Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F11: Dopants and Defects in Semiconductors  TheoryFocus

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Sponsoring Units: DMP DCOMP FIAP Chair: John Lyons, Naval Research Lab Room: LACC 303A 
Tuesday, March 6, 2018 11:15AM  11:51AM 
F11.00001: Theoretical studies of defects in oxide thin films Invited Speaker: Ulrich Aschauer Coherent epitaxial strain in thin films and heterostructures can not only induce changes in the crystal structure but also affect the defect population within the thinfilm material. The effect can be understood in terms of redox reactions that accompany defect formation and lead to changes of the ionic radii around the defect. This talk will give an overview of the basic defect chemistry in strained materials, based mostly on results from density functional theory (DFT) calculations and highlight experimental observations of this coupling between mechanical deformation and the stoichiometry. We will also show how the charge state of a defect or more generally the valence of ions can be affected by different biaxial and isostatic strain states. 
Tuesday, March 6, 2018 11:51AM  12:03PM 
F11.00002: HSE hybrid functional tuned to generalized Koopmans condition for defect calculations in GaN Denis Demchenko, Michael Reshchikov Generalized Koopmans condition can be used to tune HSE hybrid functional to enforce the linearity of total energy with respect to the occupation. In such tuned HSE the defect state eigenvalues are equal to the electron addition energies. The latter are related to the optical transition levels. Therefore a Koopmans tuned HSE allows using the unoccupied defect state eigenvalues to calculate defect photoluminescence peaks. Lattice relaxation energies can be used to calculate zero phonon lines. This approach does not rely on any correction scheme for the electrostatic interactions in a charged supercell and is less sensitive to other artificial interactions. We describe the HSE tuning procedure based on the generalized Koopmans condition and demonstrate the accuracy of this approach using several acceptors in GaN. 
Tuesday, March 6, 2018 12:03PM  12:15PM 
F11.00003: Ab initio Calculation of Nonradiative Carrier Recombination in Cu_{2}ZnSnS_{4} JiQiang Li, ZhenKun Yuan, Shiyou Chen, Xingao Gong, Suhuai Wei Clarifying the nonradiative carrier recombination centers in photovoltaic materials is of both fundamental interest and technological significance. For a defect with considerable concentration in the semiconductor material, whether it is an effective recombination center and limits the photovoltaic efficiency should be quantitatively judged by its carriercapture cross sections, which are difficult to determine in both experiment and theory. The direct experimental measurement is often difficult, especially to identify the responsible defects, highlighting the importance of using an ab initio approach to clarify the situation. Here we use a recently developed method to effectively calculate the carriercapture cross sections of deeplevels defects in Cu2ZnSnS4. All the physical parameters are quantitatively determined based on the stateoftheart ab initio calculations, which makes the result more accurate and reliable. Furthermore, the microscopic mechanics of recombination and the favored growth conditions for highefficiency Cu2ZnSnS4 solar cells are also revealed. Similar calculations can be used for studying the influence of various defects on the photovoltaic performance of other solar cell materials, shedding light on the design of highefficiency solar cells. 
Tuesday, March 6, 2018 12:15PM  12:27PM 
F11.00004: Grownin beryllium diffusion in indium gallium arsenide: An ab initio, continuum theory and kinetic Monte Carlo study Wenyuan Liu, Siew Ann Cheong, Mahasin Alam Sk, Sergei Manzhos, Ignacio MartinBragado, Francis Benistant A roadblock in utilizing InGaAs for scaleddown electronic devices is its anomalous dopant diffusion behavior; specifically, existing models are not able to explain available experimental data on beryllium diffusion consistently. In this talk, we propose a more comprehensive model, taking selfinterstitial migration and Be interaction with Ga and In into account. Density functional theory (DFT) calculations are first used to calculate the energy parameters and charge states of possible diffusion mechanisms. Based on the DFT results, continuum modeling and kinetic Monte Carlo simulations are then performed. The model is able to reproduce experimental Be concentration profiles. Our results suggest that the FrankTurnbull mechanism is not likely, instead, kickout reactions are the dominant mechanism. Due to a large reaction energy difference, the Ga interstitial and the In interstitial play different roles in the kickout reactions, contrary to what is usually assumed. The DFT calculations also suggest that the influence of As on Be diffusion may not be negligible. 
Tuesday, March 6, 2018 12:27PM  12:39PM 
F11.00005: Magnetic Behavior of Asantisite Defect in Lowtemperature GaAs from Firstprinciples Bandstructure with Spin Orbit Interaction Mary Clare Escano, Yu Osanai, Masahiko Tani Study of defect’s nature in widegap semiconductor can give light into its use as THz detector/emitter. In lowtemperature GaAs (LTGaAs), a twostep photon absorption via midgap states is proposed to explain the LTGaAsbased PC’s detection of THz radiation when probed with 1.55μm probe laser. So far, within firstprinciples, the defect’s magnetic properties using realistic defect concentration (1.01.3%) and within the broken inversion symmetry of GaAs is still lacking. Here, DFT calculations on a 216atom GaAs bulk using hybrid exchange correlation functionals are conducted. The symmetry is accounted for by including spinorbit (SO) interaction via projector augmented wave method. We found that at the level of DFT+SO, a 1.46eV bandgap and 0.337eV splitoff band at Γ are obtained in agreement with experiments (1.43eV, 0.341eV). Among the defects tested: Asantisite, Gaantisite and Gavacancy, the As_{Ga} leads to a midgap state. Spinresolved bandstructure of the GaAs with As_{Ga}, reveals a paramagnetic nature of the defect, in agreement with ESR. The nonsplit behavior of the midgap state is due to induced tetrahedral symmetry when a Ga atom is replaced by As. The state arises from charge density within the tetrahedra and not solely on As_{Ga}. 
Tuesday, March 6, 2018 12:39PM  12:51PM 
F11.00006: Treatment of defects and defect levels in ternary alloys using special quasirandom structures: InGaAs Peter Schultz While progress has been made toward obtaining demonstrably accurate defect properties in crystalline semiconductors (e.g. GaAs or InAs) using stateoftheart density functional theory, ternary alloys, such as InGaAs, are equally important technologically and pose significant new conceptual and computational challenges to modelling. With a random composition of In and Ga, lack of periodic crystallinity requires that the conventional supercell approaches be generalized, and local variability in the random alloy requires a statistical approach to assessing defect properties. I describe how one models intrinsic defects in In(0.5)Ga(0.5)As using a special quasirandom structure (SQS), including demonstrating the validity and adequacy of the model (convergence to bulk limits, consistency of chemical potentials), and statistical analysis of defect formation and level energies for vacancies, divacancies, antisites, and some interstitials. 
Tuesday, March 6, 2018 12:51PM  1:03PM 
F11.00007: Descriptorbased approach for the prediction of cation vacancy formation energies and transition levels Joel Varley, Amit Samanta, Vincenzo Lordi Point defects largely determine the observed optical and electrical properties of a given material, yet the characterization and identification of defects has remained a slow and tedious process, both experimentally and theoretically. We demonstrate a model derived from explicit hybrid functional calculations that can reliably predict the formation energies of cation vacancies as well as the location of their electronic states in a large set of IIVI and IIIV materials. Our model uses inputs derived from parameters obtained from the defectfree bulk primitive unit cell consisting of only a few atoms and is found to reproduce the calculated defect transition levels within approximately 0.2 eV. We apply our model to ordered alloys within the CdZnSeTe, CdZnS, and ZnMgO systems and find excellent agreement between the predicted defect chargestate transition levels and those that were explicitly calculated. Our results suggest descriptorbased approaches for predicting point defect formation energies can yield useful accuracy without the need for the expensive and largescale calculations typically required. 
Tuesday, March 6, 2018 1:03PM  1:15PM 
F11.00008: Atomicscale study of aging effects in polycrystalline CdTe solar cell Jinglong Guo, Fatih Sen, Luhua Wang, Seungjin Nam, Moon Kim, Maria Chan, Robert Klie CdTe is a widelyused photovoltaic (PV) material due to its near optimum band gap and ease of lowcosting manufacturing. However, practical efficiencies are well below the theoretical Shockley efficiency limit.One factor limiting the efficiency is recombination at grain boundaries. Due to the variety of grain boundary structures in polycrystalline CdTe, understanding grain boundary contribution to the solar cell efficiency is very challenging. As such, an atomicscale understanding of grain boundaries becomes crucial in improving efficiency. 
Tuesday, March 6, 2018 1:15PM  1:27PM 
F11.00009: Dangling bond defects in SiC: an ab initio study Blair Tuttle We report firstprinciples microscopic calculations of the properties of defects with dangling bonds in crystalline 3CSiC. Specifically, we focus on hydrogenated Si and C vacancies, divacancies and multivacancies. The latter is a generic model for an isolated dangling bond within a bulk SiC matrix. Hydrogen serves to passivate electrically active defects to allow the isolation of a single dangling bond defect. We used hybrid density functional methods to determine energetics and electrical activity. The present results are compared to previous 3CSiC calculations and experiments. Finally, we identify homopolar carbon dangling bond defects as the leakage causing defects in nanoporous SiC alloys. 
Tuesday, March 6, 2018 1:27PM  1:39PM 
F11.00010: Unraveling the role of vacancies in potentially promising thermoelectric Ba_{8}Zn_{x}Ge_{46xy}■_{y} clathrates Saswata Bhattacharya, Amrita Bhattacharya Thermoelectric clathrates consists of semiconducting framework of groupIV host encapsulating metal guest. Filling of guest often results in bizzare structural changes such as the formation of vacancies (■), which in turn changes their electronic and vibrational properties. We use densityfunctional theory to compute the formation energies of typeI Ba_{8}Zn_{x}Ge_{46xy}■_{y} clathrates with y vacancies in their framework as a function of Zn substitutions x [1]. Our study confirms the experimental observation that the framework vacancies are destabilized with increase in Zn substitution. Up to three vacancies per formula unit can be stabilized for 0 <x < 6, while they are unstable for x ≥ 6. This behavior is driven by the high energetic gain associated with the population of the valence electronic states of Zn as compared to the energetic gain upon saturation of the electronic vacancy states. We further analyse the thermodynamic stability and temperature induced changes in the carrier concentration of these compositions. 
Tuesday, March 6, 2018 1:39PM  1:51PM 
F11.00011: Firstprinciples calculations on intrinsic point defects in CsPbBr_{3} Jun Kang, LinWang Wang The formation energies and chargetransition levels of all possible intrinsic point defects in CsPbBr_{3} are studied from firstprinciples calculations. The dominant defect under Brrich and moderate growth condition is found to be Cs vacancy, whereas under Brpoor condition, Br vacancy becomes dominant. It is also found that the formation energy of dominant defect under Brrich condition is quite small, thus moderate or Brpoor growth condition can help to avoid the formation of defects. Furthermore, most of the intrinsic defects only induce shallow transition levels. Defects that can create deep transition levels have quite high formation energy. Therefore CsPbBr_{3} is highly defecttolerant in terms that its good electronic quality can be maintained despite the presence of defects. The absence of bonding−antibonding interaction between the conduction bands and valence bands of CsPbBr_{3} is expected to be the origin of the defect tolerance. 
Tuesday, March 6, 2018 1:51PM  2:03PM 
F11.00012: FristPrinciples Study on the Intrinsic Point Defects in the QuasiOneDimensional Photovoltaic Semiconductor Sb_{2}Se_{3} Menglin Huang, Dan Han, Shiyou Chen As a novel thinfilm solar cell absorber semiconductor, Sb_{2}Se_{3} has attracted increasing attention recently and a 5.93% lighttoelectricity conversion efficiency has been achieved. Different from the conventional covalent photovoltaic semiconductors such as CdTe, Cu(In,Ga)Se_{2} and Cu_{2}ZnSn(S,Se)_{4}, Sb_{2}Se_{3} is a quasionedimensional material in which the [Sb_{4}Se_{6}]_{n} atomicchains (ribbons) bind with each other through van der Waals forces. Here we studied the intrinsic point defects in Sb_{2}Se_{3} using the density functional theory calculations with both the generalized gradient approximation and the hybrid functionals. In a Serich condition, the shallow acceptor, Se_{Sb} antisite, is the dominant defect with the lowest formation energy, accounting for the observed ptype conductivity, while in a Sepoor condition, Sb_{Se} and V_{Se} are the dominant donor defects. Those cationreplaceanion and anionreplacecation antisite defects cannot form with high concentration in conventional covalent semiconductors, but they can be dominant in Sb_{2}Se_{3}. The results are weakly influenced by the functionals. 
Tuesday, March 6, 2018 2:03PM  2:15PM 
F11.00013: Abinitio phonondefect scattering and thermal conductivity of Graphene, Si, Diamond, InN and BAs Carlos Polanco, Lucas Lindsay We present parameterfree calculations of thermal conductivity using the PeierlsBoltzmann transport equation combined with an abinitio Green’s function methodology to describe the scattering of phonons with point defects. Specifically, we include phonondefect scattering by substitutional atoms and vacancies in Graphene, Si and InN as well as antisite defects in BAs and NitrogenVacancy centers in Diamond. Our calculations demonstrate the importance of including changes of the interatomic force constants (IFCs) locally near the defect, which yields scattering rates that challenge our intuition built from perturbative approaches. For example, substitutional atoms with larger mass perturbation do not necessarily result in larger scattering rates. Neglecting the changes on the IFCs can result in scattering rates well below an order of magnitude of those from the full calculation. Finally, we discuss important simulation details of the Green’s function methodology, including IFC symmetries, convergence with nearest neighbor shells, and the conundrum of enforcing the acoustic sum rule. 
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