Textured Si Substrates Research Articles

Study of silicon rich oxide light emitter capacitors using textured substrates by metal assisted chemical etching

Mono and multilayer silicon rich oxide light-emitting capacitors (SRO-LEC) were fabricated using both polished and textured Si substrates. The textured substrate surface was treated by metal-assisted chemical etching (MACE) for 10 s and 20 s forming nanoneedles. Monolayer devices fabricated using textured substrates required lower energy to emit light and present at least 40% higher emission intensity than non-textured substrates. On the other hand, multilayer devices fabricated on textured and polished substrates showed that both LECs required similar energy to start the emission, however, after the bias is increased up to 5.5 MV/cm the textured LECs presented 36% higher emission intensity. The evidence shows that the electric field is screened by the nanocrystals in the SRO with Ro = 10 at electric fields lower than 5.5 MV/cm.

Surface texturisation for the reduction of light reflection in ZnO/Si heterojunction

ABSTRACT In this paper, the impact of pyramidal texture on a silicon substrate in ZnO/p-Si heterojunction was investigated. The texturisation of p-type silicon (100) substrate was obtained using the KOH anisotropic wet chemical etching method for different etching times. The RF magnetron sputtering technique was used to deposit ZnO thin films on textured Si substrates and planar Si substrates to form ZnO/Si heterojunction. The surface morphology was studied with field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Optical properties were investigated using UV-Visible spectroscopy and photoluminescence (PL). The results show that the PL intensity in the visible region of the electromagnetic spectrum increases with the etching time, while a significant reduction is observed in the reflectance. Due to impressive anti-reflection response, ZnO/Si (textured silicon-TS) heterojunction can be effective in improving the efficiency of solar cells.

Inter-facet composition modulation of III-nitride nanowires over pyramid textured Si substrates by stationary molecular beam epitaxy

InGaN nanowires (NWs) are grown on pyramid textured Si substrates by stationary plasma-assisted molecular beam epitaxy (PA-MBE). The incidence angles of the highly directional source beams vary for different pyramid facets, inducing a distinct inter-facet modulation of the In content of the InGaN NWs, which is verified by spatial element distribution analysis. The resulting multi-wavelength emission is confirmed by photoluminescence (PL) and cathodoluminescence (CL). Pure GaN phase formation dominates on certain facets, which is attributed to extreme local growth conditions, such as low active N flux. On the same facets, InGaN NWs exhibit a morphology change close to the pyramid ridge, indicating inter-facet atom migration. This cross-talk effect due to inter-facet atom migration is verified by a decrease of the inter-facet In content modulation amplitude with shrinking pyramid size. A detailed analysis of the In content variation across individual pyramid facets and element distribution line profiles reveals that the cross-talk effect originates mainly from the inter-facet atom migration over the convex pyramid ridge facet boundaries rather than the concave base line facet boundaries. This is understood by first-principles calculations showing that the pyramid baseline facet boundary acts as an energy barrier for atom migration, which is much higher than that of the ridge facet boundary. The influence of the growth temperature on the inter-facet In content modulation is also presented. This work gives deep insight into the composition modulation for the realization of multi-color light-emitting devices based on the monolithic growth of InGaN NWs on pyramid textured Si substrates.

Barrier performance of ITO film on textured Si substrate

Indium tin oxide (ITO) film is the most widely used as front electrodes in solar cells with a copper metallization scheme. No work has focused on the barrier properties of the ITO layer on the textured silicon for solar cells. In this work, a thin indium tin oxide barrier layer and copper metal layer were deposited on textured (001) silicon by a sputtering. The stacks present Cu/ITO/Si. The structures of Cu/ITO/Si characterized by scanning transmission electron microscope, energy-dispersive X-ray spectrometer, and powder X-ray diffraction. The results show that the stacks of Cu/ITO/Si can be preserved up to 600 °C. The 35-nm thickness ITO layer was found to be a diffusion barrier against Cu up to 600 °C. The copper thin films were agglomerated and formed the particle at a temperature of 700 °C. The failure of Cu/ITO/Si can be attributed to agglomerate copper thin films and breakdown of ITO thin films at a temperature of 700 °C.

Failure Behavior of Nickel Silicide Diffusion Barrier between Electroplating Cu and Textured Si Substrate

Failure Behavior of Nickel Silicide Diffusion Barrier between Electroplating Cu and Textured Si Substrate

TiO2 thin films on Au/Ti/SiO2/textured Si substrates as high capacity anode materials for Li-ion batteries

In this paper, we investigate the structural and electrochemical properties of TiO2 thin films deposited on multilayered Au/Ti/SiO2/(100) textured-Si substrates by electron-beam evaporation technique at various substrate temperatures in the range 25 ≤ Ts ≤ 350 °C. Phase-pure and well-crystallized TiO2 thin films grown at Ts = 250 °C exhibit the typical (101) Bragg line of the tetragonal anatase structure with crystallite size of about 30 nm. The surface morphological analysis reveals the uniform growth of prismatic shaped grains (40–120 nm in size) deposited on pyramidal architectures of textured substrates. The electrochemical tests show that TiO2 thin films electrodes deposited at Ts of 250 °C deliver a specific discharge capacity of 74 μAh cm−2 μm−1 at a current density of 1 mA cm−2 with 96% capacity retention after 100 cycles. Hence, the experimental results demonstrate that TiO2 thin films can be used as anodes of planar solid-state Li-ion microbatteries.

Electrochemical approach for preparing conformal methylammonium lead iodide layer

Monolithic perovskite/Si tandem solar cells have attracted particular interest because of the potential to achieve high power conversion efficiencies. However, tandem cells require the use of textured Si substrates for efficient light harvesting, and conformal deposition of the perovskite absorption layer on textured Si substrates remains challenging. Here, we introduce a process to prepare a conformal methylammonium lead iodide (MAPbI3) film on the various substrates regardless of their morphologies via the electrodeposition followed by vapor reaction. First, PbO2 films were electrodeposited on the planar indium tin oxide/NiO substrates in aqueous electrolyte, with their thickness and grain size controlled by adjusting the potential and reaction time. XPS and XRD analyses confirmed that the PbO2 film was fully reduced to PbO by annealing under a reducing atmosphere. Finally, the PbO films were converted into conformal MAPbI3 via MAI vapor reaction for 25 min at 180 °C. We also demonstrated that the PbO2 films could be evenly deposited on textured Si/ITO substrates using pulsed electrodeposition and were then converted into conformal MAPbI3 using the same vapor reaction process. The proposed approach thus provides a novel route for the preparation of high-quality perovskite films on both planar and textured substrates.

A Study of the Wettability of Single-Walled Carbon Nanotube Films on Flat and Textured Si Substrates.

Contact angle measurements are investigated on the surface of single-walled carbon nanotube (SWNT) films directly formed on flat and textured Si substrates using a thermal chemical vapor deposition method. The SWNT films on the textured Si consist of a multiscale structure composed of nanoscale SWNTs and a microscale textured Si. They show superhydrophobic properties in which the water contact angle was around 161°. A direct surface treatment to them increase the contact angle to 174°. The reversible wettability of the SWNT films formed on the textured Si substrates is confirmed through the oxidation process using an acid mixture of nitric and sulfuric acids and a successive reduction procedure via heating treatment in an NH₃ environment.

White light-driven photo response of TiO2 thin films: Influence of substrate texturing

In this work, the role of film thickness on white light-driven photo response and electrical properties of TiO2/Si heterojunctions is investigated. Two types of substrates, viz. pristine- and chemically prepared pyramidally textured-Si are used for simultaneous growth of TiO2 films using radio frequency (RF) magnetron sputtering technique. X-ray diffraction study reveals the amorphous nature of as-grown TiO2 thin films. In addition, it is observed that the surface reflectance of conformally grown TiO2 overlayers on textured-Si substrates can be brought down to 0.73% for 5 nm and 0.77% for 20 nm, whereas in case of pris-Si substrates it is 40% for 5 nm and 30% for 20 nm-thick films (in the wavelength range of 400–800 nm). Further, TiO2/Si heterostructures exhibit diode-like rectifying behavior under both dark and white light illumination. The 5 nm-thick films exhibit very low photoactivity in terms of photocurrent, whereas 20 nm-thick films show a remarkable enhancement in the photocurrent up to 10.25 and 78.68 μA (under reverse bias) when grown on pris-Si and txt-Si substrate, respectively. In addition to the transient photocurrent, the responsivity and sensitivity are also higher for 20 nm-thick films. These results are explained in terms of change in their optical and electrical properties. The present finding will be certainly important for fabricating high speed optoelectronic devices based on reverse biased TiO2/Si heterojunctions.

Study of Optical Properties of Nanocrystalline Zinc Phosphide Thin films

Zinc phosphide (Zn3P2), a II–V group semiconductor compound has long been considered as a very interesting and suitable candidate for several applications especially in photovoltaics. Nanocrystalline Zn3P2 thin films were successfully synthesized on glass and different silicon-based substrates by a combined physico-chemical method. The properties and morphology of Zn3P2 films were investigated. SEM images showed that all films displayed a nanoscale granular, polycrystalline morphology. It depends dramatically on the surface state of the substrate and follows the substrate its morphology. X-ray diffraction (XRD) spectra revealed a preferred orientation of the Zn3P2 nanocrystalline film along the (102) and (405) direction. The transmittance of the Zn3P2 films was found to be high of the order of 87%. The optical gap of the film was determined using the optical transmission spectra and the obtained optical band gap value is 1.96 eV. A decrease of the average reflectance from 15% to 4.25%, after deposition of the nanocrystalline Zn3P2 on a textured Si substrate, was observed. This result was compared to the one obtained with SiNx layer deposited on the same Si substrate. A difference of 1% was noticed. We assume that the combination of nanocrystalline Zn3P2 thin film and a textured Silicon surface could increase the efficiency of photovoltaic silicon solar cell by using Zn3P2 as an antireflection layer.

UV–visible light detection with TiO2 thin film deposited on chemically textured p-Si substrate

This paper reports a study on the photodetection properties of TiO2 thin film deposited on chemically textured p-Si substrate and is compared to those deposited on pristine p-Si substrate. The structural properties of both the heterostructures were investigated using XRD analysis. FESEM images confirmed the deposition of TiO2 thin film on chemically pyramidal textured Si substrate. The average total reflectance of the textured Si substrate was reached to ~ 7.6% in the wavelength range of 300–900 nm. It was further decreased to ~ 6.5% after the deposition of 55 nm thick TiO2 on the top of the textured Si substrate. A systematic study was carried out to correlate the structural, optical and electrical properties of both the heterostructures. The electrical parameters of the heterojunction diodes were measured and compared under dark and illuminated conditions using UV and solar simulated light. UV as well as visible light detection property of the heterostructure of TiO2 thin film deposited on pyramidal textured Si substrate was improved compared to the one deposited on pristine Si by the factor 2.0 and 1.86, respectively, under the bias of − 2 V.

Evaluation of the charge carriers’ transportation through the grown MgFe2O4 on the nanotextured silicon surface in the presence of hydrogen gases

Here, we report, for the first time, the solution growth of n-type MgFe2O4 spinel ferrite nanoparticles on nano-textured p-type silicon (100) substrate. Water soluble MgFe2O4 spinel ferrite nanoparticles are prepared by polyol technique. The MgFe2O4 spinel ferrite nanoparticles were characterized by transmission electron microscopy both at low and high resolution, selected area electron diffraction, energy dispersive spectroscopy, and Raman spectroscopy. The texturing of the surface of the Si(100) substrate to create well-organized nanopillar-like shapes was carried out by a nanosecond laser lithography technique. The water soluble MgFe2O4 spinel ferrite nanoparticles were deposited on the textured Si(100) substrate. The sample was characterized by scanning electron microscopy and X-ray diffraction. The charge carriers transport mechanism was discussed in terms of the variation of the barrier height under the exposure to various gases. A comparison between the MgFe2O4 spinel ferrite nanoparticles grown on planar and textured p-type Si(100) surfaces showed that the latter demonstrated an improvement of gas sensitivity and accelerated response time. These two characteristics, combined with high performance stability, make these sensors promising for practical applications.

Growth and characterization of textured well-faceted ZnO on planar Si(100), planar Si(111), and textured Si(100) substrates for solar cell applications.

In this work, textured, well-faceted ZnO materials grown on planar Si(100), planar Si(111), and textured Si(100) substrates by low-pressure chemical vapor deposition (LPCVD) were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and cathode luminescence (CL) measurements. The results show that ZnO grown on planar Si(100), planar Si(111), and textured Si(100) substrates favor the growth of ZnO(110) ridge-like, ZnO(002) pyramid-like, and ZnO(101) pyramidal-tip structures, respectively. This could be attributed to the constraints of the lattice mismatch between the ZnO and Si unit cells. The average grain size of ZnO on the planar Si(100) substrate is slightly larger than that on the planar Si(111) substrate, while both of them are much larger than that on the textured Si(100) substrate. The average grain sizes (about 10–50 nm) of the ZnO grown on the different silicon substrates decreases with the increase of their strains. These results are shown to strongly correlate with the results from the SEM, AFM, and CL as well. The reflectance spectra of these three samples show that the antireflection function provided by theses samples mostly results from the nanometer-scaled texture of the ZnO films, while the micrometer-scaled texture of the Si substrate has a limited contribution. The results of this work provide important information for optimized growth of textured and well-faceted ZnO grown on wafer-based silicon solar cells and can be utilized for efficiency enhancement and optimization of device materials and structures, such as heterojunction with intrinsic thin layer (HIT) solar cells.

Boron-doped p-BaSi2/n-Si solar cells formed on textured n-Si(0 0 1) with a pyramid structure consisting of {1 1 1} facets

BaSi2 films were fabricated on textured Si(001) substrates that consisted of {111} facets using molecular beam epitaxy. The light-trapping effect of these films and their performance when incorporated into solar cells were measured. X-ray diffraction and reflectivity measurements showed that the BaSi2 films were grown epitaxially on the textured Si(001) substrate and confirmed the light-trapping effect. The critical thickness over which BaSi2 relaxes increased from approximately 50 to 100nm when comparing the BaSi2 films on a flat Si(111) substrate and the textured substrate, respectively. p-BaSi2/n-Si solar cells were fabricated with varying BaSi2 layer thickness and with hole concentrations in the range between 2.0×1018 and 4.6×1018cm−3. These cells exhibited a maximum energy conversion efficiency of 4.62% with an open-circuit voltage of 0.30V and a short-circuit current density of 27.6mA/cm2 when the p-BaSi2 layer was 75nm-thick. These results indicated that the use of BaSi2 films on textured Si(001) substrates in solar cells shows great promise.

Laser Processing of Low Optical Reflection Micro/Nano-patterned Si Substrates for SERS

ABSTRACTLight collection efficiency and specific molecular detection are crucial factors for the performance of bio-chemical molecule sensors. In this paper, the low optical-reflection silicon (Si) substrates which combine reduced optical reflectivity by light trapping effect and high Raman enhancement ability of gold nanoparticles (Au-NPs) coated textured Si substrates are investigated for surface-enhanced Raman scattering (SERS). A fast, single-step and highly controllable nanosecond (ns) laser processing technique is employed to fabricate textured Si substrates under ambient conditions. Parallel arrays of micro-pyramids are fabricated on Si surface by direct laser writing two-dimensional structures. SEM micrographs clearly show well-ordered surface features in the form of micro-pyramid shape with well-defined sharp tips on the laser processed Si substrates. The aggregation of Si micro/nanoparticles on Si surface forms nanocavities and nanogaps and further enhances the surface roughness in order to minimize the optical reflection. The low optical reflection Si substrates exhibit optical reflection below 15% over a broad wavelength range from 300 nm to 1200 nm. The textured Si substrates with high signal reproducibility are successfully applied as SERS substrates to detect a very small concentration of Rhodamine B molecules with an average enhancement factor of the order of ∼107. The low optical reflection and SERS signal amplification are also altered by the variation of laser pulse energy resulting into low optical reflection and high SERS signal intensity over the entire laser-patterned area. The effect of surface roughness on water contact angle was studied after the modification with Polydimethylsiloxane (PDMS), the surfaces show perfect superhydrophobicity with almost no water adhesion. This approach provides a novel high-speed and cost-effective method for fabricating SERS substrate with micro/nano-scale surfaces roughness and low optical reflection for high Raman signal enhancement.

Growth of TiO2 thin films on chemically textured Si for solar cell applications as a hole-blocking and antireflection layer

In this work, we investigate the broad-band photoabsorption of an n-TiO2 thin film and its hole-blocking properties when a heterostructure is grown on a chemically textured p-Si substrate. We demonstrate that average specular reflectance of conformally grown TiO2 thin films on chemically prepared pyramidally textured Si substrates can be brought down to ∼0.2% (in the wavelength range of 300–1200nm), which increases up to ∼0.53% after annealing at 673K in air for 1h. X-ray diffraction data reveal the amorphous nature of as-grown TiO2 thin films which undergoes a transition to a crystalline one after annealing. In addition, bulk current-voltage characteristics show that the leakage current increases after annealing which corroborates well a with change in the band gap, as is measured from the optical absorption spectra, due to a transition from amorphous to crystalline (anatase phase) of TiO2. Moreover, TiO2/Si heterojunction allows the transport of electrons but blocks the transport of holes. The present results are not only important for the fundamental understanding of the charge transport across TiO2/Si heterostructures but also to design hole-blocking solar cells.

X-ray photoelectron spectroscopic studies of CeO2 thin films deposited on Ni-W (100), c-Al2O3 (0001) and Si (100) substrates

The oxidation states of CeO2 films, deposited on biaxially textured Ni-W(100), c-Al2O3(0001) and Si(100) substrates, were investigated by using X-ray photoelectron spectroscopy (XPS). The CeO2 films were deposited by RF magnetron sputtering under same deposition conditions. X-ray diffraction (XRD) studies of the films revealed that preferred (200) orientation of CeO2 was observed in case of Ni-W substrate while (111) orientation on Al2O3 and Si substrates. The O1s and Ce3d spectra reveal that the films mostly consist of Ce4+ oxidation states with ∼72.6%, 74.7% and 74.9% on Ni-W, Al2O3 and Si substrates, respectively. The less Ce4+ content in case of Ni-W substrate has been attributed to the migration of oxygen atoms from film to the metallic substrate. The decrease of O2p states in the valence band spectra also in support with the presence of more oxygen vacancies in CeO2/Ni-W compared to that in other substrates. Further, the position of valance band maxima is almost identical (∼2.6 eV) for all the deposited films indicating that all films are n-type in nature.

Carbon nanotube–silicon heterojunction solar cells with surface-textured Si and solution-processed carbon nanotube films

Solution-processed carbon nanotube films fit with textured Si substrates, yielding solar cells with dark surface and improved power conversion efficiency.

Simultaneous integration of different nanowires on single textured Si (100) substrates.

By applying a texturing process to silicon substrates, we demonstrate the possibility to integrate III-V nanowires on (100) oriented silicon substrates. Nanowires are found to grow perpendicular to the {111}-oriented facets of pyramids formed by KOH etching. Having control of the substrate orientation relative to the incoming fluxes enables not only the growth of nanowires on selected facets of the pyramids but also studying the influence of the fluxes on the nanowire nucleation and growth. Making use of these findings, we show that nanowires with different dimensions can be grown on the same sample and, additionally, it is even possible to integrate nanowires of different semiconductor materials, for example, GaAs and InAs, on the very same sample.

Enhanced electrochemical properties of as grown LiCoO2 film cathodes: Influence of silicon substrate surface texturing

Influence of Si substrate texturing on growth, microstuctural and electrochemical properties of lithium cobalt oxide (LiCoO2) cathode films was investigated. A batch of rf magnetron sputtered LiCoO2 films were prepared on both Au/Ti/SiO2/(polished) Si and Au/Ti/SiO2/(textured) Si substrates and the film properties were studied, systematically. As-grown films on polished Si substrates were exhibited partially ordered rock-salt structure with a very poor electrochemical performance. However, the as-grown films on textured Si substrates exhibited relatively predominant (0 0 3) orientation with R 3¯ m symmetry and exhibited an initial discharge capacity of 57.5 μAhcm−2 μm−1 with an appreciable capacity fade rate of 0.07%, even after 50 cycles. Electrochemical performance of these films was in close comparison with the annealed (650 °C) LiCoO2 films of Au/Ti/SiO2/(polished) Si substrates. The experimental observations were thoroughly demonstrated and suggested that the as-grown LiCoO2 films on textured Si substrates can be useful for all types of 2D solid state Li+-ion microbattery applications.