Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Y53: Thin Films and NanostructuresFocus Session Live
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Sponsoring Units: DMP DCOMP FIAP Chair: Elif Ertekin, University of Illinois at Urbana-Champaign |
Friday, March 19, 2021 11:30AM - 12:06PM Live |
Y53.00001: Manipulating Impurities and Defects During Semiconductor Epitaxy with Light Invited Speaker: Kirstin Alberi While controlling impurity and defect incorporation is a primary concern during semiconductor epitaxy, only a few process variables are typically available to regulate incorporation mechanisms. In the case of vapor phase epitaxy, they include substrate temperature and atomic or molecular flux. Access to additional control parameters may therefore prove useful for manipulating impurity and defect populations. This talk will focus on the use of light as an independent and tunable energy source that can be applied to modify growth processes. Observed changes in semiconductor materials grown under illumination have largely been linked to modification of adatom desorption rates and defect formation enthalpies in the presence of photogenerated carriers. Specific examples will be discussed along with opportunities for using photo-assisted techniques to control impurities and defects. |
Friday, March 19, 2021 12:06PM - 12:18PM Live |
Y53.00002: Investigating Cation Disorder in ZnGeP2 Thin Films Using Resonant Energy X-ray Diffraction Rekha Schnepf, Ben Levy-Wendt, Marshall Brooks Tellekamp, Brenden Ortiz, Celeste Melamed, Laura Schelhas, Kevin Stone, Michael Toney, Eric Toberer, Adele Tamboli Ternary materials are being increasingly studied for their potential integration in solar cell and LED devices. Controlling cation disorder in these materials offers the potential to tune properties at nearly fixed compositions and lattice parameters. However, quantification of cation disorder is challenging. In this work, we present two methods used to quantify cation disorder in ZnGeP2 thin films: a stretching parameter calculated from lattice constants, c/a, and an order parameter determined from site occupancies, S. We use high resolution X-ray diffraction to determine c/a and resonant energy X-ray diffraction (REXD) to extract S. REXD is necessary for distinguishing between elements with similar Z-number (Zn and Ge). We found that films with a c/a corresponding to the ordered structure had partially disordered S values. The optical absorption onset showed a trend that is consistent with the expected band gap narrowing as disorder is increased, indicating that S better represents the disorder in these films. This work highlights the complexities in characterizing cation disorder and the importance in choosing a metric that best reflects the physical properties of interest. |
Friday, March 19, 2021 12:18PM - 12:30PM Live |
Y53.00003: Self-trapped exciton assisted energy transfer from the band edge to Mn dopant in Mn2+-doped 2D organometal halide perovskites Som Sarang, William Delmas, Vivien Cherrette, Sara Naghadeh, Jin Zhang Organo-metal halide perovskites (OMHPs) are relatively new entrants in the arena of doping as a means of tuning semiconductor functionalities, although initial efforts have demonstrated improved quantum yield and broadband emission in Mn-doped OMHPs. We investigated Mn2+ doped ethyl-ammonium lead bromide (EA2PbBr4:Mn2+), a two Dimensional OMPH, using low-temperature optical spectroscopy techniques. Our results show that while for temperatures T > 120 K, photoluminescence (PL) is dominated by emission from Mn2+, with complete suppression of band-edge (BE) emission. For T < 120 K, in addition to BE emission, PL is observed from self-trapped excitons (STEs). While establishing that STEs form the most dominant route in energy transfer from the BE to Mn2+ dopants for 20 K < T < 120 K, using spin-polarized spectroscopy we further demonstrate strong exchange coupling between the quantum confined host carriers and dopant ions. |
Friday, March 19, 2021 12:30PM - 12:42PM Live |
Y53.00004: Sub-10 meV Light Emission from Chemically Controlled Donor-Acceptor Defect Pairs in Solution-Processed 2D Hybrid Perovskites Adedayo M. Sanni, Aaron Rury Low dimensional hybrid perovskites formed from solvated chemical precursors possess properties central to next generation optoelectronic technologies. In this presentation we highlight a materials synthesis method that controls light emission below the optical gap from defects in hybrid lead iodide self-assembled quantum wells (SAQWs). We change cation concentrations to control crystal growth, and drive the formation of lead iodide SAQWs whose sub-gap photoluminescence (PL) spectra range from possessing a single broad peak to featuring several significantly narrower peaks. Power dependent PL measurements suggest we form I- vacancies predominantly in the presence of high cation concentrations, while significant densities of amine impurity-iodide vacancy defective donor-acceptor pairs form under lower cation concentrations. Furthermore, we find some the narrowband peaks characteristic of low cation materials correspond to nearly degenerate, bound excitons whose dephasing dynamics lead to sub-10 meV peak widths. These results indicate bulk chemical characteristics of materials synthesis can act as an effective means to control the formation of point defects whose light emission may be useful for next generation quantum optoelectronic and photonics technologies. |
Friday, March 19, 2021 12:42PM - 12:54PM Live |
Y53.00005: Semiconductor Quantum Dots: Dopant versus Free Carrier Profiles Alexandra Zimmerman, Grace Fedele, Jenna Walrath, Christian Greenhill, Davide Del Gaudio, Rachel Goldman Semiconducting quantum dots (QDs) can be used to enhance the performance of a variety of devices encompassing optoelectronic, thermoelectric, and alternative energy technologies. Often, heterovalent dopants are added to the semiconducting QDs to provide extra electrons and improve conductivity. Since each QD is expected to contain fewer than 10 dopants, both the extra electrons and their “parent” dopants have been difficult to locate. In an earlier study of InAs/GaAs QDs using scanning thermoelectric microscopy,1 fewer electrons were observed within the interior of the QD than in the surrounding substrate, presumably due to a preference of the dopant to stay outside of the QDs. In this work, we are investigating the locations of the extra electrons and their parent donors using a combination of experimental and computational methods, namely local-electrode atom-probe tomography and self-consistent Schrödinger-Poisson simulations based on effective mass theory. A comprehensive description of the relative preferences of the (parent) dopants and extra electrons with respect to the QDs and surrounding substrate will be provided. |
Friday, March 19, 2021 12:54PM - 1:06PM Live |
Y53.00006: "Point Defects in Lead Sulfide: A first-principles study"
N. Mishra and G. Makov
Dept. of Materials Engineering, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel Neeraj Mishra, Guy Makov The energetic and electronic properties of point defects in lead sulfide were studied using first-principles methods. In particular, intrinsic defects including single-site and double-site defects were considered as well as extrinsic oxygen-containing defects. A novel, stable interstitial site was identified. The convergence of the calculations with supercell size was examined and found to be well-converged for most defects in 250 atom supercells. For intrinsic defects, it was found that, after accounting for the chemical potentials of Pb and S in the environment, the lowest formation energies are associated with lead vacancies in S-rich conditions and sulfur vacancies in Pb-rich conditions and not with Schottky defects, as previously reported. The electronic band structure was affected by the presence of intrinsic defects. The charged states of the point defects were examined and found to be preferred over the neutral states. The formation energies of oxygen defects are highly competitive energetically with those of intrinsic defects, and therefore, oxygen point defects are expected to play a significant role in determining material properties. |
Friday, March 19, 2021 1:06PM - 1:18PM Live |
Y53.00007: Exciton–phonon coupling in resonant Raman scattering: intrinsic attributes and extrinsic tunability in ZnTe of different dimensionalities Yingyan Yi, Jason K Marmon, Yuanping Chen, Fan Zhang, Tao Sheng, Priyalal S. Wijewarnasuriya, Haitao Zhang, Yong Zhang The dependence of electron-phonon coupling (EPC) on nanostructure size has been controversial over three decades. Often, the EPC was probed by resonant Raman scattering (RRS) using the 2LO to 1LO intensity ratio R21 to extract the Huang-Rhys factor (S) by applying Albrecht’s theory, where the bulk reference S was calculated using a theoretical model developed for a bound exciton with Fröhlich interaction. We show that in ZnTe, in contrast to the previous reports, R21 exhibits a much larger intrinsic value and minimal change from bulk to 30 nm nanowire, indicating previously reported size dependences were likely affected by extrinsic mechanisms. In fact, the ratio can be tuned extrinsically over one order in magnitude controllably either during or post growth, allowing for programing EPC in nanoscale devices. We point out that R21 is not directly related to Huang-Rhys factor, lattice relaxation is minimal for bulk and moderately small nanostructures, and Albrecht’s theory is not applicable to RRS [1,2]. This work provides unambiguous experimental results for validating EPC theories with reduced dimensionality. |
Friday, March 19, 2021 1:18PM - 1:30PM Live |
Y53.00008: Emission from localized states in few-layer InSe (Part1: Theory) Kok Wee Song, Samuel Magorrian, Vladimir Falko The localized hole that binds to the acceptor (defect) in indium selenide (InSe) thin film has an important implication for the material’s optical properties since this localized hole in the valance band can recombine with the electron in the conduction band. To investigate this localized state, we build a mesoscopic model based on the GW computed quasiparticle energy. With this model, we find that the scattering processes between different quantized modes due to quantum confinement play a crucial role in forming the hole-acceptor bound pair. As a result, the charge density of the hole bound state is highly inhomogeneous and strongly depends on the acceptor position in the out-of-plane direction. This leads to interesting electric-field dependence of the bound state energy due to the inversion symmetry breaking. |
Friday, March 19, 2021 1:30PM - 1:42PM Live |
Y53.00009: Emission from localized states in few-layer InSe: Experiment Zhengguang Lu, Kok Wee Song, Dmitry Shcherbakov, Yuxuan Jiang, Shahriar Memaran, Wenkai Zheng, Kenji Watanabe, Takashi Taniguchi, Samuel Magorrian, Luis Balicas, Chun Ning Lau, Vladimir Falko, Dmitry Smirnov Indium selenide (InSe), a layered metal-chalcogenide semiconductor with a layer-dependent band structure, high electron mobility and strong light-matter interaction, has gained considerable interest as promising material for optoelectronics. Here we report the observation of free-exciton emission and localized-states emission in photoluminescence (PL) spectra of hBN-encapsulated few-layer InSe devices. We show that the emission from both excitons and localized states can be controlled by varying carrier density, electric or magnetic field. The PL lines from these localized states are separated by ~100meV from the main exciton PL line, in excellent agreement with theoretical calculations, and exhibit extremely narrow linewidths suggesting that few-layer InSe may provide another 2D platform to host single photon emitters. |
Friday, March 19, 2021 1:42PM - 1:54PM On Demand |
Y53.00010: Carrier localization in quaternary Ga1-xMnxAs1-yPy ferromagnetic semiconductor films Logan Riney, Sining Dong, Xinyu Liu, Lei Guo, Ren-Kui Zheng, Jiashu Wang, Xiang Li, Seul-Ki Bac, Jacek Kossut, Malgorzata Dobrowolska, J K Furdyna, Badih A Assaf Motivated by the fact that holes in the Ga1-xMnxAs family of ferromagnetic semiconductors play a key role in determining their ferromagnetic properties, we have measured hole concentrations in a series of three Ga1-xMnxAs1-yPy alloys grown by MBE with varying amounts of phosphorus and fixed Mn. This was carried out by anomalous Hall Effect measurements on a series of samples (10%<y<22%), both annealed and as grown. By comparing the total hole concentrations obtained from the number of acceptors and compensating donors to the Hall carrier density, we find that the number of itinerant holes is significantly less that the total hole concentration. This indicates that a sizable fraction of those holes become localized with increasing P concentration, reaching a high resistivity regime for y=21% at low temperature. We also find that the Curie temperature described by the Zener model is determined by the itinerant holes rather than by the total hole concentrationOur results indicate that that ferromagnetism in Ga1-xMnxAs1-yPy vanishes when the total hole concentration falls below a certain Mott-like threshold, suggesting that the holes reside in the acceptor impurity band created by the Mn acceptors. |
Friday, March 19, 2021 1:54PM - 2:06PM On Demand |
Y53.00011: Surface electronic structure of H/InAs(001)-4×2 studied by synchrotron radiation Chien Wen Chuang, Yi-Ting Cheng, Tun-Wen Pi, Ashish Chainani The free surface electronic structure of undoped and n-type InAs(001) is well-known to exhibit electron accumulation while p-type InAs(001) shows an inversion layer on the surface. We report a high-resolution synchrotron radiation (hv = 40 - 160 eV) photoemission study to clarify effects of hydrogenation on the electronic structure of undoped, n-type, and p-type InAs(001). Chemically treated surfaces annealed at 420°C show a clear 4×2 reconstruction. In 4d/As 3d core levels reveal a single component surface contribution with surface core-level shifts of ~200 meV. They appear at higher/lower binding energy (BE) than the bulk, suggestive of a charge redistribution of surface In and As atoms as in InGaAs(001)-4×2. Upon exposure to atomic hydrogen (H+ and H-) generated by a UHV cracker, the valence band maximum shifts to higher BEs, suggestive of n-type doping. Concurrently, the In 4d and As 3d surface components show reduced intensity with appearance of Hydrogen-induced components. The induced In 4d/As 3d component occurring at low/high BE is associated with H-/H+, respectively. The results suggest surface In atoms get charge enriched upon H bonding, and most likely cause the re-transformation from the (4×2) to the original (1x1) structure as confirmed by LEED measurements. |
Friday, March 19, 2021 2:06PM - 2:18PM On Demand |
Y53.00012: Structural and Electronic Properties of 3x1 Si (Ge)-Terminated Diamond (100) Surfaces Hector Gomez, Michael Groves, Mahesh R Neupane, Dmitry A Ruzmetov, A. Glen Birdwell, James Weil, Pankaj Shah, Tony Ivanov With an increasing demand for high-powered control electronics in harsh environments, discerning the electronic and physical properties of diamond surfaces are critical for device applications because of their superior electronic and thermal properties. These surfaces exhibit attractive surface dependent structural and electronic properties. Motivated by this, we perform a DFT study into clean and oxidized variants of the reconstructed Si (Ge)-terminated diamond (100) surfaces. Moreover, utilizing the nudged elastic band (NEB) approach, a reconstruction mechanism between Si (Ge)-terminated ketone and ether surfaces are predicted. Electronic properties reveal a phase transition from metallic to semiconducting properties from the clean surface to Ge- and Si-terminated regimes. When oxidized, Si- and Ge-terminates exhibited a return to metallic properties in the bridged-ether configurations but displayed an increased bandgap from the clean surface of approximately 80% and 73%, respectively in the ether configuration. Furthermore, novel Si- and Ge- tilted terminates revealed topological insulating properties and provide interesting device fabrication opportunities. |
Friday, March 19, 2021 2:18PM - 2:30PM On Demand |
Y53.00013: Band Gap Engineering of host GaAs through deposited PbS quantum dots Mithun Bhowmick, Akhilesh Kumar Singh, Puspendu Barik, Haowen Xi, Bruno Ullrich The hetero-pairing of colloidal quantum dots (QDs) with semiconducting hosts considerably enlarges the technological application bandwidth of this material platform, which suits mass-market production. In this talk, we report photoluminescence studies in solvent deposited PbS quantum dots on undoped GaAs substrates. The QD thin films were characterized by transmission (TR), reflection (RE) and photoluminescence (PL) measurements as well as transmission electron microscopy (TEM). In the PL measurements, we see alteration of the optical emission by the electronic influence of the deposited QDs. Our previous work has demonstrated an enhancement of GaAs PL in presence of PbS QD, and a follow up is needed to fully understand the potential of the process. Through this work, we attempt to reconcile the observations from PbS QD experiments with the already reported classical models in semiconductor heterostructures. The findings give new insights in optical device engineering using charge transfer between bulk and quantized matter. |
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