David Ginley, National Renewable Energy Laboratory
Shyam Dwaraknath, Lawrence Berkeley National Laboratory
Laura Schelhas, SLAC National Accelerator Laboratory
Abdelilah Slaoui, Laboratoire des Sciences de l’ingénieur, de l’Informatique et de l’Imagerie, iCUBE-CNRS
EP01.01: Computational Design of New Materials
Monday AM, November 26, 2018
Hynes, Level 1, Room 103
8:30 AM - EP01.01.01
Optimization of Si/ZnO/PEDOT:PSS Tri-Layer Heterojunction Photodetector by Piezo-Phototronic Effect Using Both Positive and Negative Piezoelectric Charges
Fangpei Li1,Wenbo Peng1,Zijian Pan1,Yongning He1
Xi'an Jiaotong University1Show Abstract
Piezo-phototronic effect has been extensively introduced to improve the performances of optoelectronic devices by utilizing external-strain-induced positive or negative piezoelectric charges (piezo-charges) to modulate the generation, separation, transportation, and recombination of charge carriers. However, in most cases till today, only the piezo-charges with one polarity (i.e., positive or negative) are effectively utilized. In this work, we fabricated an n-Si/n-ZnO/p-PEDOT:PSS tri-layer heterojunction photodetector (HPD) and systematically investigated the piezo-phototronic effect on its performances simultaneously utilizing both positive and negative piezo-charges for the first time.
In experiment, the photo-responses of the HPD to 405 nm and 648 nm laser illuminations under different externally applied compressive strains indicate the existence of an optimized compressive strain to achieve the maximized enhancements. For example, the photoresponsivities to 405 nm and 648 nm laser illuminations are gigantically improved, and reach 0.218 A/W (under -10.73‰ compressive strain) and 0.012 A/W(under -6.52‰ compressive strain), respectively. Compared to photoresponsivities under strain free condition, the enhancements achieve over 3000% and 1800%, respectively. Other figure of merits as a function of compressive strain, such as photocurrent and specific detectivity, also exhibit a similar optimizing tendency.
The optimizing phenomena are due to the positive and negative piezo-charges at n-Si/n-ZnO and n-ZnO/p-PEDOT:PSS interface, respectively, that introduce different adjustments to the local energy band diagrams which have either enhancing or weakening effects on the bahaviors of photo-generated carriers. Under a relatively small compressive strain, the enhancing influences play a dominant role so the photo-responses are improved. As strain rises, some weakening influences outgrow others, therefore the photo-responses are degraded. This competition mechanism is a combined result of both positive and negative piezo-charges, and eventually produces an optimized modulation to the photo-responses of the HPD. Theoretical validation is implemented by finite element analysis simulations and simulation results show that the strain-induced variations in energy band diagrams in the vicinity of the n-Si/n-ZnO and n-ZnO/p-PEDOT:PSS interfaces are both in good accordance with the proposed working mechanisms.
This work not only presents the utilization of both positive and negative piezo-charges to optimize the performances of the HPD by the piezo-phototronic effect, but also provides a deep understanding of how the piezo-charges of two opposite polarities work together in one optoelectronic device, hopefully proposing the idea of introducing the piezo-phototronic effect into three-/multi-layer devices in future applications.
8:45 AM - EP01.01.02
Defective Metal Oxides—New Generation of Electrostrictor Materials
Simone Santucci1,Simone Sanna1,Nini Pryds1,Vincenzo Esposito1
Technical University of Denmark1Show Abstract
Lead Zirconate Titanate (Pb(Zr,Ti)O3) (PZT) is the dominating electromechanically active functional material with a wide range of applications in electronics and micro-actuation, e.g. in MEMS. However, currently it is difficult to grow highly crystalline PZT directly on silicon due to the interfacial chemical reactions between the lead (Pb) and silicon at elevated temperatures required for the PZT crystallization. A possible solution to avoid interdiffusion is to grow PZT on insulating diffusion barrier layers such as ZrO2 or TiO2 that protect the silicon wafer substrate. This solution, however, brings complex processing steps and can result in an overall decreasing of the device electromechanical performances.
The recent discovery of “non-classical” electrostriction in some defective metal oxides such as (Y, Nb)-Stabilized δ-Bi2O3 (Bi7Nb2-xYxO15.5-x)  and gadolinium-doped ceria (Ce1-xGdxO2-δ) (CGO)  drew a great interest as a promising candidate for the new generation of electromechanical micro devices. Particularly, CGO is not only an environmental friendly material but it is also highly compatible with silicon technology since cerium does not diffuse into silicon. Moreover, CGO shows better performances as compared to the best performing commercial lead based ceramics, e.g. the electrostrictive coefficient of CGO is in a range between 20-110 m4/C2 [1,2,3] vs 0,02 m4/C2 of Pb(Mg1/3Nb2/3)O3 (PMN) .
In this work, we demonstrate the great potential and some limitations of CGO by growing thin films directly on TiN/Si substrates, where a TiN deposition of 80 nm serves as bottom electrode for the CGO electrostrictor. The direct deposition yields impressive electrostrictive performances (50 m4/C2) and long term stability for GCO films of ca. 1 µm in thickness.
1. N. Yavo et al., Adv. Funct. Mater. 2016, 26, 1138–1142.
2. R. Korobko et al., Adv. Mater. 2012, 24, 5857–5861.
3. R. Korobko et al., Sensors and Actuators A 2013, 201, 73– 78.
4. J. Kuwata et al 1980, Jpn. J. Appl. Phys. 19 2099.
9:00 AM - EP01.01.03
First-Principles Studies of the Effects of Oxygen Vacancies on the HfO2-Based Ferroelectric Tunnel Junction
Jinho Byun1,Taewon Min1,Jaekwang Lee1
Pusan National University1Show Abstract
Owing to the recent advances in the oxide growth technology, ferroelectricity has been stabilized even in a few nm-thick films, which makes it possible to realize the oxides-based ferroelectric tunneling junction (FTJ) combining the quantum-mechanical tunneling phenomena and switchable spontaneous polarization into novel device functionality. Among various ferroelectric oxides, HfO2 is the most promising material for FTJ devices since it has the great advantage of complementary metal-oxide-semiconductor (CMOS) process compatibility. Despite this considerable attention, the influence of oxygen vacancies on the tunneling current has not been clearly understood yet. Here, using first-principles density functional theory calculations, we explored the role of interfacial oxygen vacancy on the tunneling current in the TiN/HfO2/metal devices at the atomic scale. We find that the tunneling current in defective HfO2 is enhanced by over three orders of magnitude compared to plain HfO2 thin film. Our results show that the modulation of electronic properties via interfacial oxygen vacancy has a significant impact on HfO2-based FTJ device performance.
This research was supported by the MOTIE (Ministry of Trade, Industry & Energy (#10080643) and KSRC (Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device.
This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (2018R1A2B6004394)
9:15 AM - EP01.01.04
Dynamical Mean Field Theory Investigation of Piezoresistive Thin-Film Rare Earth Compounds Contacted to Metal Electrodes
Ivan Rungger1,Evgeny Plekhanov2,Debalina Banerjee2,Andrea Droghetti3,Dennis Newns4,Cedric Weber2,Glenn Martyna4
National Physical Laboratory1,Kings College London2,University of the Basque Country3,IBM Thomas J Watson Research Center4Show Abstract
The emerging piezoelectric transistor technology is based on heterostructures combining piezoelectric materials and piezoresistive thin films acting as ON/OFF switches and memories. Rare earth piezoresistive compounds such as SmS, SmSe and SmTe exhibit a reversible metal-insulator phase transition driven by either light, voltage or pressure, which can be applied by the piezoelectric. For device applications the contact with the metal electrodes critically affects switching behaviour in nanoscale piezoresistive materials, which has not been studied so far. Here we present first principles calculations to model these phase transitions both in the bulk and in nanoscale thin films used in transistor applications, and predict how switching can be induced by mechanical and electrical means in nanoscale devices. Importantly, density functional theory with semi-local exchange correlation functionals cannot correctly treat the strongly correlated electrons in the f-orbitals of Sm. We overcome this limitation by using our recent implementation of the dynamical mean field theory, and show good agreement with experimental data for the electrical and mechanical switching properties.
9:30 AM - EP01.01.05
Three-Dimensional Interconnected Piezoelectric Ceramic Foam Based Composites as Flexible, High-Performance Piezo/Pyroelectric Materials for Concurrent Mechanical and Thermal Energy Harvesting
Sulin Zhang1,Qing Wang1,Guangzu Zhang2,Peng Zhao1
The Pennsylvania State University1,Huazhong University of Science and Technology2Show Abstract
Flexible Piezoelectric (PZT)-polymer composites with superior piezoelectric effect have received much attention for a wide range of applications, particularly in energy harvesting. However, classical PZT-polymer composites with low-dimensional ceramic fillers suffer from low piezoelectricity, owing to the poor load-transfer efficiency from the polymer matrix to the active ceramic fillers. The fundamental mechanics is that the load-transfer efficiency for these composites scales with the ratio of the stiffness of the polymer matrix to that of the ceramic fillers, a value typically on the order of 10-5. Here we introduce a cost-effectively producible ceramic-polymer composite consisting of three-dimensional (3-D) interconnected piezoelectric microfoams in polydimethylsiloxane (PDMS) matrix. The resulting composite breaks the conventional scaling law of the load-transfer efficiency, and enables continuous strain and heat transfer, giving rise to exceptionally improved piezo and pyroelectric effects as compared to those based on low-dimensional ceramic fillers. The 3-D composite is also mechanically flexible, robust, and durable, able to sustain thousands of thermomechanical cycles without noticeable degradation, while yielding stable piezo/pyroelectrical signals. We further demonstrate that combining the piezo and pyroelectric effects of the 3-D composites enable concurrent mechanical and thermal energy harvesting. These attributes, along with the scalable production, make the 3-D composite attractive to a wide range of applications in soft robotics, wearable electronics, and artificial muscles and skins, etc.
9:45 AM - EP01.01.06
Potential Ferroelectric Binary Oxides Beyond Hafnia
Rohit Batra1,2,Huan Tran1,Brienne Johnson3,George Rossetti1,Jacob Jones3,Rampi Ramprasad2
University of Connecticut1,Georgia Institute of Technology2,North Carolina State University3Show Abstract
In the past couple of years, there have been extensive empirical and theoretical efforts to elucidate the surprising phenomenon of ferroelectricity recently discovered in hafnia (HfO2) thin films (<30 nm) [1-5]. While the origin of this unexpected ferroelectric (FE) behavior is associated with the formation of the metastable orthorhombic Pca21 phase owing to unusual thermodynamic or processing conditions [2,4], the most critical lesson to be learned from the example of hafnia is that even binary oxides can be FE if low-lying metastable (or stable) polar phases are present. Thus, in this contribution, we extend the findings from the case of hafnia to discover new FE binary oxides, as opposed to the traditionally explored class of perovskite-structured oxides, using computations. We employed a combination of structural search methods, first principles computations and group-theoretical considerations to find at least six simple oxides as potential ferroelectric candidates. Among them, a previously unexplored candidate, CaO2, was successfully synthesized in the polar Pna21 phase, in accordance with our theoretical predictions. Furthermore, the high occurrence (~40 %) of low-energy polar phases among the oxides considered in this work strongly advocates the possibility of discovery or engineering ferroelectricity in many more simple oxides beyond hafnia.
 M. H. Park et al., Advanced Materials 27, 1811 (2015)
 T. D. Huan et al., Physical Review B 90, 064111 (2014)
 R. Batra et al., Applied Physics Letters 108, 172902 (2016)
 R. Batra et al., Journal of Physical Chemistry C, 121, 4139 (2017)
 R. Batra et al., Chemistry of Materials, 29, 9102 (2017)
10:30 AM - EP01.01.07
Accelerated Materials Design of Novel Polar Materials
University of California, Berkeley1,Lawrence Berkeley National Laboratory2Show Abstract
Novel polar multifunctional materials are needed for next generation sensors, energy converters, and high-performance computing. Leveraging the growing body of computational resources, from the prediction of novel materials with target properties to their characterization and synthesis, it is possible to accelerate the pace of discovery. In this talk we will utilize the data and analysis resources of the Materials Project (www.materialsproject.org) which is harnessing the power of supercomputing coupled with a sophisticated software infrastructure that carries out, organizes and disseminates 100-1000s of calculations per week – enabling effective screening, prediction and tandem exploration together with experimental teams. We will survey the available methods and data, exemplified through a recent realization of a novel metastable piezoelectric material, from prediction to successful synthesis and testing. Finally, we will comment on future directions in this exciting field, in particular the need for predictive synthesis.
11:00 AM - EP01.01.08
Kinetic Monte Carlo Simulations of Organic Ferroelectrics
Tim Cornelissen1,Indre Urbanaviciute1,Martijn Kemerink1
Linköping University1Show Abstract
Organic ferroelectric materials are emerging as a class of materials that may find application in a broad range of fields; for instance, they might solve the ‘missing memory’ problem in printed electronics. However, a full understanding of their switching kinetics on all length and time scales is still lacking. A variety of computational models have been employed to tackle this problem and to study different aspects of organic ferroelectrics. However, these are usually restricted to idealized morphologies or short time scales.
In contrast, we have developed an electrostatic model that, when used in kinetic Monte Carlo simulations, can reproduce the ferroelectric properties and kinetics on experimental time scales and for realistic 3D morphologies. We apply this model on the prototype small molecular ferroelectric trialkylbenzene-1,3,5-tricarboxamide (BTA).
We simulate hysteresis loops and depolarization curves and find a good agreement with experiments. Like the experiments, the dependence on frequency and temperature of our model results can be interpreted in the framework of thermally activated nucleation limited switching. Specifically, we find two different modes of switching, each associated with their own kinetics and energetics. One mode corresponds to a full rotation of the dipoles, while the other mode only flips the component along the polarization axis. The existence of these two modes is confirmed by molecular dynamics simulations. Both simulation methods find that the second mode has a lower coercive field and thus is the one occurring in polarization switching experiments.
We also investigate the effect of structural disorder on the ferroelectric properties. When the disorder in the system is increased, the retention time decreases dramatically, while the coercive field remains mostly unchanged. For device applications a high retention time and moderate coercive field is required. Aside from providing a detailed insight into polarization switching processes on experimental length and time scales, our model thus is also able to provide guidance in improving the performance of ferroelectric devices.
11:15 AM - EP01.01.09
Lone Pair Engineering for Multi-Functional Polar Semiconductors
Imperial College London1Show Abstract
Beyond the group oxidation state (N), post-transition metals can adopt a lower (N-2) oxidation state, which is associated with a metal s2 lone electron pair. Solid-state lone pairs, as found in the compounds formed of ions such as In(I), Sn(II), Sb(III), and Te(IV), are linked to the formation of asymmetric local coordination environments and non-centrosymmetric crystal structures . Lone pairs underpin the physical properties of many piezoelectric, pyroelectric and ferroelectric materials.
I will discuss progress in the understanding of structure and reactivity of lone pair containing compounds, including the driving force for structural distortions and how they can be controlled to enable novel functionality. Applications areas to be discussed will include thermoelectric devices that incorporate high levels of phonon anharmonicity (e.g. SnSe ), photovoltaic cells based on photoferroic semiconductors (e.g. Pb and Sn halide perovskites ), as well as new classes of ternary V-VI-VII semiconductors based on Bi and Sb chalcohalides [4,5] that encompass photocatalysts, Rashba semiconductors, and topological insulators.
1. Stereochemistry of post-transition metal oxides: revision of the classical lone pair model. Chem. Soc. Rev. 40, 4455 (2011)
2. Anharmonicity in the high-temperature Cmcm phase of SnSe: soft modes and three-phonon interactions. Phys. Rev. Lett. 117, 075502 (2016)
3. Spontaneous octahedral tilting in the cubic inorganic caesium halide perovskites CsSnX3 and CsPbX3 (X = F, Cl, Br, I). J. Phys. Chem. Lett. 8, 4720 (2017)
4. Quasi-particle electronic band structure and alignment of the V-VI-VII semiconductors SbSI, SbSBr, and SbSeI for solar cells. Appl. Phys. Lett. 108, 112103 (2016)
5. Bismuth oxyhalides: synthesis, structure and photoelectrochemical activity. Chem. Sci. 7, 4832 (2016)
EP01.02: Experimental Realization of Predicted Materials Including Synthesizability
Monday PM, November 26, 2018
Hynes, Level 1, Room 103
1:30 PM - EP01.02.01
Enhancement of Ferroelectricity in Perovskite Oxides by Sulfurization
Muhammad Sheeraz1,Ill Won Kim1,Chang Won Ahn1,Tae Heon Kim1
University of Ulsan1Show Abstract
Sulfurization, an anion substitution to oxide materials is considered a progressive route for designing new multi-functional materials artificially and realization of unusual physical properties which do not exist in nature. Sulfur among the other anions has got major attraction due to