AVS 67 Session EM-Contributed On Demand: Electronic Materials and Photonics Contributed On Demand Session

Due to significant copper (Cu) resistivity size-effects and limitations in scaling the thickness of the associated high resistivity tantalum- (Ta) based diffusion barrier, there has been significant interest in identifying alternative metallization schemes with lower overall effective resistivities. To help identify potential metals with improved resistivity dimensional scaling properties relative to Cu, the product of electron mean free path (λ) and bulk metal resistivity (ρ_ο) has been recently proposed as a potential figure of merit (FOM) based on the semi-classical Mayadas-Shatzkes and Fuchs-Sondheimer equations describing surface and grain boundary electron scattering in metals. Based on this FOM, over a dozen metals have been predicted to have the potential to outperform Cu at reduced geometries. However, there have been relatively few experimental investigations for some of the most promising metals identified (i.e. Ir, Rh, and Os) due to their prohibitive expense.

In this presentation, we address the limited information on platinum group resistivity scaling as well as the costs impeding their investigation and application. For the former, we have performed an expansive thin film resistivity literature search on all the low-λρ_ο FOM candidate metals to robustly establish the resistivity scaling performance of rare platinum group metals (PGMs). For the latter, we have examined the supply chain for PGMs from earth to usable form in semiconductor manufacturing (i.e. sputter target, organometallic precursor, …) to assess factors that influence pricing as well as search for opportunities to drive future cost reductions. Through the combined examination of a broader thin film resistivity dataset and associated supply chain considerations, we identify and suggest metals that may merit greater consideration as well as methods to potentially improving their economics for use in the semiconductor industry.

Lithium-ion batteries are ever-present in our everyday lives in cell phones and laptops. Improving cathode materials is one of the ways to satisfy the need for a better energy storage solution. Developing new types of positive electrode materials to increase the cell voltage and capacity with improved stability is the best way towards the development of next‐generation Li-ion rechargeable batteries. To achieve this goal, understanding the principles of the materials and recognizing the problems confronting the state‐of‐the‐art cathode materials are essential prerequisites. Fluoride-based conversion high‐energy cathode materials can be used to build next‐generation lithium‐ion batteries. FeF₃ andCuF₂ show a theoretical specific capacity value of 713 mAh/g, and 527.17 mAh/g, respectively. Similarly, Li-FeF₃ and Li-CuF₂ show a higher theoretical energy density of 900 Wh/kg. The insulating nature of LiF and limited splitting of LiF during charging are some of the challenges for lithiated fluorides.Lithiated fluorides also show some issues due to the lack of a presence of built-in Li source, poor capacity retention, and poor rate performance. To overcome these issues, we incorporate Fe, a transition metal with higher electrical conductivity, into LiF to form a composite material. A highly conformal and smooth surface area of transition metal lithiated fluoride composite thin film sample was achieved using pulsed laser deposition, both with and without annealing. To establish a baseline of performance, coin cells of slurry-made composites were created and compared to the thin-film counterparts. We expect the thin-film-based batteries to show a superior performance due to the improved uniformity and homogeneity of the composition and morphology. Structure and surface morphology of the thin film will be carried out using XRD, FESEM, and AFM. Electrochemical characterizations will include charge/discharge profile of battery assembly and cyclic voltammetry. This research finding will shed the light on the use of transition metal-doped LiF as promising cathode materials with improved rate performance and capacity retention.

Funder Acknowledgement(s): This work is supported by Sandia National Laboratories (Contract Agreement # 2175640), NSF-CREST Grant number HRD 1547771, and NSF-CREST Grant number HRD 1036494.

Current electronic devices are gradually being based on 3-dimensional (3-D) complex structures of thin films to meet the growing demand for higher device density and speed. The high aspect ratio 3-D device structures together with rising thermomechanical stresses have put increasing demand for the alternative interconnect materials with superior mechanical and physical properties. Titanium Nitride (TiN) thin films are being widely used in the microelectronics industry as interconnects. Structural failure of TiN in 3-D high-aspect ratio electronic devices is a major concern for reliability and yield of electronic devices. The failure modes such as defects, bending, buckling have been observed to cause by inadequate physical properties of TiN film such as hardness, and modules of TiN film. In this work we show that by systematically adding SiN into TiN in the Atomic Layer Deposition (ALD) process, thin films of composite material TixSi(1-x)N grown show superior hardness and modulus compared to TiN thin films of similar thickness. ALD coatings of TixSi(1-x)N also have excellent step coverage and superior surface smoothness compared to TiN films.

TixSi(1-x)N films were deposited using Eugenus ALD deposition system by varying TiN:SiN ratio and SiN pulse duration. The films were characterized by various characterization techniques: ellipsometry, XRR, XRD, XPS, Nanoindentation, AFM, and TEM. It is observed that the deposited TixSi(1-x)N films maintained good crystallinity up to 10% Si doping. As Si doping % increase in the TiN matrix, the texture of TixSi(1-x)N thin films shift from (111) orientation to (002). Average crystallite size is measured by applying Scherrer analysis to the XRD peaks. The crystallite size decreases as Si content increased. By increasing Si percentage in the TixSi(1-x)N films improvement in hardness up to 38 GPa (TiN~18GPa) is observed. This increase in hardness is likely due to the grain-boundary hardening effect. The higher the Si%, the smaller the growth of TiN grains, hence higher the density of grain boundaries. Any movement of grains under external force becomes very difficult because of such network of grain boundaries, hence effectively rise in the hardness and modulus. Modulus of TixSi(1-x)N films increased as high as 350 GPa (TiN~170 GPa) by the addition of Si. TixSi(1-x)N films show excellent uniformity and good step coverage (> 90%) as measured using cross-sectional TEM images of HSC device structures. TixSi(1-x)N films (RMS Roughness 0.27 nm) show superior surface smoothness compared to TiN films (RMS Roughness 0.67 nm).

we report an approach to grow nanostructured carbon thin films using a pair of AC-biased copper electrodes and fabricate carbon thin film field-effect transistors (CFETs). Graphite rod was evaporated in an ultrahigh-vacuum chamber using e-beam evaporation method, and nanostructured carbon thin films were grown between a pair of AC voltage-biased copper electrodes at a temperature of 400 ^oC. The electrodes with the carbon film were finally fabricated into the carbon thin film field-effect transistor (CFET), where the carbon thin film between the electrodes functioned as the channel of the transistor. The carbon thin film was analyzed with high-resolution tunneling electron micrograph (HRTEM), showing wiggling nanostructures in it. The electrical property of the fabricated CFET was measured before and after subject to an electrical breakdown, demonstrating much better electrical current (I)-voltage (V) curves and transfer characteristics with on/off current ratios of over 200 after the electrical breakdown process. The growth of nanostructured carbon film is novel, and the fabrication of CFET is compatible with the silicon-based semiconductor fabrication and can be wafer-scale.

Over the past two decades, there has been considerable progress in engineering the spectrum, directionality, polarization and temporal response of thermally emitted light using nanostructured materials [1].

Laser induced emission from self-assembled nickel wires, between 125-200 nm in diameter and tens of micrometers long, prepared by electrochemical deposition, emits strong infrared light when excited with a cw Ar⁺ ion laser at 488 nm or a pulsed femtosecond Ti: Sapphire laser at 800 nm. The emission spectra from aggregates of Ni nanowires (NWs) heated by the absorption of laser light are investigated as a function of the power of the excitation laser. The emitted intensity increases exponentially with laser power which is taken as an indication of a thermal process. Through time response of the emission to a time varying laser excitation, the local temperature variation of the nanowires is determined. The radiation from the nanowires is describe by the classical Planck law modified by finite-size effects in nanoparticle emissivity. Similar emission spectra are observed for the two types of lasers. Theoretical modelling based on Mie’s theory[2] and Planck’s radiation law, using nanowires and nanocrystals of different sizes, is developed to fit the emission spectra.

The emission grows exponentially with pump power and over time the emission decays. The results point to thermal radiation process, modulated by size-effects, and strongly influenced by local plasmon modes (hot spots) that may lead to very large electric fields enhancements.

[1] Denis G. Baranov et al., “Nanophotonics engineering of far-field thermal emitters”, Nature materials, 18, 920-930 (2019).

[2] C.F.Bohren, D.F. Huffman, “Absorption and Scattering of Light by Small Particles”, John Wiley and Sons, 1983.

Acknowledgments

The author acknowledges Portuguese Science and Technology Foundation FCT UIDB/FIS00068/2020. Ana Silva acknowledge Aalborg University, Physics and Nanotechnology Department for the excellent experimental conditions made available.

This work investigates the wake up and endurance of ferroelectric behavior of atomic layer deposited (ALD) hafnium zirconium oxide (HZO) using reactively sputtered niobium nitride and niobium electrodes. With ferroelectricity in doped HfO₂now advancing into CMOS based devices, perturbations of the dopants has expanded from silicon into mixtures utilizing yttrium and zirconium and with electrodes ranging from platinum to tungsten and nitrides such as titanium nitride and tantalum nitride. New to the set of materials able to, in-part, stabilize the orthorhombic phase are other superconducting electrodes such as NbN and, in this work, Nb which we use to demonstrate stable ferroelectric behavior of Hf_0.5Zr_0.5O₂. With the atomic similarities between Ta and Nb, a natural extension the electrode materials’ set to include NbN was explored in this work for the wake up and endurance properties.

Metal/Ferroelectric/Metal (MFM) capacitors tested at room temperature (RT) demonstrated ferroelectric behavior as determined by polarization vs. electric field (P-E) loops, remanent polarization, and capacitance vs voltage (C-V) measurements. Devices were made with either Nb or NbN bottom electrodes (BE), an ALD mediating layer of alumina, ALD HZO, and then a top electrode (TE) layer of NbN. Wake up cycling suggested a pristine state of tetragonal phase mixed with orthorhombic, as measured by P-E loops and C-V curves and moves to a more orthorhombic phase after modest wake up, for both a Nb and NbN BE. However, the Nb BE had only about half of the remanent polarization, 7 uC/cm², as to that of NbN BE at 13 uC/cm² suggesting that although an intermediate layer of alumina separated the HZO from the BE, the BE plays a critical role in HZO phases and electrical performance. Further, this work shows that with a NbN bottom electrode, a wake up of positive or negative pulses only contribute to full remanent polarization, 3 and 5 uC/cm² respectively whereas a full negative to positive of the same electric field generates a 7 uC/cm²This work will discuss the implications of these wake up measurements, discuss life time cycling of these devices and compare to other electrodes.

Understanding the wake up and endurance of ferroelectric HZO on superconducting electrodes play into the exciting field of integration of ferroelectric thin films with superconducting films.

We have previously found that gated monolayer MoS₂ exhibits a high temperature coefficient of resistance (TCR) of +0.27 %/K compared to ultrathin metal films [5], and could enable sensors with low thermal mass due to their three-atom thinness. Here we fabricate flexible two-terminal (ungated) monolayer MoS₂ temperature sensors and obtain even larger (in absolute value) but negative TCR of -1.8 %/K between 30°C and 80°C. Preliminary analysis indicates that here space-charge limited current with shallow traps leads to the negative TCR, rather than phonon scattering causing a positive TCR in gated MoS₂. Furthermore, the sensors reveal a rapid real-time response of at least 150°C/min (limited by our heater stage) and reversibility.

In addition, the excellent optical absorption properties of TMDs and their near-ideal band gaps for single-junction and tandem solar cells (with Si) make this technology attractive for powering Internet-of-Things sensors at an ultrahigh specific power (>50 kW/kg), especially in wearables and environmental sensing systems [2, 6, 7]. We fabricated flexible WSe₂ solar cells with graphene top electrodes and MoO_x doping/passivation layer, where the whole active material is embedded within the flexible substrate, enabling a vertical cell architecture. We achieve a record-high power conversion efficiency of ~5%, while stable under mechanical bending to a radius of 4 mm. Concluding, this work provides important ingredients for flexible electronic systems where all active components benefit from the unique properties of atomically thin TMDs.

Ref.: [1] L. Gao, Small, 13, 1603994 (2017). [2] D. Jariwala et al., ACS Photonics, 4, 2962 (2017). [3] D. Akinwande et al., Nat. Commun., 5, 1 (2014). [4] A. Daus et al., Nat. Electron., (accepted). [5] A.I. Khan et al., Appl. Phys. Lett., 116, 203105 (2020). [6] K. Nassiri Nazif et al., Nano Lett., 21, 3443 (2021). [7] C.M. Went et al., Sci. Adv., 5, eaax6061 (2019).

A primary challenge for 3D integration and flexible electronics is the ability to integrate high performance devices at temperatures limited by the thermal budget of the substrate or pre-existing device layers. Present approaches mostly involve hybrid bonding techniques where epitaxial films are first grown on lattice-matched substrates and then transferred to the host substrate at a device scale, circuit scale, chip scale, or wafer scale. Although the devices made using these approaches are of excellent quality, this approach is usually limited by cost, time, limited materials, and scalability perspectives. Monolithic integration approaches attempt to directly grow materials on the host substrate, but device performance is usually poor from solution-based or vapor-phase grown semiconductors on non-epitaxial substrates which give submicron-scale grain polycrystalline films. Here we show results from a liquid-vapor-phase growth approach, referred to as Low Temperature Templated Liquid Phase (LT-TLP) growth. Templates of group III materials capped with SiO₂ are first realized on the non-epitaxial substrate by lithography, evaporation, and liftoff methods. These are then heated in the growth furnace at the intended growth temperature (between 200 to 400 ⁰C), and group V precursor is introduced in the gas phase as pre-cracked V-hydride. The flux of the group V precursor is controlled to ensure single nucleation in each template, which grows with time to yield single crystal III-V in each template, confirmed by electron backscatter diffraction (EBSD) imaging. Photoluminescence measurements for different growth temperatures give an optimal growth window of 280-320 ⁰C, where optoelectronic quality is found to be comparable to single crystal commercial wafer. InAs grown at 300 ⁰C shows room temperature mobility of ~6000 cm²/V-s. Comparing the highest electron mobilities reported from different material families grown directly on amorphous dielectric surfaces, it is seen that TLP III-Vs have the best mobilities, with LT-TLP InAs being about 2 orders of magnitude higher than the majority. These low temperature growths have been performed on rigid dielectric substrates like SiO₂ and HfO₂, as well as on flexible polyimide. Further, these high quality single crystalline mesas have been used as growth seeds for epitaxial films by MOCVD. Growth parameter variations are studied to obtain the best MOCVD InP-on-TLP InP morphology and optoelectronic properties. This potentially opens up a scalable and cost-effective method of integrating high quality III-V materials and devices on inexpensive amorphous dielectric surfaces for 3D integration.

Atomic Layer Deposition (ALD) of ternary TiSi_xN leads to nanocomposites of metallic TiN atomically mixed with insulating Si₃N₄. Formulating TiSi_xN films with various Ti:Si ratios lead to the emergence of a temperature regime where resistivity is independent of thermal drift, denoted as near-zero temperature coefficient of resistivity (nz-TCR).¹ Further, the ease with which nanocomposites of TiSi_xN can be deposited using ALD offer precise tunability in Ti:Si ratio, thickness, mass density, crystallinity and electrical properties.

Recently, our group explored TiSi_xN films deposited using a Eugenus® 300 mm commercial QXP mini-batch system by modulating the ratio of Ti and Si precursors with NH₃ as a co-reactant.Si-content was varied from 0 at % (pure TiN) to 24.2 at % Si while maintaining thickness ~ 140 nm. The X-ray reflectivity and grazing incidence X-ray diffraction measurements showed a reduction in film density and transition from nano-crystalline to pure amorphous phase with increase in Si-fraction. Spectroscopic ellipsometry revealed the optical constants, composition, and electrical resistivities and were supported by X-ray photoelectron spectroscopy and electrical measurements. Room-temperature resistivity measurements show an increase in film resistivity with increasing at % Si. Temperature-dependent Van der Pauw measurements found a nz-TCR of -23 ppm K^-1 in the temperature range of 298 K – 398 K and at 3.4 at % Si content.

We have now discovered that an at % Si = 3.0% induces a nz-TCR of -5.7 ppm K^-1 from 80 K – 420 K – one of the best reported nz-TCR values for ALD thin films. Fine tuning the at % Si in TiSi_xN films, possible only via ALD, significantly elongated the temperature window of nz-TCR behavior. Mapping the local conductivity of individual grains through conductive atomic force microscopy (c-AFM) indicated higher resistance at the grain boundaries. The local composition at the grain boundaries may play a major role in determining the nz-TCR behavior of TiSi_xN films. In addition, variable temperature Hall effect measurements were performed to provide deeper insights into the nz-TCR mechanism, decoupling carrier concentration from carrier mobility effects while determining film resistivity.

Compared to other nz-TCR films, which are deposited using physical vapor deposition techniques, ALD based nz-TCR films presents a unique synthesis platform for interconnect technology in topologically complex, 3D devices, circuits and sensors that undergo large temperature variation during operation but need to maintain stability in their electrical characteristics.

Quantum materials with novel phases of matter are the key building blocks of energy-efficient quantum electronics and powerful quantum computation. Exploiting control of those materials is fascinating to achieve new functionalities and information algorithms in future quantum devices. Quantum nanomaterials like layered materials have revealed many exotic properties such as extremely large magnetoresistance (MR)¹, type-II Weyl electron transport, and diverging Berry curvature². On the other hand, the nature of layered materials leads to ultra-large tunability of physical properties via external stimuli.

Here we report the manipulation of quantum geometrical properties in a ferroelectric semimetal (WTe₂) belonging to layered Weyl materials (Fig. 1). With such control and various characterization means, we observed substantial modulation in optical and electrical responses associated with the unique stacking orders in such exotic ferroelectric semimetal. Further nonlinear Hall transport measurements show the observed transitions are locked with the variation of topological and geometrical property (Fig. 2). Our findings demonstrate a new low-energy cost, electrically controlled topological memory in the atomically thin limit³.

1. Ali, M. N. et al. Large, non-saturating magnetoresistance in WTe₂. Nature514, 205–8 (2014).
2. Armitage, N. P., Mele, E. J. & Vishwanath, A. Weyl and Dirac semimetals in three-dimensional solids. Rev. Mod. Phys.90, 015001 (2018).
3. Xiao, J. et al. Berry curvature memory through electrically driven stacking transitions. Nat. Phys.16, 1028–1034 (2020).

Although silicon (Si) currently dominates the semiconductor industry, its small band gap (1.1 eV) limits its maximum operating temperature, restricting its use in high-temperature, high-power devices. Gallium nitride (GaN) is an attractive semiconductor with its wide bandgap (3.4 eV), high electron mobility, large critical breakdown field, and thermal stability. While the semiconductor itself can endure harsh operating conditions, the reliability of the metal/semiconductor contacts can be a limiting factor for its use. Schottky contacts should provide a high barrier height and low reverse leakage current, and they must be electrically stable over the lifetime of the device.

The MoN_x/n-GaN Schottky diode was chosen for study because of the reported high work function of MoN_x (5.33 eV)¹ and its conductive and refractory nature. It is also reported to be in thermodynamic equilibrium with GaN². Films were deposited by plasma atomic layer deposition and were examined by x-ray photoelectron spectroscopy (XPS), grazing incidence x-ray diffraction (GIXD), and transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) to determine their composition and structure. TEM reveals an abrupt interface between MoN_x and n-GaN with a cubic phase that is further confirmed with GIXD and EDS. XPS show a significant amount of carbon within the cubic phase. The barrier heights were investigated using current-voltage (I-V) and capacitance-voltage (C-V) measurements. Both techniques demonstrated that the barrier height increased after an anneal at 600°C for 5 min, yielding a barrier height of 0.87 eV with an ideality factor of 1.02 by I-V measurements, while the C-V measurements revealed a barrier height of 0.94 eV. Rectifying behavior was maintained upon annealing in N₂ at 700°C.

Future work will involve stress testing followed by materials characterization to provide more information on stable metallizations for high-power GaN devices. This work was funded by the Office of Naval Research under Grant N000141812360, distribution A, approved for public release, distribution is unlimited (DCN# 43-8038-21).

1. H. Matsuhashi and S. Nishikawa, Jpn. J. Appl. Phys., 33, 1293, (1994).

2. H. S. Venugopalan and S. E. Mohney, Z Metallkd.,89, 184-186, (1998).

The semiconductor industry is pushing its boundaries in device scaling technology by way of novel processing methods and increasingly complex patterning schemes. This requires a variety of functional and patterning-assist materials as well as advanced deposition techniques. For years, Si-based materials have been used to meet these needs; however, these alone cannot fulfill the range of material requirements moving forward. Boron carbide has shown promise due to compelling dielectric, thermal, mechanical, chemical, and etch properties. Toward applying this material to next-generation integration schemes, we have been exploring the potential of going beyond traditional growth processes (e.g., plasma-enhanced chemical vapor deposition) and investigating innovative area selective atomic layer deposition (AS-ALD) strategies. Herein we explore schemes for the selective metal/dielectric deposition of boron carbide using layer-by-layer methods. X-ray photoemission spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques are employed for characterization and imaging of the resulting surfaces.

With the continued evolution of microelectronic devices and their miniaturization, energy storage devices with reduced dimensions, especially Li-ion batteries, are critically needed. Solid-state lithium thin-film batteries (TFBs) offer exceptional energy storage performance with high energy density, long cycle life, and enhanced safety. The current-state-of-the-art thin film cathode, LiCoO₂ (LCO), offers a charge storage capacity of 67 µAh cm^-2 µm^-1 (equivalent to 135 mAh g^-1). Because the overall energy density of TFBs is largely determined by the thin film cathode, developing materials with higher specific capacity is a key strategy to enhancing the stored energy. In this talk, our efforts to engineer novel, energy dense thin film cathodes prepared at low temperatures will be discussed.

The first project to be discussed utilizes polymeric charge-transfer complexes. These complexes are formed through the vapor phase infiltration of I₂ or ICl into poly(4-vinylpyridine) (P4VP) films prepared by initiated chemical vapor deposition (iCVD). iCVD enables room-temperature synthesis of well-defined films directly on the surface of Pt current collectors. After infiltration with I₂ or ICl, the cathodes are coated nominally with 1 μm of lithium phosphorous oxynitride (LiPON) electrolyte and an evaporated Li metal anode. The P4VP-I₂ and P4VP-ICl deliver capacities of 8.7 and 36.2 µAh cm^-2 µm^-1, respectively, with an average voltage of 2.2V and 3.15V. The cathodes appear to be irreversible under normal operating conditions, limiting their application to primary electrochemical cells. However, it has been shown that these cathodes are readily prepared on flexible, temperature sensitive substrates, as well as complex, three dimensional architectures, which should allow them to be readily integrated into wearable, low cost devices and enable additional energy-intensive applications.

In the second project, a class of lithium metal oxide cathode materials are prepared by RF magnetron sputtering and incorporated into solid state thin film batteries (consisting of LiPON electrolyte and Li metal anode). Charged to 4V vs. Li/Li⁺, specific capacities in excess of 110 mAh cm^-2 µm^-1 have been achieved, which is 64% larger than state-of-the-art LCO cathodes. When cycled at a rate of 0.6C (100 minutes for charge/discharge), 83% of the maximum capacity is retained. Moreover, the cathodes are highly reversible with coulombic efficiencies in excess of 99.8%, resulting in greater than 94.7% capacity retention over 100 galvanostatic charge/discharge cycles. Efforts to further enhance rate performance and cycle lives will be discussed, in addition to demonstrations of these cathodes on flexible, polymeric (temperature sensitive) substrates.

To be a commercial success, perovskite solar cells must not only be efficient relative to their cost, but also stable over time. Recent work demonstrates that the power conversion efficiency of methylammonium-chloride-lead-iodide (MAPbI_3-xCl_x) perovskite solar cells (PSCs) can be increased by approximately 40% by applying up to 7 MPa of pressure. [1] The accompanying SEM images before and after the application of pressure show improved contact at the interface between the compact TiO₂ and the fluorine-doped tin oxide.In subsequent layer-by-layer deposition, the interface roughnesses were in the range of 10 to 40 nm RMS as measured by AFM.Initial results from energy dispersive spectroscopy demonstrate significant interlayer diffusion and cracking in pressurized solar cells, particularly of iodine, lead, and tin, but limited diffusion and much lower incidence of cracking in unpressurized devices.The devices with higher diffusion and cracking had lower power-conversion efficiencies and lower stability.[2]Diffusion was also studied as a function of annealing time and temperature.We will discuss the competition between improved contact and diffusion/cracking in pressurized PSCs and their implications for the improvement of long-term power conversion efficiency.

1. Oyelade, O. V., et al. "Pressure-Assisted fabrication of perovskite Solar cells." Scientific reports 10.1 (2020): 1-11.
2. Oyewole, D., et al. “Pressure-Induced Void and Crack Closure Improve the Photoconversion Efficiency and Stability of Perovskite Solar Cells,” submitted

In particular, the non-stoichiometric silicon oxide (SiO_x) has been proposed as a cheap and effective alternative to develop ultraviolet absorbers or light emitters. SiO_x films can be deposited by several deposition techniques but they can be obtained at Room Temperature by Sputtering deposition technique. New devices based on SiOx films include different structures of stacked films like multilayers or superlattices.

This work presents a study of the optical, structural and electrical properties of non-stoichiometric silicon oxide on silicon oxide (SiO_x /SiO₂₎ multilayers obtained by sputtering deposition technique. Non-stoichiometric silicon oxide films were deposited using a combination of Silicon and quartz (SiO₂) targets. Therefore, the study of the optical and structural properties of non-stoichiometric silicon oxide films by using silicon and silicon oxide targets is an interesting route for the design of optoelectronic devices based on Silicon technology. The SiO_x/SiO₂ multilayer structure was formed by five stacked bilayers with the different power application on target silicon.All samples were deposited on silicon substrates with low resistivity.

The research trend on new materials and alternatives to improve energy generation devices, includes the synthesis and development of absorbent coatings. In particular, silicon solar cells can be optimized with coatings capable of capturing more or less energetic wavelengths than silicon can assimilate, this could be possible through silicon rich nitride (SRN). Silicon nitride has been used in many industry sectors as a protective coating, but the SRN also has convenient optical characteristics to achieve an improvement on efficiency of silicon solar cells keeping in mind the best cost-efficiency. This can be achieved by the down conversion effect. In this work, we propose an optimization on the deposition conditions of SRN films obtained by LPCVD to achieve the down-conversion effect. SRN films were obtained using NH₃ mixed with SiH₄ as precursor gases with a ratio of Ro_n between 4 and 80, the temperature was varied from 600°C to 720°C and thermal annealing was applied to some samples to compare with as-deposited films. Ellipsometry measurements showed that thickness and the refractive index can be well controlled by the gases ratio and deposition temperature. Fourier transform infrared (FTIR) spectra showed characteristic peaks of Si-N matrix and N-H vibration modes. The images of AFM showed that surface roughness morphology can be also affected by the deposition temperature. Energy dispersive spectroscopy measurements were obtained to estimate the SRN films composition, the results showed a silicon enrichment dependence on temperature. SRN films showed a clear photoluminescence (PL) at room temperature (RT), the main band was located between 380 to 650 nm. PL emission was related to donor acceptor decays between traps promoted by defects.

The optical, structural and morphological characteristics SRN films showed a clear dependence on the deposition time, the ratio of the precursor gases and the deposition temperature. Suitable refractive index, surface roughness and PL emission were obtained with a flow ratio of 4 and deposition temperature of 700 °C. These deposition conditions assure convenient optical characteristics of SRN films to achieve down conversion effect and they suppose a low influence on diffusion of PN junctions when SRN is used as UV absorption coating.

Keywords: Silicon rich nitride, LPCVD, Photoluminescence

Acknowledgment:Authors want to thank to CONACYT, CIDS-BUAP, VIEP-BUAP and INAOE to develop the present research.

Presenting author´s email: cross.ride1234@gmail.com

Novel computation challenges including neuromorphic networks, memory-centric computation, machine learning, or steep-slope transistors require to go beyond traditional MOSFET architecture and instead explore high-k thin films for ferroelectric or resistive random access memory (RRAM) technology. Typically, such ferroelectric or RRAM thin films are deposited on Si substrates, which still is the standard material within electronics industry. However, III-V semiconductors such as InAs or InGaAs offer a much higher charge carrier mobility and more flexibility for low-power applications. We are investigating HfO₂ RRAM and Hf_1-xZr_xO₂ (HZO) ferroelectric thin films on InAs and InGaAs substrates and gate-all-around nanowire structures, the latter for reaching ultimate electrostatic control. In order to obtain state-of-the-art device performance and outperform silicon technology, we need to thoroughly understand and optimize the materials properties of the III-V/high-k interface.

Previously, we performed various synchrotron X-ray photoemission (XPS) studies of InAs/HfO₂ and InAs/Al₂O₃ interfaces of MOSFET devices, where we analyzed the role of different As sub-oxides and defect states, obtained As-oxide and In-oxide interface depth profiles, and also looked at interfacial thermal oxides. It turned out that best device performance was reached with as little interfacial oxide as possible. By implementing atomic layer deposition of HfO₂ at an ambient-pressure XPS synchrotron beamline, we could even reach perfect self-cleaning and reveal new insights on the surface chemistry involved in the self-cleaning mechanism.

An understanding of time-dependent dielectric breakdown (TDDB) in SiO₂ gate dielectrics has long been of great interest. Several models have been proposed involving the generation of oxide traps which eventually form a percolative leakage path through the dielectric. However, little direct experimental evidence about the traps exists. Electrically detected magnetic resonance (EDMR), and near-zero-field magnetoresistance (NZFMR) can provide this atomic scale information in real devices. We present EDMR and NZFMR studies of defects generated during the high-field gate stressing of Si/SiO₂ MOSFET arrays. Our studies substantially extend earlier resonance studies which were only able to identify one interface defect [1,2]. We subject our devices to gate stressing conditions and periodically interrupt the stress to measure interface recombination current, and spin-dependent interface recombination (SDR) current via EDMR and NZFMR. A nearly perfect correspondence between recombination current and SDR response is found at all stressing conditions. Interface state buildup occurs more rapidly early in the device lifetime, and more slowly as time goes on. By performing EDMR at multiple magnetic field orientations, we identify the stress-induced interface defects as P_b0 and P_b1 centers, dangling bond centers at the Si/SiO₂ interface. In addition, we observe a weaker SDR response in lower temperature (200K) measurements due to traps created within the oxide, likely oxide silicon dangling bonds known as E’ centers. Of particular interest, we find that the NZFMR response exhibits subtle changes in lineshape after different durations of gate stress, which we attribute to changes in the population of hydrogen in the vicinity of the Si/SiO₂ interface.

[1] Warren, W. L. and Lenahan, P. M. Appl. Phys. Lett. 49 19. (1986). 2887-2889.

[2] Stathis, J. H. and DiMaria, D. J. Appl. Phys. Lett. 61 24. (1992). 1296-1298.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

FeRh is widely studied because of its novel temperature-dependent antiferromagnetic (AFM) to ferromagnetic (FM) phase transition. This AFM-FM phase transition, which is accompanied by a significant change in resistivity, occurs at a critical temperature that can be fine-tuned over a wide range through substitutional doping, strain, and patterning.^[1,2] Because the transition is temperature-dependent, the state can be manipulated via Joule heating. Recent reports show the AFM-FM transition occurs on a sub-picosecond timescale, a range appropriate for switching applications where operating speeds should be in excess of GHz frequencies. In this work we demonstrate ultrafast memristive switching of FeRh wires. The thermally-induced AFM-FM transition was evaluated using two-terminal devices consisting of an FeRh wire and metal contacts. By using FeRh wires of varying dimensions, we were able to identify geometrical dependencies and found the AFM-FM transition temperature scaled with both current density and wire length. Pulsed I-V measurements were used to investigate the dynamic Joule heating effects, including the device switching speed and resulting power switching losses accompanying the AFM-FM transition. The upper bound of our device switching speeds, measured to be near 300 nanoseconds, was limited by measurement equipment limitations, not the material system. The performance of this rudimentary device is comparable to other phase change memory technologies with more intricate device architectures. FeRh could be the basis for a very fast, phase-change approach to future computing.

Photolithography has been the most widely used technique for semiconductor fabrication and large-scale mass production of silicon-based devices. By 2025, the photolithography equipment will have a market worth of $18 billion. Commercial, thin film transistors are developed using the process of photolithography. One technique we plan to introduce to fabrication TFT is 3D printing mask technique. 3D printed technology, commonly referred to as additive manufacturing, is a process used to reduce cost of various deposition techniques. 3D printed mask technology was used to deposit the active layer and the dielectric layer of our devices. The indium-free oxide-based channel material such as aluminum-doped zinc oxide (AZO) is the active material and can be fabricated on glass substrate or silicon for TFT application.High quality AZO thin films were grown using radio frequency (RF) sputtering technique and pulsed laser deposition on p-type silicon and glass for characterization purposes. The effect of Al content on zinc oxide crystal lattice were investigated by Atomic Force Microscopy (AFM), X-ray diffraction, Raman Spectroscopy, Ultra-violet visible spectroscopy, and Keithley 4200 Semiconductor Characterization System (SCS). AFM provided details information about the roughness, grain size, and surface morphology of thin films. FE-SEM measurement was performed to show cross sectional view of the fully developed thin film transistor. Raman Spectroscopy provided vibrational frequencies and a fingerprint of thin film used for the device fabrication. Finally electrical transistor characteristics were carried out using Keithley 4200 SCS provided including on/off ratio, mobility, and threshold voltage. The present work will provide valuable scientific input of AZO based active materials TFTs for the improvement of devices performance.

The synthesis of high-quality NbSe₂ thin films is of significant interest for potential applications in thermomagnetic energy conversion. Molecular beam epitaxy (MBE) is a promising route towards this aim as it provides fine control over growth conditions. For thermomagnetic energy conversion, the metallic 2H phase of NbSe₂ is desired. However, a number of competing phases are found to form during synthesis by MBE and likely include metastable phases, such as semiconducting 1T-NbSe₂. It has been previously reported in literature that metastable 1T-NbSe₂ forms at higher temperatures than the 2H phase. Conversely, higher growth temperatures are potentially beneficial for growing high-quality 2H-NbSe₂ because of improved adatom mobility that results in better crystalline quality. We will report on an investigation of the competing effects of crystal quality versus mixed phase growth with a goal of optimizing growth conditions for thermomagnetic energy conversion. In-situ X-ray photoelectron spectroscopy (XPS) and reflection high energy electron diffraction (RHEED) will be performed to analyze the intrinsic chemical composition and growth mode of the synthesized material prior to atmospheric exposure. Ex-situ Raman spectroscopy will aid in phase identification. In order to obtain the Nernst coefficient, which quantifies the material’s ability to generate thermomagnetic power, ex-situ measurements will be carried out on NbSe₂ films grown on insulating muscovite.