Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P28: Dopants and Defects in Semiconductors VIIFocus

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Sponsoring Units: DMP FIAP DCOMP Chair: Joel Varley, Lawrence Livermore National Laboratory Room: 291 
Wednesday, March 15, 2017 2:30PM  3:06PM 
P28.00001: Defects and Small Polarons on Oxide Surfaces Invited Speaker: Anderson Janotti The presence and behavior of defects on the surface of oxides are central in many research areas, including catalysis, photochemistry, solar cells, and surface science in general. Experimental characterization of individual defects and their activities are challenging and often requires special preparations of the surface. Firstprinciples calculations based on density functional theory are a powerful tool to study surfaces and defects, often providing information on properties that are difficult to access experimentally. Here we discuss the behavior of defects on oxide surfaces from the perspective on firstprinciples calculations. We use the oxygen vacancy on TiO$_{\mathrm{2}}$ surface as example, a system that has been extensively reported in the literature. Using DFT with a hybrid function, we discuss surface states induced by the defect and localization of the excess charge in the form of small polarons [1,2]. We then discuss the effects of hydrogen and compare the behavior of these defects on the surface with that in the bulk [3]. We also compare our recent results with previous theoretical studies and experiments. Finally, we generalize the findings on TiO$_{\mathrm{2}}$ to the surfaces of other oxides. [1] M. Setvin, C. Franchini, X. Hao, M. Schmid, A. Janotti, M. Kaltak, C. G. Van de Walle, G. Kresse, and U. Diebold, Phys. Rev. Lett. \textbf{113}, 086402 (2014). [2] P. G. Moses, , A. Janotti, C. Franchini, G. Kresse, and C. G. Van de Walle, J. Appl. Phys. \textbf{119}, 181503 (2016). [3] A. Janotti, C. Franchini, J. B. Varley, G. Kresse, and C. G. Van de Walle, Phys. Status Solidi RRL \textbf{7}, 199 (2013). [Preview Abstract] 
Wednesday, March 15, 2017 3:06PM  3:18PM 
P28.00002: Quantum Monte Carlo study of the oxygen vacancy in vanadium dioxide Jaron Krogel, Ye Luo, Anouar Benali, Janakiraman Balachandran, Panchapakesan Ganesh, Olle Heinonen, Paul R. C. Kent Transition metal oxides (TMO's) have presented fundamental challenges for accurate fully ab initio calculations. Vanadium dioxide, in particular, has remained difficult to describe in a consistent and predictive manner for leading theoretical approaches, such as density functional theory (DFT). Quantum Monte Carlo (QMC) methods present an attractive alternative to DFT as they have been shown to be accurate for a range of TMO's, including bulk phases of VO$_2$. In this work we expand the application of QMC to inquire into the behavior of isolated oxygen vacancies in VO$_2$, carefully controlling for known sources of systematic error. We compare our preliminary results with broadly used DFT approximations including hybrid functionals and HubbardU type approaches. [Preview Abstract] 
Wednesday, March 15, 2017 3:18PM  3:30PM 
P28.00003: A linear scaling ab initio study of impurities and the metalinsulator transition in doped silicon Yang Wang, Conrad Moore, Markus Eisenbach, Yi Zhang, KaMing Tam, Mark Jarrell Impurities in silicon are responsible for the states in the band gap, and they play a key role in modulating the conductivity of semiconductor devices. In this presentation, we discuss our computational efforts to investigate the metalinsulator transition of these states, particularly, in Titanium and Sulfur doped silicon. Both are potential highly efficient photovoltaic materials and are also targeted materials for the study of Mott and Anderson localization. We introduce a supercell scaling ansatz to identify the transition and validate it on the singleband Anderson model. We then apply the locallyself consistent multiple scattering (LSMS) method to the calculation and characterization of these midgap states. The LSMS method is a linear scaling ab initio method based on real space multiple scattering theory and Green function technique, and is one of the few scientific application codes capable of demonstrating performance beyond the petascale. To accurately describe the single impurity states, we employ large unit cells with more than 10,000 atomic sites. [Preview Abstract] 
Wednesday, March 15, 2017 3:30PM  3:42PM 
P28.00004: Comparing deep level transient spectroscopy with firstprinciples calculations Chris Van de Walle, Darshana Wickramaratne, Cyrus Dreyer, JimmyXuan Shen, John Lyons, Audrius Alkauskas Deep level transient spectroscopy (DLTS) has been used extensively to determine the ionization energy and capture cross sections of defects in semiconductors. We examine the standard formulation used to analyze DLTS measurements, and perform firstprinciples calculations of ionization energies and nonradiative capture coefficients using density functional theory with a hybrid functional. A critical evaluation highlights discrepancies that can arise in the analysis of DLTS measurements. We apply our analysis to gallium vacancy complexes and impurities in GaN. The ionization energy extracted from a DLTS measurement includes a barrier for nonradiative capture. Our calculations show this barrier is unique to each defect and can be as large as 0.6 eV. The barrier can also have a strong temperature dependence. We comment on the consequences of failing to account for this barrier when interpreting activation energies extracted from DLTS measurements. [Preview Abstract] 
Wednesday, March 15, 2017 3:42PM  3:54PM 
P28.00005: Combining DFT, Cluster Expansions, and KMC to Model Point Defects in Alloys N. A. Modine, A. F. Wright, S. R. Lee, S. M. Foiles, C. C. Battaile, J. C. Thomas, A. Van der Ven 
Wednesday, March 15, 2017 3:54PM  4:06PM 
P28.00006: Abstract Withdrawn Charged defects pose serious challenges to atomistic calculations based on the use of periodic boundary conditions. In this paper, a general atomistic polarizable model to correct energies of charged defects in supercell {\it first principles} calculations is introduced and validated on bulk, surface, and aperiodic systems. The energy scheme relies on atomistic model structures, a minimal set of parameters to reproduce the dielectric properties, and an affordable numerical method to solve the electrostatic problem of a localized charge embedded in a periodic material system and compensated by a uniform charge background. The corrective scheme is applied to charged defects in model bulk systems, and to the Cl$^$ vacancy defect in the bulk and at the surface of NaCl crystals. An application to charged sulfur vacancy defects in 2D MoS2 is used to illustrate the complexity of the electrostatic problem in the case charged aperiodic systems, and to demonstrate the versatility, efficiency, and accuracy of our method 
Wednesday, March 15, 2017 4:06PM  4:18PM 
P28.00007: ManyBody Theory for PointDefect Effects on ElectronEnergyLoss and Optical Absorption Spectra in Layered Semiconductors Danhong Huang, Andrii Iurov, Fei Gao, Godfrey Gumbs, David Cardimona For a layered and doped semiconductor system, in the presence of point defects by proton radiation, the changes of both electronenergy–loss and optical absorption spectra can theoretically be related to the Coulomb renormalized polarization and opticalresponse functions, respectively. The ladder approximation has been employed first for calculating the pointdefect induced vertex correction to the Feynman’s bubble diagram for the polarization function of noninteracting subband electrons in layered semiconductors. Based on the randomphase approximation, the intralayer screening from both intrasubband and intersubband electronic excitations in the system, as well as the interlayer Coulomb coupling of electrons, are also taken into account by computing the inverse dielectricfunction matrix and solving the selfconsistent Dyson equations at the same time. [Preview Abstract] 
Wednesday, March 15, 2017 4:18PM  4:30PM 
P28.00008: Charge Carrier Scattering with Defects from FirstPrinciples Calculations ITe Lu, JinJian Zhou, Luis Agapito, Marco Bernardi Phonons and defects are the main sources of charge carrier scattering in materials. While firstprinciples electronphonon calculations are being actively studied, electrondefect scattering has not been explored extensively from first principles. Scattering due to defects is important both because defects are naturally present in materials and because it limits carrier mobility at low temperature, and at room temperature in highly doped samples. We discuss the formalism to compute electrondefect scattering from first principles. The main quantities in the calculation are the matrix elements of the defect perturbation potential in a KohnSham basis. Both the local perturbation potential due to electrons and ions and the nonlocal contribution from the pseudopotential are considered. We interpolate these matrix elements on fine girds to calculate the carrier relaxation time and low temperature mobility in silicon due to elastic scattering with neutral defects, such as vacancies and Frenkel pairs, using Fermi’s golden rule and the Born approximation. The development of efficient parallel algorithms for electrondefect calculations is also discussed. [Preview Abstract] 
Wednesday, March 15, 2017 4:30PM  4:42PM 
P28.00009: Origin of the distinct diffusion behaviors of Cu and Ag in covalent and ionic semiconductors SuHuai Wei, HuiXiong Deng, JunWei Luo, ShuShen Li Group IB elements Cu and Ag are important contact materials in semiconductor devices due to their low resistivity. However, they have shown puzzling diffusion behaviors in semiconductors: Cu diffuses much faster than Ag in covalent semiconductors like Si and GaAs, but Ag diffuses faster than Cu in more ionic IIVI semiconductors such as CdS and CdTe despite Ag has larger size than Cu. In this work, we reveal the underlying mechanisms of these different diffusion behavior by combining the firstprinciples calculations and group theory analysis. We identified the important roles of the crystal symmetry enforced sd coupling as well as the Coulomb energy and strain energy in determining the diffusion behaviors of Cu and Ag in the covalent and ionic semiconductors. We show that the sd coupling is absent in pure covalent semiconductors but increases with the ionicity of the zincblende semiconductors, and the coupling strength of Cu, owing to its higher d orbital energy, is much larger than Ag. In conjunction with the Coulomb interaction and strain energy, the sd coupling is able to explain all the diffusion behaviors of Cu and Ag in covalent to ionic semiconductors. H.X. Deng, J.W. Luo, S.S. Li, S.H. Wei, Phys. Rev. Lett. 117, 165901 (2016). [Preview Abstract] 
Wednesday, March 15, 2017 4:42PM  4:54PM 
P28.00010: Ab initio calculations of surface effects on Raman spectra of BPcodoped Si nanocrystals Joshua C. Neitzel, James R. Chelikowsky We use a realspace pseudopotential method implemented within density functional theory to calculate Raman spectra for Bdoped, Pdoped, and (B,P)codoped Si nanocrystals. We consider the role of dopant location, bonding structure, and nanocrystal size on these spectra. We find that features of the Raman spectra can be correlated with the dopant structure. [Preview Abstract] 
Wednesday, March 15, 2017 4:54PM  5:06PM 
P28.00011: Improvisation of photocurrent of bismuth vanadate (BiVO$_{\mathrm{4}})$ photo catalyst by Nb doping Hori Pada Sarker, Muhammad N. Huda Bismuth vanadate (BiVO$_{\mathrm{4}})$ is a good candidate as a photo catalyst for hydrogen evolution via water splitting and environmental remediation by degrading chemical pollutants. The conduction band minima of BiVO$_{\mathrm{4}}$ is mostly composed of V  3d bands which are very localized. Due to this localization nature of the V  3d band, the charge carriers transport is not easy within BiVO$_{\mathrm{4}}$. In this present study, density functional theory (DFT) has been used to study the Nb incorporation on both cation site of bismuth vanadate with and without oxygen vacancy. It shows that Nb incorporation on both cationic site replaces the V  3d localized band by the less localized Nb  4d bands. Nb doping in BiVO$_{\mathrm{4}}$ creates a shallow donor level which is beneficial for charge carrier transport. The solubility of Nb in BiVO$_{\mathrm{4\thinspace }}$has also been studied and it shows high solubility of Nb in BiVO$_{\mathrm{4}}$ with both oxygen rich and poor growth condition. Finally, the single phase stability of BiVO$_{\mathrm{4\thinspace }}$via the chemical potential landscape analysis will be presented. [Preview Abstract] 
Wednesday, March 15, 2017 5:06PM  5:18PM 
P28.00012: Pseudomorphic growth of Ge$_{\mathrm{1}}_{y}$Sn$_{y}$ (y $=$ 0.06  0.17) films and devices on Ge/Si(100) \textit{via} chemical precursors Patrick Wallace, Charutha Senaratne, Chi Xu, Patrick Sims, John Kouvetakis, Jose Menendez Epitaxial films of Ge$_{\mathrm{1}}_{y}$Sn$_{y}$~have been grown pseudomorphically on Gebuffered Si(100) using gassource molecular epitaxy. Ultralow temperatures (150200~$^{\circ}$ C) and low pressures in conjunction with specialized precursors such as Ge$_{\mathrm{4}}$H$_{\mathrm{10}}$~and SnD$_{\mathrm{4}}$~resulted in films with compositions (y $=$ 0.060.17). Thorough characterization illustrates that the thin films possess excellent crystal quality and low defectivites with thicknesses 39370 nm; these thicknesses match or exceed those previously reported for pseudomorphic films attained~\textit{via}~traditional growth methods. The introduction of P(GeH$_{\mathrm{3}})_{\mathrm{3}}$~during growth was used to achieve~\textit{in}~\textit{situ}~$n$type doping, SIMS analysis indicates uniform distributions of carriers with concentrations up to 1.7x10$^{\mathrm{19}}$~cm$^{\mathrm{3}}$. Prototype GeSn~\textit{pn}~diodes were fabricated and demonstrate the typical tunneling diode IV characteristics associated with this type of device structure. In contrast to typical MBE methods, pseudomorphic growth using this technique allows for scaleup and \textit{in situ} doping as needed for commercial realization. [Preview Abstract] 
Wednesday, March 15, 2017 5:18PM  5:30PM 
P28.00013: Using Scanning Microwave Impedance Microscopy (sMIM) to characterize defects in dopants and dielectrics in semiconductor devices Stuart Friedman, Yongliang Yang, Fred Stanke, Oskar Amster As semiconductor technologies adopt advanced designs and materials, it becomes critical to be able to characterize, at the nanoscale, dopant distributions, dielectric properties and interface and thinfilm quality. Scanning Microwave Impedance Microscopy (sMIM) is an atomic force microscope (AFM) based electrical measurement technique that measures local permittivity and conductivity at nanoscale dimensions. It can also measure the capacitance of the tipsample junction or nanostructures. Nonlinear properties of samples and nanostructures can be probed by applying a bias to the sMIM tip and recording capacitancevoltage curves. This talk will present results of characterizing and imaging a number of materials and structures from advanced semiconductor technologies. Examples will include (1) quantifying the doping level and imaging the doping distributions of both Si and IIIV devices, and (2) quantifying dielectric properties including the use of capacitancevoltage curves to characterize defects in buried gate oxides. [Preview Abstract] 
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