Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P21: Semiconductors and Quantum Dots for Energy Applications |
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Sponsoring Units: GERA Chair: Robert Kaplar, Sandia National Laboratories Room: 302 |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P21.00001: A Computational Survey of Semiconductors for Power Electronics Prashun Gorai, Robert W McKinney, Nancy M Haegel, Andriy Zakutayev, Vladan Stevanovic Power electronics (PE) are used to control and convert electrical energy in a wide range of applications from consumer products to large-scale industrial equipment. While Si-based power devices account for the vast majority of the market, wide band gap semiconductors such as SiC, GaN, and Ga2O3 are starting to gain ground. However, these emerging materials face challenges due to either non-negligible defect densities, or high synthesis and processing costs, or poor thermal properties. We performed a broad computational search aimed at identifying promising materials for future power electronic devices beyond SiC, GaN, and Ga2O3. We consider 863 oxides, sulfides, nitrides, carbides, silicides, and borides reported in the crystallographic database and exhibit finite calculated band gaps. We utilize ab initio methods with models for intrinsic carrier mobility, and critical breakdown field to compute the Baliga figure of merit. We also compute the lattice thermal conductivity as a screening parameter. In addition to correctly identifying known power electronic materials, our survey has revealed a number of promising candidates exhibiting the desirable combination of high figure of merit and high lattice thermal conductivity, which we propose for further experimental investigations. |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P21.00002: Towards efficient green emitters: Heteroepitaxial ZnGeN2 on GaN by molecular beam epitaxy Marshall Tellekamp, Celeste Melamed, Andrew Norman, Adele Tamboli GaN-based LEDs have revolutionized the lighting industry, yet phosphor converters are still required to achieve green and amber wavelengths in a white light emitter. The ‘green gap’ refers to this lack of efficient emitters from 510 nm – 610 nm. InGaN active layers theoretically can reach this range, however the increased In-content results in complications including phase separation and increased spontaneous polarization mismatch which leads to decreased radiative recombination efficiency. |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P21.00003: Combinatorial Investigation of Structural and Optical Properties of Cation-Disordered ZnGeN2 Celeste Melamed, Rekha Schnepf, Jie Pan, Allison Mis, Rachel Woods-Robinson, Karen Heinselman, Jacob Cordell, John Perkins, Stephan Lany, Eric Toberer, Adele Tamboli In this work, we present a combinatorial study of sputtered ZnGeN2 thin films with cross-cutting applications in fundamental materials science and novel device development. The II-IV-N2 materials offer the possibility of groundbreaking optoelectronic properties through greater chemical and structural tunability than the III-Ns. ZnGeN2 is lattice-matched to GaN and is predicted to exhibit a direct bandgap with strong absorption, but experimental studies to date report inconsistent optical properties. Additionally, minimal work has explored variation with cation composition, which has been shown to impact properties of other II-IV-N2 materials. Here, we present a study of combinatorial ZnGeN2 grown by RF co-sputtering. X-ray diffraction reveals phase-pure films in the expected cation-disordered wurtzite structure for cation compositions from 30% to 60% Zn/(Zn+Ge) and synthesis temperatures from 200°C to 600°C. Changes in crystallinity are explored as a function of cation composition, synthesis temperature, and in-situ and ex-situ annealing. Finally, spectroscopic ellipsometry is performed to investigate optical properties with changing synthesis conditions. This study re-affirms the potential for tunability of thin film ZnGeN2 as a direct- and wide- bandgap optoelectronic material. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P21.00004: Cathodoluminescence measurement of high bandgap CdTe-based devices Aida Torabi, Claudia Beck, Amit Munshi, Carey Reich, Walajabad Sampath, Taylor Harvey High band-gap CdTe-based devices are being developed as top films to be used in tandem solar cells. CdTe can be alloyed with Mg and Zn to form CdxMg1-xTe (CMT) or CdxZn1-xTe (CZT) to increase the band gap; however, doping and passivation of these films continue to be a fundamental challenge. Films exhibiting better recombination lifetimes have been demonstrated by incorporating Se in CMT and CZT to from quaternary alloys. A fundamental understanding of the film properties are needed for all these films to realize their potential as photovoltaic absorbers. Optical characterization is one method to understand and aid in the development of high band-gap CdTe films. Scanning electron mapping of the luminescence of these film gives insight into film composition, homogeneity, and crystal quality. Herein we present our study of the optical properties of these materials using cathodoluminescence(CL). Additionally, electron beam-induced current (EBIC) is measured and correlated to the optical response. Unexpected peak shift and secondary peak presence indicate potential phase segregation or trap state formation. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P21.00005: Investigation of the photocorrosion of GaP, III-V photoanode in acid with in situ UV/vis spectroscopy Sahar Pishgar, Joshua Spurgeon Although III-V semiconductors are one of the most promising group of materials for high efficiency solar fuels applications, they are prone to self-corrosion in strongly acidic or alkaline solutions. In-situ Investigation of photo-corrosion process are now limited to very expensive and complicated methods that are not available in every lab. Developing methods that enable researchers to do in-situ study of photo-corrosion process could make a profound impact on this field. Herein we studied self-corrosion of GaP photoelectrodes, a promising III-V material for tandem top subcells, in acidic electrolyte via in-situ UV-Vis spectroscopy. In-situ measurement of concentration of dissolved Ga and P species that come off from the electrode to electrolyte , calculation of corrosion faradaic efficiency as a function of applied bias and time along with SEM and XPS characterization are utilized to expound the photo-corrosion process of n-GaP and p+-GaP photoelectrodes which have shown different corrosion behavior. In addition, TiO2 protective layer was deposited on some samples to study the change in corrosion faradaic efficiency as a function of deposition parameters. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P21.00006: Influence of epitaxial anatase and rutile TiO2 thin films as electron transport layers for perovskite solar cell Yeon Soo Kim, Hye-Jin Jin, Hye Ri Jung, Jihyun Kim, William Jo The effective electron transport layer (ETL) is essential for high-power conversion efficiency (PCE) of perovskite solar cell (PSC). TiO2 is the most widely used material for ETL owing to proper band alignment, enough optical transmittance, and high electron mobility. There are two representative thermodynamically stable crystal phases of TiO2: anatase and rutile. However, it is still debated which phase is more effective for the ETL. To solve the concern, single-phase thin film is strongly needed. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P21.00007: First-Principles Calculation of Charge Carrier Mobility using Complex Band Structure Andrew V Brooks, Yue Yu, Dmitry Skachkov, Hai-Ping Cheng, Xiaoguang Zhang We compute charge carrier mobilities from the complex band structure, using the Quantum Espresso suite and a previously developed method1. Carriers with finite lifetimes due to scattering may be represented by Bloch states with complex energies. Our method determines the constant complex potential that must be added to a perfect crystal to induce the scattering effects seen in a crystal with defects, which we deduce from a series of complex band calculations. The mean scattering lifetime is computed from the imaginary part of this complex potential, and the carrier mobility is obtained from the scattering lifetime using the Boltzmann transport theory. Mobility is calculated for graphene, hybrid organic-inorganic perovskites, and 2D FeCl2 half-metal system, as a function of temperature due to phonon scattering, impurity and absorbed molecules. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P21.00008: Towards Monolithically Integrated Thin Film Bypass Diodes Timothy Silverman, Lorelle Mansfield, Stephen Glynn, Timothy Remo, Karen Bowers, Bart Stevens, Matthew Reese Bypass diodes can make photovoltaic (PV) modules more resilient, for instance preventing local heating when one portion is shadowed and another is not. This is significant because hot spot formation due to partial shading can cause sudden, non-linear permanent degradation. Presently, if incorporated at all, bypass diodes must be integrated as discrete components. Thin film photovoltaics can be fabricated in a manner where by thoughtfully choosing growth and scribing order “monolithic” integration can be achieved. We will present electrical simulations of diodes placed in an edge configuration to highlight the tradeoffs of designing real-world modules considering such variables as lateral resistance, PV cells per diode, and diode leakage current. Simulations incorporate both optimal and experimentally grown thin film diode characteristics to allow the tradeoffs and areas for improvement to be better understood. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P21.00009: Injection-dependent non-radiative SRH recombination via interstitials and dislocations in multicrystalline Si Andrey Semichaevsky This paper deals with models of NR carrier recombination in mc-Si, which limits the efficiency of photovoltaic conversion. Experimental minority lifetimes in Si show a variety of dependences on injection levels. Models of non-radiative recombination in silicon were proposed for point defects (e.g., Fe interstitials) and extended defects (e.g., dislocations). High-resolution measurements of carrier transport are technically difficult, so models are used instead to relate carrier recombination processes in mc-Si to minority carrier lifetimes. While the SRH recombination due to shallow and deep point defects may result in a lifetime dependence on concentration with a distinct maximum, the recombination via arrays of dislocations leads to a monotonically increasing lifetime with the carrier concentration. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P21.00010: Transition Metal Doped Quantum Dots for Photovoltaic Applications Trieu Le, Thilini Ekanayaka, Annika Neufeld-Kreider, Archit Dhingra, Takashi Komesu, Andrew J. Yost, Carolina C. Ilie In recent years, semiconductor zinc sulfide (ZnS) quantum dots have been considerably studied for various applications such as light emitting diodes, flat panel display, UV sensor and solar cell application. We discuss herein the optical and transport properties of the transition metal doped quantum dots and optimize them for better photovoltaics. Zinc sulfide has an excellent optical and electronic performances due to its wide band gap. In addition, cobalt-nickel doped zinc sulfide brings a versatility of the band gap energy. This is corresponding to an enhancement in the photo-to-current efficiency of doped quantum dots in sensitized solar cell. In this study, we explore how the different dopants lead changes in the band gap and discuss the characteristic of these doped quantum dots. The absorption data shows that cobalt-nickel doped ZnS has the highest absorbance the visible range out of all the single and co-doped and tri-doped quantum dots which made it the best candidate for optoelectronic device fabrication. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P21.00011: Glucose-Derived Carbon Nanodots in Dye-Sensitized Solar Cells to Increase Efficiency Max Markuson-DiPrince, Harsh Uppala, Grace Dirks, Logan Smith, John Vosicky, Andrew G Baruth Although carbon nanodot isolation remains difficult due to the presence of molecular byproducts in a bottom-up synthesis approach using thermal treatment of carbohydrate solutions, their resultant photoluminescence shows promise for down-converting UV photons. In particular, excitation at 390nm results in significant luminescence from 490–540nm, with an excitation wavelength dependence of luminescence (peak absorption occurs at 290nm). Carbonaceous nanodot solutions were derived from high-concentration glucose solutions at 120°C for a 48 hour period and then incorporated into Ruthenium-based dye-sensitized solar cell devices to enhance external quantum efficiency for high energy photons. We found that dialysis combined with solid phase extraction retained photoluminescent properties while allowing for carbon dot isolation in acetonitrile, a soaking solvent for dye-sensitization of TiO2 nanoparticles, with minimal measurable traces of other chemical byproducts. Successful purification processes, photoluminescence, external quantum efficiency, and J-V curves of these carbon dot-modified devices will be shown to verify this low-cost, earth abundant approach to efficiency enhancement of dye-sensitized solar cells. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P21.00012: Nano-biohybrid Organisms: In-vivo Targeting of Enzymes with Quantum Dots for Light-Driven Renewable Biochemical Synthesis John Bertram, Prashant Nagpal, Yuchen Ding Living cells do not interface naturally with nanoscale materials, although such artificial organisms can have unprecedented multifunctional properties, like wireless activation of enzyme function using electromagnetic stimuli. Realizing such interfacing in a nanobiohybrid organism (or nanorg) requires (1) chemical coupling via affinity binding and self-assembly, (2) the energetic coupling between optoelectronic states of artificial materials with the cellular process, and (3) the design of appropriate interfaces ensuring biocompatibility. We have shown that many different core−shell quantum dots (QDs) couple with targeted enzyme sites in bacteria. When illuminated by light, these QDs drive the renewable production of different biofuels and chemicals using carbon dioxide, water, and nitrogen (from air) as substrates. Together, these nanorgs catalyze light-induced air−water−CO2 reduction to synthesize biofuels like isopropanol, 2,3-butanediol, C11−C15 methyl ketone, hydrogen gas; and valued chemicals such as formic acid, ammonia, ethylene, and degradable bioplastics polyhydroxybutyrate. Therefore, these resting cells function as nano-microbial factories that synthesize valuable chemicals from abundant small molecuels powered by the sun. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P21.00013: Building quantum dot-bacteria nano-biohybrids for light-driven renewable biochemical synthesis Yuchen Ding, John Bertram Live cells do not interface naturally with nanostructures, although such artificial organisms can have unprecedented multifunctional properties, like wireless activation of enzyme function using electromagnetic stimuli. Realizing such interfacing requires (1) chemical coupling via affinity binding and self-assembly, (2) energetic coupling between material optoelectronic states and the cellular process, and (3) design of appropriate interfaces ensuring biocompatibility. Here we show different core-shell quantum dots (QDs), with excitations ranging from UV to NIR, couple with targeted enzyme sites in bacteria. When illuminated by light, these QDs drive the renewable production of different biofuels and chemicals using CO2, water, and N2 as substrates. These QDs use their zinc-rich shell facets for affinity binding to the enzymes. Cysteine zwitterion ligands enable uptake through the cell, facilitating cell survival. Together, these nanorgs catalyze light-induced air-water-CO2 reduction with a high turnover number of ~106-108 (mols/mol of cells) to biofuels like C2H4, 2-propanol, 2,3-butanediol, methyl ketones, and H2; and chemicals such as formate, NH3, and bioplastics. Therefore, these resting cells function as nano-microbial factories powered by light. |
Wednesday, March 4, 2020 5:06PM - 5:18PM |
P21.00014: Alcohol Synthesis on MoS2-supported Gold Nanoparticle Tao Jiang, Duy Le, Talat S. Rahman Alcohol synthesis from syngas (CO, H2) is an important part of an economy based on renewable fuels. Rational designing of efficient catalyst material for such synthesis is in great demand because of the limitation of the current state-of-the-art catalysts. We report our density functional theory based calculations of the hydrogenation of CO on 31-atom, bilayer Au cluster supported on single-layer MoS2 (Au31/MoS2). In accordance with previous investigations [1], we found that the gold atoms at the edge were most affected by substrate interaction and lad strong affinity for CO. Furthermore, molecular H2 could only physisorb on Au31/MoS2 and the activation barrier of H2 dissociation was 0.63 eV, lower than that on Au13 [2]. We found that Au31/MoS2 offers excellent activity toward methanol synthesis, via two competitive reaction pathways: 1) CHO*→CH2O*→CH3O*→CH3OH*; 2) CHO*→CHOH*→CH2OH*→CH3OH*, the former being kinetically more favorable. We compare our findings with that on Au13 [2] to elucidate the influence of size and shape of nanoparticles on their catalytic performance. |
Wednesday, March 4, 2020 5:18PM - 5:30PM |
P21.00015: Analytical electron billiards model of geometric diodes Jeremy Low, James P Custer Jr., James Cahoon Unlike traditional diodes that require a potential barrier to generate electrical asymmetry, geometric diodes operate simply by breaking the structural symmetry on a scale comparable to the mean-free-path length of charge carriers. This gives geometric diodes unique properties that allow them to function as long wavelength energy harvesters and ultra-high speed signal processors. These devices exhibit nonlinear charge transport that is largely dictated by geometric parameters and position-dependent mean-free-path. We aim to predict the device’s dependence on these parameters through analytically calculating the proportion of possible paths ballistic charge carriers can travel through the device. Trajectories of up to an arbitrary number of internal reflections are integrated over all space inside the device. To account for the effect of applied electric field on the electron momentum distribution, a spatial distribution weighted in one direction is used and the impact on diode asymmetry is evaluated. The model is able to simulate nonlinear charge transport in both 2D and 3D nanowire geometric diodes. The model has excellent agreement with experiment, matching trends of IV curve asymmetry versus geometric parameters in silicon nanowire geometric diodes. |
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