Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session A11: Semiconductor Growths |
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Sponsoring Units: FIAP Chair: Renbo Song, Lehigh University Room: D222 |
Monday, March 21, 2011 8:00AM - 8:12AM |
A11.00001: Kinectic Monte Carlo Simulation of Strained Heteroepitaxial Growth Peter Smereka, Tim Schulze An efficient algorithm for the simulation of strained heteroepitaxial growth with intermixing in 2+1 dimensions is presented. The talk will first describe a KMC solid-on-solid model that has been modified to incorporate elastic interaction. The simulation of such models is computationally difficult due to the need to repeatedly update the elastic displacement field. This hurdle can be overcome by using local updates of the displacement field combined with a multigrid approach for global updates (when needed). The validity of this technique can be theoretically justified. This algorithm is efficient enough to allow the simulation of heteropitaxy on macroscopic time scales. Simulations will have 100 million to 10 billion atomistic moves. Results will be presented showing how various parameters (e.g. temperature, misfit, and deposition rate) effect the morphology of growing films. Annealing simulations of a single 3d island reveal something akin to the pyramid to dome transition observed for Ge islands on Si. Simulations of stacked quantum dots will be presented, these simulations show the capping layer can erode the dots and the alignment of the dots is somewhat different than is often proposed in the literature. [Preview Abstract] |
Monday, March 21, 2011 8:12AM - 8:24AM |
A11.00002: Fabrication and characterization of cryogenic complementary devices on Si/SiGe heterostructures T.M. Lu, C.-H. Lee, D.C. Tsui, C.W. Liu We have fabricated cryogenic complementary devices using undoped Si/SiGe heterostructures which contain an electron quantum well and a hole quantum well. The highest temperature in the fabrication process is as low as 440\r{ }C, preserving the quality of the epitaxial films. By properly biasing the gate voltage, two-dimensional (2D) electrons and holes are induced capacitively in the quantum wells. The electron mobility, $\sim $2$\times $10$^{4}$ cm$^{2}$/Vs, is significantly lower than that in a heterostructure without any hole quantum well. Nevertheless, the induced 2D electrons show the integer and fractional quantum Hall effect characteristics. The mobility of the 2D holes is $\sim $7$\times $10$^{3}$ cm$^{2}$/Vs, consistent with previous reports, and is limited by alloy scattering. A proof-of-principle inverter is demonstrated. [Preview Abstract] |
Monday, March 21, 2011 8:24AM - 8:36AM |
A11.00003: Mechanisms of Stranski Krastanov Growth Arvind Baskaran, Peter Smereka During the Heteroepitaxial growth of strained semiconductor films (like Ge on Si) the self assembly of quantum dots is observed. This is often reported in experiments to take place though the Stranski Krastanov (SK) growth mode, where the film grows in a layer by layer fashion up to a certain critical thickness after which islands (dots) form. In this talk we present a study of the SK growth mode using a solid on solid Kinetic Monte Carlo model. The importance of the use of such an discrete stochastic model and its merits over the continuum approach will be outlined. Entropy is found to play a very crucial role in the SK growth mode. The mechanism of the SK growth is understood in the context of a delicate balance of the energy and entropy. This is joint work with Peter Smereka. [Preview Abstract] |
Monday, March 21, 2011 8:36AM - 8:48AM |
A11.00004: High-purity germanium crystal growth for DUSEL experiments Wenchang Xiang, Yongchen Sun, Dongming Mei, Yutong Guan, Chao Zhang High-purity Germanium single crystals can be fabricated into ultra-low background detectors for dark matter and neutrinoless double-beta decay experiments at DUSEL. If the crystals are grown in underground environment, the cosmogenic production can be minimized and hence the crystals can be ultra-pure for the next generation experiments at DUSEL. Growing high-purity germanium crystals represents one of the most difficult tasks in semiconductor field. We adopt Czochralski method in growing single crystal in order to understand various technical challenges. With the pioneers' work done in the past, we are moving rapidly toward growing high quality single crystals on the surface. With the available valuable papers and accumulation of the growing experience, our growing process is being improved on weekly basis. This paper will report the grown crystals produced by our equipment and address versions issues with the growing processes. [Preview Abstract] |
Monday, March 21, 2011 8:48AM - 9:00AM |
A11.00005: Strain-promoted growth of Mn silicide nanowires on Si(001) Kazushi Miki, Hongjun Liu, James H.G. Owen, Christoph Renner We have discovered a method to promote the growth of Mn silicide nanowires on the Si(001) at 450$^\circ$C. Deposition of sub-monolayer quantities of Mn onto a Si(001) surface with a high density of Bi nanolines results in the formation of nanowires, 5-10 nm wide, and up to 600 nm long. These nanowires are never formed if the same growth procedure is followed in the absence of the Bi nanolines. The Haiku core of the Bi nanoline is known to induce short-range stress in the surrounding silicon surface, straining neighbouring dimers, and repelling step edges [1]. We discuss the possible mechanisms for this effect, including the effect of the Bi nanolines on the surface stress tensor and alteration of the available diffusion channels on the surface. \\[4pt] [1] J. H. G. Owen, K. Miki, and D. R. Bowler J. Mat. Sci. 41 4568-4603 (2006) [Preview Abstract] |
Monday, March 21, 2011 9:00AM - 9:12AM |
A11.00006: Hyperthermal epitaxy of enriched $^{28}$Si Kevin Dwyer, Joshua Pomeroy In the effort to produce devices suitable for quantum computation, it is necessary to increase as much as possible the T$_{2}$ coherence time of the electron or nuclear spin being used as a qubit. For silicon devices this means using isotopically enriched $^{28}$Si. This is because $^{28}$Si has no net nuclear spin while the spin of $^{29}$Si present in natural Si (4.67{\%}) interacts with the qubit spin and reduces the T$_{2}$ time greatly. Sufficiently long T$_{2}$ times are necessary for successful operation of quantum computers and we will demonstrate a method for producing epitaxial layers of $^{28}$Si on a Si substrate. Ideally, the silicon layers produced must not only be isotopically enriched, but chemically pure and defect free for best performance. These qualities are produced by deposition from a hyperthermal energy beam line using a mass selecting magnet. Depositing silicon epilayers at hyperthermal energies allows for greater manipulation of layer quality. This process is tested and calibrated initially using carbon dioxide. As a preliminary test, isotopically enriched $^{13}$C is implanted into semiconductor grade silicon and analyzed by secondary ion mass spectroscopy as an independent check on estimated levels of isotopic and chemical purity. [Preview Abstract] |
Monday, March 21, 2011 9:12AM - 9:24AM |
A11.00007: Anti-phase domain suppression and increased electron mobilities in InSb epilayers and quantum wells on off-axis Ge(211) and GeOI(001) substrates Mukul C. Debnath, Tetsuya D. Mishima, Michael B. Santos, Khalid Hossain, Orin W. Holland We report on the molecular beam epitaxy of InSb epilayers and Si \textit{$\delta $}-doped InSb/Al$_{x}$In$_{1-x}$Sb quantum wells (QWs) on off-axis Ge(211) and Ge-On-Insulator (GeOI)-On-Si substrates. The high carrier mobilities in $n$-type InSb and $p$-type Ge QWs provide a motivation to integrate these structures on a single substrate for an improved CMOS technology. Growth on GeOI substrates may also make possible the integration of InSb infrared detectors with Si transistors. We evaluate the suppression of anti-phase domains (APDs) through analysis of Reflection High-Energy Electron Diffraction (RHEED) patterns obtained during growth on off-axis substrates. The narrowest X-ray rocking curve width is 100 arc sec for a 4.0-$\mu $m-thick InSb epilayer. The highest room temperature electron mobilities of a 4.0-$\mu $m-thick InSb epilayer and an InSb QW are 64,000 and 23,500 cm$^{2}$/V-s for growth on off-axis Ge(211) and GeOI(001) substrates, respectively. We attribute the single-domain RHEED patterns, reduced X-ray rocking curve widths, and increased electron mobilities to the suppression of APDs in the structures grown on off-axis Ge(211) and GeOI(001) substrates. [Preview Abstract] |
Monday, March 21, 2011 9:24AM - 9:36AM |
A11.00008: Synthesis of large-area graphene on cobalt film by thermal cracker enhanced gas source molecular beam epitaxy Ning Zhan, Guoping Wang, Jianlin Liu Recently, synthesis of large-area graphene has become increasingly important. Various metal substrates have been tested. Among these substrates, cobalt (Co) has been used to absorb carbon and form hexagonal structures on its surface. Nevertheless, only small graphene piece or nano carbon islands have been achieved. Here, we propose a method to grow graphene on Co using thermal cracker enhanced gas source molecular beam epitaxy. Atomic carbon beam provided by thermal cracker impinges to Co film and forms graphene epitaxially. Raman spectroscopy and transmission electron microscopy measurements confirmed mis-oriented stacking order between layers rather than strict AB Bernal stacking. The coverage of single layer and bi-layer is more than 90{\%}. Growth temperature- and time-dependent analyses indicate a narrow growth window for the growth of few-layer graphene. [Preview Abstract] |
Monday, March 21, 2011 9:36AM - 9:48AM |
A11.00009: Studies on magneto-transport properties of dilute magnetic semiconductors R. Gupta, A. Ghosh, Y. Kolekar, K. Ghosh, P. Kahol Diluted magnetic semiconductors (DMS) are rare group of promising semiconductors in which a fraction of the constituent ions is replaced by magnetic ions. This study is aimed to understand the magneto-transport properties of magnetic ion doped In2O3 thin films. The films were grown under different temperature and partial oxygen pressures by pulsed laser deposition. The films were characterized using various techniques such as X-ray diffraction, UV-VIS spectroscopy and magneto-transport. Anomalous magneto-resistive (MR) behavior has been observed for these films, which largely depends on growth conditions. For example, Co doped In2O3 films show presence of negative as well as positive MR at low temperatures. However, the film grown at 400 0C at a partial oxygen pressure of 1$\times$10-4 mbar shows negative MR with a maximum value of around -0.3\%. Films grown under higher partial oxygen pressures show large positive MR. Maximum positive MR of 8.9\% is seen for the film grown at partial oxygen pressure of 4.3$\times$10- 4 mbar at 400 0C. The effect of growth conditions on MR properties of these films will be presented in detailed. This work is supported by National Science Foundation (Award Number DMR-0907037). [Preview Abstract] |
Monday, March 21, 2011 9:48AM - 10:00AM |
A11.00010: Phase evolution and microstructure growth of CuInSe$_{2}$ by sonochemistry Emre Yassitepe, William N. Shafarman, S.Ismat Shah Non toxic chemical routes that enable formation of high quality CuInSe$_{2}$ thin films with high materials utilization are desired for low production cost of solar cells. Sonochemistry provides a well known route to form reactive surfaces in metallic particles and , in the literature, CuSe has been reactively formed by using organic precursors. We will present results of the effects of ultrasound on the reactivity between Cu, In and Se elemental particles. The reaction between these elements facilitates binary selenide phase formation which promotes single phase growth of CuInSe$_{2}$ with further annealing. XRD analyses showed that binary phases of CuSe$_{2}$, CuSe and In$_{4}$Se$_{3}$ are formed by sonication. Annealing these binary phases led to the single phase formation of CuInSe$_{2}$ at 350\r{ }C. We have found that if In has not reacted with Se during sonication, the structure is not completely transformed to CuInSe$_{2}$ at 350\r{ }C. [Preview Abstract] |
Monday, March 21, 2011 10:00AM - 10:12AM |
A11.00011: Structural and magnetic properties of Cr and Co doped indium oxide dilute magnetic semiconductors K. Ghosh, E. Nahlik, M. Langhoff, R. Gupta, Y. Kolekar, P. Kahol Dilute magnetic semiconductors have attracted considerable attention for development of next generation multifunctional spintronics devices. Indium oxide is a wide band gap semiconductor with unique optical and electrical properties. Here, we investigate the effect of Co and Cr doping on structural and magnetic properties of Indium oxide. Different amounts of Co and Cr were doped in In2O3 using solid state reaction method. Structural and magnetic properties have been measured using standard techniques. X-ray diffraction analysis confirmed single phase Indium oxide with no impurity phases due to addition of Co and Cr. Magnetization (M) as a function of applied magnetic field (H) and temperature (T) were collected on all the samples using a superconducting quantum interference device magnetometer. M vs T measurements for Co doped Indium oxide showed the presence of a hump around 50K which could be due to paramagnetic to ferromagnetic transition and the M vs H field study show the hysteresis behavior which confirms the ferromagnetism. This work is supported by National Science Foundation (Award Number DMR-0907037) [Preview Abstract] |
Monday, March 21, 2011 10:12AM - 10:24AM |
A11.00012: High-Purity Germanium Crystal Characterization for DUSEL Experiments Dongming Mei, Chaoyang Jiang, Oleg Perevozchikov, Nick Weinandt, Yongchen Sun Understanding the nature of neutrinos and dark matter was identified by a National Academy of Sciences panel as one of the key problems facing physicists today. The CUBED (Center for Ultra-Low Background Experiments at DUSEL) collaboration is working on the development of techniques to manufacture crystals in an underground environment with unprecedented purity levels that may be used by experiments proposed for DUSEL. Growing high-purity germanium crystals depends strongly on the understanding of various impurities in the grown crystals and developing new techniques to eliminate them. This paper will present the characterization techniques to identify the impurity levels according to their energy levels and distributions. The results will provide feedback for the crystal growth process that would eliminate the impurities in the grown crystals for DUSEL experiments. [Preview Abstract] |
Monday, March 21, 2011 10:24AM - 10:36AM |
A11.00013: Stable Nanocrystals vs. Ostwald Ripening: A Theoretical Investigation Michael Clark, Sanat Kumar Previous studies have shown that stable, monodisperse-sized nanocrystals (NCs) have been produced through the use of strongly binding surfactants, e.g. Au NCs with alkylthiols or Co NCs with oleic acid, to name a few. Through a first-principles theoretical investigation, we determine that these stable sized NCs are in an equilibrium state, and we establish what conditions lead to stable, monodisperse nanocrystals instead of polydisperse nanocrystals undergoing Ostwald ripening. Our results further describe how the equilibrium NC size can be tuned through experimentally adjustable parameters (concentration, temperature, reactant proportions), providing novel concepts for controlling the synthesis of monodisperse nanocrystals. Our theoretical results are compared directly with experimental NC syntheses, providing additional insight into the microscopic properties and dynamics of these stable NC mixtures. [Preview Abstract] |
Monday, March 21, 2011 10:36AM - 10:48AM |
A11.00014: Extreme electronic sensitivity of carbon nanotubes to internal wetting Di Cao It is now possible to pass a solution of an analyte through the interior of individual single-walled carbon nanotube (SWCNT) nanofluidic channels in a planar device connecting two fluid reservoirs. By building field-effect transistor connections onto the SWCNT nanofluidic channel, we have discovered that internal wetting of the SWCNT by pure water turns semiconducting tubes on, and renders them insensitive to back gating. Transistor action is restored when the devices are dried under vacuum. In contrast, external wetting has little effect. Theoretical simulations recapitulate this behavior, showing that the difference in response to internal and external wetting is a consequence of nanoconfinement, which enabled water molecule structure ordering and enhanced the water-CNT interaction. The dipole field of ordered water locks the CNT potential and the water-CNT interaction modifies the electronic structure of the CNT. [Preview Abstract] |
Monday, March 21, 2011 10:48AM - 11:00AM |
A11.00015: CN-VFET Based Organic Nonvolatile Memory Elements Using a Floating Gate Po-Hsiang Wang, Bo Liu, Mitchell McCarthy, Andrew Rinzler We have demonstrated organic nonvolatile memory elements based on carbon nanotube enabled vertical field effect transistors (CN-VFETs) with a hybrid dielectric embedded floating metal gate used for charge storage. The electric field concentration around the high aspect ratio carbon nanotubes (acting as the source electrode in the vertical transistor) makes them excellent sources of charge injection of both polarities into the floating gate. This results in a large, fully programmable, hysteresis in cyclic transfer curves without sacrificing carrier mobility in the vertical organic channel layer. These features may provide for cost-effective, relatively high-density organic memory devices compared to more conventional TFT architecture organic devices. [Preview Abstract] |
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