Bulletin of the American Physical Society
2024 APS March Meeting
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session N03: Defects in Diamond and Other SemiconductorsFocus
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Sponsoring Units: DMP DMP FIAP Chair: Anderson Janotti, University of Delaware Room: L100C |
Wednesday, March 6, 2024 11:30AM - 12:06PM |
N03.00001: Revisiting the Formulation of Charged Defects in Solids Invited Speaker: Shengbai Zhang Defects are at the heart of microelectronics. However, calculating their properties has long been challenging due to errors associated with the use of supercell + compensating background charge. Starting with the original work on total energy of periodic system [1] and the recent work on innate vacuum level [2], we show that the popular correction on reference Fermi level amounts to a double counting. Next, we reveal the proper definition of defect charge such that, in a multipole expansion, the third-order quadrupole correction can be unambiguously defined. These allow us classify point defects into 3 categories: (i) those that maintain the bulk electron bonding network, such as a substitutional defect, for which first-order Madelung correction is sufficient, (ii) those, such as an interstitial or vacancy, for which the quadrupole correction is necessary, and (iii) those, such as a vacancy in diamond, for which even supercells of thousands of atoms are not sufficient due to a slow inverse-cell-size dependence of dielectric screening. All things considered, however, even the result of a 64-atom supercell converges to within 90 meV. |
Wednesday, March 6, 2024 12:06PM - 12:18PM |
N03.00002: Exploring Bulk 13C Nuclei at the Low Temperature and High Magnetic Field Regime Cooper M Selco, Kieren A Harkins, David Marchiori, Ashok Ajoy Large interacting spin systems approaching the thermodynamic regime have proven to be an interesting platform for a variety of applications such as quantum sensing and studies of spin transport. Hyperpolarized 13C nuclei in diamond are an excellent candidate for such experiments because of their several-second long coherence time which can be extended to 90s using a Floquet driving pulse sequence [1]. We have shown that this system can be used in high-field magnetometry and studies of spin transport [2], [3]. In these experiments, the 13C nuclei are first hyperpolarized via NV centers at low field and then shuttled to higher magnetic field to perform experiments with high chemical resolution. |
Wednesday, March 6, 2024 12:18PM - 12:30PM |
N03.00003: Photocurrent mapping in optoelectronic diamond devices Alexander A Wood, Daniel J McCloskey, Artur Lozovoi, Russell M Goldblatt, Kaih T Mitchell, David A Broadway, Christopher T Lew, Brett C Johnson, Jean-Philippe Tetienne, Carlos A Meriles, Andy M Martin Diamond has remarkable properties that make it a promising semiconductor material for high-efficiency and high-power electronic devices. However, materials synthesis challenges and impurities, notably nitrogen, frustrate efforts to realize optimal diamond devices. On the other hand, some optically-active defect center impurities offer the possibility of in-situ characterization. Here, we use charge-sensitive optical microscopy of nitrogen-vacancy (NV) centres and photocurrent measurements to investigate the generation and propagation of charges flowing in diamond. We image photocurrent by detecting charge state conversion of NV centres, while electrically monitoring the generated photocurrent. Using optical initialization protocols, we can tailor the charge state of nitrogen impurities in the diamond on demand, and observe drastically different photocurrent and images of the current flow, ranging from narrow filaments in a space-charge dominated regime to almost ballistic trajectories when the nitrogen is charge neutral. We can use light to engineer conducting channels and space charge regions ranging from diffraction-limited to hundreds of microns, offering the prospect of reconfigurable, wide bandgap designer optoelectronics. We anticipate our approach might be extended to probe other insulators (e.g., SiC, GaN) or lower-bandgap semiconductors (GaAs, Si) relevant to present electronic technologies. |
Wednesday, March 6, 2024 12:30PM - 12:42PM |
N03.00004: Solvated Electrons at the Diamond-Water Interface: Insights from NV Centers Kang Xu, Daniela Pagliero, Gustavo Lopez, Nicolas Giovambattista, Abraham Wolcott, Carlos A Meriles Solvated electrons in water, the simplest ion in chemistry, have garnered significant interest for their applications in catalysis, biology, and electrosynthesis. Diamond, being chemically inert in aqueous conditions, has been shown to generate solvated electrons with ultraviolet light illumination and subsequent chemical transformations have been confirmed. In this study, we show that near-surface nitrogen vacancy (NV) centers can inject both electrons and holes into ultrapure water at the diamond-water interface through a process of photoionization and charge migration. Using a specially designed diamond membrane-water-electrode cell, we observed photocurrents ranging from tens of femtoamps to picoamps using a bias voltage and green laser excitation. The photocurrent exhibits wavelength-dependent characteristics associated with a charge cycling ionization mechanism and can be modulated by laser power and bias voltage. These findings establish the NV center as a viable source of solvated electrons and potentially expands NV diamond as a substrate for chemical reactions. DFT calculations at the diamond-water interface elucidate the mechanism of charge injection/solvation and reinforce the experimental observations. Future work with the diamond-water interface includes demonstrating in-situ carrier sensing through measurements with the NV centers' T1 and T2 times. |
Wednesday, March 6, 2024 12:42PM - 12:54PM |
N03.00005: First-principles calculation of the Stark shift for the NV center in diamond Louis Alaerts, Yihuang Xiong, Alp Sipahigil, Sinead M Griffin, Geoffroy Hautier Point defects in semiconductors are promising candidates for several applications in quantum information sciences such as quantum computing, communication or sensing. Acting as single-photon sources, they provide the robust spin-photon interface needed for the distribution of entanglement in quantum networks. However, mechanical and electrical fluctuations in the vicinity of the defects will cause a shift of their optical zero-phonon-line (ZPL), an effect known as spectral diffusion. Spectral diffusion is a major technological issue in the deployment of high-performance quantum defects. Stark shift caused by stray electric field is usually considered as the main cause of spectral diffusion. Here, I will present the results of our density functional theory (DFT) calculations of the Stark shift on the negatively charged nitrogen-vacancy (NV) center in diamond. Using a slab model, we monitor the Stark shift by calculating the energy difference between the ground-state and the excited-state as a function of an applied electric field. We discuss the methodological challenges involved with charged slabs and compare our results with our own and previous computations using Modern theory of polarization. We discuss the advantages of the slab approach and issues with the Modern theory of polarization approach. We also compare the effect of different functionals including hybrids, compare to experimental data and provide a perspective of Stark shift computations on other quantum defects. |
Wednesday, March 6, 2024 12:54PM - 1:06PM |
N03.00006: Effective mass approximation for spatial structures of two different single acceptors imaged by STM: bismuth in silicon and manganese in indium antimonide Julian Zanon, Michael E Flatté Impurities are known for introducing discrete energies in the band gap of their semiconductor hosts caused by localized states. Interestingly, those states could be qubits platforms controlled by external electric fields [1]. Comprehending spatial structures of these acceptors, such as energy exchange and density of states (DOS), is crucial for manipulating them [2]. With STM results [3], this work characterizes a single Bi acceptor state in Si in the effective mass approximation. Using ref.[4] we solve analytically the spherical Luttinger-Kohn Hamiltonian in the zero-range potential. Following that, a cubic symmetric wave-function is constructed which at different (001) planes shows a square-like shape for the DOS due to a bigger contribution of d-like states. The results are similar to the STM images, giving support for their acceptor nature. Furthermore, we extend these calculations to describe a magnetic Mn acceptor in InSb, and the results are compared with STM images from [5]. |
Wednesday, March 6, 2024 1:06PM - 1:18PM |
N03.00007: High-pressure Thermoelectric properties of ZnAs and CdAs Zakariae Darhi, Ashima Rawat, Ravindra Pandey, Larbi Elfarh Applying pressure is an effective method for understanding the evolution of the thermoelectric properties and is important for exploring novel applications of semiconducting materials. In this talk, we present the results of the bulk and doped- CdAs and ZnAS obtained using density functional theory. The effect of high pressure on the structural and electronic properties will be assessed in terms of the lattice constant, band structure, density of states and the figure of merit ZT of these semiconducting materials. |
Wednesday, March 6, 2024 1:18PM - 1:30PM |
N03.00008: Origin of defect intolerance in low-symmetry semiconductors Menglin Huang, Shanshan Wang, Shiyou Chen Defect tolerance has been usually observed in semiconductors with an empirical rule which shows (i) antibonding states in the valence band maximum (VBM) and (ii) bonding states in the conduction band minimum (CBM). However, the defects in some novel low-symmetry semiconductors do not follow this rule. For instance, experiments revealed the defects in low-symmetry semiconductor antimony selenide are intolerant, i.e., various deep levels and short carrier lifetime have been measured, although the Sb 5s-Se 4p antibonding and Sb 5p-Se 4p bonding states exist in the band edges. Through first-principles electronic structure calculations, we attribute this phenomenon into three progressive aspects: (i) inequivalent atomic sites complicates the defect transition levels; (ii) "defect-correlation" behavior promotes the formation of deep-level defects; (iii) structural metastability and phonon anharmonicity enhance the nonradiative recombination. These results suggest the defect tolerance in low-symmetry semiconductors should be reassessed. |
Wednesday, March 6, 2024 1:30PM - 1:42PM |
N03.00009: Designing carbon-based defects in icosahedral alpha boron from first principles Yeonsoo Cho, Jelena Sjakste, Nathalie Vast We propose a new material, alpha boron as a host for quantum defects. Indeed, the insertion of carbon atoms has been shown to facilitate the formation of the alpha phase, hitherto known to be metastable with respect to the beta phase of boron [1]. |
Wednesday, March 6, 2024 1:42PM - 1:54PM |
N03.00010: Ab-initio study of the energy competition between $Gamma$ and K valleys in bilayer transition metal dichalcogenides Samuel W Olin, Wei-Cheng Lee, Erekle Jmukhadze, Allan H Macdonald Moir'e engineering in two-dimensional van der Waals bilayer crystals has emerged as a flexible platform for controlling tunable strongly correlated electron systems. The competition between different valleys for the band extremum energy position in the parent layers is crucial in deciding the qualitative nature of the moir'e model since it controls the physics of the moir'e minibands. Here we use density functional theory to examine the competition between K and $Gamma$ for the valence band maximum in homo- and hetero-bilayers formed from the transition metal dichalcogenides (TMD), $ extrm{MX}_2$ where $ extrm{M}= extrm{Mo}, extrm{W}$ and $ extrm{X}= extrm{S}, extrm{Se}, extrm{Te}$. We shed light on how the competition is influenced by interlayer separation, which can be modified by applying pressure, by external gate-defined electric fields, and by transition metal atom $d$-orbital correlations. Our findings are related to several recent experiments, and contribute to the development of design rules for moir'e materials. |
Wednesday, March 6, 2024 1:54PM - 2:06PM |
N03.00011: Modulation of optical selection rules in twisted transition metal dichalcogenide heterobilayer. Wei Li, Gautam Jha, Thomas Brumme, Thomas Heine TMDCs of group 6 transition metals MX2 (M = Mo, S, X = S, Se) exhibit layered structures with pronounced interlayer interactions, ideal for studying interlayer excitons in their van der Waals heterostructures. As their heterobilayers are incommensurable, moiré structures are present even if stacked without a twist angle. However, a comprehensive understanding of spin-valley physics at the moiré scale and its modification via twisted angles is yet to be fully explored. In this work, we explored the structural and electronic properties of these heterobilayers as function of the twist angle. We observe significant lattice reconstruction involving in- and out-of-plane relaxations, which strongly depend on the twist angle. This leads to different excitonic behaviour when compared to high-symmetry stackings. To gain a deeper insight into their excitonic behaviors, we examine the spin (Sz) and orbital (Lz) degrees of freedom of low-energy bands. We find that these depend on the consisting layers, and can be further modified by twist angles. Notably, the lattice reconstruction at small twist angles modulates the moiré minibands resulting in different optical selection rules. This implies that the optical selection rules in heterobilayers are determined not only by the high-symmetry stackings, but also by the relaxation effect in the moiré superlattice. In conclusion, we show how the twist angle as a new degree of freedom can be utilized to manipulate the interlayer excitons in the moiré structures. |
Wednesday, March 6, 2024 2:06PM - 2:18PM |
N03.00012: Langevin Dynamics/Monte Carlo Simulations of Structural and Dielectric Modulations of Moire Materials Steven B Hancock, David P Landau, Yohannes Abate We have developed a fast and flexible computational scheme to calculate the complex valued, frequency dependent dielectric function of correlated materials. We use an atomistic bilayer model that includes phenomenological bond and bond-angle interactions, as well as empirical inter-layer interactions for layered heterostructures. Such systems are then subject to an oscillating external electric field representing an AFM tip. We simulate systems of unit cells with fluctuating boundary conditions using Langevin dynamics. We show how our methodology couples with Monte Carlo methods to give us nanoscale insight into both the dielectric modulation and structural transformation of Moiré patterned two-dimensional transition metal dichalcogenides. We show the formation of stress domains that vary widely in shape and configuration with regard to inter-layer couplings. Such patterns are then keenly compared to relevant experimental results on the same systems. |
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