Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session H40: Semiconductors: Growth and Characterization |
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Sponsoring Units: FIAP Chair: Howard Branz, Energy Renewable Research Laboratory Room: Colorado Convention Center 503 |
Tuesday, March 6, 2007 8:00AM - 8:12AM |
H40.00001: Breakdown physics of low-temperature silicon epitaxy Charles W. Teplin, Pauls Stradins, Eugene Iwaniczko, Qi Wang, Kim M. Jones, Robert Reedy, Bobby To, Dean H. Levi, Helio Moutinho, Howard M. Branz We describe new insights into the mechanisms that affect low-temperature silicon epitaxy growth (T$<$630\r{ }C) by chemical vapor deposition (CVD). Experiments using hot-wire CVD show that below 500\r{ }C epitaxial growth is limited to relatively small thicknesses ($\sim $0.5$\mu $m), after which an amorphous nucleates and takes over film growth. Above $\sim $600\r{ }C, however, epitaxy is possible to very large thicknesses (at least 11 $\mu $m) and no breakdown is observed. We present an isotropic model for growth that explains the morphologies observed after breakdown to a-Si:H at low temperatures. The cause of breakdown, however, is still not well understood. However, our hot-wire CVD experiments over a large range of temperatures (200-700\r{ }C) provide important insights into the roles of roughness (that is implicated in the failure of low-T molecular beam silicon epitaxy) and hydrogen in epitaxy failure. [Preview Abstract] |
Tuesday, March 6, 2007 8:12AM - 8:24AM |
H40.00002: Silicon epitaxy onto silicon wafers above 600\r{ }C by 100 nm/min hot-wire chemical vapor deposition Paul Stradins, Charles W. Teplin, Kim Jones, Robert C. Reedy, Qi Wang, Howard M. Branz We study a new silicon epitaxy regime by hot-wire chemical deposition onto silicon surfaces above 600\r{ }C. In this regime, epitaxy proceeds at high growth rates ($>$100 nm/min) compared with lower-T growth, and does not appear to be thickness-limited. With a tantalum hot-wire operating at 1900\r{ }C in SiH$_{4}$, we obtain phase-pure Si at 77 nm/min on (100)-oriented wafers at 650\r{ }C. With a tungsten filament at 2100 \r{ }C, phase-pure epitaxy proceeds faster than 100 nm/min from 620 to 700\r{ }C. Epitaxial growth up to 11{\-}$\mu $m thick is confirmed by transmission electron microscopy, x-ray diffraction and in-situ ellipsometry. This relatively low T epitaxial growth regime could be utilized for photovoltaic devices made by epitaxial thickening of c-Si seeds on low-cost substrate such as borosilicate glass. Temperature above 600$^{o}$C and corresponding thermal dehydrogenation of the growing surface is critical for the high-quality, rapid epitaxial growth: between 450 and 600\r{ }C, there appears to be an intermediate region where epitaxy is poor or nonexistent -- even in comparison with epitaxy at 200 to 400\r{ }C. The role of gas depletion chemistry, as well as structural/electronic quality is discussed. [Preview Abstract] |
Tuesday, March 6, 2007 8:24AM - 8:36AM |
H40.00003: Study on the growth of ZnO micro and nano-structures at low temperature and atmospheric pressure M. Morales, B. Claflin, G.C. Farlow, D.C. Look Deposition of ZnO from the vapor in flowing carrier gases has been studied for use in the growth of micro- and nano- structures. We have investigated how variations in the carrier gas composition and flow rate and the position of the substrate control the morphology of the nanostructures. Source material was either Zn powder or Zn acetate, either evaporated (powder) or decomposed (acetate) in the temperature range $500^oC$ to $650^oC$ in flowing $Ar/O_2$ at atmospheric pressure. It was also found that Zn powder must be washed in HCl to achieve reliable deposition at the lower temperatures. Scanning electron microscopy (SEM) images of samples grown from a Zn acetate source show micron-sized chimneys forming at 5 cm from the source, to 100 nm dispersed crystals at 7 cm or greater distance from the source. SEM images of samples grown from a Zn powder source show forrested needles $\sim$ 100 nm in diameter by 1 micron long.Photoluminescence measurements from these samples show a dominate line at 3.36 eV with additional features at 3.32 and 3.37 eV. The line widths are $\sim$ 3.5 meV, indicating good quality material. The usual gree-band emission is also observed. [Preview Abstract] |
Tuesday, March 6, 2007 8:36AM - 8:48AM |
H40.00004: Novel ZnO nanostructures grown by the templation of SiO$_{2}$ photonic crystals Hsia Yu Lin, Yang Fang Chen ZnO nanostructures were grown on assembled silica nanoparticles by vapor-liquid-solid (VLS) method. It is found that high aspect ratio of nanotips can be obtained. Besides, the nanotips can only be grown along some restricted axial orientations. As the tip length increases, the tip shape gradually transfers from hexagonal to circular. The optical measurements show that in addition to the band edge emission, two defect states are found, which locate at different regions along the growth direction. Moreover, we show that the ZnO nanotips exhibit an excellent waveguide for steering light beam generated from the Tb nanoparticle incorporated in the central core of SiO$_{2}$ particle. Therefore, it is pointed out that the core-shell Tb- SiO$_{2}$ with the growth of ZnO nanotips on its surface can act as an optical hub. [Preview Abstract] |
Tuesday, March 6, 2007 8:48AM - 9:00AM |
H40.00005: P-type Doping and Electroluminescence in ZnO Thin Films David Norton, Hyun-Sik Kim, Jean-Marie Erie, Patrick Sadik, Stephen Pearton, Fan Ren As a direct bandgap material with emission in the ultraviolet, ZnO is being actively pursued in the areas of ultraviolet light emitting diodes and laser diodes. The critical issues in developing such optoelectronic devices include p-type doping, minority carrier injection, and defects. In this talk, the focus will be doping and transport properties of phosphorus-doped ZnO films and heterostructures, including Hall measurement characterization. [Preview Abstract] |
Tuesday, March 6, 2007 9:00AM - 9:12AM |
H40.00006: The effects of vacuum annealing on the top-most layer of 6H-SiC measured by Positron annihilation induced Auger Spectroscopy S. Mukherjee, M. Nadesalingam, B. Davis, G. Brauer, A. H. Weiss Silicon Carbide (SiC) in monocrystalline, hexagonal polytype form is a very interesting material for a wide class of novel application in electronics. The wide range of the band gap offered by different polytype with very little lattice mismatch can be utilized to grow smooth heterojunctions. Till now it has not been achieved and hence the surface characterization of such crystals is critical. Positron Annihilation induced Auger Electron Spectroscopy (PAES) is an established tool to characterize the top most atomic surface layer of solids. Here, PAES has been used to study the surface of 6H- SiC after annealing under different thermal and ambient conditions. The PAES measurements indicate that top-most atomic layer becomes C rich after vacuum annealing at 800 C. In additional a large chemical shift in the Si peak of approximately -12 eV was observed with PAES. [Preview Abstract] |
Tuesday, March 6, 2007 9:12AM - 9:24AM |
H40.00007: Improved Schottky Contacts on n-type SiC using ZrB$_{2}$ Tom Oder, Pamela Martin, Adetayo Adedeji, Tamara Isaacs-Smith, John Williams We present results on ZrB$_{2}$ Schottky contacts deposited on n-type SiC by DC magnetron sputtering at temperatures between 20 $^{o}$C and 800 $^{o}$C. The Schottky barrier heights determined by current-voltage measurements, increased with the deposition temperature from 0.87 eV for contacts deposited at 20 $^{o}$C to 1.07 eV for those deposited at 600 $^{o}$C. The RBS spectra of these contacts revealed a substantial decrease in oxygen peak with increase in the deposition temperature and showed no reaction at the ZrB$_{2}$/SiC interface. The barrier heights of the contacts annealed in nitrogen for 20 mins at 200 $^{o}$C to 500 $^{o}$C using a rapid thermal processor revealed only a slight increase. These results indicate improvement in the electrical properties and thermal stability of ZrB$_{2}$ on n-type SiC when the contacts are deposited at elevated temperatures, making them attractive for high temperature applications. [Preview Abstract] |
Tuesday, March 6, 2007 9:24AM - 9:36AM |
H40.00008: Step Arrays on Vicinal SiC Formed by Hydrogen-Etching S. Nie, R.M. Feenstra, Y. Ke, R.P. Devaty, W.J. Choyke, G. Gu SiC is a useful substrate for heteroepitaxy, with step arrays on the surface used to minimize defects in the film [1]. We have studied the formation of steps on SiC surfaces using H-etching at 1600\r{ }C. Both Si-face, (0001), and C-face, (000\underline {1}), surfaces are used, with miscut angles of 0, 3.5\r{ }, and 12\r{ } towards $<$1\underline {1}00$>$ or $<$11\underline {2}0$>$ directions. For H-etched surfaces it is known that steps tend to form with full unit-cell height (1.5 nm for 6H-SiC) and with step edges perpendicular to $<$1\underline {1}00$>$ [2]. Accordingly, we find that miscuts towards $<$1\underline {1}00$>$ result in ordered arrays of steps. On the Si-face step bunching is observed, with typical step heights of 4.5 nm for 12\r{ } miscut. In contrast, for the C-face, little step bunching is observed, with the surface forming well ordered arrays of single-unit-cell-high steps. For the case of miscut towards $<$11\underline {2}0$>$ the situation is more complicated, with meandering steps observed. We conclude that the C-face is most ideal as a vicinal template. Supported by NSF. \newline [1] C.D. Lee et al. MIJ-NSR \textbf{7}, 2 (2002). \newline [2] V. Ramachandran et al. JEM \textbf{27}, 308 (1998). [Preview Abstract] |
Tuesday, March 6, 2007 9:36AM - 9:48AM |
H40.00009: Controlling Degree of Crystalline Boron Carbide by Plasma Enhanced Chemical Vapor Deposition Joseph Sandstrom There has been a recent resurgence in the interest of semiconducting boron carbide, based on its use as a radiation hard semiconductor. Here, we present growth character and commensurate structural and electronic properties from the low temperature but large area (6" wafer) deposition of boron carbide from the solid source precursor, 1,2 - dicarbadodecaborane. Of special interest is the control over the degree of crystallinity as provided from changing plasma pressure growth. [Preview Abstract] |
Tuesday, March 6, 2007 9:48AM - 10:00AM |
H40.00010: A comparative study of dissociation pathways of silane {\&} germane on Si (001) using cluster {\&} slab formalism in density functional theory. Abir De Sarkar, Li Qiang, Hway Chuan Kang, David J. Srolovitz Si-Ge thin films are of enormous importance in view of their wide gamut of applications in electronic, opto-electronic, photonic devices, etc. Therefore, a concrete understanding of the elementary processes that lead to film growth is indispensable for an optimum control of film growth. Thin films are typically grown by chemical vapor deposition (CVD) using gas phase precursors like silane {\&} germane. Dissociation of the gas phase precursor (e.g. silane, germane) on the substrate (e.g. Si, Ge) is the first and the most crucial elementary step in film growth. In order to obtain a clear understanding and insight into this mechanism, we have investigated the different possible pathways for silane and germane dissocation on Si(001). (001) surface of Si is typically and preferably used as substrate in film growth. Both germane and silane have been found to exhibit a preference for the intradimer mode of adsorption to the interdimer mode of adsorption on Si(001) surface. Germane shows a lower barrier for dissociative adsorption and the difference of barriers between these 2 modes of adsorption is higher for silane. Unlike the barriers for hydrogen desorption from Si-Ge surface (where the cluster approach predicts a higher barrier), the barriers predicted by the slab formalism for dissociative adsorption has been observed to be higher than the cluster values. [Preview Abstract] |
Tuesday, March 6, 2007 10:00AM - 10:12AM |
H40.00011: Kinetically constraint 0-D and 1-D heteroepitaxial islands growth Zhipeng Li, Manish Kumar Singh, Eng Soon Tok, Joyce Pei Ying Tan, Min Lin, Yong-Lim Foo Direct observation of the dynamics, formation and selective growth of low dimensional epitaxial Fe$_{13}$Ge$_{8}$ structures (0-D compact islands or 1-D wires of different aspect ratios) was conducted in \textit{real time} using \textit{in-situ }ultra-high vacuum transmission electron microscopy at 350, 430, 480 and 510$^{\circ}$C. Different types of Fe$_{13}$Ge$_{8}$ islands (0-D/1-D) and aspect ratio were formed at all the different deposition temperatures. Both types of island share the same epitaxial relation to the underlying Ge substrate. The compact islands are formed preferentially at lower deposition temperature while wires, which are kinetically constrained to grow, at higher temperature. The length/width growth rate was investigated by measuring the island size/shape evolution at different deposition temperatures during growth. The effective E$_{a}$ for growth along two orthogonal azimuths of an Fe$_{13}$Ge$_{8}$ island are 0.17 and 0.95 eV. The temperature dependence in morphology evolution is due to anisotropy in ledge diffusion on orthogonal azimuth during growth. We illustrate that temperature provides an avenue to selectively control the dimensionality (O-D or 1-D) of Fe$_{13}$Ge$_{8}$growth on Ge(001) surface. [Preview Abstract] |
Tuesday, March 6, 2007 10:12AM - 10:24AM |
H40.00012: Structure and Optical Properties of Ge-Sb-Te films Heng Li, Tong Ju, Don Williamson, P. Craig Taylor Amorphous and Crystalline films in the system Ge-Sb-Te are of interest because of their use in reversible phase change optical storage media or electrical switches. These applications utilize differences in optical or electrical properties between the crystalline and amorphous phases of the same material. The most commonly employed composition is Ge$_{2}$Sb$_{2}$Te$_{5}$. We present data on amorphous films of Ge$_{2}$Sb$_{2}$Te$_{4}$, Ge$_{2}$Sb$_{2}$Te$_{5 }$ and Ge$_{2}$Sb$_{2}$Te$_{7}$ grown by RF sputtering and examine the effects of growth rate, different growth systems and growth pressure on the structure and optical properties. Small Angle X-ray Scattering results show there are elliptical ``voids'' in the films with the long axis along the growth direction. The dependent of this void structure on growth parameters will be discussed. Lower Ar Pressure during growth produce less oxygen contamination in the films. The effects of oxygen impurities on the optical properties will be discussed. [Preview Abstract] |
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