Passive Silicon Research Articles

Wireless passive polymer-derived SiCN ceramic sensor with integrated resonator/antenna

This paper presents a passive wireless polymer-derived silicon carbonitride (SiCN) ceramic sensor based on cavity radio frequency resonator together with integrated slot antenna. The effect of the cavity sensor dimensions on the Q-factor and resonant frequency is investigated by numerical simulation. A sensor with optimal dimensions is designed and fabricated. It is demonstrated that the sensor signal can be wirelessly detected at distances up to 20 mm. Given the high-temperature stability of the SiCN, the sensor is very promising for high-temperature wireless sensing applications.

On the Surface Passivation of Textured C-Si by PECVD Silicon Nitride

We investigate the surface passivation of crystalline silicon (c-Si) wafers that are textured with random upright pyramids and passivated with amorphous silicon nitride (SiN <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{x}$ </tex></formula> ). Over a large range of refractive indices <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(n$</tex></formula> = 1.89–4.1 at 632 nm), we achieve a low upper limit to surface recombination velocity on textured samples ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$S_{\rm eff,UL}$</tex></formula> < 10 cm s <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{-1}$</tex></formula> at an excess carrier density of 10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{15}$</tex></formula> cm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{-3})$</tex> </formula> . We also find that <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$S_{\rm eff,UL}$</tex></formula> is higher for textured surfaces than for planar surfaces when the NH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{3}$</tex></formula> :SiH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{4}$</tex></formula> ratio is high (and, hence, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $n$</tex></formula> is low). For example, when passivated by an N-rich SiN <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{x}$ </tex></formula> deposited with NH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{3}$</tex></formula> :SiH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{4}$</tex></formula> = 4.7 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(n$ </tex></formula> = 1.83), the vertices and/or edges of the pyramidal texture drives a 3.5 times increase in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$S_{\rm eff,UL}$</tex></formula> . As the NH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{3}$</tex></formula> :SiH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{4}$</tex></formula> ratio decreases (and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> increases), <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$S_{\rm eff,UL}$</tex></formula> of the textured surfaces decreases rapidly and approaches the same <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$S_{\rm eff,UL}$</tex></formula> as the planar surfaces when NH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{3}$</tex></formula> :SiH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{4}$</tex></formula> ≤ 0.7 ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> ≥ 2.3). By contrast, we find that irrespective of NH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{3}$</tex></formula> :SiH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{4}$</tex> </formula> ratio, and, therefore, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n, S_{\rm eff,UL}$</tex></formula> is equivalent on {100} and {111} planar surfaces. The results indicate that the increase in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $S_{\rm eff,UL}$</tex></formula> of the textured surfaces is related to the presence of vertices and/or edges of the pyramids rather than to the presence of {111}-orientated facets. By depositing varying degrees of corona charge on the samples, it is found that the increase in recombination introduced by 1) a higher NH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $_{3}$</tex></formula> :SiH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{4}$</tex></formula> ratio and 2) the vertices and edges of the pyramids is primarily due to an increase in defect density rather than a decrease in SiN <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{x}$</tex></formula> charge density.

Performance Analysis of Thin-Film Crystalline Silicon-on-Glass Solar Cells

Performance limits of a heterojunction thin-film crystalline silicon on a glass solar cell (SC) in a substrate configuration were analyzed using the computer simulation program “Advanced Semiconductor Analysis” from the Delft University of Technology. The role of light trapping, due to scattering at randomly rough interfaces, on the absorption in the individual layers of the SC was investigated. The effect of the crystalline silicon absorber thickness, quality and passivation on the external parameters of the SC was evaluated. Using light trapping, the efficiency of an SC with 1- and 10-μm-thick c-Si absorber with a minority carrier lifetime of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> s and a surface recombination velocity of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> m/s can achieve 13.8% and 17.8%, respectively.

Inline PL Inspection and Advanced Offline Evaluation of Passivation Defects, Charge and Interfaces

Recently introduced techniques for whole wafer mapping and imaging create new possibilities for root cause analysis of emitter passivation defects. Inline compatible PL imaging identifies such defects as localized regions with increased emitter saturation current and reduced implied open circuit voltage. Advanced offline evaluation of defective areas can be then performed with multiparameter noncontact measurements capable to establish the role of surface recombination, the interface trap density, or the dielectric charge that controls the field-effect passivation. The relevant novel metrologies are discussed and are illustrated using examples of advanced silicon passivation by dielectric films and by a-Si heterojunction structures.

Ultracompact linear on-chip silicon optical logic gates with phase insensitivity

All-optical integrated circuits for computing and information processing have been pursued for decades as a potential strategy to overcome the speed limitations intrinsic to electronics. However, feasible on-chip integrated logic units and devices still have been limited by their size, quality, scalability, and reliability. Here we analyse all-passive on-chip optical AND and NAND logic gates made from a directional emitting cavity connecting two ultrasmall photonic-crystal heterojunction diodes. The measured transmission spectra show more than 10 dB contrast of the logic transport with a high phase tolerance, agreeing well with numerical simulations. The building of linear, passive, and ultracompact silicon optical logic gates might pave the way to construct novel nanophotonic on-chip processor architectures for future optical computing technologies.

Effects of high-temperature treatment on the hydrogen distribution in silicon oxynitride/silicon nitride stacks for crystalline silicon surface passivation

This work investigates a double layer stack system that can be used for surface passivation of crystalline silicon. The stack consists of amorphous silicon-rich silicon oxynitride and amorphous silicon nitride on top. Both layers are fabricated by means of plasma-enhanced chemical vapour deposition. We investigate the stack in terms of changes in the hydrogen content and distribution within the different stack layers due to a high temperature treatment. For that purpose the stack is studied by Fourier-transformed infrared spectroscopy and nuclear reaction analysis before and after fast firing at 850 °C. Our results determine the bottom silicon oxynitride layer as very hydrogen-rich. Furthermore, we identify the silicon nitride capping layer as diffusion barrier to atomic hydrogen but still allowing an effusion of molecular hydrogen. We present a qualitative model that explains our findings and distinguishes between atomic and molecular hydrogen.

Femtosecond laser-induced removal of silicon nitride layers from doped and textured silicon wafers used in photovoltaics

The removal of a 75- to 90-nm-thick passivating silicon nitride antireflection coating from standard textured multicrystalline silicon photovoltaic wafers with a typical diffused 90-Ω/sq-emitter upon irradiation with near-infrared femtosecond laser pulses (790nm central wavelength, 30fs pulse duration) is studied experimentally. The laser irradiation areas are subsequently characterized by complementary optical microscopy, scanning electron microscopy and depth profiling chemical analyses using secondary ion mass spectrometry. The results clarify the thin-film femtosecond laser ablation scenario and outline the process windows for selective antireflection coating removal.

Aluminum Oxide Deposited by Pulsed-DC Reactive Sputtering for Crystalline Silicon Surface Passivation

In this paper, we report on the surface passivation of crystalline silicon (c-Si) by pulsed-dc (p-dc) reactive-sputtered aluminum oxide (AlOx) films. For the activation of surface passivation, the films were subjected to post deposition annealing (PDA) in different ambients namely N2, N2 + O2, and forming gas (FG) in the temperature range of 420-520°C. The surface passivation was quantified by surface recombination velocity, which was correlated to the interface states at the silicon-dielectric interface and fixed charges in the dielectric. A good quality surface passivation with effective surface recombination velocity Seff of 41 cm · s-1 is obtained for PDA in N2 or N2 + O2 gas ambient. PDA in FG ambient at high temperature is found to degrade the passivation. The AlOx film annealed in FG ambient shows poorer thermal stability as compared with films annealed in the other two ambients. A clear path for further improvements in surface passivation quality of p-dc reactive sputter-deposited AlOx is suggested based on cross-sectional transmission electron microscopy and X-ray photoelectron spectroscopy analysis and electrical data.

Analysis of intrinsic hydrogenated amorphous silicon passivation layer growth for use in heterojunction silicon wafer solar cells by optical emission spectroscopy

The structure and quality of intrinsic hydrogenated amorphous silicon thin films are studied with intended use as passivation layer in heterojunction silicon wafer solar cells. The thin film layers are formed by radio-frequency parallel-plate plasma-enhanced chemical vapor deposition. While the passivation quality of the films is found to improve steadily with increasing deposition temperature, a very narrow process window in terms of pressure variation is observed. The best effective lifetime is obtained at a hydrogen to silane dilution ratio of 1 and a pressure of 66.7 Pa for the used tool configuration. Raman crystallinity and Urbach energy obtained from fitting ellipsometry data confirm that the degradation of the passivation quality outside the process window is due to a phase change into microcrystalline silicon with different growth mechanisms and an increase in bonding related defects. Film growth mechanisms are proposed to account for the observed narrow process window, which are verified by optical emission spectroscopy measurements.

Silicon passivation and tunneling contact formation by atomic layer deposited Al2O3/ZnO stacks

The passivation of Si by Al2O3/ZnO stacks, which can serve as passivated tunneling contacts or heterojunctions in silicon photovoltaics, was investigated. It was demonstrated that stacks with Al2O3 thicknesses >3 nm lead to lower surface recombination velocities (Seff,max < 4 cm s−1) on n- and p-type Si than single-layer Al2O3 films for a wide range of ZnO thicknesses and irrespective of Al-doping of the ZnO. Stacks with an Al2O3 thickness of 1–2 nm were found to combine reasonable surface passivation (Seff,max = 100–700 cm s−1) with sufficiently high tunneling current densities (10–300 mA cm−2 at 700 mV).

Amorphous/crystalline silicon interface defects induced by hydrogen plasma treatments

Excellent amorphous/crystalline silicon interface passivation is of extreme importance for high-efficiency silicon heterojunction solar cells. This can be obtained by inserting hydrogen-plasma treatments during deposition of the amorphous silicon passivation layers. Prolonged hydrogen-plasmas lead to film etching. We report on the defect creation induced by such treatments: A severe drop in interface-passivation quality is observed when films are etched to a thickness of less than 8 nm. Detailed characterization shows that this decay is due to persistent defects created at the crystalline silicon surface. Pristine interfaces are preserved when the post-etching film thickness exceeds 8 nm, yielding high quality interface passivation.

Study of hydrogenated AlN as an anti‐reflective coating and for the effective surface passivation of silicon

AbstractStacks of aluminum oxide and silicon nitride are frequently used in silicon photovoltaics. In this Letter, we demonstrate that hydrogenated aluminum nitride can be an alternative to this dual‐layer stack. Deposited on 1 Ω cm p‐type FZ silicon, very low effective surface recombination velocities of 8 cm/s could be reached after firing at 820 °C. This excellent passivation is traced back to a high density of fixed charges at the interface of approximately –1 × 1012 cm–2 and a very low interface defect density below 5 × 1010 eV–1 cm–2. Furthermore, spectral ellipsometry measurements reveal that these aluminum nitride layers have ideal optical properties for use as anti‐reflective coatings. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Thin Films: Organic Vapor Passivation of Silicon at Room Temperature (Adv. Mater. 14/2013)

Thin Films: Organic Vapor Passivation of Silicon at Room Temperature (Adv. Mater. 14/2013)

Characterization of Insertion Loss and Back Reflection in Passive Hybrid Silicon Tapers

The optical properties of two hybrid silicon taper designs are investigated. These tapers convert the optical mode from a silicon waveguide to a hybrid silicon III/V waveguide. A passive chip was fabricated with an epitaxial layer similar to those used in hybrid silicon lasers. To separate optical scattering and mode mismatch from quantum-well absorption, the active layer in this paper was designed to be at 1410 nm, to allow measurements at 1550 nm. Using cutback structures, the taper loss and the taper reflection are quantified. Taper losses between 0.2 and 0.6 dB per taper and reflections below -41 dB are measured.

Investigation of the Internal Back Reflectance of Rear-Side Dielectric Stacks for c-Si Solar Cells

This paper addresses the calculation of internal back reflectance for various dielectrics that are used in rear-side passivated crystalline silicon solar cells. Optical modeling of various stack configurations is examined to explore the back-surface reflectance at the Si-dielectric interface for different film combinations and thicknesses as a function of wavelength and internal angle of incidence at the rear side. Specifically, configurations using aluminum oxide (AlOx), silicon nitride (SiNx), titanium dioxide (TiO2), and silicon dioxide (SiO2) were investigated with a focus on designing stack configurations that will also allow for high-quality passivation and are compatible with a high-volume manufacturing environment. In addition, samples were fabricated by plasma-enhanced and atmospheric pressure chemical vapor deposition of thin dielectric films onto polished and textured monocrystalline silicon wafers. Spectral reflectance curves of the samples are presented to supplement and validate the conclusions that are obtained from the optical modeling data.

Radio-Frequency Inductors on High-Resistivity Silicon Substrates with a Nanocrystalline Silicon Passivation Layer

In this paper, spiral inductors on high-resistivity silicon (HR-Si) substrates, which surfaces were passivated by different process methods, were fabricated and measured. The comparison of inductances and quality factors between these inductors shows that the inductances and quality factors of spiral inductors significantly depend on process method and thickness of surface passivation layer. The differently generated passivation layer results in different effective substrate resistivity and hence gives rise to different substrate loss. The experimental results show that using thicker nanocrystalline silicon (nc-Si) as a passivation layer will result in a smaller substrate loss and hence spiral inductors on the substrate have larger inductances and larger quality factors. In this study, the metal thickness of inductors is 1.2 µm and is about half that of the inductors provided by foundries. At higher frequencies, the thinner spiral inductors on the SiO2/nc-Si/HR-Si substrate have larger inductances and larger quality factors as compared with the inductors provided by foundries. With the same metal thickness as that adopted in standard processes of foundries, the identical-geometry inductors on the SiO2/nc-Si/HR-Si substrate probably exhibit superior quality factors.

Organic Vapor Passivation of Silicon at Room Temperature

A simple, inexpensive, efficient, and scalable method to create air-stable organic surface passivation layers on silicon using a vapor-phase treatment is demonstrated. A variant of initiated chemical vapor deposition is used to synthesize a thin film that acts as both a passivation layer and an antireflective coating. The lowest surface recombination velocity reported to date is achieved and maintained during prolonged exposure to air.

Process Control of Reactive Sputter Deposition of AlO $_{x}$ and Improved Surface Passivation of Crystalline Silicon

In this paper, we investigate the relationship between the deposition-process parameters of reactively sputtered aluminium oxide films and the passivation of silicon surfaces. A method of tuning the deposition process has been established that results in a reduced level of surface recombination, where surface recombination velocities as low as 8.5 cm/s have been achieved on 1 Ω·cm n-type monocrystalline silicon. We find that in order to achieve good surface passivation, the deposition need to be conducted at low power density and at high deposition pressure. We have found that effective passivation is achieved when a sputtering target is close to being fully oxidized-indicated by deposition rate - likely resulting in films that are less aluminium rich. Additionally, Fourier-transform-infrared spectroscopy measurements were used for film characterization; the correlation between effective lifetime and the integrated absorption of all Al and O related bonds shows that films with lower absorption in the wavenumber range 500-1060 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> result in better passivation.

Kelvin probe studies of alkyl monolayers on silicon (111) for surface passivation

A chlorination–alkylation procedure has been investigated with a view to improving the surface passivation properties on silicon. We have found that increasing surface coverage of the alkyl monolayer raises the measured SPV and recombination lifetime. A logarithmic trend is observed between the SPV and recombination, showing that monolayer preparation is an important factor in determining the lifetimes observed. The high SPVs measured by Kelvin probe suggest the presence of a silicon surface with a lower concentration of electrons, reducing surface recombination.

Passivation of Textured Silicon Wafers:Influence of Pyramid Size Distribution, a-Si:H Deposition Temperature, and Post-treatment

In this study we focus on optimizing the passivation of pyramid textured n-type crystalline silicon (c-Si) wafers by deposition of intrinsic amorphous Si (a-Si:H(i)) layers. By statistical analysis of the pyramid size distribution it is revealed that a decreased fraction of small pyramids leads to longer minority charge carrier lifetimes and, thus, a higher Voc potential for solar cells. Further, we demonstrate that optimized parameters for the deposition of a-Si:H(i) layers on planar Si(111) wafers can be transferred to the a-Si:H deposition on random pyramid textured Si(100) wafers exhibiting facets with {111} orientation. In particular the influence of the deposition temperature on the optical layer properties is elucidated. Furthermore, the favorable impact of post-deposition plasma-hydrogenation and annealing on the charge carrier lifetime (> 5ms) and the implied open-circuit voltage (up to 738mV) are demonstrated.