Si Interface Research Articles

Improving Junction Quality via Modifying the Si Surface to Enhance the Performance of PEDOT:PSS/Si Hybrid Solar Cells

PEDOT:PSS/Si hybrid solar cells have attracted wide attention due to the fabrication of an inversion layer near the Si surface by a solution method to realize high efficiency. However, Si dangling bonds on the Si surface produce surface states and lattice mismatches to deteriorate the performance of the solar cells. In this work, the aromatic rubrene is used to modify the Si dangling bonds to passivate the Si surface for improving the junction quality of PEDOT:PSS/Si. It is found that the interaction of rubrene with Si dangling bonds reduces the binding energies of Si 2p1/2 and Si 2p3/2 by 0.2 and 0.1 eV, respectively. These large shifts of Si 2p core levels are the signals that form a stronger inversion layer for a higher quality junction. In addition, rubrene increases the work function of the PEDOT:PSS film by 0.09 eV to increase the band bending of the Si interface to promote carrier separation. Finally, the power conversion efficiency (PCE) of PEDOT:PSS/Si hybrid solar cells with rubrene is 12.59%, which is 23.92% higher than that without rubrene.

Improvement of transparent conductive indium tin oxide based multilayer films on p-silicon through the inclusion of thin copper-aluminium metals interlayer

The distinguished transparent conductive indium tin oxide (ITO) based multilayer films with thin copper-aluminium (Cu-Al) metals interlayer (ITO/Cu-Al/ITO) were prepared on p-type silicon (Si) by radio frequency and direct current magnetron sputtering methods. The ITO/Cu-Al/ITO (ICAI) films structural, topological, optical and electrical properties coupled with electronic properties of ICAI/p-type Si interface were investigated at different post annealing temperature up to 600 °C. Despite the inclusion of Cu-Al metals interlayer, structural analysis results yielded an amorphous structure for the as-deposited films. The films become polycrystalline with a cubic bixbyite structure after post annealing treatment. Dominant In2O3 (222) and Cu (111) peaks intensities were observed at 500 °C and 600 °C indicating substantial enhancement in the films crystallinity at high moderate temperatures. The ICAI films reveal a smooth surface roughness with improved growth in grain size after post annealing treatment as examined by microscopic equipment.The films optical transmittance promptly increased from 73.2% (for as deposited film) to 88.7% (for annealed film at 600 °C) at 470 nm in the visible region with increasing post annealing temperature. The film annealed at 600 °C exhibits excellent electrical characteristics with a very low electrical resistivity of 2.44 × 10−5 Ω cm and sheet resistance of 3.26 Ω/sq. The ICAI films optoelectronic properties as calculated by figure of merit (FOM) show outstanding performance at 600 °C with a high FOM of 92.47 × 10−3 Ω−1 in spite of the reduced ITO films thickness. In addition, admirable ICAI/p-type Si interface quality was observed after post annealing treatment (at 600 °C) as indicated by current-voltage characteristics results. These improved ICAI multilayer films can be favourable for silicon heterojunction solar cells and other low resistance optoelectronic applications.

Interface Engineering of TiO2 Photoelectrode Coatings Grown by Atomic Layer Deposition on Silicon.

Titanium dioxide (TiO2) can protect photoelectrochemical (PEC) devices from corrosion, but the fabrication of high-quality TiO2 coatings providing long-term stability has remained challenging. Here, we compare the influence of Si wafer cleaning and postdeposition annealing temperature on the performance of TiO2/n+-Si photoanodes grown by atomic layer deposition (ALD) using tetrakis(dimethylamido)titanium (TDMAT) and H2O as precursors at a growth temperature of 100 °C. We show that removal of native Si oxide before ALD does not improve the TiO2 coating performance under alkaline PEC water splitting conditions if excessive postdeposition annealing is needed to induce crystallization. The as-deposited TiO2 coatings were amorphous and subject to photocorrosion. However, the TiO2 coatings were found to be stable over a time period of 10 h after heat treatment at 400 °C that induced crystallization of amorphous TiO2 into anatase TiO2. No interfacial Si oxide formed during the ALD growth, but during the heat treatment, the thickness of interfacial Si oxide increased to 1.8 nm for all of the samples. Increasing the ALD growth temperature to 150 °C enabled crystallization at 300 °C, which resulted in reduced growth of interfacial Si oxide followed by a 70 mV improvement in the photocurrent onset potential.

Study on the improvement of the open-circuit voltage of NiOx/Si heterojunction solar cell

Heterojunction solar cell based on nickel oxide ( NiO x ) as hole selective layer and n-type silicon as an active absorption layer is a promising high-efficiency solar cell. Unfortunately, this type of solar cells suffers from a low open circuit voltage ( V O C ) which limits any significant progress in its performance. Therefore, the main scope of this study is focused on V O C improvement. Discrete traps at the NiO x /Si interface are taken into account in the simulation to describe the real situation. The simulation was performed by SILVACO-Atlas using the interfacial traps NiO x /Si concentrations and hole mobility as tools to obtain agreement with measurement reported by Hsu et al. in [Thin Solid Films. 573 (2014) 159–163]. These parameters were found to be the cause of the low V O C value. V O C and efficiency improvements were achieved by optimizing the NiO x thickness and insertion a hydrogenated amorphous Si (a-Si:H) thin layer with optimal properties (electron affinity, bandgap and thickness)as a buffer layer between NiO x and Si. V O C increased from 423 to 906.16 mV and a good promising efficiency of η = 12.73 % is obtained in comparison to the initial efficiency (4.50%). • NiO x /Si heterojunction solar cell suffers from a low open circuit voltage. • This study focuses on finding the reason of low open circuit voltage. • A good agreement with the measured values was achieved. • An amorphous hydrogenated silicon buffer layer is inserted and optimized.

A Feasible Alternative to FDSOI and FinFET: Optimization of W/La2O3/Si Planar PMOS with 14 nm Gate-Length.

At the 90-nm node, the rate of transistor miniaturization slows down due to challenges in overcoming the increased leakage current (Ioff). The invention of high-k/metal gate technology at the 45-nm technology node was an enormous step forward in extending Moore’s Law. The need to satisfy performance requirements and to overcome the limitations of planar bulk transistor to scales below 22 nm led to the development of fully depleted silicon-on-insulator (FDSOI) and fin field-effect transistor (FinFET) technologies. The 28-nm wafer planar process is the most cost-effective, and scaling towards the sub-10 nm technology node involves the complex integration of new materials (Ge, III-V, graphene) and new device architectures. To date, planar transistors still command >50% of the transistor market and applications. This work aims to downscale a planar PMOS to a 14-nm gate length using La2O3 as the high-k dielectric material. The device was virtually fabricated and electrically characterized using SILVACO. Taguchi L9 and L27 were employed to study the process parameters’ variability and interaction effects to optimize the process parameters to achieve the required output. The results obtained from simulation using the SILVACO tool show good agreement with the nominal values of PMOS threshold voltage (Vth) of −0.289 V ± 12.7% and Ioff of less than 10−7 A/µm, as projected by the International Technology Roadmap for Semiconductors (ITRS). Careful control of SiO2 formation at the Si interface and rapid annealing processing are required to achieve La2O3 thermal stability at the target equivalent oxide thickness (EOT). The effects of process variations on Vth, Ion and Ioff were investigated. The improved voltage scaling resulting from the lower Vth value is associated with the increased Ioff due to the improved drain-induced barrier lowering as the gate length decreases. The performance of the 14-nm planar bulk PMOS is comparable to the performance of the FDSOI and FinFET technologies at the same gate length. The comparisons made with ITRS, the International Roadmap for Devices and Systems (IRDS), and the simulated and experimental data show good agreement and thus prove the validity of the developed model for PMOSs. Based on the results demonstrated, planar PMOSs could be a feasible alternative to FDSOI and FinFET in balancing the trade-off between performance and cost in the 14-nm process.

Aluminum Nitride to Silicon Direct Bonding for an Alternative Silicon-On-Insulator Platform.

The next generation of microelectromechanical systems (MEMS) requires new materials and platforms that can exploit the intrinsic properties of advanced materials and structures, such as materials with high thermal conductivity, broad optical transmission spectra, piezoelectric properties, and miniaturization potential. Therefore, we need to look beyond standard SiO2-based silicon-on-insulator (SOI) structures to realize ubiquitous MEMS. This work proposes using AlN as an alternative SOI structure due to several inherent material property advantages as well as functional advantages. This work presents the results of reactively sputtered AlN films on a Si handle wafer bonded with a mirror-polished Si device wafer. Wafer bonding was achieved by using hydrophilic wafer bonding processes, which was realized by appropriate polymerization of the prebonding surfaces. Plasma activation of the AlN surface included O2, Ar, SF6, SF6 + Ar, and/or SF6 + O2, which resulted in a change in the chemical and topography state of the surface. Changes in the AlN surface properties included enhanced hydrophilicity, reduced surface roughness, and low nanotopography, components essential for successful hydrophilic direct wafer bonding. Wafer bonding experiments were carried out using promising surface activation methods. The results showed a multilayered bonding interface of Si(Device)/SiO2/ALON/AlN/Si(Handle) with fluorine in the aluminum oxynitride layer from the proceeding AlN surface activation process. More notably, this work provided wafer bonding tensile strength results of the AlN alternative SOI structure that compares with the traditional SiO2 SOI counterpart, making AlN to Si direct bonding an attractive alternative SOI platform.

Multi-scale simulations of hydrogen diffusion and induced defects in amorphous-SiO2/Si interface

It is a consensus that hydrogen is the essential mobile impurity associated with the degeneration of silicon devices in ionization radiation. Specifically, it is proton that extends interfacial defects in SiO 2 /Si interface. In this work, the proton diffusion and the induced defects in the amorphous-SiO 2 /Si (a-SiO 2 /Si) interface are simulated at multi-scales. The diffusion activation energy and pre-exponential factor are obtained by fitting the Arrhenius law, and the interfacial defects associated with the proton diffusion are identified from the diffusion trajectories. Moreover, the pathways and barriers of proton migration in the a-SiO 2 /Si interface are calculated by the climbing image nudged elastic band (CI-NEB) method, which indicates a potential barrier of 0.2–0.6 eV for a proton to migrate between the bridging O atoms. Further by comparing the energy barrier profiles in the lateral and perpendicular directions, it is suggested that the proton diffusion is anisotropic in the a-SiO 2 /Si interface. A proton is more likely to migrate laterally in the first few Si layers beneath the interface, rather than crossing over the interface, and it may be trapped in the latter process due to the unevenly distributed strain in a-SiO 2 /Si interface. • Multi-scale simulations predict the anisotropic performance of hydrogen diffusion in amorphous-SiO 2 /Si interface. • The first unoxidized Si layer beneath the interface is proved to be an effective sink for hydrogen. • The diffusion-induced defects of protons are identified in terms of the trajectories via visual molecular dynamics program.

Femtosecond Laser-Induced Crystallization of Amorphous Silicon Thin Films under a Thin Molybdenum Layer.

A new process to crystallize amorphous silicon without melting and the generation of excessive heating of nearby components is presented. We propose the addition of a molybdenum layer to improve the quality of the laser-induced crystallization over that achieved by direct irradiation of silicon alone. The advantages are that it allows the control of crystallite size by varying the applied fluence of a near-infrared femtosecond laser. It offers two fluence regimes for nanocrystallization and polycrystallization with small and large crystallite sizes, respectively. The high repetition rate of the compact femtosecond laser source enables high-quality crystallization over large areas. In this proposed method, a multilayer structure is irradiated with a single femtosecond laser pulse. The multilayer structure includes a substrate, a target amorphous Si layer coated with an additional molybdenum thin film. The Si layer is crystallized by irradiating the Mo layer at different fluence regimes. The transfer of energy from the irradiated Mo layer to the Si film causes the crystallization of amorphous Si at low temperatures (∼700 K). Numerical simulations were carried out to estimate the electron and lattice temperatures for different fluence regimes using a two-temperature model. The roles of direct phonon transport and inelastic electron scattering at the Mo–Si interface were considered in the transfer of energy from the Mo to the Si film. The simulations confirm the experimental evidence that amorphous Si was crystallized in an all-solid-state process at temperatures lower than the melting point of Si, which is consistent with the results from transmission electron microscopy (TEM) and Raman. The formation of crystallized Si with controlled crystallite size after laser treatment can lead to longer mean free paths for carriers and increased electrical conductivity.

Analyses and Excess Oxygen Investigations by Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy at AlOx/Si Interfaces in Passivated Emitter and Rear Solar Cells

Progressive optimization of the surface passivation of Si solar cells requires access to the elemental composition and chemical bonding characteristics of ultrathin layers and buried interfaces on textured or structured surfaces. The passivation of the rear side of passivated emitter and rear solar cells, for instance, can be realized through AlOx/SiNx stacks, which are known to provide an additional field effect passivation on top of the chemical surface passivation. Herein, transmission electron microscopy is used at locally prepared cross‐sections of such stacks. Electron energy loss spectroscopy is used to extract depth‐resolved information of elemental composition and chemical bonding at nanometer scale. With this, the interfacial excess O fraction, which is crucial for the field effect passivation, is successfully determined for the first time for AlOx passivation layer systems on industrially produced Si solar cells.

First-Principles Calculations of Silicon Interstitial Defects at the Amorphous-SiO2/Si Interface

First-Principles Calculations of Silicon Interstitial Defects at the Amorphous-SiO₂/Si Interface

Achieving a Record Open‐Circuit Voltage for Organic/Si Hybrid Solar Cells by Improving Junction Quality

Nanostructured Si has attracted widespread attention due to its strong light‐harvesting ability, which is beneficial to improve the performance of solar cells. However, the poor contact of the organic/nanostructured Si interface and the large number of recombination centers on the Si surface result in an unsatisfactory open circuit voltage (VOC) and fill factor (FF) of the device. Herein, a simple and versatile method, Si nanowires modified with tetramethylammonium hydroxide (TMAH) and poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) doped with 3‐glycidoxypropyltrimethoxydsilane (GOPS), is proposed to improve the contact quality of the heterojunction. TMAH treatment adjusts the morphology of the Si nanowires and makes the surface smoother, effectively inhibiting surface recombination at the heterojunction interface. Moreover, the GOPS‐doped PEDOT:PSS solution can achieve conformal contact on the surface of nanostructured Si, which is more conducive to the extraction and separation of charges. As a result, a record VOC of 660 mV is obtained for PEDOT:PSS/nanostructured Si hybrid solar cells. In addition, the short circuit current density (JSC) is as high as 33.00 mA cm−2, and the FF is as high as 69.03%; therefore, the efficiency of the device reaches 15.01%. The results provide a simple and feasible strategy to improve the junction quality and performance of organic/Si solar cells.

Passivation and dissociation of P b-type defects at a-SiO2/Si interface* *Project supported by the Science Challenge Project, China (Grant No. TZ2016003-1-105), the Tianjin Natural Science Foundation, China (Grant No. 20JCZDJC00750), and the Fundamental Research Funds for the Central Universities, Nankai University (Grant Nos. 63211107 and 63201182).

It is well known that in the process of thermal oxidation of silicon, there are P b-type defects at amorphous silicon dioxide/silicon (a-SiO2/Si) interface due to strain. These defects have a very important impact on the performance and reliability of semiconductor devices. In the process of passivation, hydrogen is usually used to inactivate P b-type defects by the reaction P b + H2 → P bH + H. At the same time, P bH centers dissociate according to the chemical reaction P b H → P b +H. Therefore, it is of great significance to study the balance of the passivation and dissociation. In this work, the reaction mechanisms of passivation and dissociation of the P b-type defects are investigated by first-principles calculations. The reaction rates of the passivation and dissociation are calculated by the climbing image-nudged elastic band (CI-NEB) method and harmonic transition state theory (HTST). By coupling the rate equations of the passivation and dissociation reactions, the equilibrium density ratio of the saturated interfacial dangling bonds and interfacial defects (P b, P b0, and P b1) at different temperatures is calculated.

Impact of vacuum on the resistive switching in HfO2-based conductive-bridge RAM with highly-doped silicon bottom electrode

Moisture can modulate the resistive switching dynamics in oxide-based electrochemical metallization devices. Unconventional testing environments such as vacuum, could possibly shift the device characteristics, requiring therefore a careful investigation. This work investigates the write/erase behavior of Cu/HfO2(~80-nm-thick)/p+-Si devices in ambient atmosphere and vacuum, under similar electrical bias applied to the top Cu electrode. In vacuum (~5.3 × 10−3 Pa), a parasitic negative SET (N-SET) readily arises during the “erase” operation, unlike in ambient air. The electrical studies and physicochemical analyses of electrically-biased and pristine devices reveal that the “erase” process is sensitive to the environment. Vacuum facilitates the electric-field-controlled generation of an oxygen-vacancy-based path that likely induces a parasitic N-SET at the negative voltage. This path is aided by the presence of partially-ruptured copper filaments at the HfO2/p+-Si interface. Thevacuum effects leading to the N-SET are eliminated by introducing a passivating gas environment (zero-air or nitrogen), or device encapsulation.

Nanolayer boron-semiconductor interfaces and their device applications

Nanolayers of pure boron (PureB) deposited on Si form p+-type regions at deposition temperatures from 50 °C to 700 °C. At 700 °C, commercial PureB photodiodes are produced for advanced detection systems including those in extreme-ultraviolet (EUV) lithography systems. In addition, potent MEMS applications of B-nanolayers have been demonstrated. Attractive diode characteristics were also found for devices where Ga wetting-layers were applied to the Si surface, both with/without an additional B capping-layer. The resulting “PureGa” and “PureGaB” diodes are assessed here in the light of investigations focused on the B-Si interface properties in PureB diodes. A very high density of acceptor states at the Si interface appears to be related to the p-dopant property of both B and Ga, even though diffusion into the Si is not expected for the applied processing temperatures from 50 °C to ~ 450 °C.

A practical Tamm plasmon sensor based on porous Si

We report the fabrication and characterization of a new type of porous Si sensor using the Tamm plasmon resonance. The sensor consists of a photonic crystal created by periodic electrochemical anodization of crystalline Si, followed by partial thermal oxidation. The photonic crystal is transferred to a Au-coated glass substrate to allow optical measurements of surface modes at the metal/porous Si interface. This configuration greatly simplifies sensing since an analyte can be introduced in the pores from the opposite side of the metal layer without disrupting the optical path. The fabricated device exhibits a Tamm plasmon resonance within the photonic bandgap at a wavelength of 794 nm with a quality factor of 25. We observe a wavelength shift of the resonance when the nanosized pores are infiltrated with different concentrations of a toluene/ethanol solution. The measured sensitivity reaches 139 nm/RIU, in agreement with scattering matrix simulations and more than twice larger than those previously reported for Tamm plasmons. The quality factor and sensitivity yield a sensor figure of merit of 4. We also show that the electric field within the Tamm device is confined within a mode volume twice smaller than within a Fabry–Pérot resonator of comparable size according to calculations.

The impact of interfacial Si contamination on GaN-on-GaN regrowth for high power vertical devices

The development of gallium nitride (GaN) power devices requires a reliable selective-area doping process, which is difficult to achieve because of ongoing challenges associated with the required etch-then-regrow process. The presence of silicon (Si) impurities of unclear physical origin at the GaN regrowth interface has proven to be a major bottleneck. This paper investigates the origin of Si contamination at the epitaxial GaN-on-GaN interface and demonstrates an approach that markedly reduces its impact on device performance. An optimized dry-etching approach combined with UV-ozone and chemical etching is shown to greatly reduce the Si concentration levels at the regrowth interface, and a significant improvement in a reverse leakage current in vertical GaN-based p–n diodes is achieved.

Comparative Study of Tungsten Films Grown By Atomic Layer Deposition with Newly Synthesized Metalorganic and Halide Precursor

For continuous scaling down of semiconductor devices, metal deposition has been developed as a plug filling process for interlayer connecting. Tungsten (W) has a wide range of industrial applications since it has a relatively good electrical conductivity and a high electromigration durability due to its high melting point of 3380 °C. [1] Among various techniques, atomic layer deposition (ALD) has been investigated to find the most feasible way to grow uniform, dense, conformal, and conductive W thin film to thicknesses of a few nanometers in more complicated structures, since its growth mechanism is entirely based on self-limited surface reaction. [2] To date, several W precursors have been employed. Among them, the halide precursors have been widely used as precursors for metal deposition since it can fabricate a high-purity film compared to metal organic precursors. Tungsten hexafluoride (WF6) is the most widely reported halide-based precursor to date due to its simple structure and high reactivity. [3] However, the toxic by-product (HF) can provoke the interfacial Si consumptions and corrosion of devices. In this respect, in halide-based precursors, fluorine (F)-free tungsten precursors have recently received attention, but study on development of F-free tungsten precursor is still in its infancy. In contrast, the organic precursor is free from the formation of corrosive by-product. However, the carbon species derived from the organic ligand of the precursor can deteriorate film properties and device performance. [4] For this reason, studies for pure tungsten metal deposition with organic precursors have not been reported. Eventually, since the halide and organic precursors have their own strengths and weaknesses, there has been considerable controversy over the choice of precursors between the two groups.In this work, we fundamentally investigated the growth characteristics, chemical composition, crystallinity of W films on SiO2 substrate using two newly synthesized precursors (tungsten pentachloride (WCl5) and ethylcyclopentadienyltungsten(Ⅴ) tricarbonyl hydride (HEtCpW(CO)3)). Ar/H2 plasma as the reactant was generated between the showerhead and the substrate during the reactant exposure by capacitively coupled plasma (CCP) with a radiofrequency (RF) of 13.56 MHz at 200 W. We used Commercial showerhead type ALD chamber which has 8-inch wafer capacity, and the precursors were contained in individual stainless-steel bubblers and evaporated at 135 and 55 °C, respectively, to obtain a sufficient vapor pressure. The delivery lines were heated to a temperature approximately 10–15 °C higher than that of the bubbler to prevent the condensation of the precursor. The microstructure of W film were analyzed using Grazing-incidence X-ray diffraction (GIXRD), the film density of W film was analyzed via X-ray reflectivity (XRR), and the resistivity was electrically measured via Four point probe (FPP) with semiconductor analyzer. Growth characteristics and film properties were significantly affected by ligands of precursors. In addition, the electrical properties, including resistivity depending on the ALD cycles, and conformality at trench were evaluated for potential application. These results provide fundamental and useful information, with respect to the selection of the suitable precursor, for practical implementation of device fabrication.

Quantitative phase-field simulation of the entire solidification process in one hypereutectic Al–Si alloy considering the effect of latent heat

The multi-phase-field (MPF) model coupled with reliable CALPHAD thermodynamic/atomic mobility descriptions, appropriate faceted anisotropy and key experimental validation is employed to perform the quantitative simulation of the microstructure evolution of the hypereutectic Al-16 ​wt%Si alloy during solidification. By considering the effect of latent heat released during the eutectic phase transformation in the simulation, the appropriate entire solidification sequence is obtained. All the characteristics in the as-cast microstructure can be nicely reproduced, including the primary (Si) encircled by the second primary (Al) halo, and the coupled eutectic grains appearing at the Liquid/(Al) interface rather than Liquid/(Si) interface. Moreover, three types of growth patterns of eutectic (Si) with different lengths are distinguished according to the distance between primary (Si) and the nucleation position of eutectic (Si). Furthermore, the evaluated ratios of width to length for 50 eutectic (Si) grains due to the MPF simulation are in good agreement with the experimental data. The quantitative phase-field simulation of the entire solidification process of the hypereutectic Al-16 ​wt%Si alloy in the present work is anticipated to pave the way for revealing the grain refinement mechanism in hypereutectic Al–Si alloys in the future studies.

Study using ReaxFF-MD on the CMP process of fused glass in pure H2O/aqueous H2O2

Based on ReaxFF-MD simulation, our work is carried out to study the chemical mechanical polishing (CMP) process of fused glass. We explored the oxidation reaction between fused glass surface and aqueous H2O2 on the atomic scale, and analyzed the micro-influence mechanism of aqueous H2O2 concentration in polishing slurry. The simulation results show aqueous H2O2 can promote the oxidation degree of fused glass surface and has a double-sided effect on atom removal. On the one hand, surface oxidation makes it difficult to form interfacial Si(substrate)-O-Si(abrasive) bridge bonds between substrate and abrasive, less interfacial bridge bonds cause atoms difficulty in falling off from substrate; on the other hand, surface oxidation weakens the bonding strength of Si-O bonds, then substrate surface structure becomes more unstable, promoting atom removal. In our simulation, the removal form of polishing in 5% aqueous H2O2 is dominated by single-particle atom removal, that causes better surface quality and is a more expected removal form in ultra-precision machining; but at other concentrations, cluster removal or chain removal is more likely to occur. This work provides a more microscopic understanding of the influence of aqueous H2O2 or other oxidants on the surface removal behavior of silicon-based materials.

Photoinduced hydrophilic behavior of TiO2 thin film on Si substrate

Photoinduced hydrophilic behavior of TiO2 thin film synthesized by atomic layer deposition method on p-Si wafer as well on SiO2-coated glass has been studied. In contrast to the TiO2 film on SiO2-coated glass, the TiO2 film on the Si wafer initially had a moderate hydrophobicity and became more hydrophobic upon visible light exposure. Such a significant difference was explained by the formation of a type-II TiO2–Si heterostructure that was confirmed by the alteration of the work function. The role of photoelectrons in the mechanism of light-induced hydrophilic conversion of the TiO2 surface was elucidated, which reduces to the deactivation of both active surface sites responsible for the superhydrophilic transition and already existing hydrophilic sites. Reversible hydrophilic-to-hydrophobic surface conversion upon switching UV exposure by visible light has been demonstrated for TiO2/Si coatings. Similar to the tensiometric data, a cyclic change in the work function value was found. The observed cycles in values of water contact angle and work function were gradually ceasing. This phenomenon was associated with the formation of the interfacial SiOx layer as a result of light-induced passivation of silicon at the TiO2–Si interface.