Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V17: Semiconductor Surfaces and Nanostructures |
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Sponsoring Units: DCMP Chair: Dan Dougherty, North Carolina State University Room: LACC 306A |
Thursday, March 8, 2018 2:30PM - 2:42PM |
V17.00001: Self-assembled Iridium quantum dots on Silicon(110) surface Rasika Mohottige, Soumya Banerjee, Nuri Oncel Self-assembled quasi periodic Quantum Dots (QDs) were grown by depositing two monolayers of Ir on Si(110) surface. We investigated the physical and chemical properties of these QDs with the help of Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and X-ray Photoelectron Spectroscopy (XPS). STM images showed that the surface was covered with large terraces corrugated with quasi periodic superstructure of QDs. XPS data suggests that the terraces are made out of Ir and at the interface between Ir terraces and Si(110) surface, Ir-silicide forms. The shifts in position of the Ir 4f and Si 2p peaks associated with Ir-silicide were comparable with the previously known bulk Ir-silicides. |
Thursday, March 8, 2018 2:42PM - 2:54PM |
V17.00002: Tuning of 1D Plasmon properties in Au-induced quantum wires on Si(hhk) surfaces Zamin Mamiyev, Timo Lichtenstein, Christoph Tegenkamp, Herbert Pfnuer Gold-induced atomic wires on Si(hhk) surfaces possess intriguing properties of collective electron excitations, which are strongly responsive to the electronic state and also to structural motifs. The modification and control of plasmonic excitations in metallic nanowires are of particular interest due to their fundamental and technological importance. In this work, the effect of O2 and H2 adsorption on the plasmons in arrays of single [Si(557)-Au] and double chains of gold [Si(553)-Au] have been experimentally examined by an EELS with high resolution both in energy and momentum. Theoretical results show that oxygen and hydrogen atoms bind preferably not to the Au chains directly, but to adjacent Si-honeycomb chains (Si-HC) and Si-adatom rows (The latter exist only in Si(557)-Au). The Si-HC turns out to be mostly responsible for the plasmonic changes. While atomic H reduces the plasmon frequency on Si(553)-Au, as predicted theoretically, adsorbed oxygen leaves it unchanged. On the Si(557)-Au, however, a frequency increase is found to be induced by oxygen, indicating a change in band structure. Comparing the oxygen adsorption on Si(553)-Au and Si(557)-Au, both the structural motifs, as well as electronic distributions across the terraces play a role in plasmonic excitations. |
Thursday, March 8, 2018 2:54PM - 3:06PM |
V17.00003: Thermal Studies of Si-Ge Heterostructure Interfaces by Film-Wafer Bonding Qing Hao, Dongchao Xu, Sien Wang, Bo Xiao For a twist grain boundary (GB), previous studies suggest that interfacial thermal resistance (RK) has a strong dependence of the crystal misorientation at the GB. For heterostructure interfaces, the interfacial atomic structures and phonon transport are more complicated. In this study, Si thin films are hot pressed onto Ge substrates to represent a Si-Ge heterostructure interfaces formed in SiGe nanocomposites. The interfacial RK is measured using an offset 3ω method for varied crystal orientations. GB strain is also measured with Raman spectroscopy to reveal its connection with RK, along with interfacial structure characterization by transmission electron microscopy. Our detailed interfacial thermal studies can provide important guidance for interface engineering to tune the heat transport inside a material or device. |
Thursday, March 8, 2018 3:06PM - 3:18PM |
V17.00004: Non-invasive SOI gating of 2D electron systems on pristine hydrogen-terminated Si surfaces Luke Robertson, Bruce Kane Silicon has a variety of surface terminations in which surfaces states are passivated and where 2D electron or hole surface accumulation layers are possible through electrostatic gating. Because of the simplicity and high degree of perfection, we use a wet chemical treatment to terminate Si(111) surfaces with hydrogen and have developed techniques to probe 2D transport on these passivated surfaces. While other chemical terminations of different Si surfaces exist (i.e. Cl, Br, I), we have focused exclusively on H-Si(111), but are in process of extending our study to include H-Si(100) surfaces as their 2+2 valley degeneracy are more favorable platforms for quantum information processing. We are now developing techniques to probe pristine hydrogen-terminated Si(111) and Si(100) surfaces using a non-invasive SOI flip-chip gating method in which all device fabrication is performed on the SOI piece. Extremely high mobilities in excess of 300,000 cm2/Vs have been demonstrated in our devices, and further refinement of techniques to preserve the pristine nature of the terminated Si surfaces is expected to yield even higher mobilities. Architecture details and ohmic contact tests will be presented as well as ongoing low temperature device characterization measurements. |
Thursday, March 8, 2018 3:18PM - 3:30PM |
V17.00005: Selective deposition of polycrystalline diamond film on Si, SiNx, SiO2, AlN, GaN and Ti surface using hot filament chemical vapor deposition Raju Ahmed, Anwar Siddique, Jonathan Anderson, Mark Holtz, Edwin Piner Due to its promising high thermal conductivity, polycrystalline Chemical Vapor Deposited (CVD) diamond has received significant interest as a heat spreader in electronic devices. Selective deposition of polycrystalline diamond is proposed to realize its ultimate potential as an on-wafer layer for spreading heat. In this study, we report photolithography based selective seeding techniques and CVD polycrystalline diamond on semiconductors (Si, AlN, and GaN), dielectrics (SiO2, SiNx) and metal (Ti) surfaces. Selectivity and properties of the diamond films were evaluated with scanning electron microscopy (SEM), atomic force microscopy (AFM), surface profilometry and micro Raman spectroscopy. Selectivity of diamond growth on AlN and GaN were hampered by decomposition of the semiconductor in the CVD environment. A thin layer of dielectric mitigated this problem. Interdiffusion of carbon in Si and the dielectrics was observed from energy dispersive x-ray (EDX) study. For Ti, x-ray diffraction confirmed a thin layer of TiC at the interface between diamond and Ti. Successful seeding and selective growth of CVD diamond have been achieved for all surfaces on 100 mm substrate with feature size as small as 5µm. |
Thursday, March 8, 2018 3:30PM - 3:42PM |
V17.00006: Progress in Cesium-Free III-Nitride Photocathodes Based on Control of Polarization Charge Lloyd Bell, Emma Rocco, Jon Marini, Shouleh Nikzad, Fatemeh Shahedipour-Sandvik III-nitride photocathodes have many applications for ultraviolet (UV) detection; the wide bandgaps available in the AlGaN family provide intrinsic solar blindness, and the wavelength cutoff may be tuned by control of composition. Negative electron affinity (NEA) is desirable for these structures in order to maximize quantum efficiency (QE). Normally surface cesiation is used to create low or negative electron affinity; however, the resulting reactive surface must be protected from air during fabrication and use, necessitating a sealed-tube configuration. Cesium-free photocathodes would offer lower cost, improved robustness, and greater chemical stability, in addition to the major advantage of higher QE. We report on the use of polarization engineering in order to achieve permanent low electron affinity without the use of Cs. We will discuss progress in design, fabrication, and characterization of polarization-engineered III-nitride photocathodes. An important component of these designs is the use of N-polar GaN and AlGaN. The nitride polarity affects the interface and surface polarization charge, and the ability to achieve NEA depends critically on this charge. We will present results demonstrating high (>10%) QE for non-cesiated N-polar GaN photocathodes. |
Thursday, March 8, 2018 3:42PM - 3:54PM |
V17.00007: The effects of c-Si/a-SiO2 interface atomic structure on its band alignment: an ab initio study Fan Zheng, Hieu Pham, Lin-Wang Wang The crystalline-Si/amorphous-SiO2 (c-Si/a-SiO2) interface is an important system used in many applications. However, the question of how this interface band offset would be affected by the transition region thickness and its local atomic arrangement, has yet fully investigated. Here, by controlling the parameters of the classical Monte-Carlo bond switching algorithm, we have generated the atomic structures of the interfaces with various thickness, as well as containing Si at different oxidation states. Hybrid functional method, are used to calculate the electronic structure of the heterojunction. We find that although the systems with different thickness show quite different atomic structure near the transition region, the calculated band offset tends to be the same, unaffected by the detail interfacial structure. It is shown that our band offset calculation agrees well with the experimental measurements. When the reactive force field is used to generate the a-SiO2 and the c-Si/a-SiO2 interface, the band offset significantly deviates from the experimental values by about 1 eV. |
Thursday, March 8, 2018 3:54PM - 4:06PM |
V17.00008: Photogenerated carriers at defect states in polycrystalline GaN using sub-bandgap laser-excited scanning tunneling spectroscopy F.-M. Hsiao, M. Schnedler, V. Portz, Y.-C. Huang, B.-C. Huang, M.-C. Shih, C.-W. Chang, L.-W. Tu, C.-S. Chang, H. Eisele, R. E. Dunin-Borkowski, Ph. Ebert, Ya-Ping Chiu Photo-induced carriers at defect states in GaN layers dominates the performances of nitride-based compound devices. In this work, sub-bandgap laser-excited cross-sectional scanning tunneling microscopy and spectroscopy demonstrate a great potential to obtain photo-induced electronic properties at defect-rich GaN films under the illumination condition. A spectacular enhancement in the tunneling current at positive voltages is observed in the defect-rich GaN layers under illumination, resulting from the excitation of free charge carriers at defect states. Thus, sub-bandgap laser-excited scanning tunneling spectroscopy provides us an opportunity to characterize the existence of charge carriers at defect states and demonstrates the behavior of photo-induced carriers in GaN layers. |
Thursday, March 8, 2018 4:06PM - 4:18PM |
V17.00009: Comparing e-beam to magnetron sputtered a-Si with an eye toward eliminating Two-Level Systems Matthew Abernathy, Thomas Metcalf, Xiao Liu, Manel Molina-Ruiz It has previously been shown that amorphous silicon (a-Si) thin films can be produced that are free of tunneling Two-Level Systems (TLS) by e-beam depositing the films at elevated substrate temperatures, and there appears to be a strong correlation between the density of these films and the number of TLS. We have prepared higher-density films using magnetron sputtering at elevated temperatures comparable to those used in the e-beam studies. Here, we compare the atomic densities measured using RBS, and the number of TLS calculated using internal friction measurements at cryogenic temperatures of magentron sputtered a-Si flms to those of the e-beam prepared films. |
Thursday, March 8, 2018 4:18PM - 4:30PM |
V17.00010: STM-based lithography on chlorine-terminated Si(100) Robert Butera, Michael Dreyer Scanning tunneling microscopy (STM) based, hydrogen depassivation lithography is a proven technique for the fabrication of atomic-scale quantum devices in silicon for which a single atomic layer of hydrogen is utilized as a lithographic mask. To date, this device fabrication process has been focused almost exclusively on hydrogen-based chemistries. Here, we present results of our investigation into STM-based lithography on Cl-Si(100), in which we study the desorption of chlorine as a function of STM tip bias, current, and total dose at sample temperatures from 300-600 K. We identify several reactions induced on the surface and find a strong dependence of the chlorine desorption yield on temperature. We optimize the experimental parameters for lithographic patterning and discuss the use of chlorine atoms as a lithographic mask for future device fabrication utilizing halogen-based dopant precursor molecules. |
Thursday, March 8, 2018 4:30PM - 4:42PM |
V17.00011: Metastable states in the interface of constrained Zn dots and Si(111), and related physical phenomena Li-Chi Kao, Bo-Chia Huang, Shang-Jui Chiu, Ching-Shun Ku, Kuang Yao Lo A strategic magnetron radio frequency sputtering is performed to fabricate Zn nano dots coherently grown on Si(111) substrate from a liquid phase to a solid phase. The structural evolution of constrained Zn dots grown on Si(111) were systematically analyzed by a compensative optical methods (Reflective second harmonic generation (RSHG) and synchrotron XRD). Under kinetic-favoring growth, tiny Zn dots prefer arranging themselves with a tilted c-axis to the Si(111) substrate toward any of the sixfold in-plane Si<110> directions. Upon growth, Zn dots would evolve themselves to a metastable state with a smaller tilting angle toward selective <110> directions. Metastables states existing in the interface of partially constrained Zn dots and Si(111) suppress the development of complete relaxation and then the critical dot size of full relaxation would be extended. We analyzed the relaxation and reconstraint of Zn nanodots on Si(111) by the structural evolution of constrained Zn dots via thermal annealing. The competition between reconstraint and relaxation of Zn dots on Si(111) due to thermal disturbance, the influence of metastable states to the further relaxation of constrained Zn dots due to thermal budge. |
Thursday, March 8, 2018 4:42PM - 4:54PM |
V17.00012: Atomic and Electronic Structure of the In-Bi Bilayer on the Si(111) Surface× Cho-Ying Lin, Yu-Zhang Huang, Han-De Chen, Deng-Sung Lin Recently, several 2D III-V materials, such as GaBi, InBi, TlBi, TlSb, and TlN are predicted to be topological insulators. Using the synchrotron radiation core-level photoemission spectroscopy and scanning tunneling microscopy (STM) has been utilized explore the interface and structure evolution during the sequential growth of In and Bi on the Si(111) surface by molecular beam epitaxy. Growth of 1.0-ML Bi on In/Si(111)-(4 × 1) at room temperature result in BiIn-(4 × 2), Bi0.75In-(2 × 2) domains after post annealing below 400 °C. A phase transform to In0.75Bi-(2 × 2) is observed following annealing at 460 °C . With reverse growth sequence, Growth of 1.0-ML In on β-Bi/Si(111)-(√3 × √3) surface following by 460 °C annealing leads to the In0.75Bi-(2 × 2) structure. The apparent height between In0.75Bi-(2 × 2) and β-Bi/Si(111)-(√3 × √3) is 2.0 Å, in addition, the height difference between Bi0.75In-(2 × 2) and In/Si(111)-(4 × 1) is 2.7 Å. Scanning tunneling spectroscopy also shows that the Bi0.75In-(2 × 2) and In0.75Bi-(2 × 2) have different electronic properties. DFT calculation shows a small energy difference for the two structures. |
Thursday, March 8, 2018 4:54PM - 5:06PM |
V17.00013: Quantum interference of bimetallic Pb/Ag films on Si(111) Woojoo Lee, Siyuan Zhu, Hyoungdo Nam, Chih-Kang Shih A previous study on bimetallic Pb/Ag films on Si(111) performed by M. K. Brinkley, et. al. [1] using angle-resolved photoemission (ARPES) revealed a long phase-coherence length throughout the Pb and Ag films. This study verified the electronic coherence by comparing normal emission data with simulation result. However, quantum interference away from the gamma point was not reported. By growing high quality thin films of Pb/Ag/Si(111), whose surfaces were characterized using scanning tunneling microscopy, we found that for a film with an atomically uniform surface, ARPES data revealed clear band structures of Pb/Ag bimetallic system far from the gamma point with fine structures. We investigated the quantum interference between the electronic states originating from the Ag film and those originating from the Pb film. Implications on the superconductor-normal metal proximity effect are also discussed. [1] Brinkley, M. K., et al. Phys. Rev. Lett. 103, 246801 (2009) |
Thursday, March 8, 2018 5:06PM - 5:18PM |
V17.00014: Algorithm of Calculating Absolute Semi-polar Surfaces Energies of Wurtzite Crystal: An Example of GaN Jingzhao Zhang, Yiou Zhang, Junyi Zhu A complete knowledge of absolute surface energies with any arbitrary crystal orientation is important for the improvements of devices. It determines the crystal shapes of nanostructures. It is also crucial for thin film crystal growths and surface effect studies. However, obtaining accurate absolute energies is still a huge challenge for the semipolar surfaces of compound semiconductors, mainly resulting from the asymmetry of crystal structures, and complex reconstructions of the surfaces. Here we propose a general approach to calculate the absolute surface energies for semipolar surfaces of wurtzite materials, using first-principles calculations and taking GaN as an example. We mainly focused on two common surface families: a-family (11-2X) and m-family (10-1X). For all the surfaces calculated in this work, the estimated errors are within 1.5 meV/Å2, which justifies the applicability of our method. It is applicable and straight forward to apply this idea to other materials. Our approach provides a powerful tool to investigate high index surfaces and crystal shapes for compound semiconductors accurately. |
Thursday, March 8, 2018 5:18PM - 5:30PM |
V17.00015: Excitonic absorption and optical properties of ZnO films Nuwanjula Samarasingha Arachchige, Zachary Yoder, Stefan Zollner, Dipayan Pal, Aakash Mathur, Ajaib Singh, Rinki Singh, Sudeshna Chattopadhyay The analysis of excitonic effects on the optical properties of thin films is crucial for technological applications. Wide band gap materials like ZnO exhibit strong excitonic features in the dielectric function (ε). The influence of this excitonic absorption on ε was described by Tanguy. Here we demonstrate the behavior of excitons at interfaces in c-axis oriented ZnO thin films on Si and SiO2 substrates using visible/UV and FTIR ellipsometry. We also performed XRD, XRR, and AFM to characterize the structural properties of our ZnO films. The real and imaginary parts of ε in thin ZnO films on Si are much smaller than in bulk ZnO. We find that the excitonic enhancement decreases monotonically with decreasing film thickness and disappears in thin films. A similar behavior can be seen for ZnO films on SiO2 as a function of thickness. We will fit our ellipsometric spectra by describing the dielectric function of ZnO using the Tanguy model. We will analyze the dependence of the excitonic Tanguy parameters on film thickness and substrate material. |
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