Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K28: Dopants and Defects in Semiconductors V: Solar and Detector MaterialsFocus
|
Hide Abstracts |
Sponsoring Units: DMP FIAP DCOMP Chair: David Scanlon, UCL Room: 291 |
Wednesday, March 15, 2017 8:00AM - 8:36AM |
K28.00001: Defect physics in halide perovskites, double perovskites and perovskite alternatives Invited Speaker: Yanfa Yan Despite the rapid improvement in record power conversion efficiency (PCE) over the past six years, the commercialization of organic--inorganic Pb halide perovskite solar cells is still facing serious challenges such as cell instability against moisture and temperature and the inclusion of toxic Pb. Recently, non Pb containing halide perovskites, double perovskites and perovskite alternatives have attracted attention. To evaluate the potential of these non Pb-containing halide materials as photovoltaic absorbers, it is necessary to understand and compare the defect properties in both Pb halide and non Pb-containing halide materials. In this talk, we will first review our theoretical understanding of the superior defect tolerance properties, i.e., the dominant defects exhibit shallow levels and do not cause serious nonradiative recombination, in Pb halide perovskites through first-principles density-functional theory calculations. We will elucidate that the superior defect properties are attributed to the combination of strong antibonding coupling between Pb lone-pair $s$ orbitals, perovskite symmetry, high ionicity and large lattice constant. We will further discuss the effects of the crystal structures and chemical compositions of double perovskites and perovskite alternatives on the defect properties. We will then show that the defect tolerance properties decrease in double perovskites and perovskite alternatives, suggesting less promising photovoltaic properties. [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 8:48AM |
K28.00002: First principles investigations of defect-mediated carrier recombination centers in cadmium telluride Jie Pan, Wyatt Metzger, Stephan Lany Cadmium telluride (CdTe) is a leading thin film photovoltaic (PV) material for its low manufacturing cost. To improve the conversion efficiency and open-circuit voltage, it is necessary to investigate the structures and energies of defects in CdTe which can shed lights on the defect-mediated carrier recombination pathways. However, standard density functional theory (DFT) calculations can not accurately describe defect structures in CdTe, especially for the defects with open shells. To overcome this challenge, we developed a Hartree-Fock/DFT hybrid functional that can fully correct the band gap of CdTe. Based on this hybrid functional, we examined the atomic configurations, formation energies, and transition levels of intrinsic defects, impurities (e.g., Cu, Cl), and defect complexes in CdTe. According to the defect levels relative to the band edges in CdTe, the mechanisms of defect-mediated carrier recombination, e.g., radiative, non-radiative, were proposed. [Preview Abstract] |
Wednesday, March 15, 2017 8:48AM - 9:00AM |
K28.00003: Theoretical study of bismuth-doped cadmium telluride E. Menendez-Proupin, J. A. Rios-Gonzalez, J. L. Pena Cadmium telluride heavily doped with bismuth has been proposed as an absorber with an intermediate band for solar cells. Increase in the photocurrent has been shown recently, although the overall cell efficiency has not improved [1]. In this work, we study the electronic structure and the formation energies of the defects associated to bismuth impurities. We have performed electronic structure calculations within generalized density functional theory, using the exchange-correlation functional HSE($w)$, where the range-separation parameter $w$ has been tuned to reproduce the CdTe bandgap. Improving upon previous reports [2], we have included the spin-orbit interaction, which modifies the structure of the valence band and the energy levels of bismuth. We have found that interstitial Bi (Bi$_{\mathrm{i}})$ tends to occupy Cd vacancies, cadmium substitution (Bi$_{\mathrm{Cd}})$ creates single donor level, while tellurium substitution (Bi$_{\mathrm{Te}})$ is a shallow single acceptor. We investigate the interaction between these point defects and how can they be combined to create a partially filled intermediate band. [1] O. Vigil-Galan et al, J. Mater. Sci: Mater Electron (2016) 27: 6088. [2] Y. Seminovski et al, Solar Energy Materials {\&} Solar Cells (2013) 114: 99 [Preview Abstract] |
Wednesday, March 15, 2017 9:00AM - 9:12AM |
K28.00004: Self-passivation Rule and the Effect of Post-treatment in GBs of Solar Cell Materials Chengyan Liu, Shiyou Chen, Hongjun Xiang, Xingao Gong Grain boundaries (GBs) existing in polycrystalline semiconductors alloys inducing a great deal of deep defect levels are usually harmful to cells' photovoltaic performance. Experimental and theoretical investigations verified that these defect levels come from the GBs' dangling bonds. We find that, the defect levels in anion core of GB can be passivated by its cations, called by self-passivation. For instance, the post-treated by CdCl2, Cd can eliminate the defect levels by saturating Te dangling bonds in the grain boundary of CdTe. We verify that the idea of self-passivation rule can perfectly explain the benign GBs of CISe and CZTS by sodium treatment. The present work reveals a general mechanism about how dopants in GBs eliminate the defect states through passivating the dangling bonds in covalent polycrystalline semiconductors, and sheds light on how to passivate dangling bonds in GBs with alterative processes. [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:24AM |
K28.00005: Chlorine impurities near stacking fault in CdTe Walter Orellana, Eduardo Menendez-Proupin, Mauricio Flores Thin-film cadmium telluride (CdTe) is an important low-cost photovoltaic material. However, transmission electron microscopy has revealed high density of extended defects like stacking faults in as-grown CdTe samples. It has also been observed that the presence of chlorine (Cl) and its interaction with stacking faults plays an important role in the production of high efficiency thin-film CdTe solar cell. Here, we investigate the stability and electronic properties of the Cl impurity at a stacking-fault defect in CdTe, using density functional theory calculations, including hybrid functional. We find that the presence of the stacking fault removes the degeneracy of the valence band maximum, inducing a reduction of the bandgap of about 0.1 eV. When chlorine is incorporated close to the stacking fault, the substitutional Cl$_{\rm Te}$ has lower formation energy, showing a $p$-type characteristic. On the other hand, interstitial chlorine (Cl$_i$) shows three stable sites with similar formation energies. The most stable one is located at the stacking fault center, exhibiting a half-occupied midgap level. [Preview Abstract] |
Wednesday, March 15, 2017 9:24AM - 9:36AM |
K28.00006: Electronic properties of grain boundaries in III-V materials Jonny Dadras, Christian Ratsch III-V semiconductors, have many applications in the field of optoelectronics. InAs, in particular, is known for its high electron mobility and narrow band gap (\textasciitilde 0.4 eV) and is commonly used in infrared detectors as well as a terahertz radiation sources. Grain boundaries (GBs) generally degrade a material's performance by introducing \textit{interface-states} that reduce charge carrier mobility. The present work employs state of the art all-electron DFT calculations, using the FHI-AIMS code. The GBs are modeled as interfaces between several low-index planes. Hence, the relevant electronic structure is seen to arise from \textit{surface-surface interactions} between thermodynamically favorable surface reconstructions. The recently developed Interface Builder is used to guide construction of surface interfaces. Detailed Projected Density of States (PDOS) difference and charging analyses are performed in order to understand the nature of the local bonding that can arise and, therefore, how best to dope or alter the material to minimize the defective electronic structure. The research is extended to a few cases of the ternary In-As-Sb system. [Preview Abstract] |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K28.00007: Role of electrodeposition parameters on stoichiometry of InSb nanowires Abhay Singh, Usha Philipose The effect of electrolyte pH on the properties of electrodeposited indium antimonide (InSb) nanowires grown in anodic alumina oxide (AAO) template will be presented. At a pH of 1.7, the InSb nanowires were found to be rich in antimony (Sb) and had rough surfaces. Though the surface and bulk of the InSb nanowire is intrinsically n-type, when InSb is grown as a Sb-rich material it shows p-type behavior, attributed to the Sb antisite and indium (In) interstitial defects. At low-pH, the effect of citrate ions on the electrodeposition is minimal, resulting in different deposition potential of In and Sb. The low pH favors adsorption of Sb anions, resulting in a high density of intrinsic defects in the nanowire. The p-type behavior was verified by measuring the electrical properties of a single InSb nanowire connected in a field-effect-transistor type configuration. The nanowires had a hole concentration of \textasciitilde 1.9$\times$ 10$^{\mathrm{16\thinspace }}$cm$^{\mathrm{-3}}$ with a field effect hole mobility of \textasciitilde 507 cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}}$, and high on-off current ratio of the order of 10$^{\mathrm{3}}$. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K28.00008: Magnetic Resonance Characterization of Defects in Icosahedral and Cubic Boron Arsenide Bulk Crystals E.R. Glaser, J.A. Freitas, Jr., C.D. Cress, F.K. Perkins, S.M. Prokes, L.B. Ruppalt, J.C. Culbertson, C. Whiteley, J.H. Edgar, F. Tian, Z. Ren, J. Kim, L. Shi Low-temperature electron spin resonance (ESR) at 9.5 GHz and optically-detected magnetic resonance (ODMR) at 24 GHz were employed to investigate point defects in icosahedral and cubic Boron Arsenide bulk crystals. These semiconductors are of interest for use in high radiation and/or high temperature environments. ESR of the (001) B$_{12}$As$_{2}$ (E$_{g\, }=$ 3.47 eV) mm-size platelets revealed two distinct features of unknown origin. The first signal is characterized by Zeeman splitting g-values of g$_{\vert \vert } \quad =$ 2.017, g$_{\bot } \quad =$ 2.0183 while the second with g$_{\vert \vert } \quad =$ 2.0182, g$_{\bot } \quad =$ 1.9997. Most notably, the second signal was also observed from ODMR on the broad 2.4 eV ``yellow/green'' photoluminescence band previously reported$^{1}$ for these crystals and suggests its direct involvement in this likely defect-related radiative recombination process. Preliminary ESR obtained for the 100-300 micron-size cubic BAs crystals$^{2,3}$ revealed a signal with g-value of 2.018 (very similar to that found for the B$_{12}$As$_{2}$ crystals) and broad FWHM value of 182 G. Possible origins of these defects will be discussed. $^{1}$P.B. Klein et al., J. Appl. Phys. \textbf{112}, 013508 (2012). $^{2}$Bing Lv et al., Appl. Phys. Lett. \textbf{106}, 074105 (2015). $^{3}$Jaehyun Kim et al., Appl. Phys. Lett. \textbf{108}, 201905 (2016). [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K28.00009: Hybrid Functional Study of Sodium and Potassium Incorporation in Cu$_{\mathrm{2}}$ZnSnS$_{\mathrm{4}}$ Kin Fai Tse, Manhoi Wong, Yiou Zhang, Jingzhao Zhang, Junyi Zhu The thermodynamics of Na and K incorporation and its effects in Cu2ZnSnS4 (CZTS) is studied using density functional theory with hybrid functional. The allowed chemical potential of Na/K in CZTS is established. Formation energy calculations shows that Na can be significantly incorporated as both substitutional defects and interstitial defects, and incorporation of K related defects are generally less favorable. Transition energy calculations is performed showing that both Na and K exhibit benign defect properties and act as a p-type dopant. The qualitative disagreement between GGA with rigid band edge shifting and HSE calculations, formation of defect complexes, and implications in experiment will also be discussed. The understandings on the defect properties of Na and K provides an essential knowledge to further understand the surfactant effects of Na and K observed in experiments. [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K28.00010: Electronic structure and defect properties of hybrid chalcohalides Hg$_{\mathrm{3}}$Q$_{\mathrm{2}}$I$_{\mathrm{2}}$ (Q$=$S, Se and Te) for radiation detection$^{\mathrm{1}}$ Oleg Y. Kontsevoi, Yihui He, Bruce W. Wessels, Mercouri G. Kanatzidis Heavy metal chalcohalides Hg$_{\mathrm{3}}$Q$_{\mathrm{2}}$I$_{\mathrm{2}}$ (Q$=$S, Se and Te) have shown significant promise as X-ray and $\gamma $-ray detector materials. To assess the fundamental physical properties important for their performance as detectors, theoretical calculations were performed for the electronic structure, band gaps, electron and hole effective masses, and native defect properties. The calculations were based on first-principles density functional theory (DFT) and employ the highly precise full potential linearized augmented plane wave method and the projector augmented wave method and include nonlocal exchange-correlation functionals to overcome the band gap underestimation in DFT calculations. The calculations show that Hg$_{\mathrm{3}}$Q$_{\mathrm{2}}$I$_{\mathrm{2}}$ have either indirect (Q$=$S, Se) or direct (Q$=$Te) band gaps within 1.9-2.25 range which is optimal for a detector material, and very small electron effective masses (0.19 m$_{\mathrm{0}}$ for Hg$_{\mathrm{3}}$Se$_{\mathrm{2}}$I$_{\mathrm{2}})$ which could result in a good carrier mobility-lifetime product $\mu \tau $. We further investigated a large set of native defects in the most promising candidate material, Hg$_{\mathrm{3}}$Se$_{\mathrm{2}}$I$_{\mathrm{2}}$, to determine the optimal growth conditions for application as $\gamma $-ray detectors. The results suggest that the prevalent intrinsic defects are iodine vacancies, mercury vacancies, and selenium vacancies followed by antisite defects. The effect of various chemical environments on defect properties was examined and the optimal conditions for material synthesis were suggested. $^{\mathrm{1}}$Supported by DHS (Grant No. 2014-DN-077-ARI086-01). [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K28.00011: Band gap engineering of BaZrS$_{\mathrm{3}}$ by Ti doping Xiucheng Wei, Samanthe Perera, Chuan Zhao, Hao Zeng, Yi-Yang Sun, Shengbai Zhang, Haolei Hui Although first synthesized some 5 decades ago, the chalcogenide perovskites are scarcely investigated compared to their oxide counterparts. The recent advances in organic-inorganic halide-perovskites as solar absorbers demonstrating power conversion efficiencies in the 20{\%} range has led to revived interests in these materials, in an effort to address the instability and toxicity issues that plague halide perovskites. BaZrS$_{\mathrm{3}}$ is a prototypical chalcogenide perovskite. It is shown to be a direct band gap semiconductor with a band gap of 1.7-1.8 eV, slightly higher than the optimum value for a single junction solar cell of 1.3-1.5 eV. In this work, we report band gap engineering of BaZrS$_{\mathrm{3}}$ by cation alloying with Ti. Since the Ti 3d states have energy lower than 4d states of Zr, substitutional Ti doping can lower the band gap by pushing down the conduction band minimum. A series of BaZr$_{\mathrm{1-x}}$Ti$_{\mathrm{x}}$S$_{\mathrm{3\thinspace }}$powder samples (with X smaller than 0.2) were synthesized. XRD results showed a systematic shift of the diffraction peaks to higher angles with increasing x, suggesting a decrease in lattice spacing. UV-Vis absorption was also measured to determine the bandgaps. The band gap was found to be reduced to 1.5 eV with moderate Ti doping; while at higher doping concentration, secondary phases were detected. Our work demonstrates that cation alloying is a viable approach for band gap engineering of chalcogenide perovskite for PV applications. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K28.00012: Optimal first-principles evaluation of electrostatic potentials: applications to interfacial band alignment and charged defect energies in bulk, surfaces and 2D materials Yuan Ping, Ravishankar Sundararaman First-principles calculations of band alignment and charged defect formation energies require comparing electrostatic potential of different atomic configurations, which is made challenging by the strong oscillation of this potential at the atomic scale. We introduce a method to suppress these strong oscillations by eliminating the deep wells in the potential at each atom. We demonstrate that this method considerably improves the system-size convergence of a wide range of first-principles predictions that depend on alignment of electrostatic potentials, including band offsets at solid-liquid interfaces, and formation energies of charged defects in solids and at solid surfaces in vacuum and solution. In the end we show that our new approach of computing the charged defects significantly improved the supercell convergence for charged defects in 2D materials, which has been a long-standing problem in the field. [Preview Abstract] |
Wednesday, March 15, 2017 10:48AM - 11:00AM |
K28.00013: First-principles study of complex halide scintillators for radiation detection Qingguo Feng, Byungkyun Kang, Jonathan mize, Koushik Biswas Current demands for cost-effective and high-performance scintillators have led to a discernible shift from simple binary halides (e.g., NaI, CsI) toward host compounds that are structurally and electronically more complex. Eu-doped SrI$_2$ is a prominant example. Despite its advanced properties, improvements are needed for extensive deployment at low cost. Codoping techniques are often useful to improve the electronic response of such insulators. Using first-principles based approach we report on the influence of codoping with aliovalent and isovalent impurities. We find all codopants induce deep levels, show amphoteric character, and may bind with I-vacancy forming charge compensated donor-acceptor pairs. Lack of deep-to-shallow behavior upon codoping and its ramifications will be discussed. We studied another set of stable monoclinic phase of ternary ns$^2$ containing iodides, e.g. TlBa$_2$I$_5$. One objective is to explore them as scintillators where ns$^2$ ions play a central role. Interestingly, we predict Eu$^{2+}$ activation will be rendered ineffective in these compounds, caused by changes in the valence and conduction band edges. However, the prospect of fast electron capture at ns$^2$ sites and self-activated scintillation could be important for detector applications. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700