Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A11: Defects in Semiconductors -- 1D, 2D, and Layered MaterialsFocus
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Sponsoring Units: DMP DCOMP FIAP Chair: Annemarie Exarhos, Lafayette College Room: BCEC 152 |
Monday, March 4, 2019 8:00AM - 8:12AM |
A11.00001: Nanoscale Conductivity Measurements of Biased Silicon Nanowires with Infrared Near-Field Optical Microscopy Clayton Casper, Earl T Ritchie, David J Hill, Taylor S Teitsworth, Samuel Berweger, James F Cahoon, Joanna M Atkin Vapor-liquid-solid (VLS) growth of Si nanowires (SiNWs) allows for precise control of dopant density and type. These encoded dopant superlattices have enabled microscopic diodes for a wide range of optoelectronic applications. However, performance of these diodes depends critically on the behavior of carriers at junctions, which is influenced by dopant activation, geometry, and defect states. Furthermore, junctions in SiNWs are abrupt (<100 nm), making it difficult to apply traditional characterization methods. Here we use mid-infrared scattering-scanning near-field optical microscopy (s-SNOM) to image the carrier distribution in axial p-i-n junction SiNWs in operando. The high spatial resolution (< 20 nm) allows us to directly measure the free-carrier concentration arising from not only the native doping, but also from band bending. Combined with finite element modeling, we can semi-quantitatively determine the local carrier concentration and mobility, and examine the effect of bias on junction lengths and space-charge regions. These measurements will demonstrate that s-SNOM can be used to study the I-V characteristics of SiNWs with unprecedented spatial resolution. |
Monday, March 4, 2019 8:12AM - 8:24AM |
A11.00002: Real space pseudopotential calculations for the Raman spectra of doped Si and C nanostructures Joshua C Neitzel, James Chelikowsky We use a real-space pseudopotential method implemented within density functional theory to calculate Raman spectra for doped Si and C nanostructures. We examine the role of dopant location, local structure, and quantum confinement on the Raman spectra. We contrast these nanoscale spectra with those of bulk crystals. |
Monday, March 4, 2019 8:24AM - 8:36AM |
A11.00003: Doping of Partially Saturated Nanothreads within Density Functional Theory Tao Wang, Vincent Henry Crespi A novel one-dimensional carbon nanomaterial, known as nanothreads, has recently been synthesized by slowly compressing crystalline, solid benzene from high pressure. A comprehensive advanced solid-state NMR analysis reveals that approximately a third of carbon atoms reside in the partially saturated structures, the degree-4 nanothreads, with isolated double bonds retained in the recovered sample. Some enumerated degree-4 structures, like IV-12 and IV-18, have much smaller distances between the double bonds than that in normal materials due to the rigid sp3 backbone, which leads to very dispersive bands near the Fermi level and may make these threads feasible to be doped. We investigated such doping computationally, using jellium models, alkali intercalation, and nitrogen substitution on the carbon backbone in both pristine and partially fluorinated IV-12 and IV-18 threads. Under doping, the IV-12 thread collapses to fully saturated structures, probably due to the strongly overlapping of the double bonds. There is no clear evidence for charge transfer in the pristine IV-18 thread, but the partially fluorinated IV-18 thread can be doped; this system may constitute a new type of conductive polymer. |
Monday, March 4, 2019 8:36AM - 8:48AM |
A11.00004: Stability of defects at MoS2/InAs hybrid heterostructures Zackary Santos, Pratik P Dholabhai Vertical van der Waals heterostructures created from two chemically different two-dimensional (2D) materials have made significant headway in the current electronic manufacturing landscape. They demonstrate enhanced electronic properties and have the potential to be used in high performance electronic devices. Among the various van der Waals heterostructures, molybdenum disulfide (MoS2) thin film on an indium arsenide (InAs) substrate has shown promising opto-electronic properties. This hybrid heterostructure gives stronger optical absorption properties than a 2D layer of graphene on InAs due to smaller equilibrium spacing. To realize the true potential of these heterostructures, it is imperative to understand not only their stability, but also the thermodynamic stability of various defects at the heterointerface. We have performed first principles density functional theory calculations to study MoS2(100)/InAs(111) heterostructures with two different terminations of the substrate. We will discuss the thermodynamic stabilities of In-terminated and As-terminated heterostructures and shed light on the stabilities of S, In, and As vacancy defects at the heterointerface. Overall, our results offer insights into the fundamental role of defects in van der Waals heterostructures. |
Monday, March 4, 2019 8:48AM - 9:00AM |
A11.00005: Modification of electronic properties of GaN monolayer by group III−VI dopants: A first-principles study Naresh Alaal, Iman Roqan We explored the electronic properties of 2D gallium nitride (GaN) monolayer doped with group III−VI elements, such as boron (B), carbon (C), phosphorous (P) and oxygen (O) , using a first-principles based density-functional theory approach. In the analyses, we consider that the doping atoms are substituted at Ga or N positions. Our results explains that electronic properties of 2D GaN are modified upon doping with the aforementioned elements. We found that 2D GaN retains semiconducting properties when a Ga or N atom is replaced with an equivalent-valence atom (B or P). On the other hand, 2D GaN displays spin-polarized behavior with a finite magnetic moment when an O (C) atom is substituted at the Ga (N) site. Conversely, the doped GaN exhibits n-type semiconducting behavior when Ga (N) is replaced with a C (O) atom. Moreover, the doped GaN shows direct band gap behavior based on the dopant type and concentration. Therefore, our calculations explore that 2D GaN electronic properties can be tuned, from those characteristic of a semiconductor to metal-like behaviors. These findings will help use this material in the fabrication of semiconductor optoelectronic and sprintronic devices, as well as in other applications. |
Monday, March 4, 2019 9:00AM - 9:36AM |
A11.00006: Integrating quantum emitters in low-dimensional materials with nanocavities Invited Speaker: Stefan Strauf It was recently shown that low-dimensional materials such as 1D single-walled carbon nanotubes (SWCNTs) as well as 2D materials such as transition-metal dichalcogenides (TMDCs) and hexagonal boron nitride (hBN) can host 0D-confined quantum emitters. These quantum emitters hold great promise for future quantum technologies, particularly through covalent sidewall functionalization of SWCNTs resulting in quantum |
Monday, March 4, 2019 9:36AM - 9:48AM |
A11.00007: Deterministic Quantum Emitter Formation in Hexagonal Boron Nitride via Controlled Edge Creation Joshua Ziegler, Rachael Klaiss, Andrew Blaikie, David Miller, Viva Horowitz, Benjamin J Aleman Quantum emitters (QEs) in 2D hexagonal boron nitride (hBN) are extremely bright, stable under harsh conditions, and have the potential for strong coupling to hybrid devices due to their 2D host crystal. However, due to the difficulty of precisely creating these QEs, this potential for coupling into hybrid devices has been difficult to utilize. Motivated by recent studies showing that QEs in hBN tend to form at edges, we use a focused ion beam (FIB) to mill patterns in hBN. We optically characterize these milled hBN sheets and find that optimal FIB parameters create single QEs with a nearly Poisson-limited yield of 35%, and a 94% chance of creating at least one QE. We use atomic force microscopy to understand why these parameters are optimal and find that single QE yield is highest with a smooth milling profile on smooth hBN. This technique dramatically broadens the usefulness and convenience of hBN QEs – enabling facile integration into optoelectronic devices to fully take advantage of the appealing hBN QEs. |
Monday, March 4, 2019 9:48AM - 10:00AM |
A11.00008: Quantifying the Effects of Sample Treatments on Quantum Emitters in Hexagonal Boron Nitride Stanley Breitweiser, Annemarie L Exarhos, Raj Patel, Jennifer Saouaf, Benjamin Porat, Lee Bassett Hexagonal boron nitride (hBN) has emerged as a leading two-dimensional van der Waals material for next-generation quantum technologies. In particular, recent studies have identified spin-dependent quantum emission from defect states within the bandgap of hBN, making it a promising platform for quantum information processing and sensing applications. These optical-frequency emitters are among the brightest known, but they display heterogenous properties and are poorly understood at the microscopic level. Confounding this, samples have undergone a variety of treatments in reported experiments - the two most common treatments being low-energy (keV) electron-beam irradiation and high-temperature (850C) annealing in inert gas - with only a qualitative understanding of their effects. Here we systematically and quantitatively study the effect of these treatments using an analytical model which relates pixel intensity distributions from large-area confocal photoluminescence images to the density and brightness distributions of emitter ensembles. The results inform future efforts to control the formation and stabilization of quantum emitters in hBN. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A11.00009: Stark shifts observed in single-photon emitters in hexagonal boron nitride Gichang Noh, Daebok Choi, Jin-Hun Kim, Dong-Gil Im, Yoon-Ho Kim, Hosung Seo, Jieun Lee Atomic defects, such as diamond NV-centers and SiC divacancies, have been widely studied as single-photon emitters, which are key ingredients of quantum information technology. Recently, two-dimensional (2D) materials are also found to host atomic defects that generate single-photons. Of particular interest is hexagonal boron nitride (h-BN) which possess single-photon emitters operating at room temperature. In this talk, we show the Stark-shift induced energy control of single-photon emitters in h-BN1). By fabricating van der Waals heterostructures of h-BN with graphene gates, we observe linear Stark shifts as large as 7 meV induced by an out-of-plane electric field. We propose possible defect structures with out-of-plane dipoles, which are supported by theoretical calculations. We will also present other types of Stark shifts which have quadratic components. These Stark shifts are measured not only at low temperatures around 10 K, but also at room temperature. Our results demonstrating the on-demand energy control of atomic defects in h-BN show the potential of 2D-based single photon emitters for quantum information applications. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A11.00010: Optical Properties of Defect-Laden Single-Layer Hexagonal Boron Nitride Tao Jiang, Volodymyr Turkowski, Talat S. Rahman By employing density functional theory (DFT) and time-dependent DFT (TDDFT), we study the electronic and optical properties of monolayers of pure (h-BN) and defect-laden hexagonal Boron Nitride dh-BN (with boron vacancy (VB), nitrogen vacancy (VN), boron substitution for nitrogen (BN), nitrogen substitution for boron (NB), carbon substitution for boron (CB) and carbon substitution for nitrogen (CN)). The DFT analysis traces the defect-induced changes to the orbital- and spin-projected density of states of h-BN and their implications for the optical properties of the system. The TDDFT results show that the long-range nature of the exchange-correlation kernel significantly affects the excitation energy, and hence the absorption and emission properties of the systems. We demonstrate that experimental data on the emission in dh-BN can be explained by the VN defects only. Namely, the conduction band-to-VN electron transitions give the dominant contribution to the photoluminescence spectrum, observed experimentally [1]. We discuss possible applications of the results in optoelectronic single-photon emitting devices. |
Monday, March 4, 2019 10:24AM - 10:36AM |
A11.00011: Dielectric environment effects on charged defects in 2D materials Dan Wang, Ravishankar Sundararaman Two-dimensional (2D) materials are the subject of significant ongoing research for technological applications in electronics, optoelectronics and quantum computing. These applications critically depend on the properties of charged defects, which has necessitated the development of computational methods to evaluate energies of charged defects in 2D materials. Such methods overcome the energy divergence from the Coulomb interaction of a charged defect with its periodic images and the compensating background charges. However, these methods do not easily account for the effects of substrates on charged defect properties, which is vital for realistic treatment of 2D materials that cannot be free-standing for most applications. We present a general technique for predicting properties of charged defects in 2D materials with substrates, bringing together accurate prediction techniques for free-standing charged defects with continuum solvation theories. Application of this method to defects in molybdenum disulfide (MoS2) on various substrates reveals how charge transition levels of these defects evolve with environmental screening effects and will guide the design of defects for 2D devices. |
Monday, March 4, 2019 10:36AM - 10:48AM |
A11.00012: Electrically tunable quantum emitters in an ultrathin graphene - hexagonal boron nitride van der Waals heterostructure Alessio Scavuzzo, Shai Mangel, Ji-Hoon Park, Sanghyup Lee, Dinh Loc Duong, Christian Strelow, Alf Mews, Marko Burghard, Klaus Kern The recent discovery of solid-state single-photon emitters in two-dimensional host systems has unveiled a huge potential for quantum information processing and integrated nanophotonics. |
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