Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V12: Semiconductor Growth and Etching |
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Sponsoring Units: DMP DCMP Chair: Melissa Hines, Cornell University Room: 308 |
Thursday, March 19, 2009 8:00AM - 8:12AM |
V12.00001: Morphological Study of MBE Grown Iron Nitride Films on Zinc-Blende GaN(001) Jeongihm Pak, Wenzhi Lin, Yinghao Liu, Kangkang Wang, Abhijit Chinchore, Arthur Smith, Kai Sun Iron nitrides are attractive materials for their high magnetic moments, corrosion, and oxidation resistance. We present the successful epitaxial growth of iron nitride (FeN) film on zinc-blende gallium nitride ($c$-GaN) using molecular beam epitaxy with Fe $e$-beam evaporation and rf N-plasma source at substrate temperature of 210 \r{ }C. The film growth is monitored \textit{in-situ} using reflection high energy electron diffraction (RHEED) and the samples are analyzed \textit{ex-situ} using x-ray diffraction (XRD), cross-sectional TEM and atomic force microscopy (AFM). By monitoring the structure, morphology, and lattice constant evolution of the FeN films, the crystal phase and orientation with respect to the $c$-GaN substrate are deduced to be zinc-blende phase with the epitaxial relationship [001]$_{FeN} \quad \vert \vert $ [001]$_{GaN}$ and [100]$_{FeN }\vert \vert $ [100]$_{GaN}$. Surface morphological studies by AFM show cubic structures ranging from 250-400 nm in size and having smooth plateaus with roughness of 6 {\AA}. This work has been supported by DOE (Grant {\#}DE-FG02-06ER46317). [Preview Abstract] |
Thursday, March 19, 2009 8:12AM - 8:24AM |
V12.00002: Iron and Iron Nitride Layers on Wurtzite Gallium Nitride Studied Using MBE/STM Wenzhi Lin, Jeongihm Pak, Yinghao Liu, Kangkang Wang, Abhijit Chinchore, David Ingram, Arthur Smith, Kai Sun It is of interest to study epitaxial growth of iron and iron nitride (FeN) layers on wurtzite gallium nitride (w-GaN) as a possible magnetic/wide-gap semiconductor system for spintronics. X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED) of Fe deposited on GaN(0001) suggest the existence of the epitaxial relationship [110]$_{Fe}\vert \vert $ [0001]$_{GaN}$. Furthermore, multi-streak RHEED patterns indicate the formation of a multi-domain but smooth film. Also, we have investigated the growth of $\sim $ 1:1 iron nitride on w-GaN(0001) using nitrogen plasma-assisted molecular beam epitaxy (MBE). Both reciprocal and real space techniques were used to study the growth of FeN, including RHEED and scanning tunneling microscopy/spectroscopy (STM/STS). Bulk characterization was also applied, including XRD and transmission electron microscopy (TEM). The results indicate that zinc-blende FeN grows on GaN(0001) with the epitaxial relationship [111]$_{FeN }\vert \vert $ [0001]$_{GaN}$, and initial atomically-smooth FeN layers are formed. This work has been supported by DOE (Grant {\#}DE-FG02-06ER46317). [Preview Abstract] |
Thursday, March 19, 2009 8:24AM - 8:36AM |
V12.00003: Stability of Mg-incorporated InN surfaces: first-principles study T. Akiyama, K. Nakamura, T. Ito, J. -H. Song, A. J. Freeman InN films are attractive materials for electronic and optelectronic applications. The growth of InN eptitaxial films with $n$-type and $p$-type conductivity has traditionally been performed along the polar $<$0001$>$ direction\footnote{R.E. Jones et al., Phys. Rev. Lett, {\bf 96}, 125505 (2006)}, which may result in large polarization fields along the growth direction, reducing the radiative efficiency of quantum-well light emitters. To overcome this drawback, the growth along nonpolar orientation such as (10$\bar{1}$0) and (11$\bar{2}$0) planes and its $p$-type doping have been recently carried out. We have addressed this issue by performing first-principles pseudopotential calculations for Mg-incorporated InN surfaces in various orientations, including (10$\bar{1}$0) and (11$\bar{2}$0) as well as (0001) and (000$\bar{1}$) surfaces\footnote{J.-H. Song et al., Phys. Rev. Lett. {\bf 101}, 106803 (2008)}. The calculated surface energies demonstrate that qualitative trends in the stability of Mg-incorporated surfaces agree with those on GaN surfaces \footnote{J.E. Northrup, Appl. Phys. Lett. {\bf 86}, 122108 (2005)}, although several surface reconstructions different from those on GaN surfaces are obtained. The effects of growth conditions on $p$-type doping are also discussed. [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 8:48AM |
V12.00004: Ferromagnetic $\delta -MnGa$ On Wurtzite GaN(0001): Interface Formation And Film Properties Kangkang Wang, Abhijit Chinchore, Wenzhi Lin, Jeongihm Pak, Arthur Smith, Kai Sun Ferromagnetic (FM) metal/wide band-gap semiconductor contacts are of great interest due to their potential for novel spintronics applications, such as blue and ultra-violet spin light-emitting diodes$^{[1]}$. One promising candidate is $\delta -MnGa$ on wurtzite GaN, whose epitaxial growth has recently been reported$^{[2]}$ , with controllable magnetism via controlling of the Mn:Ga flux ratio. Here we report further studies on MnGa/GaN system grown by N$_{2}$-plasma equipped molecular beam epitaxy (MBE). Reflection high-energy electron diffraction (RHEED) data suggests a quicker and more abrupt interface formation when grown on Ga-polar GaN surface as compared to N-polar. \textit{In-situ} scanning tunneling microscopy (STM) measurements on the first few monolayer's as well as thicker MnGa films will be presented, revealing details of interface formation and other film properties. Stoichiometry dependence of the growth and magnetic properties will also be discussed. This work is supported by DOE (Grant No.DE-FG02-06ER46317) and NSF (Grant No. 0730257). Equipment support from ONR is also acknowledged. [1] S.A.Wolf \textit{et al}, Science \textbf{294}, 1488 (2001) [2] E.Lu \textit{et al}, Phys.Rev.Lett. \textbf{97}, 146101 (2006) [Preview Abstract] |
Thursday, March 19, 2009 8:48AM - 9:00AM |
V12.00005: Low-temperature transport properties of disordered tantalum and tantalum nitride films Nicholas Breznay, Mihir Tendulkar, Aharon Kapitulnik Tantalum nitride thin films are used in a wide range of electronic applications, such as in thin film resistors and diffusion barriers in silicon microstructures. Growth and thorough characterization of ultrathin tantalum nitride films may prove useful in potential applications and also facilitate the study of disordered, low-dimensional systems. We will discuss the low-temperature transport properties of reactively sputtered tantalum and tantalum nitride ultrathin films as a function of film structure and composition, and connect our results to recent studies of both these and other similar two-dimensional disordered systems. [Preview Abstract] |
Thursday, March 19, 2009 9:00AM - 9:12AM |
V12.00006: First Principles Phases of Sub-Monolayer Sr and La on Si (001) Kevin Garrity, J.W. Reiner, F.J. Walker, C.H. Ahn, S. Ismail-Beigi The epitaxial integration of complex oxides with semiconductors is a key requirement for many emerging technologies. In the short term, the scaling down of the dielectric layer in current CMOS technology will soon require new materials with higher dielectric constants to prevent quantum mechanical leakage currents. More generally, the epitaxial integration of complex oxides with semiconductors would allow new devices to take advantage of the wide range of oxide properties. To date, the first step of the only known method to grow complex oxides on silicon epitaxially has required 1/2 ML of an alkaline earth metal, usually Sr, to be deposited on a clean silicon surface at about 600 C. Using first-principles density functional theory calculations, we examine the growth of sub-monolayer coverages of both Sr and La on Si (100). For Sr on Si, we report on a novel 1/6 ML structure which explains the complex temperature dependence observed experimentally below 1/2 ML Sr. We compare these results to the case of La on Si and elucidate some differences which hinder the growth of epitaxial oxides on La template layers. Our results predict an experimentally verified low temperature path to epitaxy using a Sr template layer. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:24AM |
V12.00007: From STM Images to Chemical Understanding: Kinetic Monte Carlo Simulations of Si(100) Etching Ankush Gupta, Ian T. Clark, Brandon S. Aldinger, Melissa A. Hines Etching reactions literally write a record of their chemical reactivity in the morphology of the etched surface -- a record that can be read using scanning tunneling microscopy (STM) and decoded with the help of simulation. We have developed a fully atomistic kinetic Monte Carlo simulation of Si(100) etching that is appropriate for aqueous etchants that produce fully H-terminated surfaces [e. g., NH$_{4}$F(aq), KOH(aq) and even H$_{2}$O]. The model assumes that the reactivity of individual surface sites is determined by the local geometry. As an example, we simulate the production of near-atomically flat Si(100) surfaces, recently observed experimentally, and show that interadsorbate stress plays a crucial role in determining the steady-state etch morphology. The simulated morphologies are in good agreement with experimental observations. [Preview Abstract] |
Thursday, March 19, 2009 9:24AM - 9:36AM |
V12.00008: Atomic-Scale Effects of Applied Strain on Etching of Si(100) Marc F. Faggin, Brandon S. Aldinger, Ankush Gupta, Melissa A. Hines An ideal hydrogen-terminated Si(100) surface would be highly stressed due to unfavorable steric interactions between neighboring surface sites (i.e. neighboring silicon dihydride species). As a result, some aqueous etchants selectively remove every other silicon dihydride to relieve the stress, producing an unusual striped morphology. In these experiments, we apply a uniaxial strain to the surface during etching. Using a combination of scanning tunneling microscopy and surface infrared spectroscopy, we show that applied strains dramatically alter the etch morphology and the surface species, in some cases promoting the formation of hillocks. These effects are explained in terms of the site-specific reactivity of the etching silicon surface. [Preview Abstract] |
Thursday, March 19, 2009 9:36AM - 9:48AM |
V12.00009: Aqueous Etching Produces Si(100) Surfaces of Near-atomic Flatness Brandon S. Aldinger, Ankush Gupta, Ian T. Clark, Melissa A. Hines The production of atomically flat Si(100) surfaces is a long-standing technological challenge, as these surfaces are the basis for today's microelectronic devices. We use a combination of STM and vibrational spectroscopy to show that a simple aqueous etch can produce Si(100) surfaces of suprising and unprecedented smoothness. The etched surfaces are characterized by long rows of H-terminated Si atoms. The chemical origins of this perfection are uncovered, in part, by a new polarization-based, spectral deconvolution technique that significantly simplifies the analysis of the well-know H/Si(100) vibrational spectrum. Kinetic Monte Carlo simulations yield further insights into the site-specific chemical reactions that govern the steady-state etch morphology. The effects of interadsorbate stress, etchant pH, and gas evolution will also be discussed as time permits. [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:00AM |
V12.00010: Quantitative Correlations of Stress Field and Threading Dislocation Configurations in Si/Si$_{1-x}$Ge$_{X}$/Si(100) Strained Layers Chi-Chin Wu, Robert Hull The equilibrium configurations of the threading dislocation connecting misfit dislocation dipoles in Si/Si$_{1-x}$Ge$_{x}$/Si(100) heterostructures have been analyzed by simulation, and compared to experimental images to investigate the correlations of stress field variations and dislocation configuration in capped heteroepitaxial thin films. Calculations are based on the energy equations for dislocations in elastically isotropic crystals over all possible dislocation angular configurations, and the orientations with the minimum total energy are determined as functions of the magnitude and variations of the film stresses. It is determined that the configuration with the misfit dislocation leading at the cap/film interface (as opposed to the film/substrate interface) is increasingly favored either with increasing magnitude of local film stress/strain or with the variation in calculated geometry of the threading dislocation. [Preview Abstract] |
Thursday, March 19, 2009 10:00AM - 10:12AM |
V12.00011: Ordering mechanisms of periodic stripe arrays on boron-doped Si(100) Ivan Ermanoski, Gary Kellogg, Norman Bartelt We have used low energy electron microscopy to determine the factors that control the degree of order in self-assembled periodic stripe arrays on the atomically flat Si(100) with high boron doping. The stripes consist of extremely elongated vacancy islands of single atomic height, formed at $\sim $900C, confined in micrometer-sized pits. ``Perfect'' arrays of parallel stripes (in pits of up to $\sim $10um in size) were formed by allowing various defects to heal over relatively long periods of time. Sublimation was compensated for by an external Si doser, allowing observation of stripe evolution over the course of hours, with no net loss or gain of Si from the area of interest. Stripe formation and ordering mechanisms include spontaneous nucleation and growth of new islands, longitudinal splitting, as well as coarsening due to surface diffusion. Stripe periodicity depends on temperature, allowing for control of this property. Stripes are stable in a range of $\sim $100C, outside of which they assume the familiar shape of elongated islands, shaped by the anisotropy in step energy. Stripe order can be preserved to room temperature by quenching. References: [1] J.-F. Nielsen et al., Appl. Phys. Lett. 79 (2001) 3857 [Preview Abstract] |
Thursday, March 19, 2009 10:12AM - 10:24AM |
V12.00012: On the Growth Mechanisms of Plasma Deposited Amorphous Silicon Thin Films Dimitrios Maroudas, Sumeet Pandey, Tejinder Singh We present a theoretical study of the growth mechanism of plasma deposited amorphous silicon (Si) thin films based on kinetic Monte Carlo simulations according to a transition probability database constructed by first-principles density functional theory calculations. Based on the results of the study, we propose a comprehensive mechanism of amorphous Si thin film growth by plasma deposition under conditions that make the silyl radical the dominant deposition precursor. The growth mechanism consists of various surface kinetic events including radical-surface interactions, adsorbed radical-radical interactions, radical surface diffusion, and surface hydride dissociation reactions. Of particular importance to the Si film growth process and the resulting surface composition is the radical dissociative adsorption mediated by Si over-coordination defects along the reaction pathway. The proposed mechanism explains the experimentally measured surface composition of plasma deposited Si films under the deposition conditions considered. [Preview Abstract] |
Thursday, March 19, 2009 10:24AM - 10:36AM |
V12.00013: Fundamental Study of Boron Carbide Sputtering Sudarshan Karki, Dae Yeoun, Saad Janjua, Marcus Driver, Anthony Caruso Boron-rich carbides belong to a special class of solids whose main structural unit is the twelve atom icosahedra. When depositing thin films of boron carbide (nominally B$_{4}$C) by RF or pulsed DC magnetron sputtering, the individual sputtered or ablated cluster size and the temperature of the substrate to which the clusters adsorb to form the film, greatly affects the bulk film physical and electronic structure. This talk will present mass spectrometry data of the target clusters as a function of RF power, DC bias and chamber pressure toward the goal of modeling and understanding how the icosahedral based boron-rich materials sputter and the resultant control over the final film properties. Argon trapped into the film during the deposition as determined by X-Ray photoemission will also be discussed. [Preview Abstract] |
Thursday, March 19, 2009 10:36AM - 10:48AM |
V12.00014: Correlation between Bonding Geometry and Band Gap States at Organic -- inorganic interfaces: Catechol on Rutile TiO$_{2}$ (110) Ulrike Diebold, Shao-Chun Li, Jian-guo Wang, Peter Jacobson, Xue-Qing Gong, Annabella Selloni Adsorbate-induced band gap states in semiconductors are of particular interest due to the potential of increased light absorption and photoreactivity. A combined theoretical (DFT) and experimental (STM, photoemission) study of the molecular-scale factors involved in the formation of gap states in TiO$_{2}$ is presented. Using the organic catechol on rutile TiO$_{2}$(110) as a model system it is found that the bonding geometry strongly affects the molecular electronic structure. At saturation catechol forms an ordered 4 $\times $ 1 overlayer. This structure is attributed to catechol adsorbed on rows of surface Ti atoms with the molecular plane tilted from the surface normal by about $\pm $27\r{ } in an alternating fashion. In the lowest-energy structure one of the two terminal OH groups at each catechol dissociates and the O binds to a surface Ti atom in a monodentate configuration, while the other OH group forms a H-bond to the next catechol neighbor. Through proton exchange with the surface this structure transforms into one where both OH groups dissociate and the catechol is bound to two surface Ti in a bidentate configuration. Only bidendate catechol introduces states in the band gap of TiO$_{2.}$ [Preview Abstract] |
Thursday, March 19, 2009 10:48AM - 11:00AM |
V12.00015: Theoretical adhesion strength of diamond coating with metallic interlayers. Haibo Guo, Yue Qi, Xiaodong Li Metallic interlayers are often needed to enhance the adhesion of diamond coatings to substrates and to promote diamond nucleation and growth. The interfaces between diamond coatings and metallic interlayer materials with different carbide formation enthalpies, Cu, Al, and Ti, are studied using density functional theory. The ideal interface strength or the work of separation is found to decrease with the carbide formation enthalpy. Analysis to the electronic structure shows that covalent metal-carbon bonds form at the interface, and the perturbation from the interface weakens nearby metal phase. Comparing the work of separation at the interface with the fracture energy of the metal, a fracture is likely to initiate in the metal phase near the interface, therefore a tough metal with a large surface energy is needed to achieve a higher overall toughness. In addition, when the surface energy is larger than the interface energy, a wetted diamond/metal interface is formed during diamond nucleation, which also contributes to good adhesion. The interface energy, which is an energy barrier to diamond nucleation, is found to decrease with the carbide formation enthalpy. These results indicate strong carbide formability and a large surface energy of the interlayer enhance the adhesion and the fracture resistance of the interface, and also conduce to the diamond nucleation on the interlayer. [Preview Abstract] |
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