Thick SiO2 Research Articles

GaAsSb/InGaAs tunnel FETs using thick SiO2 mask for regrowth

The regrowth conditions for lateral tunnel FETs featuring heterojunctions involve a tradeoff between selective growth and heavy doping. This study mitigated the connection between single crystals on the InP layer and polycrystals on the SiO2 mask by significantly increasing the thickness of the SiO2 mask to surpass that of the growing GaAsSb layer. We successfully fabricated p-GaAsSb/i-InGaAs tunnel FETs using a thick SiO2 mask, wherein the carrier concentration of the p-GaAsSb source was 5 × 1019 cm−3, and the growth temperature was maintained at 500 °C. The observed current–voltage (I–V) characteristics exhibited an on/off ratio of 5 × 104 and demonstrated ambipolar current behavior, confirming the presence of a p-type source. However, the observed subthreshold swing (SS) was limited to 120 mV dec−1. In comparison with the I–V characteristics of the planar transistor, degradation of SS can be explained by interface state, and the factor that characterizes the change of the drain current with the surface potential dΨs/d(log10ID) is estimated as 52 mV dec−1.

The Performance of Organic Field Effect Transistor Affected by Different Thickness of Active Semiconductor Layer and Thickness of Gate Insulator

The purpose of this paper is to fabricate organic field effect transistor and to investigate the effect of the thickness of the pentacene active layer and the thickness of gate insulator layer on MOSFET performance. The fabricated structure is top-contact. When the thickness of the insulator gate layer increases from 10 nm to 30 nm, the magnitude of the drain source current, when VGS = VDS = -4 V, decreases from 1813 nA to 214 nA and then the threshold voltage shifts from -1.4 V to -2.4 V. When the thickness of the pentacene increases from 9 nm to 40 nm, the threshold voltage voltage shifts slightly in the negative direction from -1.4 V to -1.6 V for SiO2 thickness of 10 nm. In case of SiO2 thickness of 20 nm, the threshold voltage voltage shifts from -1.9 V to -2.2 V. In case of SiO2 thickness of 30 nm, the threshold voltage voltage shifts from -2.4 V to -2.9 V. Besides that, the mobility decreases from around 0.31 cm2/(Vs) to 0.15 cm2/(Vs) when the pentacene thickness increases from 9 nm to 40 nm.

Controlling the shell thickness of SiO2 on TiO2 NPs: Characterization, linear and nonlinear optical properties

TiO2 nanoparticles (NPs) were prepared by the sol-gel method and then encapsulated with different thicknesses of SiO2 as a shell using the Stöber method. The crystal, chemical structure, and morphology of the core-shell TiO2@SiO2 NPs were characterized using XRD, FTIR, and TEM techniques. The amorphous nature of the shell (SiO2) was shown by XRD examination, which influenced the crystallinity of the TiO2 NPs, while FTIR data verified the association between SiO2 and TiO2, and a TEM study validated the coating of TiO2 NPs with SiO2. The optical absorption of TiO2 NPs was characterized by a sharp absorption edge around 343 nm, which redshifted to a higher wavelength region with increasing shell thickness. The direct bandgap decreased as the shell thickness of TiO2@SiO2 increased. The measurements revealed a clear trend, with the bandgap values falling from 3.97 eV for TiO2 to 3.60, 3.37, and 3.26 eV for shell thicknesses of approximately 2.5, 5.5, and 8 nm, respectively. Significant improvement in the optical conductivity of TiO2 NPs was observed with an increase in shell thickness, accompanied by an increase in refractive index and extinction coefficient. This enhancement could potentially lead to breakthroughs in the field of nanotechnology. The Wemple-DiDomenico model was applied to compute the nonlinear refractive index (n2), first- and third-order (χ(1) & χ(3)) susceptibilities values. The addition of a SiO2 shell to the TiO2 core resulted in a remarkable improvement in all nonlinear optical parameters. The (χ(3)) value was increased from 2.08 × 10−14 for pure TiO2 NPs to 3.04 × 10−09 for the core-shell TiO2@SiO2 sample with a shell thickness of 8 nm.

O2 and Ar plasma processing over SiO2/Si stack: Effects of processing gas on interface defect generation and recovery

Defect generation and recovery at the interface of a silicon dioxide/silicon (SiO2/Si) stack are studied in oxygen (O2) or argon (Ar) plasma processing and post-annealing. Defect generation is recognized to be dependent on the processing gas and the SiO2 layer thickness. O2 plasma processing shows a strong incident-ion energy dependence, where ion’s implantation, diffusion, and reactions in the SiO2 layer play important roles in defect generation. A similar dependence is observed for Ar plasma processing; however, it also shows the photon effects in defect generation for a thick SiO2 layer. Defect recovery is demonstrated by annealing, where recovery depends on the annealing temperature as well as the amount of defects generated at the interface.

Analysis of the Effects of Parameters on the Performance of Resonators Based on a ZnO/SiO2/Diamond Structure

With the development of communications technology, surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices have become hotspots of the competitive research in the frequency band above GHz. It imposes higher requirements on the operating frequency, temperature coefficient of frequency (TCF), and electromechanical coupling coefficient (k2) of SAW devices. In this work, we reported on a novel ZnO/SiO2/diamond-layered resonator structure and systematically investigated its propagation characteristics by using finite element methods. A comparative study and analysis of k2 and acoustic velocity (vp) for both the excited Rayleigh mode and the Sezawa mode were conducted. By selecting the appropriate ZnO piezoelectric film, SiO2, and electrode thickness, the Sezawa mode was chosen as the main mode, effectively improving both k2 and vp. It was observed that the k2 of the Sezawa mode is 7.5 times that of the excited Rayleigh mode and nearly 5 times that of piezoelectric single-crystal ZnO; vp is 1.7 times that of the excited Rayleigh mode and nearly 1.5 times that of piezoelectric single-crystal ZnO. Furthermore, the proposed multilayer structure achieves a TCF close to 0 while maintaining a substantial k2. In practical applications, increasing the thickness of SiO2 can compensate for the device’s TCF reduction caused by the interdigital transducer (IDT). Finally, this study explored the impact of increasing the aperture width and IDT pairs on the performance of the single-port resonator, revealing the changing patterns of quality factor (Q) values. The results reported here show that the structure has great promise for the fabrication of high-frequency and low-TCF SAW devices.

INVESTIGATION OF CARBON-ALUMINUM COMPOSITE WITH A BARRIER COATING ON CARBON FIBERS

Barrier SiO2 coatings on the surface of carbon fibers were deposited by the sol-gel solutions (dip coating) based on tertraethoxysilane Si(C2H5O)4. The average thickness of the barrier SiO2 coating on carbon fibers is 127 ± 30 nm. Carbon-aluminum composites were obtained by a type of liquid-phase infiltration — by the shell molding process. The components of the composite were placed in a steel hermetic shell, then after the shell evacuate and heat until the aluminum melts, the fibers were infiltrated by the melt under the external pressure, followed by cooling. Composites with SiO2 coating and without coating on carbon fibers were obtained. After extracting the composite from the metal shell, the structure, phase composition, and mechanical properties of the samples were studied. Studies of the structure of composites showed that the interfiber space is filled with aluminum melt, without porosity and macroscopic defects. The study of the phase composition of the composite reinforced with uncoated carbon fibers showed that aluminum carbide peaks are observed at the angles 2θ = 41°, 67°, 74°. Quantitative analysis carried out by the Rietveld method revealed that the amount of aluminum carbide in the composite is 12.0 ± 1.3 %. The deposition of a barrier SiO2 coating on carbon fibers leads to a decrease in the intensity of the main peaks of aluminum carbide, while the amount of Al4C3 decreases by 4 times, to 3.0 %. An analysis of the fracture surface of the samples after mechanical testing revealed that the fracture of the composite reinforced with uncoated carbon fibers is almost flat. No protrusions and relief are observed on the fracture surface. The fracture surface of a composite reinforced with coated carbon fibers has a relief surface, and separately sticking out fibers are observed. Mechanical tests of samples for three-point bending showed that the barrier coating on the fibers increases the strength to 520 ± 50 MPa, the strength of the uncoated composite is 350 ± 8 MPa. Barrier SiO2 coating applied to the surface of carbon fibers prevents the formation of aluminum carbide and fiber degradation in the carbon-aluminum composite.

Opportunity to achieve an efficient SiC/SiO2 interface N passivation by tuning the simultaneous oxidation modes during the SiC surface nitridation in N2 + O2 annealing

We investigated a possible guideline to design the SiC surface nitridation process for an efficient interface N passivation in high-temperature N2 + O2 annealing, based on the understandings of SiC surface nitridation kinetics. Based on the findings of the time-dependent transition of the simultaneous SiC surface oxidation mode from passive to active during the annealing with reduced O2 partial pressure condition, it was proposed that an efficient SiC surface nitridation is achievable by following these steps: triggering the passive-to-active transition of the simultaneous surface oxidation by tuning the thermodynamic conditions and SiO2 thickness, and terminating the surface reaction at the beginning of the active-oxidation-dominant period by controlling the annealing time. It is confirmed that the observed interface passivation would be attributable to the N introduction to SiC/SiO2 interface, suggesting an opportunity to achieve an efficient interface N passivation following the proposed guideline.

Electron-enhanced atomic layer deposition of Ru thin films using Ru(DMBD)(CO)3 and effect of forming gas anneal

Ruthenium (Ru) thin films were deposited utilizing electron-enhanced atomic layer deposition (EE-ALD). Sequential exposures of Ru(DMBD)(CO)3 (DMBD = 2,3-dimethylbutadiene) and low-energy electrons at ∼125 eV were used to grow the Ru films at temperatures ≤160 °C. The electrons were obtained from a hollow cathode plasma electron source that provided an electron current of ∼200 mA over a surface area of ∼4 cm2. Low-energy electrons can desorb surface ligands derived from Ru(DMBD)(CO)3, such as CO, through electron-stimulated desorption. The desorbed surface ligands leave chemically reactive sites for subsequent Ru(DMBD)(CO)3 precursor absorption. Ru EE-ALD film growth was monitored utilizing in situ spectroscopic ellipsometry (SE). The electron exposures resulted in rapid Ru film nucleation and growth. Under saturation conditions at 160 °C, the growth rate for Ru EE-ALD was 0.2 Å/cycle. The electron efficiency factor for Ru EE-ALD was ∼21 500 electrons/deposited Ru atom. There was no film growth without electron exposures. Ru growth was observed on various substrates including silicon with native oxide and titanium. Ru growth was also obtained on insulating substrates such as 400 nm thick thermal SiO2 substrates. XPS analysis measured <1 at. % oxygen in the deposited Ru films. XRD, x-ray reflectivity, and SE were used to characterize the Ru films before and after forming gas anneal (FGA). FGA successfully removed carbon impurities from the as-deposited Ru films. The resistivity of the Ru EE-ALD films after FGA was determined to be as low as 17 μΩ cm for a film thickness of 6.7 nm. SE measurements of the imaginary part of the pseudodielectric function, 〈ɛ2〉, were utilized to characterize the as-deposited Ru films and the high purity Ru films after FGA. The low resistivity of the Ru films after FGA was consistent with a prominent Drude absorption in the ⟨ε2⟩ spectrum at ≤1 eV. Various reactive background gases such as H2, NH3, and H2O were utilized during EE-ALD to attempt to remove the carbon from the as-deposited Ru EE-ALD films.

Reactively-sputtered super-hydrophilic ultra-thin titania films deposited at 120 °C

Abstract We investigate super-hydrophilic TiO2 (titania) films for concentrated solar-thermal power applications. Reactive magnetron sputtering has been used to deposit 8 to 12 nm thick titania thin films onto borosilicate microscope glass slides, low-Fe extra-clear architectural glass, or Si(100) wafers with a 500 nm thick thermal SiO2 layer. The effects of deposition temperature and O2 fraction of the O2/Ar working gas were investigated. We demonstrate the importance of the O2 fraction for obtaining optically transparent, super-hydrophilic (contact angle below 1°) thin films. In particular, we show that as the O2 fraction increases, contact angle decreases, obtaining super-hydrophilic titania thin films at deposition temperatures as low as 120 °C. Our work enables to develop low thermal budget cost-efficient industrial synthesis processes, paving the way for commercial applications.

Enhancement of electrical performance in indium-zinc oxide thin-film transistors with HfO2/Al2O3 gate insulator deposited via low-temperature ALD

Several studies have been conducted on amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) with the aim of applying them to the next-generation low-power displays. To improve the electrical performance of conventional AOS TFTs, which are known for their poor switching characteristics, we fabricated indium-zin oxide (IZO) TFTs with HfO2/Al2O3 gate insulator deposited via low-temperature atomic layer deposition (ALD). We optimized the electrical performance of the fabricated TFTs by varying the thickness of the IZO channel and Al2O3 insulator, respectively. Compared to the samples with a thermally grown 150 nm thick SiO2 gate insulator, the samples with a 10 nm thick IZO channel and a 10/70 nm thick HfO2/Al2O3 gate insulator exhibited the subthreshold swing of 0.24 V/dec, saturation carrier mobility of 7.49 cm2/V∙s and on–off current ratio of 1.09 × 107, which were improved by more than 47 %, 64 % and 5 times, respectively. Also, the threshold voltage shift in positive and negative bias stress conditions were improved to + 0.90 and – 1.75 V, respectively.

Improving the minority carrier lifetime of PERC solar cells via bi-layer rear interface passivation strategy

Passivated emitter and rear contact (PERC) based solar cells are dominating the current photovoltaic (PV) market due to their high power conversion efficiency (PCE) and low cost. However, issues like the lower minority carrier lifetime (MCLT) and high density of surface dangling bonds are limiting their further improvement in PCE. To overcome this issue, a bi-layer rear interface passivation strategy is developed with the ultra-thin Al2O3 and SiO2 layers in PERC solar cells. Applying single (Al2O3) and double (SiO2/Al2O3) passivation layers revealed that each process parameter such as plasma conditions, deposition temperature, post-annealing temperature, and the film thickness in the ALD process affect the MCLT values as well as overall device performance. Especially, post-annealing treatment which improves crystallinity, and reduces interfacial defects was found to be most influential for the MCLT value. The single Al2O3 layer applied in PERC solar cells revealed an increase and decrease in MCLT values at a relatively lower (<10 nm) and higher thickness (>15 nm), respectively. Further, integration of SiO2 with the Al2O3 layer showed its more prominent effect than just single Al2O3 and SiO2 passivation layers. An optimal SiO2 thickness combination (4 nm) with an Al2O3 layer (12 nm), demonstrated reduced density of surface dangling bonds and diffusion of Al atoms from Al2O3 layers. As a result, it improved the carrier extraction yield by increasing the negative fixed charge. Finally, SiO2/Al2O3 (4/12 nm) double passivation layer post-annealed at 450 °C for 15 min delivers improved PCE from 19.4% to 19.9% in PERC solar cells.

A multi resonant wave-absorbing honeycomb sandwich structure with excellent electrical performance damage tolerance

Wave-absorbing honeycomb sandwich structure (HSS) is widely used in aviation equipment, playing an important role in the integration of load-bearing and stealth shielding. The high-intensity service of aviation equipment beyond design condition accelerates damage and complicates failure triggers. In this work, a decentralized construction strategy with multiple resonant absorption peaks is proposed to enhance the electrical performance damage tolerance (EDT) of wave-absorbing HSS in 4–18 GHz frequency band. The designed multi resonant absorption peaks for 30 mm thick wave-absorbing honeycomb with 1 mm thick SiO2 fiber reinforced epoxy resin (SiO2f/ER) composites as top and bottom panels occur in the vicinity of 5 GHz, 9 GHz, 13 GHz, and 17 GHz, respectively. When the panel damage area accounts for 72 % or the penetrating damage area accounts for 18 %, the effective absorption bandwidth (EAB) of proposed HSS covers 4–18 GHz, indicating excellent EDT. By analyzing the normalized impedance, Smith chart, as well as power loss density, the excellent EDT is attributed to the pinning effect at each resonant frequency point, which benefits both impedance matching and electromagnetic wave (EMW) attenuation.

Effect of SiO2 gate insulator on electrical performance of solution processed SnO2-Based thin film phototransistor

SnO2-based TFTs were fabricated by using the sol-gel spin coating method. SnO2 semiconductor films used as active layers were coated on oxidized Si with different SiO2 thicknesses. AFM was used to analyze the surface morphology. The oxidation states of SnO2 film for Sn3d and O1s were determined by XPS. The parameters demonstrating the electrical performance of a transistor such as mobility (μ), threshold voltage (Vth) and sub-threshold swing (SS) have been determined depending on the thickness of the dielectric layer. The thickness of the dielectric layer played an important role in the device's performance. The highest mobility and Ion/off values were obtained as 7.1 cm2/V.s and 6.98x104 for TFT fabricated with a 150 nm thick SiO2 layer. All the TFTs exhibited photosensing behavior at different light intensities and these results are an indicator that the SnO2 TFT can be effectively utilized in visible photo-detecting device applications.

Origin of Enhancement of Orbital Magnetic Moment in SiO2-Coated Fe3O4 Nanocomposites Studied by X-ray Magnetic Circular Dichroism.

In this study, magnetic Fe3O4 nanoparticles (NPs) were dispersed uniformly by varying the thickness of the SiO2 coating, and their electronic and magnetic properties were investigated. X-ray diffraction confirmed the structural configuration of monophase inverse-spinel Fe3O4 NPs in nanometer size. Scanning electron microscopy revealed the formation of proper nonporous crystallite particles with a clear core-shell structure with silica on the surface of Fe3O4 NPs. The absorption mechanism studied through the zeta potential indicates that SiO2-coated Fe3O4 nanocomposites (SiO2@Fe3O4 NCs) possess electrostatic interactions to control their agglomeration in stabilizing suspensions by providing a protective shield of amorphous SiO2 on the oxide surface. High-resolution transmission electron microscopy images demonstrate a spherical morphology having an average grain diameter of ∼11-17 nm with increasing thickness of SiO2 coating with the addition of a quantitative presence and proportion of elements determined through elemental mapping and electron energy loss spectroscopy studies. Synchrotron-based element-specific soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) techniques have been involved in the bulk-sensitive total fluorescence yield mode to understand the origin of magnetization in SiO2@Fe3O4 NCs. The magnetization hysteresis of Fe3O4 was determined by XMCD. At room temperature, the magnetic coercivity (Hc) is as high as 1 T, which is about 2 times more than the value of the thin film and about 5 times more pronounced than that of NPs. For noninteracting single-domain NPs with the Hc spread from 1 to 3 T, the Stoner-Wohlfarth model provided an intriguing explanation for the hysteresis curve. These curves determine the different components of Fe oxides present in the samples that derive the remnant magnetization involved in each oxidation state of Fe and clarify which Fe component is responsible for the resultant magnetism and magnetocrystalline anisotropy based on noninteracting single-domain particles.

The effect of SiO2 interlayer on magnetic interactions in multilayer composites ribbons

This article studies the influence of dipole interactions on the magnetic properties. Specifically, FINEMET/SiO2 and FINEMET/SiO2/Fe20Ni80 composite ribbons were prepared by magnetron sputtering. During the manufacturing process, the Fe20Ni80 film with a fixed thickness of 260 nm and the FINEMET ribbon were separated by the SiO2 layer, and the SiO2 layer thickness could be adjusted within a range of 0–150 nm. This configuration enabled the exchange coupling gradually reduced with the SiO2 layer thickness increased, allowing dipole interactions to become the dominant factor. This study not only excludes the influence of the SiO2 in the composite ribbons but analyzes the effect of the exchange couple and dipole interactions for the GMI, respectively. The experimental results show the GMI ratio decreases initially and then increases with the thickness of SiO2, where the optimization of GMI ratio was explored in FINEMET/Fe20Ni80 ribbons. On the other hand, the minimum peak field was shown with the SiO2 thickness of 5 nm. Furthermore, the results also elucidate that both dipole interactions and exchange couple have affected the peak field of GMI, which could be used for the design of multilayer composite ribbons with better performance. Thus, the analysis we showed in this work is thought to be valuable in revealing the mechanism of multilayer composite ribbons for future sensing applications.

Investigating the effect of SiO2 nanoparticle addition and thickness of face-coverings on COVID-19 protection using molecular dynamics approach

This study investigates the penetration of coronavirus (COVID-19) and oxygen (O2) in different commercial face coverings like surgical and N-95 masks using a molecular dynamics approach. For this purpose, the effects of the thickness of the masks and the addition of SiO2 nanoparticles are studied. We could demonstrate quantitatively the advantages of N-95 masks over surgical masks for coronavirus protection. The temperature (T) in all the simulated structures converges to 300 K after 20 ns. By increasing the thickness and decreasing the concentration of the coronavirus, the stability of the coronavirus was reduced. For the surgical mask, the atomic ratio of O2 molecules that penetrated was 73 %, and for the N-95 mask, it was 78 %. With the increase in mask thickness from 15 nm to 1000 nm, the atomic ratio of O2 molecules in surgical masks decreased from 73 % to 67 %. Furthermore, the atomic ratio of the coronavirus in this mask decreased from 11 % to 5 %. The atomic ratio of O2 molecules decreased from 78 % to 71 % as thickness increased. Also, the atomic ratio of coronavirus decreased from 6 % to 3 % in the N-95 mask. For the surgical mask, with the increase of SiO2 from 1 % to 10 %, the atomic ratio of O2 increased from 78 % to 80 %. Also, the atomic ratio of the coronavirus remained constant with the addition of carrier particles. For the N-95 mask, with the increase of SiO2 from 1 % to 10 %, the atomic ratio of O2 increased from 83% to 85%. Additionally, the atomic ratio of the coronavirus increased from 9 % to 8 % by adding nanoparticles.

From design to realization of high diffraction efficiency Littrow configuration diffraction gratings based on multilayer dielectric mirrors patterned with electron beam lithography

Diffraction efficiency (DE) and laser-induced damage threshold of Chirped pulse amplification (CPA) system diffraction gratings (DGs) are one of the main limiting factors for the anticipated progress of high peak power lasers. Optimization of a high reflectivity dielectric multilayer ZrO2/SiO2 stack mirror with a DG etched in the top SiO2 layer was carried out employing the Rigorous coupled wave analysis method. Two families of solutions possessing DE > 0.99 over the bandwidth of the 1030 nm wavelength ultrashort laser and withstanding different fabrication margins were identified for the Littrow configuration. DGs were produced and verified experimentally. Structures permitting variation in both the depth of the DG and filling factor without loss in DE were obtained for the 690 nm thick SiO2 layer. While the 770 nm thick layer permitted separation of the two parameters requiring either rigorous control of the DG depth or filling factor. DG realization technology was proposed employing electron beam lithography and inductively coupled plasma reactive ion etching. Measurements of the fabricated structures demonstrated 0.91 DE for the first diffraction order over the 60 nm bandwidth and under a 6° mounting error from the Littrow configuration. Spectral angular reflectance DE simulations and respective measurements indicated quantitative agreement. The work provides an integrated overview of high DE periodic structure numerical optimization and manufacturing roadmap which could be applied for the high-peak-power laser CPA system development.

Effects of Thermal-Strain-Induced Atomic Intermixing on the Interfacial and Photoluminescence Properties of InGaAs/AlGaAs Multiple Quantum Wells.

Quantum-well intermixing (QWI) technology is commonly considered as an effective methodology to tune the post-growth bandgap energy of semiconductor composites for electronic applications in diode lasers and photonic integrated devices. However, the specific influencing mechanism of the interfacial strain introduced by the dielectric-layer-modulated multiple quantum well (MQW) structures on the photoluminescence (PL) property and interfacial quality still remains unclear. Therefore, in the present study, different thicknesses of SiO2-layer samples were coated and then annealed under high temperature to introduce interfacial strain and enhance atomic interdiffusion at the barrier-well interfaces. Based on the optical and microstructural experimental test results, it was found that the SiO2 capping thickness played a positive role in driving the blueshift of the PL peak, leading to a widely tunable PL emission for post-growth MQWs. After annealing, the blueshift in the InGaAs/AlGaAs MQW structures was found to increase with increased thickness of the SiO2 layer, and the largest blueshift of 30 eV was obtained in the sample covered with a 600 nm thick SiO2 layer that was annealed at 850 °C for 180 s. Additionally, significant well-width fluctuations were observed at the MQW interface after intermixing, due to the interfacial strain introduced by the thermal mismatch between SiO2 and GaAs, which enhanced the inhomogeneous diffusion rate of interfacial atoms. Thus, it can be demonstrated that the introduction of appropriate interfacial strain in the QWI process is of great significance for the regulation of MQW band structure as well as the control of interfacial quality.

Breakdown-Voltage Degradation Under AC Stress of Thick SiO2 Capacitors for Galvanic Insulation

Breakdown-Voltage Degradation Under AC Stress of Thick SiO₂ Capacitors for Galvanic Insulation

Bias-voltage photoconductance and photoluminescence for the determination of silicon-dielectric interface properties in SiO2/Al2O3 stacks

This paper presents an advanced measurement method for controlling the surface charge carrier density of passivated silicon wafers during photoconductance and photoluminescence measurements, by employing semitransparent poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) electrodes with an applied bias voltage. This is employed to study and analyze charge carrier dynamics in dielectric layers by measuring their direct influence on effective lifetime. With this method, the carrier population at the surface and the effective carrier lifetimes of n- and p-type samples can be investigated, from which the fixed charge carrier density Qf of the passivation can be extracted. Additionally, the defect density Dit can also be derived from the minimum lifetime values at flatband voltage. In SiO2/Al2O3 stacks with varying SiO2 interlayer thickness, it was shown that by changing the SiO2 thickness, the carrier density Qf can be tuned to a wide range of values, which corresponds to the results obtained in other studies. An increase in interlayer thickness resulted in a decrease in Qf. Varying the SiO2 thickness, the behavior of the respective effective lifetime under bias voltage also changes, exhibiting hysteresis-like effects, which are attributed to additional charges getting trapped at the surface during bias-voltage application. This effect is much more pronounced for samples with a thinner SiO2 layer as well as for the n-type samples. Additionally, the doping type also influences the magnitude of Qf, with p-type samples generally reaching lower absolute values. It was also shown that aging of the samples had a significant effect on the measured Qf, which was increased compared to the initial Qf of the passivation. This effect was more pronounced for the n-type samples. The measurements were realized by a cost-effective and easy-to-use microcontroller-based potentiostat, which can be used as a simple add-on to existing photoconductance or photoluminescence measurement setups.