm and the volume density of (3±1)×1018 (#/cm3) in Si-rich SiC film with R=70% are observed after annealing at higher temperature.

Nanoscale Observation of the Distribution Polarization in Lithium Niobate Thin Films

ABSTRACTIn this work, an Atomic Force Microscope in the so-called Piezoresponse mode and Kelvin mode is used to image the grains, ferroelectric domains and surface potential in lithium niobate thin films. A RF magnetron sputter system was used to deposit LiNbO3 thin films on (100)-oriented Si substrates with SiO2 layer. The surface of the sample shows small grains which diameter ranges from 70 nm to 150 nm and roughness is less than 13 nm. Using the electric field from a biased conducting AFM tip, we show that possible to form and subsequently to visualize ferroelectric state. Also, we report surface charge retention on ferroelectric thin films by Kelvin probe microscope in comparison with the piezoresponse signal.

Crystalline growth of germanium thin films on single crystal silicon substrates by solid phase crystallization

We have studied the epitaxial-like growth of germanium (Ge), due to solid phase crystallization (SPC) from amorphous Ge (a-Ge) deposited on single crystal silicon (Si) substrate. The crystalline growth of Ge following the orientation of Si substrates was successfully obtained by the SPC at 400°C or higher. The preferential growth on Si (111) substrates continues up to 10,000Å. Different orientations from the substrate orientation in XRD patterns are slightly observed in the growth on Si (100) substrates at 450°C, but the preferential growth of (100) orientation continued in the whole film thickness in TEM images. The epitaxial-like growth of Ge may be more preferable on the Si (111) substrate than the (100) one.

The thermally-induced reaction of thin Ni films with Si: Effect of the substrate orientation

The solid-state reaction between thin Ni films and Si substrates was investigated using in situ synchrotron x-ray diffraction as well as ex situ three-dimensional reciprocal space maps and transmission electron microscopy analyses. Our results indicate that the orientation of the crystalline Si substrate strongly affects the reaction pathways, thereby altering the phase formation sequence upon annealing. On Si(001), the reaction begins with the formation of orthorhombic Ni2Si grains having a strong fiber texture. The metastable hexagonal θ phase and the NiSi phase then form through texture inheritance. The reaction on Si(111) is characterized by the appearance of multiple epitaxial phases. The as-prepared Ni samples contain a small amount of θ. Upon annealing, epitaxially textured Ni2Si along with other very thin epitaxial interfacial layers that may contain NiSi2 first appear. Once Ni2Si has completely consumed Ni, epitaxial Ni3Si2 grows while the complete consumption of Ni2Si triggers the formation of NiSi. Texture inheritance on Si(001) facilitates the nucleation and growth of NiSi, thus explaining the lower formation temperature on Si(001) than on Si(111).

Epitaxial growth of relaxed germanium layers by reduced pressure chemical vapour deposition on (110) and (111) silicon substrates

The growth of Ge on (110) and (111) oriented Si substrates is of great interest to enhance the mobility of both holes and electrons in complementary metal oxide semiconductor transistors. However, the quality of thick, relaxed Ge layers grown epitaxially on these surfaces is usually much lower than similar layers grown on (100) Si, resulting in both higher defect densities (i.e. threading dislocations and stacking faults) and rougher surfaces. In this work we have investigated the growth of Ge layers on (110) and (111) Si substrates by reduced-pressure chemical vapour deposition using a two temperature process. We have found that the combination of suppressing the Ge seed layer roughness and high temperature post-growth annealing can reduce the rms surface roughness of (110) Ge layers to below 2nm and the threading dislocation density to below 1×107cm−2. Thick (111) Ge layers were found to exhibit a very high density of stacking faults, that could not be reduced by post-growth annealing and a higher rms surface roughness of around 12nm, which was limited by the Ge seed layer.

Different Properties of Erbium Silicides on Si(100) and Si(551) Orientation Surfaces

The electrical and physical properties of ErSix on n-type Si(100) and Si(551) surfaces are reported. The Schottky barrier heights (SBHs) depend on the Si substrate orientation. On a Si(100) surface, a low electron SBH around 0.3 eV is obtained and the obtained SBH is larger than 0.4 eV on a Si(551) surface, while this difference is caused by the quantity of Si atoms in ErSix and on Si(100) this is less than on Si(551). These silicidation reactions are very important to develop the future high current drivability devices using any surface orientation.

P-Type Tunneling Field-Effect Transistors on (100)- and (110)-Oriented Si Substrates

p-Type tunneling field-effect transistors (TFETs) on (100)- and (110)-oriented Si substrates were fabricated, and their electrical characteristics were studied. High-k dielectric and metal gate were integrated as a gate stack, and the gate-last process was performed to obtain a high-quality dielectric layer and prevent crystallization. The orientation effect of p-type TFETs on (100) and (110) Si wafers is a high ION in the case of the (110) orientation as compared with that of the (100) p-type TFET, which is a high band-to-band tunneling current. The junction profile and effective mass were discussed to determine possible reasons for the orientation effect of p-type TFETs on (100) and (110) Si wafers.

P-Type Tunneling Field-Effect Transistors on (100)- and (110)-Oriented Si Substrates

p-Type Tunneling Field-Effect Transistors on (100)- and (110)-Oriented Si Substrates

Preparation and characterization of close-packed nanostructured sol–gel ceria thin films prepared using cerium-sec-butoxide as precursor

Polycrystalline, close-packed, homogeneous nanostructured ceria thin films were prepared by sol–gel process via dip-coating technique on soda-lime glass and (100)-oriented Si substrates. To produce the films, a sol was prepared using, as precursor, a home made cerium sec-butoxide dissolved in secondary butanol. The chemical composition, the microstructural/morphological characteristics and the optical properties of the coatings were investigated in detail. The experimental results clearly demonstrate that the ceria films are nanocrystalline (CeO2, cubic phase \( {\text{Fm}}\bar{3}{\text{m}} \)) with an average grain size of about 2–3 nm for the samples grown on glass and of about 4–5 nm for the samples grown on silicon. The analyses of ceria layers grown on silicon show that the ceria coatings are free from organic residues and that a Si-oxide layer is formed at the film/substrate interface. The optical results evidence a red shift of the energy gap of about 0.5 eV that can be ascribed to conversion of relevant Ce4+ sites to Ce3+ sites and a consequent creation of oxygen vacancy at the surface of the ceria grains.

Photoabsorption properties of β-FeSi 2 nanoislands grown on Si(111) and Si(001): Dependence on substrate orientation studied by nano-spectroscopic measurements

Photoabsorption properties of β-FeSi 2 nanoislands epitaxially grown on Si(111) and Si(001) have been discussed using photoabsorption nano-spectroscopy based on scanning tunneling microscope. The obtained spectra exhibit clear features around 0.86–0.91 eV and around 0.71–0.74 eV, which are explained as a direct and an indirect photoabsorption edge of β-FeSi 2, respectively. We also observed a blue shift of spectrum obtained from β-FeSi 2 nanoislands on Si(111) substrates, compared to those on Si(001) substrates. We attributed the dependence on Si-substrate orientation not to a quantum confinement effect but to an effect of elastic strain in the β-FeSi 2 nanoislands epitaxially grown on the substrate.

Growth and characterization of Bi 2Se 3 thin films by pulsed laser deposition using alloy target

Bi 2Se 3 thin films were deposited on the (100) oriented Si substrates by pulsed laser deposition technique at different substrate temperatures (room temperature −400 °C). The effects of the substrate temperature on the structural and electrical properties of the Bi 2Se 3 films were studied. The film prepared at room temperature showed a very poor polycrystalline structure with the mainly orthorhombic phase. The crystallinity of the films was improved by heating the substrate during the deposition and the crystal phase of the film changed to the rhombohedral phase as the substrate temperature was higher than 200 °C. The stoichiometry of the films and the chemical state of Bi and Se elements in the films were studied by fitting the Se 3d and the Bi 4d5/2 peaks of the X-ray photoelectron spectra. The hexagonal structure was seen clearly for the film prepared at the substrate temperature of 400 °C. The surface roughness of the film increased as the substrate temperature was increased. The electrical resistivity of the film decreased from 1 × 10 −3 to 3 × 10 −4 Ω cm as the substrate temperature was increased from room temperature to 400 °C.

Magnetic properties of EuS spin filter tunnel contacts to silicon

We investigate the magnetic properties of the ferromagnetic insulator EuS in view of its potential in spin-filter tunnel contacts to silicon. We prepared thin polycrystalline EuS films directly on (001) oriented Si substrates that show well-defined magnetic properties down to the monolayer regime. Addressing the question of magnetic coupling between a EuS magnetic tunnel barrier and a CoO/Co magnetic electrode, we succeeded in realizing an independent magnetic switching behavior in this spin-valve-type system. These results are important prerequisites for future spin-dependent transport experiments.

Evaluation of Curvature and Stress in 3C-SiC Grown on Differently Oriented Si Substrates

To assess deformation issues in SiC/Si, different pre-growth procedures were investigated, involving the addition of SiH4 to C3H8 during the temperature ramps used for the carbonization. 3C-SiC layers were deposited on (001) and (111) Si substrates by VPE. The mechanical deformation of the wafer was measured by makyoh, obtaining 2D maps of the entire wafers. For the same pre-growth procedures, the substrate curvature depends strongly on the orientation of the substrate, (001) or (111), being generally lower for (111) substrates. The deformation results were compared with XRD and Raman spectroscopy. Plastic deformation of the substrate was evidenced by XRD, while the presence of tensile stress is suggested by Raman analysis.

A Multi-Process Microfabrication Simulatorb on Cellular Automata

We describe a 3D simulator for several fabrication techniques utilized to create MEMS. The software is based on a cellular automata model and allows the user to simulate several processes, such as anisotropic wet etching in alkaline solutions and DRIE on (100) oriented Si substrates. The simulator allows for arbitrarily shaped masking materials and several processes can be applied in sequence to the same substrate. This enables the software to simulate the fabrication of MEMS devices which require more than one etching step. Although the automata used are not the most complex available, many of the results shown here are still acceptable from an engineering point of view.

Selective area growth of high quality InP on Si (001) substrates

In this work, we demonstrate the selective area growth of high quality InP layers in submicron trenches on exactly (001) oriented Si substrates by using a thin Ge buffer layer. Antiphase domain boundaries were avoided by annealing at the Ge surface roughening temperature to create additional atomic steps on the Ge buffer layer. The mechanism of Ge surface atomic step formation and the corresponding step density control method are illustrated. The elimination of antiphase boundaries from the optimized Ge buffer layer, together with the defect necking effect, yield defect-free top InP layers inside the trenches.

On the anisotropic wafer curvature of GaN-based heterostructures on Si(1 1 0) substrates grown by MOVPE

We highlight the challenges of GaN growth on (1 1 0)-oriented Si substrates with respect to the substrate-induced anisotropic strain state. A 5:4 lattice matching relationship, which is valid for AlN and Si(1 1 1), is also expected for AlN on Si(1 1 0) along the [1 1 –2 0]AlN/[1 −1 0]Si direction. This reduces the effective lattice mismatch for AlN on Si(1 1 0) along [1 1 –2 0] AlN/[1 −1 0] Si from 23.4% to −1.3% (compressive), while in the [1 −1 0 0] AlN/[0 0 1] Si direction, the mismatch value remains at 0.7% (tensile). The opposite signs of the two mismatch values lead to an anisotropic strain state of the deposited AlN and GaN films, which makes it difficult to balance the tensile strain induced by thermal mismatch. For a simple growth scheme using 1 μm GaN on top of a 40 nm AlN layer, this situation is reflected in an aspherical wafer curvature, anisotropic X-ray diffraction (XRD) Ω scan full width at half maximum (FWHM) values, greater surface roughness and cracking, predominantly occurring parallel to the [1 1 –2 0] direction. The anisotropic XRD FWHM may be explained by a strain-induced anisotropic nucleation mechanism for GaN on AlN. Also, a partial relaxation of the GaN film during growth caused by very high tensile strain along [1 –1 0 0] AlN/[0 0 1] Si is assumed to contribute to the XRD anisotropy. The insertion of an AlN/GaN superlattice structure in between the AlN and GaN films inhibits this relaxation process and leads to a smoother surface morphology with less visible cracks.

MBE growth of PbSe thin film with a 9×10 5 cm −2 etch-pits density on patterned (1 1 1)-oriented Si substrate

PbSe thin film was grown on a patterned Si substrate with (1 1 1)-orientation by molecular-beam epitaxy (MBE). On the mesa, a low dislocation density of 9×10 5 cm −2 was confirmed by the etch-pits density (EPD) wet-etching technique. The photoluminescence (PL) intensity at room temperature from the low dislocation PbSe film was much higher than that from the PbSe film grown on the planar area, which further indicated the high-quality of PbSe thin film grown on patterned Si substrate.