Growth Of Si Films Research Articles

Si(111) islands on β-phase Si(111)√3 × √3R30°-Bi

β-phase √3 × √3R30°-bismuth (Bi) on silicon (Si)(111)7 × 7 surface has been exploited as a template for growing Si films. Two-dimensional Si islands with √3 × √3 reconstruction, parallel to that of Si(111)√3 × √3R30°-Bi, have been resolved by means of scanning tunneling microscopy, grazing-incidence X-ray diffraction (XRD) and low electron energy diffraction. Auger electron spectroscopy and scanning tunneling spectroscopy gave interesting electronic features on two-dimensional Si islands, with the evidence of a reduced band gap to ~0.55 eV, related to the presence of the underneath Bi layer, and atomic structural properties typical of Si(111). These experimental findings fully confirm the recently reported calculation based on the first-principles density functional theory, on the prediction of Si(111) growth on top of β-phase √3 × √3R30°-Bi/Si(111)7 × 7 reconstruction, shedding new light on silicon structures.

Transformation of SiO2 Particles to Si Film via Al-Assisted Electrochemical Reduction in Molten CaCl2

A Si film was formed from SiO2 particles in CaCl2 molten salt by electrochemical reduction using liquid Al-Si alloys. The liquid Al-Si alloys, formed from electrochemically reduced Si and metallic Al during the electrochemical reduction of the SiO2 particles, not only promoted electrochemical reduction, but also induced Si thin film formation. The Si film growth was observed by optical imaging, while the morphology and composition of the films were characterized by scanning electron microscopy and X-ray diffraction analysis. A pulse reduction technique was introduced to promote SiO2 reduction. The effect of the on/off time ratio on the Si film formation was investigated, with efficient SiO2 reduction achieved via on/off time ratio optimization. At the optimized ratio, a 0.9-mm-thick Si film with a Si purity of 96 at% was obtained. This effective Si production system might contribute to the fabrication of low-cost solar cells and Si-related electronic devices that require Si films.

Epitaxial growth of Si thin films with hexagonal close-packed structures on metal substrates.

We have studied the epitaxial growth of Si thin films on the Cd(0001) surface using low-temperature scanning tunneling microscopy. When deposited at low temperatures (100K), Si atoms form dendritic islands with triangular shapes, indicating the existence of anisotropic edge diffusion in the process of Si film growth. After annealing to elevated temperatures, the triangular dendritic Si islands become hexagonal compact islands. Moreover, the 2D Si islands located on two different substrate terraces exhibit different heights due to the influence of quantum-well states in Cd(0001) films. Based on high-resolution scanning tunneling microscopy images, it is observed that the first, second, and third Si layers show the pseudomorphic 1 × 1 structure. In particular, the first and second layer islands reveal the opposite triangles, indicating the hexagonal close-packed stacking of Si atoms. These results provide important information for the growth of pristine Si films on metal substrates and the understanding of Si-metal interaction.

High-Rate Epitaxial Growth of Silicon Using Electron Beam Evaporation at High Temperatures

This paper describes the high-rate (~1.5 μm/min) growth of Si films on Si supporting substrates with (100) crystallographic orientation at 600 °C, 800 °C, and 1000 °C in a vacuum environment of ~1 × 10−5 mbar using electron beam (e-beam) evaporation. The microstructure, crystallinity, and conductivity of such films were investigated. It was established that fully crystalline (Raman spectroscopy, EBSD) and stress-free epi-Si layers with a thickness of approximately 50 µm can be fabricated at 1000 °C, while at 600 °C and 800 °C, some poly-Si inclusions were observed using Raman spectroscopy. Hall effect measurements showed that epi-Si layers deposited at 1000 °C had resistivity, carrier concentration, and mobility comparable to those obtained for c-Si wafers fabricated through ingot growth and wafering using the same solar grade Si feedstock used for the e-beam depositions. The dislocation densities were determined to be ∼2 × 107 cm−2 and ∼5 × 106 cm−2 at 800 and 1000 °C, respectively, using Secco etch. The results highlight the potential of e-beam evaporation as a promising and cost-effective alternative to conventional CVD for the growth of epi-Si layers and, potentially, epi-Si wafers. Some of the remaining technical challenges of this deposition technology are briefly indicated and discussed.

Si epitaxy on Cl-Si(100)

Current atomically-precise fabrication methods in Si utilize a scanning tunneling microscope (STM) to pattern a monatomic resist adsorbed on Si(100). Recent interest in the use of Cl-based resists has necessitated further investigations on the impact of the tightly bound Cl to the overall device fabrication process. In particular, impacts to the crystallinity of the Si capping layer used to encapsulate the active device region can have dramatic effects on the functionality of atomic-scale quantum devices. Here, the epitaxial growth of Si films on Cl-Si(100) was studied to identify and characterize the Si thin film growth process. Adatoms diffusion on the surface was simulated based on the experimental results of the number density and distribution of Si adatom chains after <0.10 ML of Si deposition at temperatures ranging from 300–850 K. A diffusion barrier within 0.66–0.88 eV for Si adatoms on Cl-Si(100) was found. SIMS depth profiling of ∼25 nm thick Si films verified that Cl segregated towards the growth surface during Si deposition and was effectively removed below SIMS detection limits from both the buried interface and Si film at 850 K. TEM imaging confirmed good film crystallinity was achieved at temperatures as low as 600 K.

Metal Sheet of Atomic Thickness Embedded in Silicon.

The controlled confinement of the metallic delta-layer to a single atomic plane has so far remained an unsolved problem. In the present study, the delta-type structure with atomic sheet of NiSi2 silicide embedded into a crystalline Si matrix has been fabricated using room-temperature overgrowth of a Si film onto the Tl/NiSi2/Si(111) atomic sandwich in ultrahigh vacuum. Tl atoms segregate at the growing Si film surface, and the 1.5-3.0 nm thick epitaxially crystalline Si layer forms atop the NiSi2 sheet. Confinement of the NiSi2 layer to a single atomic plane has been directly confirmed by transmission electron microscopy. The NiSi2 delta-layer demonstrates a p-type conductivity associated with the electronic transport through the two hole-like and one electron-like interface-state bands. The basic structural and electronic properties of the NiSi2 delta-layer remain after keeping the sample in air for one year.

Electrodeposition of Grop Ⅳ Semiconductor Thin Film

This presentation describes our latest work in the growth of Si films by electrochemical liquid phase epitaxy (ec-LPE). This method is an advanced form of the electrochemical liquid-liquid-solid crystal growth process, where a liquid metal serves both as a cathode for electrodeposition and as a solvent for crystal growth. Using tailored thin liquid metal film electrodes and non-aqueous electrolytes, it is possible to electrodeposit crystalline Si at unusually low temperatures. Data will first be presented that describes suitable electrolytes for Si ec-LPE. Results will then be presented that describe how the liquid metal identity impacts material quality. Finally, the attainable material quality and the requirements for solar grade crystalline Si will be discussed.

Features of the Initial Stage of the Heteroepitaxy of Silicon Layers on Germanium When Grown from Silicon Hydrides

Data on the dependence of the growth rate of Si layers deposited onto Ge(111) by the hydride method on their thickness at the initial heteroepitaxy stage are reported. The effect of a Ge substrate within ten grown silicon single layers on the Si-film growth rate is demonstrated. Based on the data obtained, the kinetic coefficients responsible for the rate of the main physicochemical processes related to the interaction of hydride molecular beams with the growth surface are calculated. An analysis of the capture probability and rates of pyrolysis of the adsorbed Si(Ge) hydride molecules on the pure Ge(Si) surfaces reveals the dependence of their behavior on the growing-layer thickness. Comparison of the results obtained during Si-layer growth on Ge shows that the pure germanium surface has higher adsorption and catalytic abilities with respect to silane molecules than the pure Si surface. The unstrained pure Si surface has higher adsorption and catalytic characteristics with respect to Ge-hydride molecules.

Diffusion of hydrogen atoms in silicon layers deposited from molecular beams on dielectric substrates

In the paper, the processes occurring during low-temperature growth of non-hydrogenated amorphous Si and polycrystalline Si films on multilayer Si3N4/SiO2/c-Si substrates from molecular beams under conditions of ultrahigh vacuum are studied in detail. Diffusion of hydrogen atoms from a dielectric layer into the growing film is shown to accompany the growth of a silicon film on a Si3N4 layer deposited by CVD or on a SiO2 layer obtained by thermal oxidation of a silicon wafer. The process of hydrogen migration from the dielectric substrates into the silicon film is studied using FTIR spectroscopy. The reduction of IR absorption at the bands related to the NH bonds vibrations and the increase of IR absorption at the bands relating to the SiN bonds vibrations in IR spectra demonstrate that hydrogen atoms leave Si3N4 layer during Si deposition from a molecular beam. The absorption band assigned to the valence vibrations of the SiH bond at ∼2100 cm–1 emerging in IR spectra obtained at samples deposited both on Si3N4 and SiO2 layers indicates the accumulation of hydrogen atoms in silicon films. The difference in chemical potentials of hydrogen atoms in the dielectric layer and the silicon film explains the transfer of hydrogen atoms from the Si3N4 or SiO2 layer into the growing silicon film.

Direct synthesis of biaxially textured nickel disilicide thin films by magnetron sputter deposition on low-cost metal tapes for flexible silicon devices

Nickel silicides are widely used as contact materials for electronic devices based on silicon (Si). However, they have been predominantly fabricated by annealing separate Ni and Si phases which leads to phase and structural complexity. In this letter, direct epitaxial growth of a single-phase nickel disilicide (NiSi2) thin film by sputter deposition of NiSi2 is achieved on low-cost and flexible Hastelloy tapes which offers a promising route to fabricate low-cost, flexible electronic devices. Biaxially textured titanium nitride (TiN) is applied as the seeding layer and the diffusion barrier under NiSi2. An epitaxial relationship of (001)⟨100⟩NiSi2 ǁ (001)⟨110⟩TiN is observed with an extra-large lattice mismatch (∼10.3%) between NiSi2 and TiN. Both the bonding similarity and the passivation effect by hydrogen promote the epitaxial growth of NiSi2 on TiN. The flat and smooth NiSi2 thin film consists of grains with a size of 50–100 nm. An epitaxially grown Si film on NiSi2 further demonstrates the potential of manufacturing high-performance Si flexible electronics with NiSi2/TiN/Hastelloy as the direct contact through this approach.

Особенности начальной стадии гетероэпитаксии слоев кремния на германии при их выращивании из гидридов кремния

AbstractData on the dependence of the growth rate of Si layers deposited onto Ge(111) by the hydride method on their thickness at the initial heteroepitaxy stage are reported. The effect of a Ge substrate within ten grown silicon single layers on the Si-film growth rate is demonstrated. Based on the data obtained, the kinetic coefficients responsible for the rate of the main physicochemical processes related to the interaction of hydride molecular beams with the growth surface are calculated. An analysis of the capture probability and rates of pyrolysis of the adsorbed Si(Ge) hydride molecules on the pure Ge(Si) surfaces reveals the dependence of their behavior on the growing-layer thickness. Comparison of the results obtained during Si-layer growth on Ge shows that the pure germanium surface has higher adsorption and catalytic abilities with respect to silane molecules than the pure Si surface. The unstrained pure Si surface has higher adsorption and catalytic characteristics with respect to Ge-hydride molecules.

Electrochemically controllable coating of a functional silicon film on carbon materials

A silicon deposit of various forms was successfully coated on graphite by electrodeposition in molten CaCl2 containing nano-SiO2 as a silicon precursor. The morphologies of the deposited silicon can be tuned from Si nanowires to a dense film by controlling constant electrolysis cell voltage. In addition to controlling electrochemical polarizations, the substrate plays a key role in forming a dense silicon film. By analyzing the interface between the Si film and graphite substrate, a thin transition layer comprising of Si, SiC and C enables the good adhesion of the Si film with the carbon substrate and thereby helps the growth of a dense Si film. Besides the application for photovoltaics, the electrolytic p-type Si film was employed as a binder-free anode for lithium-ion batteries delivering a capacity of over 2500 mAh g−1 in the first 10 cycles and retaining 800 mAh g−1 after 40 cycles. Moreover, this method was applied for coating Si on carbon fibers, which could be a general way to prepare Si with controllable forms and silicon/carbon core-shell structures for functional materials.

Transition from silicene monolayer to thin Si films on Ag(111): comparison between experimental data and Monte Carlo simulation.

Scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low energy electron diffraction have been used to follow the growth of Si films on Ag(111) at various temperatures. Using a simple growth model, we have simulated the distribution of film thickness as a function of coverage during evaporation, for the different temperatures. In the temperature regime where multilayer silicene has been claimed to form (470–500 K), a good agreement is found with AES intensity variations and STM measurements within a Ag surfactant mediated growth, whereas a model with multilayer silicene growth fails to reproduce the AES measurements.

The mechanism for the stabilization and surfactant properties of epitaxial silicene

Using real-time in situ scanning tunneling microscopy and density functional theory simulations, we have studied the growth of Si films on Ag(111) beyond the silicene monolayer, evidencing the existence of metastable phases and an original growth mechanism. Above monolayer Si coverage, an initial structure forms, which is identified as an Ag-free Si bilayer with additional Si adatoms. With further deposition, this structure is replaced by a distinct bilayer structure covered by Si trimers and Ag atoms. The formation of these bilayers follows counterintuitive dynamics: they are partially inserted within the Ag substrate and form by expelling, from the underlying substrate, the atoms that reinsert below the adjacent silicene layer. The growth is therefore characterized by an unexpected "surfactant competition" between Ag and silicene: while silicene is a metastable surfactant for the Ag(111) surface, Ag plays the role of a surfactant for thicker diamond-like Si islands. In spite of being thermodynamically unfavoured, the silicene monolayer is, thus, a remarkably stable structure because of the high kinetic barrier for the growth of thicker layers.

Electron-enhanced atomic layer deposition of silicon thin films at room temperature

Silicon thin films were deposited at room temperature with electron-enhanced atomic layer deposition (EE-ALD) using sequential exposures of disilane (Si2H6) and electrons. EE-ALD promotes silicon film growth through hydrogen electron stimulated desorption (ESD) that creates reactive dangling bonds and facilitates Si2H6 adsorption at low temperatures. Without hydrogen ESD, silicon growth relies on thermal pathways for H2 desorption and dangling bond formation at much higher temperatures. An electron flood gun was utilized to deposit Si films over areas of ∼1 cm2 on oxide-capped Si(111) substrates. The silicon film thickness was monitored in situ with a multiwavelength ellipsometer. A threshold electron energy of ∼25 eV was observed for the Si film growth. A maximum growth rate of ∼0.3 Å/cycle was measured at electron energies of 100–150 eV. This growth rate is close to the anticipated growth rate assuming dissociative Si2H6 adsorption on dangling bonds on representative single-crystal silicon surfaces. The Si growth rate also displayed self-limiting behavior as expected for an ALD process. The silicon growth rate was self-limiting at larger Si2H6 pressures for a fixed exposure time and at longer electron exposure times. The silicon growth rate versus electron exposure time yielded a hydrogen ESD cross section of σ = 5.8 × 10−17 cm2. Ex situ spectroscopic ellipsometry showed good conformality in thickness across the ∼1 cm2 area of the Si film. Si EE-ALD should be useful for a variety of applications.

On the creation of ordered nuclei by ion bombardment for obtaining nanoscale si structures on the surface of CaF2 films

The effect of preliminary low-energy (~1 keV) and low-dose (~1012–1014 cm–2) ion bombardment on the initial stages of growth of Si films on a CaF2/Si surface is investigated. Ordered nanocrystal phases (thickness less than 5–6 monolayers) and homogeneous epitaxial nanofilms (thickness more than 8–10 monolayers) of silicon are shown to be formed after annealing.

Multilayer silicene: clear evidence of Ag-terminated bulk silicon

The existence of silicite, a new allotrope of silicon based on a stacking of hexagonal silicene planes, is one of the most discussed topics in the field of two-dimensional materials. Using grazing incidence x-ray diffraction (GIXD), we have followed the in situ growth of Si films on Ag(1 1 1) in the low-temperature growth regime (510–520 K). GIXD experiments demonstrate that Si films have a diamond-like structure, with an average lattice constant slightly different from that of bulk Si. The diffracted intensities associated with Si films are well reproduced by the Ag/Si(1 1 1) honeycomb chain model, whereas models with Ag-free Si surfaces fail to reproduce the experimental data.

A Facile Method for Heteroepitaxial Growth of Homogeneous 3C-SiC Thin Films on Both Surfaces of Suspended Si Wafer by Conventional Chemical Vapor Deposition

Although epitaxial growth of Si films on both surfaces of silicon wafer (epi-Si/Si-wafer/epi-Si) can be realized in foundry by means of mounting certain amounts of silicon wafers in a boat in commercial specialized chemical vapor deposition equipment (s-CVD), for its counterpart epi-SiC/Si-wafer/epi-SiC, neither is it readily realized in s-CVD, nor is it easily achieved in conventional chemical vapor deposition equipment (c-CVD) which is generally used for growth of 3C-SiC on single surface of silicon wafer (epi-SiC/Si-wafer). Since the growth of epi-SiC/Si-wafer/epi-SiC in one run is more efficient, and is anticipated, in this work, we demonstrated a facile method for growth of epi-SiC/Si-wafer/epi-SiC in c-CVD. The Si wafer was double-side polished and mounted in a suspension mode on the susceptor in the c-CVD chamber. It was found that homogeneous 3C-SiC(100) films were heteroepitaxially grown on both surfaces of the suspended Si(100) wafer simultaneously. The structural and electrical properties of the obtained 3C-SiC films on both surfaces were investigated by means of SEM, XRD, Raman and J-V measurements. Results showed that each film was uniform and continuous, with same trend of slight degradation from the inner to the outer region of the wafer. This indicated a possible way of making mass production of high quality 3C-SiC films on Si wafers in one run in c-CVD for the potential applications such as sensors, with working principle based on voltage drop difference of two back-to-back diodes on epi-SiC/Si-wafer/epi-SiC, or graphene growth from epi-SiC/Si-wafer/epi-SiC templates.

Suppression of the epitaxial growth of Si films in Si heterojunction solar cells by the formation of ultra-thin oxide layers

The epitaxial growth of silicon (Si) films during the catalytic chemical vapor deposition (Cat-CVD) of intrinsic amorphous Si (i-a-Si) passivation films on crystalline Si (c-Si) wafers is suppressed by the oxidation of c-Si surfaces simply by dipping the c-Si wafers in hydrogen peroxide (H2O2). This oxidation treatment is also effective for (111)-oriented c-Si surfaces particularly at high a-Si deposition temperatures. The suppression of the epitaxial growth leads to the better effective minority carrier lifetime (τeff) of c-Si wafers passivated with Cat-CVD i-a-Si films. SHJ solar cells show remarkably high open-circuit voltage (Voc) exceeding 0.7 V. These results clearly show the effectiveness of the insertion of SiOx layers on the improvement in Cat-CVD a-Si/c-Si interfaces.

Formation of the seed layers for layer-transfer process silicon solar cells by zone-heating recrystallization of porous silicon structures

Thin-film crystalline silicon is promising for photovoltaic application to reduce the cost of photovoltaic energy. Porous silicon structures have been intensively studied as a seed layer for epitaxial growth of thin Si film and layer-transfer process (LTP). In this article, another approach for LTP has been proposed. The seed layers for epitaxial silicon growth have been formed by zone-heating recrystallization of double-layer por-Si structures. The influence of annealing parameters on porous silicon structures was studied. The transformation of por-Si layer to crystalline Si was observed with the formation of smooth continuous surface with the roughness 0.3 nm, peak-to-valley distance around 3.5 nm, and reduced density of pores. The mechanism of the transformation of por-Si surface due to the action of hydrogen in the passivated pores with preventing surface oxidation was proposed.