Oriented Si Substrates Research Articles

The peculiarities of Si/SiO2 interfaces in the Si–SiO2 systems with Si nanocrystals

Abstract Si-rich-SiO2 layers with excess silicon of 45–50% were grown by RF magnetron co-sputtering from pure SiO2 and Si targets and were studied by Raman scattering, HRTEM, electron-paramagnetic resonance and X-ray diffraction (XRD) methods as well as by photo-voltage technique operated at different temperatures. The effect of Si substrate orientation of (1 1 1) or (1 0 0) on the layers properties was investigated. It was shown that high-temperature annealing in inert atmosphere stimulates a formation of Si crystallites in the film volume and of quartz crystallites near the layer/substrate interface. The dependences of the space orientation and the total volume of the formed quartz crystallites on substrate orientation were observed. The concentration of quartz crystallites in the films grown on the (1 0 0) Si substrate was found to be higher in several times than that in the films grown on the (1 1 1) Si substrate. The effect of the mechanical stresses on the layer–substrate interface states was observed for the layer prepared on the (1 1 1) Si substrate. It was shown that the natural oxidation of the layers before the annealing at high-temperature results in an increase of the positive fixed charge in the layer. At the same time it was found the formation of EX-centers containing Si vacancies close to crystallite/matrix interface.

Metalorganic vapor-phase epitaxy of GaN layers on Si substrates with Si(1 1 0) and other high-index surfaces

We report on the influence of different surface orientations of Si substrates on the properties of GaN-based layer structures grown by metalorganic vapor-phase epitaxy. By using a high-temperature AlN seed layer, a monocrystalline and c-axis-oriented GaN-layer can be obtained on all substrates with Si(1 1 0), Si(1 1 1), Si(1 1 5), Si(1 1 7), and Si(1 1 9) surface planes. In particular, the samples on Si(1 1 0) substrates exhibit a high quality of the GaN layer, which is comparable or even better than that of identically grown test structures on standard Si(1 1 1) substrates. This result can be explained by a more suited epitaxial relation between the c-plane of the high-temperature AlN seed layer and the Si(1 1 0) surface. The crystallographic structure of approximately 500-nm-thick GaN layers on Si(1 1 0) and Si(1 1 1) are analyzed by X-ray diffraction measurements, their surface morphologies by atomic force microscopy, and the optical properties are investigated by photoluminescence measurements. The improved crystallographic quality of GaN on Si(1 1 0) comes along with a more efficient effect of strain compensating interlayers in comparison to GaN layers on Si(1 1 1).

Influence of Oxygen Post-Growth Annealing on Optical and Electrical Properties of PbSe Thin Films

PbSe thin films grown on (111)-oriented Si substrates by molecular-beam epitaxy were annealed under an oxygen atmosphere with a variety of temperatures and times. The photoluminescence intensity from the sample annealed at 350°C for 2 h was increased by 400-fold with frontside pumping and increased by 40-fold with backside pumping, respectively, in comparison with the as-grown sample. Furthermore, the mobility was increased twofold after annealing. Such large photoluminescence increases and mobility improvements could be attributed to the surface passivation and the dislocation and defect passivation caused by oxygen diffusion and reaction with the PbSe film.

Growth and characterization of GaAs layers on polished Ge/Si by selective aspect ratio trapping

Epitaxial GaAs layers have been deposited on polished Ge film grown on exactly (0 0 1) oriented Si substrate by metal-organic chemical vapor deposition (MOCVD) via aspect ratio trapping (ART) method. Double-crystal X-ray diffraction shows that the full-width at half-maximum (FWHM) of the (4 0 0) reflection obtained from 1 μm GaAs is 140 arcsec. Scanning electron microscopy (SEM) of the GaAs layer surface shows that the amount of antiphase domain defects (APD) raised from GaAs/Ge interface using Ge ART on Si is dramatically reduced compared to GaAs layers grown on exact (0 0 1) Ge substrate. Defect reduction and Ge diffusion at vicinal GaAs/Ge interface were investigated via cross-section transmission electron microscopy (X-TEM) and secondary ion mass spectrometry (SIMS). Film morphology and optical properties were evaluated via SEM and room temperature photoluminescence (PL).

Towards Large Area (111)3C-SiC Films Grown on Off-Oriented (111)Si

The choice of off-axis (111) Si substrates is poorly reported in literature despite of the ability of such an oriented Si substrate in the reduction of stacking faults generation and propagation. The introduction of off-axis surface would be relevant for the suppression of incoherent boundaries. We grew 3C-SiC films on (111) Si substrates with a miscut angle from 3° to 6° along <110> and <11 >. The film quality was proved to be high by X-Ray diffraction (XRD) characterization. Transmission electron microscopy was performed to give an evaluation of the stacking fault density while pole figures were conducted to detect microtwins. Good quality single crystal 3C-SiC films were finally grown on 6 inch off-axis (111)Si substrate. The generated stress on both 2 and 6 inch 3C-SiC wafers has been analyzed and discussed.

3C-SiC Films on Si for MEMS Applications: Mechanical Properties

Single crystal 3C-SiC films were grown on (100) and (111) Si substrate orientations in order to study the resulting mechanical properties of this material. In addition, poly-crystalline 3C-SiC was also grown on (100)Si so that a comparison with monocrystaline 3C-SiC, also grown on (100)Si, could be made. The mechanical properties of single crystal and polycrystalline 3C-SiC films grown on Si substrates were measured by means of nanoindentation using a Berkovich diamond tip. These results indicate that polycrystalline SiC thin films are attractive for MEMS applications when compared with the single crystal 3C-SiC, which is promising since growing single crystal 3C-SiC films is more challenging. MEMS cantilevers and membranes fabricated from a 2 µm thick single crystal 3C-SiC grown on (100)Si under similar conditions resulted in a small degree of bow with only 9 µm of deflection for a cantilever of 700 µm length with an estimated tensile film stress of 300 MPa. Single crystal 3C-SiC films on (111)Si substrates have the highest elastic and plastic properties, although due to high residual stress they tend to crack and delaminate.

Growth and properties of YAlO film synthesized by RF magnetron sputtering

YAlO films are synthesized on (1 0 0)-oriented Si substrates by RF magnetron sputtering method. Al 2O 3 wafer is used as a target material, and some small pieces of Y bulk material are put on the Al 2O 3 target to synthesize YAlO films. Y composition ratio is varied from 0 to 34%. Amorphous YAlO films are characterized. An electrical resistivity as high as 3.4 × 10 14 Ω-cm is achieved for the YAlO film with Y composition ratio of 10%. The dielectric constant increases with increasing Y composition ratio, and the YAlO film with Y composition ratio of 34% has a dielectric constant of 10.2. The bandgap energy of the YAlO film is suggested to be wider than 6.5 eV. YAlO films with a surface roughness of 0.4–1.3 nm are obtained irrespective of the Y composition ratio.

Void Formation in Differently Oriented Si in the Early Stage of SiC Growth

This study refers, through different microscopies, about the carbonization effects on differently oriented Si surfaces. A statistical study on the relationship between some process parameters (such as temperature, process time) and void dimensions and density, for three Si substrate orientations, is reported.

Growth of 3C-SiC on Si: Influence of Process Pressure

In this work a comparison between atmospheric pressure (AP) and low pressure (LP) carbonization as the first step in the growth process of 3C-SiC on Si substrates is presented. Three different Si substrate orientations have been studied and compared. Characterization analysis has been performed by Atomic Force Microscopy (AFM), X-ray Diffraction Spectroscopy (XRD) and Transmission Electron Microscopy (TEM). XRD and AFM analysis show a lower roughness and a better quality for LPCVD carbonized samples. Substrate orientation plays an important role both in the generation as well as in the effect of such defects in the subsequent growth process, leading to a rougher SiC surface for growth on (110) Si while micro-twin effects are limited for growth on (111) Si, resulting in an extremely flat film.

3C-SiC Heteroepitaxy on (100), (111) and (110) Si Using Trichlorosilane (TCS) as the Silicon Precursor.

The aim of this work is to improve the heteroepitaxial growth process of 3C-SiC on Si substrates using Trichlorosilane (SiHCl3) as the silicon growth precursor. With this precursor it has been shown that it is possible to simultaneously increase the growth rate of the process and avoid the nucleation of silicon droplets in the gas phase. Growth experiments were conducted on three (3) Si substrate orientations in order to assess the impact of the Si substrate on the resulting 3C-SiC film. X-ray Diffraction (XRD), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) analysis show the important role of the substrate orientation for the growth process. The different orientation of the substrate modifies the morphology of the 3C-SiC crystalline structure, mostly by changing the density of micro-twins and stacking faults inside the film.

Comparison of structural and optical properties of GaSb/AlGaSb quantum well structures grown on different oriented Si substrates

We report on the molecular beam epitaxy (MBE) of GaSb films and GaSb/AlGaSb multiple quantum well (MQW) structures grown on Si(1 1 1) and Si(0 1 1) substrates using an AlSb initiation layer. The structural and optical properties of the films on the different oriented Si substrates were characterized by cross-sectional transmission electron microscopy (TEM), high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and photoluminescence (PL) measurements. The GaSb films and the MQW structures grown on Si(0 1 1) were found to have rather rough surfaces and of poor crystallinity under the present growth condition with the AlSb initiation layer. In contrast, the films grown on Si(1 1 1) indicated a mirror surface, definite MQW structures, and HRXRD patterns. The PL emissions within the 1.3–1.5 μm for the MQW structures on Si(1 1 1) and Si(0 1 1) were observed at the temperatures up to 300 and 200 K, respectively. We found that the PL peak energy, around 1.5 μm, of the MQW structures grown on Si(1 1 1) is almost temperature independent up to ∼120 K and exhibits a smaller variation with increasing temperature compared to those of the samples grown on Si (0 0 1) substrates. In the case of the MQW on Si (0 1 1), the PL peak energy as a function of temperature showed an intermediate behavior between those grown on Si(1 1 1) and Si(0 0 1) substrates.

3D Simulation Software for Visualization of MEMS Microfabrication Processes

In this paper we present a software for 3D visualization and simulation of the microfabrications process utilized in micro-electro-mechanical systems (MEMS) development. The simulations are based on a geometric approach and, differently from other academic and free distributed tools, the software include modules for simulation of both, bulk and surface micromachining, and for atomistic visualization of etched crystalline structures. Sophisticated rendering tools for coloring, illumination and transparency, as well as, tools to create and edit arbitrary 2D geometries and 3D solids were implemented. Related to the simulation capabilities, the bulk micromachining module lead with the anisotropic etching of (100) oriented Si substrates in alkaline solutions (KOH). The surface micromachining module works with the deposition and etching of up to 6 levels of structural and sacrificial films, which can be deposited on surfaces with complex 3D topography, and simulate the etching of sacrificial layers through etch holes in a structural layer.

Simulation of Anisotropic Etching of Silicon using a Cellular Automata Model

In this work we present a 3D simulation software for anisotropic etching of crystalline silicon substrates in KOH solutions. The software is based on conventional cellular automata model, and integrates in the same environment, the simulator itself with different 2D and 3D graphics tools to define simulation parameters and for visualization purposes. The software simulates the etching of (100) oriented Si substrates through open regions in a masking material with arbitrary geometry, with any number of holes and island in the masking material, which can be isolated or one inside the others. The simulator also works with both, front and back side etching of the substrate at the same time. The results show that, even though the model is based on fixed and simple transitions rules to determine if a specific atom is removed or not by the etching process, the simulation results exhibit a quite good accordance with the experimental results.

Growth of InAs on Si substrates at low temperatures using metalorganic vapor phase epitaxy

The growth behavior of InAs on Si using metalorganic vapor phase epitaxy (MOVPE) was studied. The large lattice mismatch of InAs to Si, ∼12%, results in island formation under typical MOVPE growth conditions, which prevents the development of the thin coherent films of InAs needed for high-speed device applications. The growth of InAs at low temperature is expected to lead to rapid nucleation and low surface mobility, resulting in the formation of a coherent film at low thicknesses. This study explored the growth behavior of InAs on Si at low temperatures, i.e. <350 °C and varying V/III ratio. InAs films were grown on {1 0 0}-, {1 1 1}- and {2 1 1}-oriented Si substrates using trimethyl indium, tertiary butyl arsine and AsH 3. Small islands ranging from 15 to 30 nm form on the samples at growth temperatures <325 °C. Subsequent annealing of this thin layer at 600 °C for 5 min leads to island coarsening. High-resolution X-ray diffraction, atomic force microscopy and scanning electron microscopy were used to characterize InAs layer grown on Si.

Formation of epitaxial gold nanoislands on (100) silicon

Coherent gold nanoislands were prepared directly on (100)-oriented Si substrates by a physical methodology, consisting of the thermal evaporation of a very thin Au film $(t\ensuremath{\sim}2\text{ }\text{nm})$ and its successive annealing in the temperature range $350\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}lTl814\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$. We found that at annealing temperature of $814\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and in the presence of residual oxygen during the annealing process, epitaxial monocrystalline gold nanoislands embedded in the Si lattice are formed. The crystallographic orientation and epitaxial relationship between the Au nanoislands and the Si lattice are well defined. In contrast, at lower annealing temperatures, namely at $350\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and $626\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$, the nanoislands are randomly oriented without epitaxial relationships. The morphology, orientation, and crystalline structure of Au nanoislands were investigated by scanning and high-resolution transmission electron microscopy and grazing-incidence x-ray diffraction. A model of the epitaxial Au nanoisland formation on (100)Si is presented in which the Si-atom out-diffusion and the formation of a liquid Au-Si droplet during the annealing process (increasing temperature) and the Si redeposition and oxidation (i.e., ${\text{SiO}}_{x}$ complex formation and removing of the excess Si in the gold islands) during the cooling process (decreasing temperature) play a fundamental role.

Formation of Ultrathin SiON Films on Si Substrates Having Different Orientations

We investigated the formation of ∼1–3 nm ultrathin SiON films by the plasma nitridation of oxidized Si substrates having different orientations, namely, (100), (110), and (111). Oxidation was performed by dry, wet, and plasma oxidation processes with rapid thermal oxidation (RTO), in situ steam generation (ISSG), and a slot plane antenna (SPA), respectively. Nitridation was performed by a plasma nitridation process with SPA. The thickness of base SiO2 films prepared by a plasma oxide process was independent of substrate orientation unlike in the dry and wet oxidation processes. Furthermore, no significant discrepancy in nitrogen areal density was observed among the SiON films grown by the plasma nitridation of differently oriented oxidized Si substrates. Our results suggest that SiON films with arbitrary nitrogen densities and thicknesses can be prepared by oxidation and plasma nitridation irrespective of the Si substrate orientation.

Influence of oxygen passivation on optical properties of PbSe thin films

A series of PbSe thin films grown on a (111)-oriented Si substrate by molecular beam epitaxy were passivated by high-purity oxygen at different annealing temperatures. The photoluminescence intensity increased by more than two orders of magnitude at 4.5μm after annealing the samples in an O2 atmosphere at 350°C. X-ray photoelectron spectroscopy revealed that PbO and SeO2 were formed during the oxidation process of PbSe, thus confirming the formation of the surface passivation layer which resulted in the observed significant increase in PL intensity.

Thermodynamic model of metal-induced self-assembly of Ge quantum dots on Si substrates

We have investigated the nucleation thermodynamics and kinetics of the Ge quantum dot (QD) self-assembly on the Au-patterned Si substrates based on the surface chemical potential theory. It is find that the minimum chemical potential on the substrate surface is located at the center site of the square lattice constructed by Au islands, which indicates that the nucleation of QD is thermodynamically favorable at the center site. The nucleation probability of QD at the center site is kinetically calculated by the mechanochemical potential-based approach. The influence of the surface orientation of Si substrates on the QD shape is addressed by the surface chemical potential theory.

Effect of surface preparation on the morphology of ZnO nanorods

The effects of Si substrate orientation and surface treatment on the morphology and density of Zinc oxide (ZnO) nanorods were investigated. The size and density of ZnO nanorods were influenced by Si substrate orientation and surface preparation. ZnO nanorods synthesized on the ideally H-terminated Si(1 1 1) prepared with an NH 4F solution resulted in the biggest size and the lowest density. It is suggested that the smoother surface of the Si substrate and lattice shape match with a larger atomic distance result in the increase of the ZnO seedlayer's grain size, which in turn enhances the size of ZnO nanorods grown on it. The optical properties of the ZnO nanorods were affected by their size and crystallinity. The smallest ZnO nanorods with a preferential c-axis orientation synthesized on the HF-treated Si(1 1 1) surface showed the highest intensity ratio of UV to visible emission, and the biggest ZnO nanorods synthesized on the N 2-sparged NH 4F-treated Si(1 1 1) surface showed the lowest intensity ratio of UV to visible emission. Therefore, it can be concluded that Si substrate orientation and surface preparation significantly affect the optical properties of ZnO nanorods.

Patterned epitaxial vapor-liquid-solid growth of silicon nanowires on Si(111) using silane

We have carried out a detailed study on the vapour-liquid-solid growth of silicon nanowires (SiNWs) on (111)-oriented Si substrates using Au as catalytic seed material. Arrays of individual seeds were patterned by electron-beam lithography, followed by Au evaporation and lift-off. SiNWs were grown using diluted silane as precursor gas in a low-pressure chemical vapor deposition system. The silane partial pressure, substrate temperature, and seed diameter were systematically varied to obtain the growth rate of the NWs and the rate of sidewall deposition. Activation energies of 19kcal∕mol for the axial SiNW growth and 29kcal∕mol for the radial deposition on the SiNW surface are derived from the data. SiNW growth at elevated temperatures is accompanied by significant Au surface diffusion, leading to a loss of Au from the tips of the SiNWs that depends on the layout and density of the Au seeds patterned. In contrast to NWs grown from a thin-film-nucleated substrate, the deterministic patterning of identical Au seeds of varying diameters allows accurate measurements of the nucleation yield of the SiNW, which is close to 100%, and analysis of the epitaxial relationship with the substrate. In addition to the vertical and the three 70.5°-inclined ⟨111⟩ epitaxial growth directions, we observe three additional 70.5°-inclined directions, which are rotated by 60°. The 60° rotation is explained by the occurrence of stacking faults in the SiNWs. The overall yield of vertically grown ⟨111⟩ NWs depends sensitively on the partial pressure of the silane and, to a lesser extent, on the growth temperature. At 80mTorr partial pressure and 470°C, up to 60% of the SiNWs grow in the vertical ⟨111⟩ direction. In situ doping of SiNWs using arsine resulted in a significant reduction of nucleation and wire growth, whereas doping with trimethylboron and phosphine exhibited no difference in growth and epitaxy compared with undoped samples.