Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P27: Synthesis and Characterization of Electronic Thin Films |
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Sponsoring Units: FIAP DCMP Chair: Amber Reed, Air Force Research Lab - WPAFB Room: 404 |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P27.00001: Effect of Scandium Nitride Film Orientation on Growth and Electrical Properties Amber Reed, David Look, Hadley Smith, Zachary Biegler, Rachel Adams, Madelyn Hill, Tyson Back, John Cetnar Scandium nitride (ScN) is a degenerate semiconductor with great potential as a complementary material to enhance GaN performance in high-power and high-speed electronic applications. Electron mobilities up to 130 cm2/(Vs) have been reported for (100)- ScN on (100)-MgO substrates. The values reported for (111)- ScN, however, are significantly lower. In this work, we investigate the effect of ScN orientation on film growth, composition and electrical properties. A series of thin ScN films were deposited on (111)-, (110)- and (100)-MgO substrates using reactive magnetron sputtering. X-ray diffraction showed that ScN grew with the same orientation as the MgO and crystalline growth and quality was dependent on growth conditions. Secondary ion mass spectroscopy showed that while the variation in the oxygen concentration was negligible, the fluorine and hydrogen concentrations differed between ScN orientations. Hall-effect measurements showed that mobility, carrier concentration, and resistivity were dependent on orientation. In this presentation we will discuss the correlation between the measured electrical properties and the ScN crystallinity and composition. |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P27.00002: High-Mobility Two-Dimentional Electron Gases at AlxGa1-xN/GaN Heterostructures Grown by Plasma-assisted Molecular Beam Epitaxy Yuxing Ren, Yongjin Cho, Austin Hickman, Reet T Chaudhuri, Phillip Dang, Menyoung Lee, Wenwen Zhao, Zexuan Zhang, Huili Grace Xing, Debdeep Jena Polarization-induced high-mobility two-dimensional electron gases (2DEGs) at AlGaN/GaN heterostructures have been studied and used for ultrafast transistors. They offer an interesting platform to study quantum transport in the high electron effective mass regime. At room temperature, the mobility is dominated by optical phonon scattering, but at low temperatures, the mobility is determined by defect and imperfection based scattering mechanisms, and weakly by acoustic phonons. In this talk, we will present how gate control of the 2DEG density helps us identify the impact of dislocations on the mobility. We have used a range of samples in which the dislocation densities vary over 4 orders of magnitude. With the help of high magnetic field oscillation studies at low temperatures we extract the effect of dislocations on the low temperature scattering processes. |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P27.00003: Electrical Properties of Highly Functionalized Ultrathin, 2-Dimensional Hexagonal Boron Nitride Daniel Choi, Stanislav Tsoi, Evgeniya Lock, Boris Feylgelson Hexagonal boron nitride (h-BN), an excellent dielectric material with a wide band gap value of ~6 eV, is widely used as insulating layer and gate dielectric in a wide variety of current electrical systems as well as emerging quantum based applications. Thus, much efforts have been invested in looking into modulating electrical properties of h-BN systems. However, much of the current state of the art h-BN studies have focused around larger flakes rather than thin films due to difficulty in uniform synthesis and surface chemistry, leading to low degree of functionalization. In this talk, we present electrical and tunneling properties of highly functionalized, ultrathin, 2D h-BN. Our h-BN are functionalized with TFPA-NH2 and TFPA-SH molecules and electrical properties probed via conductive atomic force microscopy. Our approach reveals previously unachieved, high degree of functionalization, as well as electrical and tunneling properties of this novel system. Our results provide basis for understanding effects of high degree functionalization on h-BN thin films as well as additional incorporation method of h-BN into other 2D van der Waals heterostructure systems. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P27.00004: Mobility fluctuation Controlled Linear Positive Magnetoresistance in 2D Semiconductor Bi2O2Se nano-plates Peng Li, Chenhui Zhang, Guoxing Miao, Xixiang Zhang Bi2O2Se is a promising 2D semiconductor with ultrahigh mobility and excellent stability in ambient conditions. We report the observation of positive and linear magnetoresistance in both Se-poor and Se-rich Bi2O2Se nano-plates grown by chemical vapor deposition. In Se poor Bi2O2Se nano-plates, the pronounced Shubnikov-de Hass oscillations lie in the linear magnetoresistance background. The Se-poor Bi2O2Se nano-plates show a typical 2D conduction feature with a small effective mass of 0.032m0. The average transport Hall mobility, i.e. less than 5500 cm2V-1s-1, is significantly reduced, compared to the ultrahigh quantum mobility that is as high as 16260 cm2V-1s-1. The spatial mobility fluctuation leads to the linear magnetoresistance, which are strongly supported by inhomogeneity in the scanning near-field microscopy images and Shubnikov-de Hass oscillation analyses. On the contrary, Se-rich Bi2O2Se samples with the transport mobility less than 300 cm2V-1s-1 show a smaller linear magnetoresistance ratio, which is controlled by the average mobility. Our finding expands the understanding of this 2D semiconductor and explores its potential magnetoresistive device application. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P27.00005: First-principles study of adatom interactions on the β-Ga2O3(010) surface Mengen Wang, Sai Mu, Chris Van de Walle Monoclinic β-Ga2O3 is a wide-gap (~4.8 eV)1 semiconductor with a high breakdown field. This renders Ga2O3 a promising candidate for high-power electronics and deep ultraviolet detectors. However, the growth rate and crystal quality of Ga2O3 thin films are limited by etching of the Ga2O3 surface due to suboxide (Ga2O) formation. It has been reported that the growth rate of Ga2O3 in molecular beam epitaxy can be enhanced by an additional indium supply.2 However, the mechanism by which In impacts growth remains elusive. To address this puzzle, we use density functional theory to explore the adsorption and diffusion of Ga and O adatoms on the Ga2O3(010) surface. The low-energy adsorption structures are studied for various Ga coverages. We illustrate the effect of the co-adsorption of In and Ga on the adsorption energetics and the diffusion barriers of O atoms. Our study holds clues to understanding the growth and etching mechanism of the Ga2O3 surface. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P27.00006: Temperature coefficient of resistance (TCR) measurement on vanadium pentoxide (V2O5) nanoparticles Ganga Neupane, Parameswar Hari In this work, we varied molar concentrations (0.05M, 0.1M, 0.15M, and 0.2M) of vanadium pentoxide (V2O5) to synthesize nanoparticles by hydrothermal method. Structural properties were studied using X-ray diffraction spectroscopy (XRD) and Transmission electron microscopy (TEM). XRD and TEM confirmed the increase in particle size with increasing molar concentrations with no secondary phases. Optical properties were studied using Photoluminescence and absorption measurements. Bandgap energy of nanoparticles was found to decrease from 2.25 eV to 2.20 eV with increasing molar concentration. Elemental composition was analyzed by X-ray photoelectron spectroscopy (XPS). The electrical conductivity of nanoparticles was found to increases with increasing molar concentration and also with increasing annealing temperature. The resistivity of nanoparticles (0.05M, 0.1M, 0.15M, and 0.2M) with different temperatures from 293K to 393K was measured. The temperature coefficient of resistance (TCR) value of -2.39%/K and resistivity of 0.1 Ohm-cm for 0.2 M concentration of vanadium pentoxide nanoparticles were obtained. We will discuss the significance of TCR obtained in the microbolometer application. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P27.00007: Multiscale Modeling for MOCVD Synthesis and Characterization of Transition Metal Dichalcogenides Nadire Nayir, Yuanxi Wang, Yuan Xuan, Kasra Momeni, Mert Yigit Sengul, Yanzhou Ji, Tanushree Holme Choudhury, Danielle Reifsnyder Hickey, Nasim Alem, Joan M Redwing, Vincent Crespi, Long Q. Chen, Adri C.T. van Duin MOCVD enables to synthesize high-quality TMD layers from vaporized precursors by providing flexibility in the selection of the precursors and their flow rate. Herein, we develop a multiscale approach as a combination of ReaxFF, continuum fluid dynamics, phase-field (PF) and machine learning (ML) to model the gas-phase kinetic of the MOCVD growth and to connect further the MOCVD control parameters to the morphology, size, and distribution of the synthesized TMD materials. The results of the model that we developed, first, for MOCVD gas-phase kinetic of 2D-WSe2 correlate well with the experimental thickness measurements of 2D-WSe2 and show that the model is capable of simulating the experimentally observed trend [1]. We further extend this model to the combination of ReaxFF, ML, and PF, in progress. A systematic representative data set is generated based on the ReaxFF potential to train an ML-model describing the edge energies and edge-growth rates of 2D-WSe2 flakes as a function of key parameters, then to incorporate them into the PF simulations. The target of this work is to bridge spatial scales that range from 10−9 to 10-3 m in space and explore the optimal growth conditions resulting in high-quality TMD materials. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P27.00008: DISTORTED PHASE OF SINGLE LAYER JANUS MoSTe Mehmet Yagmurcukardes, Cem Sevik, Francois M Peeters Recently synthesized monolayer of Janus MoSSe structure has attracted great attention on those out-of-plane anisotropic materials. Here, we investigate the electronic, vibrational, elastic, and piezoelectric properties of two dynamically stable crystal phases of monolayer Janus MoSTe, namely 1H-MoSTe and 1T′-MoSTe. The 1H-MoSTe phase is found to be an indirect band-gap semiconductor while 1T′-MoSTe is predicted as small-gap semiconductor. The calculated Raman spectrum of each structure shows unique character enabling us to clearly distinguish the stable crystal phases via Raman measurements. The systematic piezoelectric stress and strain coefficient analysis reveals that out-of-plane piezoelectricity appears in 1H-MoSTe and the noncentral symmetric 1T′-MoSTe has large piezoelectric coefficients. Static total-energy calculations show clearly that the formation of 1T′-MoSTe is feasible by using 1T′−MoTe2 as a basis monolayer. Therefore, we propose that the Janus MoSTe structure can be fabricated in two dynamically stable phases which possess unique electronic, dynamical, and piezoelectric properties. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P27.00009: Synthesis and properties of hexagonal GaBN/BN heterostructure and quantum wells. 6.3.6 Qingwen Wang, Jing Li, Jingyu Lin, Hongxing Jiang Hexagonal boron nitride (h-BN) is the only layer-structured or quasi-2D material with bandgap >6.0 eV among the members of the III-nitride semiconductor family. The unique features of h-BN make it highly attractive in novel device applications, which includes high optical emission efficiency, possibility of p-type conductivity control, promising host for single photon emitter, as well high detection efficiency for thermal neutrons. Like all other compound semiconductors, achieving the ability of bandgap tuning through alloying will further expand the applications of h-BN. Here, we report the synthesis of h-GaBN alloys using metal organic vapor deposition (MOCVD) growth. By utilizing h-BN epilayers as templates, we have successfully achieved h-GaBN alloys and h-GaBN/BN quantum wells with Ga-content up to 7%. The effects of phase separation and critical thickness have been investigated in detail and will be reported. The present study provides insights into possible ways to synthesize layered GaBN and would open up many new applications. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P27.00010: Temperature influence in the electrical conductivity of graphite oxide platelets Diego Sanchez, John Prias, Hernando Ariza Graphite oxide platelets from bamboo pyroligneous acid (GO-BPA) synthesized by using the double thermal decomposition (DTD) method at 973 K as carbonization temperature, exhibit temperature influence in the electrical conductivity like a semiconductor material. Samples were characterized by using Raman, FTIR, XRD, XPS, HR-TEM and I-V curves (two and four-points at temperatures of 20 to 300 K) techniques. Electrical measurements suggest that increased temperature increases electrical conductivity like a semiconductor material. Conduction mechanism was described mainly by 3D-variable range hopping. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P27.00011: Thermal Expansion and Residual Strain in AlN Thin Film Sensor Materials Robert Lad, Morton G Greenslit, David T Plouff, Mauricio Pereira da Cunha Aluminum nitride films are attractive materials for high temperature sensor devices because of their stable piezoelectric and semiconducting properties up to 800oC in air, above which the films degrade by oxidation. In this work, epitaxial AlN (002) films were grown at 930oC on c-cut sapphire substrates by N2-plasma-assisted Al evaporation and were characterized up to 1000oC in air using an X-ray diffraction (XRD) sample hot stage. The coefficient of thermal expansion (CTE) and homogeneous strain were determined from accurate measurements of the c-axis lattice parameter for AlN and sapphire vs. thermal processing up to 800oC, and film oxidation was evaluated above 800oC from the relative decrease in the AlN (002) XRD intensity and degradation of the (002) pole figure. AlN films grown to 200nm thickness have c-axis compressive strain, but this residual strain can be relieved by thermal cycling between 25-700oC. The CTE value of 2.5x10-6/oC for the as-deposited films decreased as the film strain was released and is below the value of 5.3x10-6/oC reported for bulk AlN. Understanding the level of residual film strain and thermal expansion matching across the relevant interfaces is key for preventing delamination, cracking, and failure of sensor packaging or sensor function itself. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P27.00012: Effects of growth parameters on faceting and defects in confined epitaxial lateral overgrowth Aranya Goswami, Simone Tommaso Šuran Brunelli, Brian Markman, Dan J Pennachio, Hsin-Ying Tseng, Sukgeun Choi, Aidan Taylor, Jonathan Klamkin, Mark Rodwell, Chris J Palmstrom Laterally grown III-V epitaxial semiconductor layers offer multiple advantages over conventional vertically-grown layers for fabricating novel semiconductor devices and III-V on Si integration for photonics. In confined epitaxial lateral overgrowth (CELO), pre-fabricated dielectric templates are used to control the growth and its direction. Such grown nano-structures however, often suffer from high densities of stacking faults and rotational twins, which limit the performance of the devices made using these materials. Here, we use scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron channeling contrast imaging (ECCI) to characterize these nano-structures grown by metal organic chemical vapor deposition (MOCVD) on patterned InP substrates. Using a combination of plan-view and cross-sectional TEMon the same nano-structure, we explore the influence of growth conditions (growth temperature and V/III ratio), template direction and substrate orientations on the evolution of facets and the nature of defects.We further show growth and characteristics of heterostructures and superlattice structures grown using CELO, as well as electrical measurements of these nanostructures. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P27.00013: Controlled Fractal Growth of Transition Metal Dichalcogenides Peijian Wang, Hao Zeng, shaoming huang We report controlled fractal growth of atomically thin transition metal dichalcogenides (TMDCs) by chemical vapor deposition, with morphological evolution from dendritic to triangular. Based on experimental observations, we tuned several important growth parameters, including the relaxation rate, adhesion coefficient, diffusion anisotropy and growth time to fabricate TMDCs with controllable fractal dimensions. Furthermore, a model based on the steps of nucleation, diffusion limited aggregation, and relaxation, was proposed to explain the morphological evolution. The computational simulation based on this model yielded good agreements with the experiments results. Our study sheds light on the growth mechanism of TMDs, which is fundamental to improving controllability of growth. |
Wednesday, March 4, 2020 5:06PM - 5:18PM |
P27.00014: Properties of SPEED Grown FTO Thin Films Deposited at Various Solution Concentrations and Ageing time Gbadebo Taofeek Yusuf There have been various reports on the scarcity of indium element which is one of the constituents of indium tin oxide (ITO). Alternative TCO material is therefore necessary before the supply eventually runs out. This research therefore focused on fluorine-doped tin oxide thin films (FTO) as a possible alternative to the ITO. FTO thin films were grown using the Streaming Process for Electrodeless Electrochemical Deposition (SPEED) technique. The structural and optical properties of the films were determined at various fluorine to tin (F: Sn) concentrations and aging time. The results, as revealed by SEM and XRD analysis show that the properties of FTO films improve as the solution concentration and aging time were jointly increased to 0.85 and 12 hours. All FTO thin films except those deposited at solution concentration (F: Sn) of 0.55 and 4 hours aging time show optical transmission above 80 % in the Visible-UV region. This study has shown that the SPEED technique is a promising technique for depositing high-quality FTO thin films for solar photovoltaic applications. |
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