Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H11: Defects in Semiconductors -- Quantum MaterialsFocus
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Sponsoring Units: DMP DCOMP FIAP Chair: Cyrus Dreyer, Stony Brook University Room: BCEC 152 |
Tuesday, March 5, 2019 2:30PM - 2:42PM |
H11.00001: Scaling Study of Disordered Antiferromagnetic Systems of Acceptors in p-Type Semiconductors Adam Durst, Ali Hyder We consider the low temperature magnetic properties of a system of randomly-distributed interacting acceptor atoms in a p-type semiconductor. For the equivalent n-type system, where donor interactions are well described by a spin-1/2 Heisenberg model with a single antiferromagnetic exchange coupling that varies exponentially with donor separation, the classic work of Bhatt and Lee [Phys. Rev. Lett. 48, 344 (1982)] provides an iterative numerical procedure for discarding irrelevant high energy excitations of strongly interacting donor pairs while renormalizing the remaining donor couplings. Due to valence band degeneracy and spin-orbit coupling, acceptor interactions are known to be more complex. Recent computations thereof suggest a six-level energy spectrum characterized by five distinct coupling parameters and a nontrivial degeneracy structure. By employing an interaction model that respects this degeneracy structure, we extend the Bhatt-Lee renormalization procedure to the acceptor case, studying the evolution of the distribution of exchange couplings, and calculating magnetic susceptibility, as a function of decreasing temperature. Results are compared with that of spin-1/2 and spin-3/2 Heisenberg models. |
Tuesday, March 5, 2019 2:42PM - 2:54PM |
H11.00002: Theory of Hyperfine Interactions and Electrically Detected Magnetic Resonance (EDMR) for Phosphorus-Doped Silicon Nicholas Harmon, Michael Flatté EDMR is a useful tool to sensitively study a spin pair’s local environment as well as spin-dependent recombination. Theoretical treatments have focused on resonances originating from differences between g-factors of two recombining spins [1]. Recently hyperfine interactions were included but in a classical manner [2]. We present a theory of EDMR where transitions take place via differences in g-factor or hyperfine interactions. The stochastic Liouville formalism is suited to account for hyperfine interactions involving multiple nuclei where each nuclear spin is a quantum spin. For a single spin-1/2 nucleus, expressions for resonances at any field are determined and agree with most measured resonances in phosphorous-doped silicon [3]. Comparisons between the model and observations lead to new understandings of the defect-induced recombination pathways. |
Tuesday, March 5, 2019 2:54PM - 3:06PM |
H11.00003: The Interplay among Localization Spin-Orbit Coupling and Ferromagnetism in the Diluted Magnetic Semiconductor (Ga,Mn)As Yi Zhang, Unjong Yu, Hanna Terletska, Ka-Ming Tam, Mark Jarrell We combine the typical medium analysis and dynamical mean field approximation to study the electronic and magnetic properties of the diluted magnetic semiconductor Ga1-xMnxAs. We use the k.p model to describe the electronic structure of GaAs with spin-orbit coupling. By using the typical medium analysis, localization due to disorder induced by the Mn doping is appropriately captured, which allows us to study the interplay among the localization, spin-orbit coupling and ferromagnetism. This study can serve as a guidance to the more realistic first-principles calculation of Ga1-xMnxAs. |
Tuesday, March 5, 2019 3:06PM - 3:42PM |
H11.00004: Spontaneous defect formation on the polar surface of giant Rashba semiconductors BiTeX Invited Speaker: Weida Wu Defects in semiconductors are crucial for the performance of modern electronics. Although there are tremendous progress on theoretical understanding of defect formation and kinetics in functional materials, visualizing the kinetics of the defect formation remains a great challenge. Herein, we report an exciting discovery of spontaneous formation of point defects below room temperature on the surface of polar semiconductors BiTeX (X=Cl, Br and I), where giant Rashba splitting of bulk bands was reported. The defect density increases over three order of magnitudes when the surface temperature increases from ~10 K to room temperature. Our scanning tunneling microscopy studies reveal formation of Frenkel pairs of Bi vacancies and interstitial Bi atoms, followed by the formation of BiTe antisites. Combined with first principle calculations, our results reveal a significant reduction of formation energy of Frenkel pairs due to surface band bending of polar surface. Our results demonstrate a dramatic modulation of defect formation via surface bending of polar surface, which is crucial for the potential technological application of giant Rashba systems. |
Tuesday, March 5, 2019 3:42PM - 3:54PM |
H11.00005: 3D imaging and manipulation of subsurface selenium vacancies in PdSe2 Giang Nguyen, Liangbo Liang, Qiang Zou, Mingming Fu, Akinola Oyedele, Bobby G Sumpter, Zheng Liu, Zheng Gai, Kai Xiao, An-Ping Li We report 3D imaging and manipulation of individual Se vacancies in PdSe2 using a STM. By imaging the characteristic charge rings of defects arising from a tip-induced band bending effect, we first determine the lateral and depth location of VSe precisely in the 3D lattice. We then use a STM tip as a movable electrostatic gate to manipulate VSe by reversibly switching the charge states of defects between neutral and negative states. We find a slightly higher bias voltage (~2.0 V) can trigger vacancy migrations, which allows us to demonstrate both direct “writing” and “erasing” of atomic defects from a particular lattice site in PdSe2. The results are corroborated by first-principles calculations that reveal the formation energy and diffusion barriers of Se vacancies in PdSe2. This work opens an opportunity for defect engineering at the atomic level to achieve controlled phase transformations, or on-demand switchable states for such as neuromorphic computing and quantum bits. |
Tuesday, March 5, 2019 3:54PM - 4:06PM |
H11.00006: Colossal thermopower from defect-induced in-gap states in FeSb2 Qianheng Du, Cedomir Petrovic The thermoelectric properties of FeSb2 are attracting attention due to its colossal thermopower and record-high thermoelectric power factor. Although this colossal thermopower was attributed to phonon-drag effect, the factors that affect the phonon-drag effect remains unclear and further. By changing the amount of defects in different FeSb2 crystals we show that thermopower maxima around 10 K change between relatively small 14 μV/K and colossal values of about 20 mV/K. The effect of crystallographic defects and impurities on the colossal thermopower coefficient is studied in single crystals of FeSb2. From the Hall effect, all the crystals show clear two-bands behavior. Defect-induced vacancy band with low Hall mobility dominates the thermal transport. Defects influence considerably phonon mean free path and low mobility band carrier concentration, revealing the source of the in-gap states that govern thermopower size. Our results explain the strong sample dependence of Seebeck coefficient in FeSb2 crystals and give a possible way to furtherly improve the thermal performance of this correlated semiconductor. |
Tuesday, March 5, 2019 4:06PM - 4:18PM |
H11.00007: Anisotropic defects and assisted scattering in InAs/GaSb superlattices FRANCESCA CAROSELLA, Hermann Detz, Gérald Bastard, Robson Ferreira Heterostructures containing antimonide-based compounds received in the last decade much attention because of their potential for designing new devices. Moreover, some InAs/GaSb heterostructures are also topological insulators thus attracting interest for fundamental research. We performed a thorough multi-scale study of the structure and electronic states of InAs/GaSb surperlattices (SL). We have implemented the envelope function formalism for the calculation of the electronic states in these SL, taking into account the strong coupling between conduction and valence states. To improve the description of interface roughness, we performed atomistic simulations (using empirical interaction potentials as well as a Monte Carlo based algorithm) of the growth of InAs/GaSb short-period SL. In particular, we found that the simulated growth of InAs on GaSb along the usual [0,0,1] axis leads to the formation of elongated islands, one ML height, one ML thick, but with a much bigger average length along the direction [1,1,0]. Finally, we tackled the effect of the interface disorder on the electronic properties of these heterostructures. To this end, we present a model to perturbatively evaluating scattering rates by an inhomogeneous ensemble of defects with such a particular aspect ratio. |
Tuesday, March 5, 2019 4:18PM - 4:30PM |
H11.00008: Scanning Tunneling Microscopy Studies of Er Adatoms on GaAs (110) Rebekah Smith, Anne Benjamin, Kevin Werner, Enam Chowdhury, Jay A Gupta Rare earth dopants in III-V semiconductors are of interest as high quality optical sources due to the preservation of sharp intra-f-shell transitions. Here we investigate Er interactions with host GaAs (110) surface with atomic resolution using STM. Er atoms were deposited via electron beam evaporation onto the GaAs surface at 5 K. We find three different Erad configurations with varying abundance upon deposition, each with a different surface site location. All three configurations exhibit long-range depressions in STM topographic images, attributed to band bending associated with a positive adatom charge state. Individual Er adatoms can be switched between these states by applying a positive voltage pulse with the STM tip. Tunneling spectroscopy on Er adsorbed at the interstitial sites reveals prominent states within the GaAs bandgap, but no evidence of sharp f-shell transitions inferred from bulk optical studies. We also form substitutional ErGa by applying a larger positive voltage pulse. Substitutional Er appears neutral, which we attribute to it being isoelectronic with Ga. We will also present preliminary studies with concurrent optical excitation. Shifts in Er defect states are interpreted as a surface photovoltage effect. |
Tuesday, March 5, 2019 4:30PM - 4:42PM |
H11.00009: A self-consistent site-dependent DFT+U approach for defects in transition metal oxides Chiara Ricca, Iurii Timrov, Matteo Cococcioni, Nicola Marzari, Ulrich Aschauer
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Tuesday, March 5, 2019 4:42PM - 4:54PM |
H11.00010: Novel II-VI compound based organic-inorganic hybrid semiconductors: intrinsic properties, defects, and long-term stability Tang Ye, Margaret Kocherga, Andrei Nesmelov, Thomas A. Schmedake, Yong Zhang The hybrid structures in this study are a family of sub-nanoscale II-VI layers or chains interconnected or coordinated with smaller organic linkers.[1] They were shown to exhibit a very high degree of structural ordering (e.g., the most perfect man-made semiconductor superlattices), and a number of extraordinary properties such as much-greater-than-kT exciton binding energy, exceedingly strong excitonic absorption, and zero thermal expansion.[2,3] Comparison between Raman, PL and XPS spectra of freshly made and approximately 15-year old samples of a prototype hybrid structure β-ZnTe(en)0.5 have revealed defect related spectroscopy signatures that appear in both newly made defective samples and aged samples. Although the old samples typically show varying degree of degradation, some are found to be as pristine as high-quality freshly made samples. The study suggests that the initial state of the defect level is pertinent to the material’s long-term stability. This is a rare example of hybrid materials exhibiting recorded long-term stability. This study has a broad impact on the long-term stability of a wide range of hybrid materials, including perovskites. |
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