Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session T34: Thermodynamic and Transport Properties |
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Sponsoring Units: FIAP Chair: Peifan Liu, Duke University Room: Room 226/227 |
Thursday, March 9, 2023 11:30AM - 11:42AM |
T34.00001: Thermodynamic constraints on photoluminescent cooling with coherent and incoherent light sources Sushrut Ghonge, Zhuoming Zhang, Masaru Kuno, Boldizsar Janko Cooling solids with anti-Stokes photoluminescence, involving the emission of photons with higher energy than incident photons, has been demonstrated in various materials, such as rare-earth-doped glasses. Requiring that the increase in entropy of radiation must be higher than the decrease in entropy of the sample imposes constraints on the efficiency of the cooling process. We study the role of the properties of the light source, such as coherence, unidirectionality, and monochromaticity, in optical cooling. We use the most general formulation of radiation entropy in terms of the von Neumann entropy of the photon field, which allows us to study a variety of light sources. We show that as long as the incident radiation is unidirectional, the loss of coherence does not significantly affect the cooling efficiency. Our results suggest that the laws of thermodynamics allow us to optically cool materials with incoherent sources like LEDs and filtered sunlight almost as efficiently as with lasers. |
Thursday, March 9, 2023 11:42AM - 11:54AM |
T34.00002: Quaternary MgSiN2-GaN alloy semiconductors for deep UV applications Ozan Dernek, Walter R Lambrecht Ultra-wide direct band gap semiconductors have been investigated extensively for their potential in deep ultraviolet optoelectronic applications. In this work, we investigate two octet-rule preserving structures of the MgSiN2-GaN alloys in 50 % mixing -- namely, Pmn21 and P1n1 space groups -- as candidates for these applications. Although the MgSiN2 has an indirect band gap of ~0.4 eV below its direct band gap of ~6.5 eV, the alloy structures we present here are nearly direct gaps in the sense that the indirect gap is less than 0.1 eV lower than the direct gap of ~4.7 eV, calculated by the quasiparticle self-consistent QSGW method. The positive mixing energies of 8 (31) meV/atom for Pmn21 (P1n1) show only a small driving force toward phase separation. Moreover, the different sign lattice mismatch in two basal plane directions between MgSiN2 and GaN could avoid the tensile strain, which is a known problem in Al_xGa_(1-x)N. Besides band structures, we also present effective masses and symmetry analysis of the valence band splitting which affects the band gap optical transition polarizations. |
Thursday, March 9, 2023 11:54AM - 12:06PM |
T34.00003: The Flux Derivatives Formalism: the Guyer-Krumhansl equation from the Boltzmann equation for general semiconductors Lluc Sendra Molins, Albert Beardo, F. Xavier Alvarez, Juan Camacho, Javier Bafaluy We present a method, the flux derivatives formalism (FDF), to derive a hydrodynamic heat transport equation (Guyer-Krumhansl equation [1]) similar to Navier-Stokes for general semiconductors. This method is valid for material where momentum-preserving collisions dominate and also for kinetic materials dominated by resistive collisions. Therefore, it can be applied to semiconductors like silicon or germanium [2]. In constrast to the common belief, this kind of materials are well-described by the Guyer-Krumhansl equation (GKE), which generalizes the Fourier’s law. |
Thursday, March 9, 2023 12:06PM - 12:18PM |
T34.00004: Transport and noise of of hot electrons in GaAs using an ab-initio-based semi-analytical model of two-phonon polar optical phonon scattering Jiace Sun, Austin J Minnich Recent ab-initio studies of electron transport in GaAs have reported that electron-phonon interactions beyond the lowest order play a fundamental role in charge transport and noise phenomena. Inclusion of the next-leading-order process in which an electron scatters with two phonons was found to yield good agreement for the high-field drift velocity, but discrepancies remained in the power spectral density of current fluctuations (PSD). The high computational cost of the ab-initio approach necessitated various approximations, such as the neglect of off-shell terms, which may account for the discrepancy. Here, we report an ab-initio-based semi-analytical transport model of electron scattering by iterated interaction with two optical phonons via the Fröhlich mechanism, allowing many of the approximations in the ab-initio treatment to be lifted. We compare the calculated and experimental transport and noise properties as well as electron lifetimes as measured by photoluminescence experiments. We find quantitative agreement within 15% for the drift velocity and 25% for the Γ valley lifetimes, and agreement with the Γ-L intervalley lifetimes within a factor of two. Considering these results and prior studies of current noise in GaAs, we conclude that the most probable origin of the PSD versus electric field is the formation of space charge domains rather than the intervalley scattering as has been assumed. |
Thursday, March 9, 2023 12:18PM - 12:30PM |
T34.00005: Entropy and Seebeck signals meet on the edges Natalia Cortes, Patricio Vargas, Sergio E Ulloa We explore the electronic entropy per particle s and Seebeck coefficient S in zigzag graphene ribbons. Pristine and edge-doped ribbons are considered using tight-binding models to inspect the role of edge states in the observed thermal transport properties. As a bandgap opens when the ribbons are doped at one or both edges, due to asymmetric edge potentials, we find that s and S signals are closely related to each other: both develop sharp dip-peak lineshapes as the chemical potential lies in the gap, while the ratio s/S exhibits a nearly constant value equal to the elementary charge e at low temperatures. This constant ratio suggests that S can be seen as the transport differential entropy per charge, as suggested by some authors. Our calculations also indicate that measurement of s and S may be useful as a spectroscopic probe of different electronic energy scales involved in such quantities in gapped materials. |
Thursday, March 9, 2023 12:30PM - 12:42PM |
T34.00006: Current-Voltage characteristics of disordered electronic system under application of electric field. Kunal Mozumdar, Jong E Han Electron wave function in a disordered potential tends to localize in space, a phenomenon well known as Anderson localization where the system behaves predominantly as an insulator. Transport in such localized system occurs via mechanism of variable range hopping (VRH). Focus of this study is the effect of DC bias on the transport of localized of electrons. We develop a quantum mechanical model of disordered electronic system under a constant electric field coupled to a bath and compute the IV characteristics and localization properties of the system. Our preliminary analysis indicates nonlinear scaling behavior of the conductance of a disordered system in the high field and low field regime. We find that there are significant differences in the nonlinear behavior under bias between our electronic model and the statistical resistor network theory[1] of disordered systems. We highlight electric field-assisted VRH as a possible mechanism for conduction in disordered electronic systems. |
Thursday, March 9, 2023 12:42PM - 12:54PM |
T34.00007: Heat transport through a qubit under continuous quantum measurement Tsuyoshi Yamamoto, Yasuhiro Tokura, Takeo Kato When one measures a quantum system, its state changes instantaneously. This backaction of quantum measurement comes from quantum mechanics, which does not appear in classical systems. In particular, in quantum many-body systems, it is known that the quantum measurements induce interesting phenomena, e.g., measurement-induced phase transition, suppression of the Kondo effect, and non-Hermitian dynamics. Furthermore, recent developments in experimental techniques have enabled us to observe the backaction of quantum measurements in well-controllable experimental systems, attracting more attention. |
Thursday, March 9, 2023 12:54PM - 1:06PM |
T34.00008: Thermal conductivity of θ-TaN polycrystal from first principles Sungyeb Jung, Hwijong Lee, Li Shi, Feliciano Giustino Thermal management is an increasingly important issue in the design of new generations of electronic and optoelectronic devices. In this context, new high thermal conductivity materials are highly desirable to reduce the power density of hot spots in ultra-scaled transistors. Recently, a first principle study has found [1] that the lattice thermal conductivity of semimetallic the θ-TaN can be as high as 1000W/mK. In this work, we perform a detailed computational study of the thermal conductivity of this compound, and we analyze and quantify the key phonon scattering mechanisms. We compare our calculations to experimental data on recently-synthesized samples of θ-TaN, and we find that the thermal conductivity of the experimental samples is primarily limited by grain boundary scattering. We discuss possible avenues to increase the thermal conductivity toward the ideal theoretical limit. |
Thursday, March 9, 2023 1:06PM - 1:18PM |
T34.00009: Empirical Test of the Kelvin Relation in Thermoelectricity Hari P Panthi The Kelvin relation (KR) π = αT, where π the Peltier coefficient, α the thermopower, and T the absolute temperature, was derived in 1851, and is a cornerstone in thermoelectricity. In 1931 Onsager showed the Kelvin relation is a specific case of a reciprocal relation governing coupled linear force-flow processes in nonequilibrium thermodynamics. While generally accepted in theory, the KR has proven difficult to verify experimentally due to problems with measuring π independently. Here, we present an accurate way to empirically test the Kelvin relation using a new method to determine π that is free of Joule heating, self-corrects for Fourier conduction, and does not require knowing any material properties of the thermoelectric materials under test. Our test measures (π /α) at several different values of temperature difference ΔT= (TH - TC) but with the same value of TAv = ½(TH + TC). If ΔT is small enough, then the validity of the KR means the measured (π /α) should be a constant equal to TAv of the thermopile under test, independent of ΔT and insensitive to thermal contact resistances. We will present the results of such measurements taken on a Bi2Te3 thermopile, where we found the KR is valid to within the measurement uncertainty of ≤ 0.5% for ΔT up to 50 K with TAv = 330.20K. Finally, the limits of the linear response assumption will be discussed. |
Thursday, March 9, 2023 1:18PM - 1:30PM |
T34.00010: HPHT Growth and Modeling of High-quality Defect-free Diamond Crystals Ilya Ponomarev, Boris Feigelson, Jeffrey Derby, Scott Dossa, Marc Hainke, Christian Kranert, Jochen Friedrich, Yuri Shvyd'ko, Paresh Pradhan, Peifan Liu Diamond substrates for next-generation quantum computation/metrology, power electronics, and X-ray optics applications require high-crystallinity crystals with minimal defects density. We developed the modified High-Pressure High-Temperature (HPHT) temperature gradient growth technology that allows growing the highest crystalline quality large diamond crystals with a dislocation density of fewer than 10 cm-2. This near-equilibrium process is carried out under extreme conditions, where diamond single crystals are grown from a carbon solution in molten metal solvent (Fe, Ni, and Co and their alloys) under pressures in excess of 5 GPa and temperatures of 1,600 K and higher. Since there are no available diagnostics to directly monitor crystal growth in the HPHT cell, both indirect experimental growth monitoring and faithful models are needed to connect experimental outcomes to system design and process conditions. We present initial results from a collaboration that includes experimental growth carried out at the Euclid Beamlabs and two modeling efforts by the University of Minnesota and Fraunhofer IISB. X-ray white beam topography of grown crystals is also discussed. This two-fold approach provides rigorous tools to both understand growth in this system and to perform subsequent optimization of growth conditions. In particular, we aim to more fully understand the fundamental aspects of diamond nucleation and growth and identify process conditions that will achieve the highest crystalline quality in large diamond crystals. |
Thursday, March 9, 2023 1:30PM - 1:42PM |
T34.00011: Molecular beam epitaxial development of AlSb on Silicon substrates for radiation detector applications ganesh balakrishnan, mega frost, Adam A Hecht, Alexander Barzilov, shea tonkinson, Alexandria ragsdale, Maya N Kutty, Charles Han, Kaleab Ayalew, Jaeyun Moon The detection technology for X-rays and gamma-rays has been significantly improved in the past decade through bulk crystal growth efforts, particularly in the development of Cadmium Zinc Telluride (CZT). There is significant effort underway to develop newer bulk crystal technologies such as Cadmium Manganese Telluride (CMT) in order to achieve higher detection efficiency, energy resolution, room-temperature operation, as well as the ability to produce such detectors at reasonable cost. A possible alternative to bulk crystals could be the use of epitaxially grown structures which could pave the way for heterostructures, avalanche detectors, and CMOS integration. |
Thursday, March 9, 2023 1:42PM - 1:54PM |
T34.00012: Hydrogen-induced ultra-low optical absorption and mechanical loss in amorphous silicon for gravitational-wave detectors Manel Molina-Ruiz, Ashot Markosyan, Riccardo Bassiri, Martin M Fejer, Matthew R Abernathy, Thomas H Metcalf, Xiao Liu, Gabriele Vajente, Alena Ananyeva, Frances Hellman The sensitivity of gravitational-wave detectors is limited by the optical absorption and mechanical loss associated with the amorphous coatings of the detectors' mirrors. Optical absorption (at laser wavelengths of 1064, 1550 and 2000 nm) and mechanical loss (at temperatures of 1, 100 and 290 K) has been measured for amorphous silicon films grown at different temperatures and in different states: as-deposited, aged, annealed and hydrogenated. The addition of hydrogen to the silicon network yields an ultra-low optical absorption (below 10 ppm) for 500 nm-thick films, and the already low mechanical loss is further reduced at all temperatures. These results show that hydrogenation is a promising strategy to reduce both optical absorption and mechanical loss in amorphous silicon, and may help to fabricate the next generation of gravitational-wave detectors with improved sensitivity. |
Thursday, March 9, 2023 1:54PM - 2:06PM |
T34.00013: Role of hydrogen in amorphous silicon – new mechanism of suppressing photon absorption Ruinan Zhou, Manel Molina-Ruiz, Gabriele Vajente, Alena Ananyeva, Thomas H Metcalf, Raymond C Robie, Xiao Liu, Ashot Markosyan, Riccardo Bassiri, Martin M Fejer, Frances Hellman Amorphous silicon (a-Si) is an attractive candidate for photovoltaics, photonics, and dielectric mirror coatings for gravitational-wave detectors. Its use however is often limited by optical absorption due to its low band gap. Due to its disordered nature, carrier recombination and photon absorption are enabled by defects in the bonding network, which poses challenges to fabricating device-quality a-Si. Hydrogenation has been shown to be effective in improving the electrical performance of a-Si. In spite of many advances made, the mechanism by which introduction of hydrogen to a-Si suppresses recombination and light absorption remains elusive. It is widely accepted that the improvement is related to hydrogen passivation of dangling bonds. However, here we report that despite only a tiny amount of hydrogen in our hydrogenated a-Si films and almost no change in dangling bond density after hydrogenation, the optical absorption in the infrared wavelength range is reduced by over 70%. We found that instead of forming bonds with undercoordinated Si, hydrogen promotes structural relaxation of the a-Si network, which in turn reduces the optical absorption. Our work provides a conceptual framework to better understand the photon absorption mechanisms in a-Si and how to suppress them. |
Thursday, March 9, 2023 2:06PM - 2:18PM |
T34.00014: Understanding dynamics and synthesis of spin defects in silicon carbide Cunzhi Zhang, Francois Gygi, Giulia Galli Controlling the creation of solid-state spin defects in solids remains one of the major challenges to fully realize their potential as qubits for quantum technology applications. We combined first-principles molecular dynamics and advanced sampling at finite temperature (T), together with constrained optimizations and DFT calculations at 0 K, to investigate the formation of a promising spin qubit in silicon carbide (SiC), the divacancy (VV). We used the Qbox code coupled with the suite of advanced sampling methods implemented in SSAGES and Quantum Espresso for our calculations. We identified the range of annealing T and Fermi level (doping) for which the formation of VV is favorable, starting from irradiated samples with Si and C mono-vacancies. We found that the creation of VV is easier in hexagonal than in 3C SiC due to a wider range of favorable annealing T and Fermi levels accessible in hexagonal samples. Our results highlight the importance of a detailed characterization of spin and charge transition states along transformation pathways, in order to understand the formation of spin defects during annealing processes. |
Thursday, March 9, 2023 2:18PM - 2:30PM |
T34.00015: Room temperature photoluminescence of bulk and doped Ge using an additional excitation source. Vijay A Gregory Over the past 50 years, silicon (Si) has been fundamental in the electronics industry. The stable oxide, silicon dioxide (SiO2) as well as the abundance of Si, has allowed for the growth of a multi-billion-dollar industry. If a proper light source could be achieved on Si it would revolutionize the photonics industry. Signal processing speed could be increased by orders of magnitude resulting in greater bandwidth in signal transmission. However, the limitations of Si prevent it from being used as an efficient light source. Germanium (Ge) can be used to create an on Si light source. Furthermore, it has been shown that doping can enhance the direct emission of Ge. In 2012, an electrically-pumped Ge diode laser was demonstrated but its efficiency was low. Understanding the luminescence properties of Ge while under high-injection conditions produced through external excitation could lead to new device designs and improvements in efficiency. In this research, we performed pump-probe experiments on bulk intrinsic and doped Ge using a 1550 nm CW external pump at a wide range of intensities combined with a 980 nm modulated probe at low intensity and measured the resulting luminescence spectrum. It was observed that direct band luminescence was enhanced with increasing pump intensity. |
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