Scanning Spreading Resistance Microscopy Research Articles

Elucidating the mechanism of microscopic conduction in cathode composites for all-solid-state batteries through scanning spreading resistance microscopy

Local resistance of cathode composites in all-solid-state batteries is investigated by scanning spreading resistance microscopy, providing microscopic insights that emphasize contact resistance within electrode composites.

Optimizing Ionic-Electronic Pathways Via Bioinspired Self-Polymerized Dopamine in All-Solid-State Composite Cathode

The research of all-solid-state batteries (ASSBs) has been the principal emphasis in recent years. By utilizing the capabilities of advanced materials science and innovative engineering, ASSBs have the potential to revolutionize industries as diverse as consumer electronics, electric vehicles, aviation, and renewable energy. Solid-state batteries with their outstanding energy density, fast charging capabilities, and resistance to thermal runaway are anticipated to revolutionize the future of energy storage and allow a new era of eco-friendly, high-performance applications.Nonetheless, the point-of-contact resistance of ASSBs is high owing to the diverse chemical and physical characteristics of the individual solid components and the nature of solid-solid contact. To further enhance the electrochemical performance of ASSBs, especially their high-rate capabilities, it is crucial to raise the electronic conductivity of the cathode composites. Improving the electrical conductivity of electrodes to achieve high-rate capacity requires the addition of carbon. Utilizing common carbon materials, such as vapor-grown carbon fibers (VGCF), enables homogeneous current distribution in the cathode layer. Nevertheless, the use of carbon additives in sulfide-based ASSBs is inhibited by significant challenges. Carbon additives provide enough electronic percolation pathways in the composite cathodes, speeding the decomposition of sulfide SSEs during the charging process. Consequently, even with minimal amounts of carbon additives, rapid deterioration of sulfide SSEs continues to occur at the electrolyte/carbon interface, causing severe side reactions and the creation of an unfavorable interfacial layer between the carbon additives and SSEs.To achieve high cycle performance, ASSBs included conductive agents in the composite cathode to promote solid contact between the active material and sulfide solid electrolyte Li6PS5Cl; nevertheless, a significant side reaction was observed between the conductive agents and solid electrolyte. To prevent a substantial side reaction and achieve improved electrochemical performance with high-rate capacity, self-polymerized dopamine (PDA) thin film was coated on the VGCF’s surface in this investigation. Dopamine hydrochloride would be oxidized and self-polymerized into polydopamine under alkaline environments (pH 8.5) without the necessity for severe reaction conditions, sophisticated equipment, costly catalysts, or hazardous organic solvents.During the electrochemical test, the improved lithium conductivity of polydopamine-coated VGCFs after cycling at 0.1 C-rate was confirmed by galvanostatic intermittent titration technique (GITT) data and electronic-blocking cells. After polydopamine coating, the electrochemical performance of VGCFs dramatically improved with better reaction reversibility, enhanced specific capacity with high C-rate, and extended cycle life, as evidenced by polydopamine-coated VGCFs achieving ~165.5 mAh.g-1 after 100 cycles, compared to ~118.7 mAh.g-1 for unmodified VGCFs. Owing to the presence of two-electron transfer redox processes per benzoquinone skeleton, which reduced to catecholate and coordinate with lithium-ion, polydopamine facilitated a shorter ion diffusion path for a more rapid and straightforward reduction reaction even if compare with non-VGCFs composite cathode.In composite cathode, electronegative elements with lone-pair electrons, such as O (oxygen functional groups on VGCFs), react with electrophilic species, such as P5+ in Li6PS5Cl (PS4 3-), resulting in the formation of P-O bonding through nucleophilic reaction on oxygen-substituted thiophosphate and thioethers. In addition, the S atom of PS4 3- can attack the electrophilic C atom in the carbonyl group on the surface of VGCFs. Intense interactions between P5+ and the electronegative element O, as well as S2 and the electrophilic atom C, thus damage the crystal structure of SSEs and contribute to the reduction in the specific capacity of the composite cathode. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were then utilized to confirm the existence of by-products such as P-S-P, S-S, Li2S, and P-O; the presence of polydopamine demonstrated its ability to minimize side reactions and preserve the solid-state electrolyte.In addition, polydopamine's excellent adhesive capabilities enable it to build a stable and homogenous coating on the VGCF's surface. This coating may enhance the adherence of the conductive agents to the electrode's components. As polydopamine-coated VGCFs exhibited low and homogeneous resistivity in the cathode's elements, scanning spreading resistance microscopy (SSRM) was used to highlight the enhancement of particle distribution to optimize the ionic and electronic pathways.This study examines, in summary, the effect of a polydopamine coating layer on the conductivity of solid-state battery conductive agents. Even though polydopamine is recognized for its insulating characteristic, it may also display strong electrical conductivity and adhesion under certain conditions. Thus, we observed that VGCFs coated with a suitable PDA thin film eliminate unneeded kinetic energy for side reactions and improve the ionic-electronic route in composite electrodes. The discovered principles and mechanism of polydopamine coated on conductive agents are applicable to a polymer manufacturing method or modification that is coated on conductive agents, therefore enhancing the electrochemical performance of ASSBs. Figure 1

Highlighting the role of 3C–SiC in the performance optimization of (Al,Ga)N‒based High‒Electron mobility transistors

AlN nucleation layer is the key issue for the performance of GaN high frequency telecommunication and power switching systems fabricated after heteroepitaxy on Silicon or Silicon Carbide. In this work, we demonstrate and explain both the low level and the origin of propagation losses in GaN/3C–SiC/Si High Electron Mobility Transistors (HEMTs) at microwaves frequencies, in view of providing efficient circuits. First, it is shown that the use of 3C–SiC as an intermediate layer between the Si substrate and the GaN epitaxial layer drastically decreases RF propagation losses. Using Secondary Ion Mass Spectroscopy (SIMS) measurements, we demonstrate that dopant in-diffusion (both Al and Ga) into the 3C–SiC pseudo-substrate remains confined beneath the interface. Furthermore, by combining scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM), the 2D profile shows the presence of a slightly conductive zone beneath the AlN/3C–SiC interface that is highly limited (less than 50 nm) whatever the growth conditions of the (Al, Ga)N layers on 3C–SiC explaining the low propagation losses obtained for such devices. This behavior differs from the one previously observed for GaN growth on Si substrate. This work demonstrates the importance and efficiency of the 3C–SiC intermediate layer when used as a pseudo-substrate increasing not only the crystalline quality of the subsequent (Al, Ga)N layers but also permits to achieve high potential GaN power devices as it is crucial.

Methodology of backside preparation applied on a MRAM to lead a logical investigation with a near-field probe

This paper presents a method for the preparation of a magnetic random access memory (MRAM) whose data are stored in magnetic tunnel junctions (MTJ) as resistance states, in order to read them by near-field probing.The goal is to be able to visualize a difference of resistance between bits at ‘0’ and at ‘1’ thanks to the current passing through several MTJs. To do so, the MRAM needs to be prepared to create an electrical access to both sides of the MTJs. The main issue is the polishing of both sides as the stack of metallization being less than 10 μm thick. A chemical etch would in that case be encouraged by literature but we take a different approach since we choose to open further than the transistors. The preferred method is a backside preparation technique that creates a bevel allowing us to access the bottom side of the MTJs through vias and the top of them thanks to the bitlines. Since the resulting chip no longer has electrical connections, we also create a dedicated electrical path thanks to a focused ion beam (FIB) operation. At the end, it is then possible to collect the current flowing through the MTJs with a near-field probe.To probe the MTJ resistance, two near-field techniques are investigated: conductive atomic force microscopy (C-AFM) and scanning spreading resistance microscopy (SSRM). C-AFM provides a quite high resistivity probably due to its sensitivity to contact resistance. Using SSRM, a resistance of 12–16 kΩ and 17–22 kΩ were determined for “0” and “1” bits, which is in agreement with literature.

Relationship between oxidation, stresses, morphology, local resistivity, and optical properties of TiO2, Gd2O3, Er2O3, SiO2 thin films on SiC

The relationship between internal mechanical stresses, surface morphology, nanoscale electrical properties, and optical characteristics in TiO2, Gd2O3, Er2O3, and SiO2 thin films on SiC substrates was investigated. The oxide films were synthesized using the rapid thermal annealing and analyzed through scanning spreading resistance microscopy, photoluminescence, and absorption spectroscopy. Tensile stresses were found in the films, they are attributed to thermal and lattice mismatch, oxidation, and grain boundaries. These stresses influence on surface morphology, resistivity variations, and photoluminescence intensity. Surface roughness and grain structure were found to correlate with variations in resistivity, which were attributed to conductive pathways along grain boundaries and possible metallic phases. Photoluminescence intensity was also observed to correlate with estimated lattice mismatch strain. Gd2O3/SiC exhibited the fewest defects, while Er2O3 and TiO2 showed more, with Er2O3 being the most mismatched and roughest. The results indicate that internal strains in oxide thin films on SiC substrates can influence on surface morphology, leading to formation of defects and spatial inhomogeneity. These fluctuations in local conductivity and luminescence center density have significant implications for dielectric and optical applications. The study provides insights for future processing refinements to mitigate internal strains and enhance the performance of oxide thin films in semiconductor and optical technologies.

Characterization of the parasitic masking layer formed during GaN SA-MOVPE using PECVD SiO2 masks

X-ray photoelectron spectroscopy (XPS) was used to study the surface composition of the parasitic masking layer formed during selective area metalorganic vapor phase epitaxy (MOVPE) of gallium nitride (GaN) using silicon dioxide (SiO2) masks deposited by plasma enhanced chemical vapor deposition (PECVD). It was shown that non-stoichiometric silicon oxynitride layer (SiOxNy) is responsible for the inhibition of GaN nucleation in the vicinity of the SiO2 mask. Atomic force microscopy (AFM) was applied to examine the surface topography, whereas scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) techniques were used for the purpose of electrical characterization of the parasitic masking layer. The overgrowth of GaN islands through the discontinuities in the SiOxNy film was shown. The SCM imaging showed the presence of a positive electric charge in the parasitic masking layer, indicating the accumulation of defects in the silicon oxynitride film.

Nanoscale electrical characterization of ambient-induced surface impurities on high-nickel cathode materials for lithium-ion batteries

One of the most critical points in the study of LIB-related materials is the extremely high reactivity of Li. In addition to pure Li metal, many Li-containing materials employed in LIBs are highly reactive under ambient conditions. Therefore, they should be stored and treated in an inert environment, such as vacuum chambers and gloveboxes filled with inert gases. In particular, most pristine cathode materials contain Li and are more reactive in air than pristine anode materials are. For instance, various impurities, mostly Li2CO3, are grown on the surface of pristine NCA (LiNixCoyAlzO2, x + y + z = 1) materials. The precise characterization of these ambient-induced surface impurities is critical for understanding the intrinsic properties of these cathode materials. In this study, we directly image and characterize ambient-induced surface impurities formed on the surface of high-Ni NCA (LiNi0.8Co0.15Al0.05O2) materials using Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM). The ambient-induced surface impurities show clearly distinguishable work functions and resistance features compared with the pristine NCA surface. In particular, it is confirmed that the resistance of ambient-induced impurities is significantly higher than that of pristine NCA materials, which can deteriorate the performance of LIB cells. This study provides direction for the fabrication, storage, and processing of LIB cathode materials.

Nanostars in Highly Si-Doped GaN.

Understanding the relation between surface morphology during epitaxy of GaN:Si and its electrical properties is important from both the fundamental and application perspectives. This work evidences the formation of nanostars in highly doped GaN:Si layers with doping level ranging from 5 × 1019 to 1 × 1020 cm-3 grown by plasma-assisted molecular beam epitaxy (PAMBE). Nanostars are 50-nm-wide platelets arranged in six-fold symmetry around the [0001] axis and have different electrical properties from the surrounding layer. Nanostars are formed in highly doped GaN:Si layers due to the enhanced growth rate along the a-direction ⟨112̅0⟩. Then, the hexagonal-shaped growth spirals, typically observed in GaN grown on GaN/sapphire templates, develop distinct arms that extend in the a-direction ⟨112̅0⟩. The nanostar surface morphology is reflected in the inhomogeneity of electrical properties at the nanoscale as evidenced in this work. Complementary techniques such as electrochemical etching (ECE), atomic force microscopy (AFM), and scanning spreading resistance microscopy (SSRM) are used to link the morphology and conductivity variations across the surface. Additionally, transmission electron microscopy (TEM) studies with high spatial resolution composition mapping by energy-dispersive X-ray spectroscopy (EDX) confirmed about 10% lower incorporation of Si in the hillock arms than in the layer. However, the lower Si content in the nanostars cannot solely be responsible for the fact that they are not etched in ECE. The compensation mechanism in the nanostars observed in GaN:Si is discussed to be an additional contribution to the local decrease in conductivity at the nanoscale.

Deciphering the critical degradation factors of solid composite electrodes with halide electrolytes: Interfacial reaction versus ionic transport

Recently, halide-type Li+ conductors have been revisited for their use in all-solid-state batteries (ASSBs) owing to their stability at high potentials. However, the realization of ASSBs is hindered by the fast performance decay of composite cathodes. From a comparative study using halide and sulfide solid electrolytes (SEs), herein, we reveal the critical degradation factors of halide-SE-based cathodes, which are different from the conventional findings of sulfide-SE-based cathodes. By using impedance decoupling combined with scanning spreading resistance microscopy and force spectroscopy, we elucidate the mechanisms behind the SE-dependent degradation of single-particle LiNi0.8Co0.1Mn0.1O2 (NCM) composite cathodes. Impedance analyses show that NCM-Li6PS5Cl (LPSCl) and NCM-Li3InCl6 (LIC) exhibit considerable increase in interfacial impedance and Li+-transport impedance, respectively, upon cycling. Based on the combined experimental and computational study of microscopic interfacial and mechanical properties, we demontrate that the degradation of NCM-LPSCl originates primarily from the formation of resistive interphases, while the crucial degradation factor of NCM-LIC is the cracking-induced mechanical deformation of the LIC under pressure. Finite element analysis results further reveal how the deformation behavior of the SE materials influences the formation and propagation of cracks in composite cathodes during cycling. This study provides insights into the design of materials and electrodes for ASSBs with high power capabilities and long cycle lifetimes.

Electrostructural and morphological features of etch pits in boron-doped HPHT-diamond single crystals and multisectoral plates

Morphological, structural, and nano-electrical features of the growth defects and sectoral boundaries revealed by selective etching in synthetic boron-doped single crystals of diamond (BDD) and multisectoral plates are characterized by a set of scanning probe microscopy (SPM) methods, confocal micro-Raman, and micro-FTIR spectroscopy. Diamond single crystals were grown under high pressure and high temperature conditions (HPHT) in the FeAlBC system. Morphology of dislocation etch pits and micro-defect related pits/protrusions compared both on the growth facets and multisectoral plates cut parallel to the {110} facet of BDD single crystals. Ex situ AFM observation of the etched surface revealed non-homogeneously distributed pits and protrusions over the growth facets correlated with irregular macroscopic growth defects. There is a center-to-periphery gradient of dislocation density in multisectoral plates. The protrusions are homogeneously distributed over plates; some often decorate dislocation pits. Micro-Raman mapping on dislocation pits (boron-rich regions) decorated by low-boron content regions revealed crystalline imperfections in three dimensions, with apparent compressive/tensile strain. The defects were mainly electrically neutral under surface potential mapping by Kelvin probe force microscopy, opposite to the inter-sectoral boundaries having pronounced surface potential steps. The scanning spreading resistance microscopy shows resistivity variations at etching-reviled surface defects and sectoral boundaries if the appropriate DC bias is applied to the SPM tip.

Characterization of unintentional doping in localized epitaxial GaN layers on Si wafers by scanning spreading resistance microscopy

Localized epitaxy of gallium nitride (GaN) on silicon (Si) is studied, with the aim of achieving material compatible with 1200 V vertical devices, in particular an unintentional doping level <1 × 1016 cm−3, which is essential to have high quality devices. In this study, three mask materials (SiN, SiO2, Al2O3) are examined and the unintentional doping concentration in GaN layers grown by metal organic vapor phase epitaxy (MOVPE) is investigated by scanning spreading resistance microscopy (SSRM). The results from SSRM are verified by secondary ions mass spectroscopy (SIMS) and show that an unintentional doping concentration lower than 1016 cm−3 is achieved when Al2O3 is used as the mask material. This value is lower than any previous studies of localized GaN growth, and in addition, this is the first time that SSRM has been used to observe such low doping concentrations in GaN.

Pulsed Laser Annealed Ga Hyperdoped Poly‐Si/SiOx Passivating Contacts for High‐Efficiency Monocrystalline Si Solar Cells

Polycrystalline Si (poly‐Si)‐based passivating contacts are promising candidates for high‐efficiency crystalline Si solar cells. We show that nanosecond‐scale pulsed laser melting (PLM) is an industrially viable technique to fabricate such contacts with precisely controlled dopant concentration profiles that exceed the solid solubility limit. We demonstrate that conventionally doped, hole‐selective poly‐Si/SiOx contacts that provide poor surface passivation of c‐Si can be replaced with Ga‐ or B‐doped contacts based on non‐equilibrium doping. We overcome the solid solubility limit for both dopants in poly‐Si by rapid cooling and recrystallization over a timescale of ∼25 ns. We show an active Ga dopant concentration of ∼3 × 1020 cm−3 in poly‐Si which is six times higher than its solubility limit in c‐Si, and a B dopant concentration as high as ∼1021 cm−3. We measure an implied open‐circuit voltage of 735 mV for Ga‐doped poly‐Si/SiOx contacts on Czochralski Si with a low contact resistivity of 35.5 ± 2.4 mΩ cm2. Scanning spreading resistance microscopy and Kelvin probe force microscopy show large diffusion and drift current in the p‐n junction that contributes to the low contact resistivity. Our results suggest that PLM can be extended for hyperdoping of other semiconductors with low solubility atoms to enable high‐efficiency devices.

Nanometer-Scale Measurement of Grid Finger Electrical Conduction Pathways to Detect Series Resistance Degradation of Utility-Scale Silicon Solar Cells

We report on an electrical conduction mechanism for series resistance (Rs) degradation observed in a utility-scale photovoltaic power plant by imaging the local resistance at the Ag/Si interface of the c-Si front metallization. Scanning spreading resistance microscopy imaging with nanometer (nm) scale spatial resolution revealed that the number of point or small-area electrical contacts decreased substantially in a degraded cell compared to an unaffected cell, demonstrating the root cause of Rs degradation. The decrease in electrical contacts is likely caused by a structural change—the Ag particles in contact with the Si cell (or via a nm-thickness tunneling glass layer) aggregate into bulk Ag, and a highly resistive glass frit forms a belt shape at the Ag/Si interface. This resistive belt, with a thickness of ∼1 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m, blocks the current conduction from the cell emitter to the Ag grid. Our microscopy results help to unravel unambiguously the degradation mechanism and demonstrate an example of the multiscale characterization approach for understanding degradation in field-weathered PV module.

Unveiling the influence of selective-area-regrowth interfaces on local electronic properties of GaN p-n junctions for efficient power devices

We report correlated nanoscale mapping of the structure, composition, and properties of regrown GaN p-n junctions to identify how etching and non-planar regrowth processes limit diode performance via the introduction of unintentional dopants and defect states. p-GaN was selectively regrown in n-GaN trenches with SiO2 masks of variable mask-to-trench-width ratio. Dilute Al layers were periodically introduced during regrowth as markers of the growth interface. Correlated nanoscale mapping of doping, conductivity, and dopant complexes was achieved with atom probe tomography (APT), scanning spreading resistance microscopy (SSRM), and cathodoluminescence (CL) spectroscopy, respectively. The Al marker layers, detected by APT, enabled reconstruction of the faceted growth interface and correlation of the dopant concentration with position and time. The p-GaN growth rate is proportional to the mask-to-trench width ratio while the dopant incorporation rate is invariant. At trench edges, magnesium incorporation is suppressed, and oxygen incorporation enhanced, due to preferential incorporation on the semi-polar growth surface, leading to compensation and less abrupt p-n junctions; the SiO2 mask is a source of oxygen. Residual etch damage below the regrowth interface induces n-type and p-type conductivity, creating leakage pathways. The non-uniform Mg incorporation is driven by crystal anisotropy and is thus inherent to non-planar regrowth, but can be mitigated by engineering the regrowth interface and process parameters. The unprecedented integration of spatially resolved mapping of dopants, impurities, conductivity, and carrier type is a powerful approach to discriminating distinct factors that limit the performance of regrown diodes, enabling the rational optimization of process and device design.

Dopant Activation Depth Profiling for Highly Doped Si:P By Scanning Spreading Resistance Microscopy (SSRM) and Differential Hall Effect Metrology (DHEM)

Heavily n-doped epitaxially grown Si layers are of great importance for source/drain (S/D) application in advanced node nMOS devices. For contact resistivity reduction, the dopant activation level is very important. Various techniques are being used to evaluate dopant activation in Si:P layers. Among these two methods are Scanning Spreading Resistance Microscopy (SSRM) and Differential Hall Effect Metrology (DHEM). SSRM uses an atomic force microscope equipped with a hard conductive probe that is scanned in contact mode on the cross-sectioned sample’s surface and measures spreading resistance. Measured resistance values as a function of depth are converted into resistivity and carrier concentration depth profiles using calibration measurements and conversion relationships. DHEM provides depth profiles of mobility, resistivity and carrier concentration through a semiconductor layer by making successive sheet resistance (Rs) and Hall voltage measurements using Hall effect/Van der Pauw techniques, as the electrically active thickness of the layer is reduced through successive oxidation steps. Controlled oxidation is achieved by electrochemical anodization. Data collected can then be processed to yield the depth profiles. In this contribution we have carried out SSRM and DHEM measurements on Si:P epi layers subjected to different processing conditions including annealing and ohmic contact fabrication. Secondary Ion Mass Spectrometry (SIMS) was used to measure the total (active + inactive) dopant profiles through the films. Effects of these processes on dopant diffusion and activation were studied and the results from DHEM and SSRM were compared.In-situ phosphorus (P) doped Si epi-layers were grown over 300mm diameter boron doped monitor wafers. While one set was kept as the reference, a second set was treated by a spike-annealing process at 1000 °C. In a third set a Ti/TiN contact fabrication process was carried out and the contact was removed before analysis. In the fourth set contact process was applied to the spike annealed wafer before removal of the Ti/TiN layers. Bulk sheet resistance measurements were made using 4-point probe (4PP) for all the samples. SSRM measurements were carried out at IMEC. Cross-shaped Van der Pauw test-patterns were formed on 8mmx8mm areas on the samples and DHEM measurements were performed at ALP. Figure below shows the dopant depth profiles obtained by SIMS and the carrier concentration profiles from DHEM and SSRM techniques for samples D02 (as deposited Si:P) and D03 (spike annealed). One can make some general observations from the data in this figure. The total dopant concentration as measured by SIMS is ~ 1.4E21/cm3. There is only a small difference in the total dopant distribution profiles (SIMS) between the as deposited sample and the spike annealed sample. However, the spike annealed sample shows much higher dopant activation as measured by DHEM. Carrier concentration is ~2.5x higher in sample D03 (~5E20/cm3) compared to sample D02 (~2E20/cm3). Activation levels measured by SSRM, however, are lower for both samples, and the peak carrier concentration value increases only slightly upon spike annealing, going from ~2E20/cm3 in sample D02 to ~2.2E20/cm3 in sample D03. DHEM clearly indicates the sharp interface between the p-type substrate and the n-type epi-layer and its depth calibration agrees well with the expected thicknesses of the epi layers. The tail of the SSRM data is much more graded. Data from other samples will be presented and discussed in the final manuscript. Figure 1

Dopant Activation Depth Profiling for Highly Doped Si:P By Scanning Spreading Resistance Microscopy (SSRM) and Differential Hall Effect Metrology (DHEM)

Heavily P-doped epitaxial Si layers were deposited over counter-doped Si substrates. P dopant activation was studied as a function of various processes used to prepare the samples. For electrical characterization, depth profiles of carrier concentration values were obtained using SSRM and DHEM techniques. Samples studied included an in-situ doped sample, a sample that was spike annealed at 1000ºC, a sample that was first coated with a Ti/TiN stack and then annealed for silicide formation before the Ti/TiN stack was removed, and a sample that was spike annealed + coated with Ti/TiN + annealed for silicide formation before the removal of the Ti/TiN stack. DHEM analysis showed substantial increase in dopant activation for spike annealed samples. SSRM results suggested lower carrier concentration values and more limited degree of activation. Formation of Ti/TiN contacts and its removal did not affect the carrier concentration values for the as-deposited epi layer. Sample that was first spike annealed and then subjected to contact formation process displaced a reduction in carrier concentration values as measured by DHEM.

Local Enhancement of Dopant Diffusion from Polycrystalline Silicon Passivating Contacts.

Passivating contacts consisting of heavily doped polycrystalline silicon (poly-Si) and ultrathin interfacial silicon oxide (SiOx) films enable the fabrication of high-efficiency Si solar cells. The electrical properties and working mechanism of such poly-Si passivating contacts depend on the distribution of dopants at their interface with the underlying Si substrate of solar cells. Therefore, this distribution, particularly in the vicinity of pinholes in the SiOx film, is investigated in this work. Technology computer-aided design (TCAD) simulations were performed to study the diffusion of dopants, both phosphorus (P) and boron (B), from the poly-Si film into the Si substrate during the annealing process typically applied to poly-Si passivating contacts. The simulated 2D doping profiles indicate enhanced diffusion under pinholes, yielding deeper semicircular regions of increased doping compared to regions far removed from the pinholes. Such regions with locally enhanced doping were also experimentally demonstrated using high-resolution (5-10 nm/pixel) scanning spreading resistance microscopy (SSRM) for the first time. The SSRM measurements were performed on a variety of poly-Si passivating contacts, fabricated using different approaches by multiple research institutes, and the regions of doping enhancement were detected on samples where the presence of pinholes had been reported in the related literature. These findings can contribute to a better understanding, more accurate modeling, and optimization of poly-Si passivating contacts, which are increasingly being introduced in the mass production of Si solar cells.

Probing intraparticle heterogeneity in Ni-rich layered cathodes with different carbon black contents using scanning probe microscopy

Much effort has been made to improve the electrochemical performance of Ni-rich layered cathodes toward high-energy density of Li-ion batteries. Nonetheless, capacity fading and chemo-mechanical behaviors during charge/discharge processes have not been fully understood yet. Herein, we report microstructural changes and capacity degradation of a polycrystalline LiNi0.88Co0.09Al0.03O2 (NCA) cathode during repeated cycles using electron microscopy and scanning probe microscopy. By varying the content of carbon black (CB; 1–4 wt%) in the NCA cathode, we evaluated cycle performance, capacity-fading, and structural degradation by scanning electron microscopy, scanning spreading resistance microscopy, and Kelvin probe force microscopy based on atomic force microscopy. CB content at 1 wt% in the NCA cathode resulted in a significant increase of electrode resistance and hence a severe capacity decay of full cells. Microscopic analyses for cycled cathode particles surrounded by different CB contents confirmed that the lack of CB around particles developed secondary particle microcracking, local heterogeneity of capacity fading, and formation of NiO-like phase, which could be responsible for degradation of the cathode during repeated cycles. Our results offer a new way to diagnose chemo-mechanical changes of Ni-rich cathodes with different electrochemical properties and highlight the significance of electrode engineering for ensuring effective charge-transport pathways.

Scanning Probe Microscopy nanoscale electrical characterization of AlGaN/GaN grown on structured GaN templates

Scanning Capacitance Microscopy (SCM), Scanning Surface Potential Microscopy (SSPM) and Scanning Spreading Resistance Microscopy (SSRM) techniques are applied to perform investigation of AlGaN/GaN heterostructures epitaxially grown on spatially structured GaN templates used for quasi vertical high electron mobility transistors (VHEMT) fabrication. The heterogeneity of electrical properties in this structures was observed that might be caused by structural defects in AlGaN barrier, with density varying in different regions of the sample. SCM one point spectroscopy measurements confirmed the existence of two dimensional electron gas (2DEG) at AlGaN/GaN interface on the slope of the transition region between reactive ion etched and unetched areas under the transistor channel. Electrical parameters of 2DEG in slope region do not differ significantly from those determined for the other areas of the sample.

Correlated Kelvin-probe force microscopy, micro-FTIR and micro-Raman analysis of doping anisotropy in multisectorial boron-doped HPHT diamonds

Boron-doped diamond single crystals of cubo-octahedral habit have been obtained by temperature gradient method at high pressures and high temperatures (HPHT) in Fe-Al-B-C system, and multisectoral plates of different orientations have been produced. Spatial distribution of uncompensated boron impurity and surface potential through the interfaces of different growth sectors of diamond plates have been studied by scanning Fourier transform infrared (FTIR) and Raman micro-spectroscopy, as well as scanning spreading resistance microscopy (SSRM) and Kelvin-probe force microscopy (KPFM). FTIR mapping showed strongly non-uniform growth-sector dependent distribution of uncompensated boron impurity gradually decreasing in a sequence {111} → {110} → {113} → {001} from ~7 · 1018 cm−3 down to 2 · 1017 cm−3. Micro-Raman mapping is used to reveal the submicron distribution of structural quality and boron content through the interfaces of different growth sectors. The inter-sectoral jumps of the surface potential in the axial and radial directions of the growth sectors were studied by KPFM, their theoretical estimates are obtained, and the features of the band structure of the inter-sector interfaces are revealed. A high level of structural perfection of inter-sectoral boundaries without electrically active defects is demonstrated.