Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Q44: Materials: Synthesis, Growth, & Processing |
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Sponsoring Units: FIAP Room: Mile High Ballroom 4C |
Wednesday, March 5, 2014 2:30PM - 2:42PM |
Q44.00001: PLD growth of multilayered MgO/Ag(001)/MgO photocathode Daniel Velazquez, Zikri Yusof, Linda Spentzouris, Jeff Terry Films of of Ag, MgO and multilayers of these were grown via pulsed laser deposition on clean Si(111) 7x7 substrates. The films were studied using reflection high-energy electron diffraction, Kelvin probe and ellipsometry. Information about crystalline and atomic structure as well as surface condition, work function and film thickness was obtained using these techniques. Deposition at various substrate temperatures and partial oxygen pressures was performed in order to understand the parameter settings that lead to higher quality crystalline films. Epitaxial films of Ag(111) were found to grow at an optimal substrate temperature of 256 $^{\circ}$C (fig 1.). The superstructure Ag(111) $\surd $3 x $\surd $3 occurs when deposition takes place at a substrate temperature of 620 $^{\circ}$C. In addition, MgO films were found to grow with small grain size on both, Si(111) 7x7 and Ag(111)/Si(111) at room temperature with a partial oxygen pressure of 5x10$^{-5}$ Torr (fig. 2). Highly-oriented, polycrystalline growth of MgO films is evidenced by their RHEED pattern. In addition, the obliquely-shaped diffraction spots indicate the growth of secondary phase precipitates, most likely due to oxygen deficit. Measurements of the work function of these multilayers indicate that the Ag(111) work function (4.75 eV) is sharply suppressed with the first few MgO shots and has a quasi-linear increase for the first few monolayers (fig. 3). As the thickness of MgO increases (a few nanometers) the work function drops again and stabilizes at the level of MgO ($\sim$ 4.2 eV). [Preview Abstract] |
Wednesday, March 5, 2014 2:42PM - 2:54PM |
Q44.00002: Light-stimulated epitaxy of GaAs(100) Charlotte E. Sanders, Daniel A. Beaton, Kirstin Alberi Light-stimulated epitaxy offers the potential to improve adatom kinetics at low growth temperatures. In II-VI semiconductors it has been shown to improve crystalline quality (i.e., to reduce defect density), to alter the growth rate, and to enhance substitutional dopant incorporation. These effects have been attributed primarily to (1) direct interaction between photons and adatoms at the growth front, and (2) participation of photogenerated carriers in bonding processes. Although these proposed mechanisms are presumably applicable to a wide array of epitaxially grown materials systems, the photoassisted approach has received little attention outside the context of II-VI growth. We report on our recent investigation of the effects of irradiation of GaAs(100) during growth by molecular beam epitaxy (MBE). The interaction of light with the growth front provides significant insight into fundamental mechanisms of dopant incorporation, and into the physics of adatom diffusion, nucleation, and desorption underlying the MBE process. This work was supported by the DOE Office of Science, Basic Energy Sciences, under contract DE-AC36-08G028308. [Preview Abstract] |
Wednesday, March 5, 2014 2:54PM - 3:06PM |
Q44.00003: Molecular Beam Epitaxy Growth of GaBi, InBi and InGaBi B. Keen, R. Makin, P.A. Stampe, R.J. Kennedy, L.F.J. Piper, B. McCombe, C.F. McConville, S.M. Durbin Recent interest in bismuth alloys of III-V semiconductors for infrared and far-infrared device applications, specifically GaAsBi and InAsBi, has indicated that further study of the III-Bi family of binary compounds would be of great help in improving the quality of these material systems. While immiscibility issues have so far frustrated the growth of GaBi and AlBi, InBi is less problematic, and we have grown it by molecular beam epitaxy on (001) GaAs substrates. However, regions of varying composition exist across the substrate due to poor wetting of the surface. In an effort to improve film quality we have continued to refine the growth parameters by adjusting substrate temperature, beam flux ratio, and deposition rate. Characterization of these films has been performed by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Additionally, we have explored growth of GaBi and In$_{1-x}$Ga$_{x}$Bi at low Ga mole fractions, and modeled this using molecular dynamics simulations. [Preview Abstract] |
Wednesday, March 5, 2014 3:06PM - 3:18PM |
Q44.00004: Effects of incident short wavelength (UV) light on the morphology of MBE grown GaAs Daniel A. Beaton, Charlotte Sanders, Kirstin Alberi The exploration of novel semiconductor materials increasingly relies on growth techniques that operate far from equilibrium in order to overcome thermodynamic limitations to synthesis. As one example, low temperature molecular beam epitaxy (MBE) offers a pathway to enhance substitutional dopant incorporation over surface segregation but adatom mobility suffers as a consequence and leads to higher concentrations of lattice defects. We explore the use of external stimuli, namely incident UV light, as a means to influence adatom kinetics; UV light is absorbed in the first few atomic layers of the as-growing epitaxial film and the effects of the incident radiation predominantly effect only the surface adatoms. GaAs homoepitaxy by MBE is studied as a model case as a function of illumination conditions under broadband Xe and KrF excimer laser irradiation. In-situ reflective high energy electron diffraction analysis paired with ex-situ atomic force microscopy measurements yields insight into the effects of photon irradiation on surface adatom mobility, morphology and smoothing processes. This work was supported by the DOE Office of Science, Basic Energy Sciences under contract DE-AC36-08GO28308. [Preview Abstract] |
Wednesday, March 5, 2014 3:18PM - 3:30PM |
Q44.00005: The origin and distribution of phosphorus in large size HP-Ge crystals Guojian Wang, Hao Mei, Gang Yang, Jayesh Govani, Mianliang Huang, Yutong Guan, Dongming Mei The high-purity germanium (HP-Ge) crystals with 12 cm in diameter were grown by the Czochralski method in highly pure hydrogen (6N) atmosphere. Phosphorus is one of the important shallow level donors in the grown HP-Ge crystals. The radial and axial distribution of phosphorus in the grown crystals was studied using Hall Effect and Photo-thermal ionization spectroscopy (PTIS). The effect of pulling rate and rotation speed on segregation coefficient of phosphorus in HP-Ge was investigated. The origin of phosphorus was analyzed. We report the results in this paper. [Preview Abstract] |
Wednesday, March 5, 2014 3:30PM - 3:42PM |
Q44.00006: Investigation of influential parameters for zone-refinement of germanium crystals Gang Yang, Jayesh Govani, Yutong Guan, Mianliang Huang, Hao Mei, Guojian Wang, Dongming Mei In zone-refining of high-purity germanium crystals, the influential parameters include vacuum level, container of germanium ingot, ambient gases, zone travel speed, zone length, etc. In the present work, the influences of zone length and zone travel speed on the purity level of the zone-refined ingot have been investigated with many experiments. The impurity level in the zone-refined ingot was characterized by van der pauw hall measurement. The shallow impurities are measured with a photothermal ionization spectroscopy (PTIS), which identifies existence of boron, aluminum and phosphor as three main impurities, in the zone-refined germanium ingot. Utilizing the multiple experiments, we have optimized the zone length and zone travel speed. We demonstrate our experimental results with solidification theory of metals. [Preview Abstract] |
Wednesday, March 5, 2014 3:42PM - 3:54PM |
Q44.00007: Dislocation distribution in large high-purity germanium crystal Hao Mei, Guojian Wang, Dongming Mei, Mianliang Huang, Gang Yang, Yutong Guan We investigated the impacts of growth rate, time-temperature profile, thermal gradient on the dislocation distribution in large high-purity germanium crystal (12 cm in diameter) grown via Czochralski along \textless 100\textgreater orientation. The time-temperature profiles of the crystal grown at different input power were investigated using direct measurements and computational modeling. The effect of crystallization speed on dislocation density is discussed from the context of thermal gradient during growth. Several samples from the grown crystals were used for this investigation. We measured dislocation density across the entire cross-section of the grown crystal through the microscope. By measuring and calculating the dislocation density, we were able to identify the denseness and the type of dislocation, which allows us to study how the thermal stress impacts the dislocation generation and distribution across the large grown crystals. [Preview Abstract] |
Wednesday, March 5, 2014 3:54PM - 4:06PM |
Q44.00008: Characterization of three planar germanium detectors fabricated with the crystals grown at USD Hossain Nazir, Mianliang Huang, Muhammad Khizar, Dongming Mei, Guojian Wang, Hao Mei, Yutong Guan We characterized the performance of planar germanium detectors developed in the University of South Dakota (USD). The planar detectors were made from high purity germanium crystals with amorphous germanium contacts. These detectors were developed possible for the neutrinoless double beta-decay measurements and dark matter search underground. They were tested in a temporary cryostat to investigate the depletion voltage, leakage current, efficiency and resolution using a $^{60}$Co $\gamma $ ray source. [Preview Abstract] |
Wednesday, March 5, 2014 4:06PM - 4:18PM |
Q44.00009: Compositional and Surface Effects of Bismuth Incorporation in GaSb Films C. Ryan Tait, Adam Duzik, Joanna Millunchick III-V-Bi semiconductor films represent a new class of highly mismatched alloys that exhibit interesting properties including large reduction in band gap, giant spin orbit bowing, and preserved electron mobility at the expense of hole mobility. These compounds have proven difficult to grow with most results coming from experimentation with GaAsBi with little known regarding GaSbBi. Various growth conditions were tested for GaSbBi and characterized with scanning electron microscopy, x-ray diffraction, and Rutherford backscattering spectroscopy. The films demonstrate Bi concentrations of up to 12{\%} with as low as 3{\%} droplet coverage. Surface Bi and Ga droplet morphology was shown to be dependent on relative flux ratios of Ga, Sb, and Bi and independent of film growth rate. Additionally it is found that As incorporates into the films with no intentional source and the incorporation being dependent on Bi incorporation. This effect is identified as an auto-compensation mechanism for the strain induced from the introduction of Bi. [Preview Abstract] |
Wednesday, March 5, 2014 4:18PM - 4:30PM |
Q44.00010: Fabrication of quantum wire circuits from MBE-grown InAs Carolyn Kan, Chi Xue, James Eckstein If topological quantum computing using Majorana fermions evolves past tabletop experiments involving manipulation of a small number of qubits, scalability of quantum circuits will become an important consideration. At present, experiments have focused on vertically grown nanowires, which must be laid out on a substrate and electrically contacted ex situ. This severely limits the flexibility of the device geometry due to randomness in how the wires fall, and thus hinders the future scalability of the nanowire architecture. We are fabricating quantum wire circuits by lithographic methods out of thin films grown by MBE. We examine high quality MBE-grown InAs material grown GaAs and GaSb substrates, and consider its potential in building Majorana circuits. In particular, better epitaxy and transport is obtained in films grown on lattice matched GaSb, and substrate conductivity appears to freeze out at low temperatures. [Preview Abstract] |
Wednesday, March 5, 2014 4:30PM - 4:42PM |
Q44.00011: The effect of bismuth surfactants on the group V incorporation in InAsSb Evan Anderson, Wendy Sarney, Stefan Svensson, Adam Lundquist, Joanna Millunchick, Chris Pearson Bismuth is a well known surfactant for strained heteroepitaxial growth in compound semiconductors, however, its effect on the incorporation of different species in alloy systems is not well understood. In this work, we investigate the role of a Bi surfactant on the composition and morphology of lattice-matched InAsSb/GaSb as a function of Bi flux and growth temperature. Rutherford Backscattering Spectrometry confirmed that no Bi was incorporated for Bi fluxes up to 4.94e-7 torr. High resolution x-ray diffraction (XRD), on the other hand, showed that the Sb composition decreased with increasing Bi flux or increasing substrate temperature. XRD also indicates that, for a constant Bi flux, Bi has a diminishing effect on film composition as the substrate temperature is increased. Atomic Force Microscopy shows that the surface RMS roughness tended to increase with increasing Bi flux, though this may be due to the fact that these films are further from the lattice matching condition due to reduced Sb incorporation. We speculate that the decrease in Sb incorporation may be a result of a stronger As-Bi interaction energy. [Preview Abstract] |
Wednesday, March 5, 2014 4:42PM - 4:54PM |
Q44.00012: Effect of annealing on $M$-plane GaN thin films grown by PAMBE on tilt-cut LAO substrate Yu-Chiao Lin, Ikai Lo, Ying-Chieh Wang, Cheng-Da Tsai, Chen-Chi Yang, Shuo-Ting You, Ming-Chi Chou The non-polar GaN thin film is a potential candidate for high-efficient photoelectric devices. In this work, we analyzed the characteristics of \textbf{\textit{M}}-plane GaN thin films which were grown on tilt-cut LiAlO$_{\mathrm{2}}$ (LAO) substrate by plasma-assisted molecular beam epitaxy (PAMBE). A series of samples were grown with different N/Ga flux ratios. The crystal structure and optical property of GaN samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and photoluminescence (PL) measurements. The peak of 32.2$^{\mathrm{o}}$ in the XRD measurement showed the [1\underline {1}00] oriented (\textbf{\textit{M}}-plane) for the GaN samples. To improve the crystal quality, we performed the thermal treatment by rapid thermal annealing (RTA) system on these samples and analyzed the crystal structure, surface morphology and optical property of the samples after thermal treatment. The effect of annealing on the \textbf{\textit{M}}-plane GaN thin films was under investigation. [Preview Abstract] |
Wednesday, March 5, 2014 4:54PM - 5:06PM |
Q44.00013: Growth of yellow-green In$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$N/GaN quantum wells by plasma-assisted molecular beam epitaxy Chia-Hsuan Hu, Ikai Lo, Wen-Yuan Pang, Cheng-Hung Shih, Yu-Chi Hsu, Ying-Chieh Wang, Chen-Chi Yang In order to achieve yellow-green In$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$N/GaN quantum-wells, we grew the In$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$N/GaN quantum-wells (QWs) with high indium concentrations by the insertion of an InGaN buffer layer between the QW and GaN template using plasma-assisted molecular beam epitaxy. The InGaN buffer layer was grown with a gradient indium content, in which the lattice mismatch between In$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$N/GaN QW and GaN template can be reduced. The optical properties of the samples were analyzed by photoluminescence measurement at room temperature. The wavelength of InGaN/GaN quantum-well is shifted from 495nm to 560nm. The XRD and SEM measurement results show the high quality crystalline and smooth surface. Therefore, the InGaN buffer layer with gradient indium content provides an effective way to reach high indium incorporation for high quality yellow-green In$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$N/GaN quantum-wells. [Preview Abstract] |
Wednesday, March 5, 2014 5:06PM - 5:18PM |
Q44.00014: Photoluminescence study of Be acceptors in GaInNAs epilayers Y. Tsai, B. Barman, T. Scrace, A. Petrou, M. Fukuda, I.R. Sellers, M. Leroux, M.A. Khalfioui We have studied the photoluminescence (PL) spectra from MBE grown GaInNAs epilayers doped p-type with Beryllium acceptors. The measurements were carried out in the 5 K -- 70 K temperature range and in magnetic fields (B) up to 7 tesla. The PL spectra contain two features at T $=$ 5 K: The exciton at 1093 meV [2] and a second broader feature at 1058 meV. The intensity of this feature decreases with increasing temperature and disappears completely by 70K while the excitonic feature persists. The emission at 1058meV is identified as the conduction band to Beryllium acceptor transition. If we take into account the binding energy of the exciton [3] we get a value of 23 meV for the Beryllium acceptor binding energy. The acceptor related transition was studied as a function of magnetic field; the energy of this transition has a linear dependence on B with a slope of 055 meV/T. [2] Y.Tsai et al, Appl Phys Lett \textbf{103}, 012104(2013) [3] K.Kashima et al., Jpn. J. Appl. Phys. \textbf{50}, 06GH09(2011) [Preview Abstract] |
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