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Bussmann E, Swartzentruber BS. Ge diffusion at the Si(100) surface. PHYSICAL REVIEW LETTERS 2010; 104:126101. [PMID: 20366550 DOI: 10.1103/physrevlett.104.126101] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2009] [Indexed: 05/29/2023]
Abstract
Using scanning tunneling microscopy movies, we directly observe individual embedded Ge atoms to be mobile within the Si(100)-(2x1)-Ge surface at temperatures as low as 90 degrees C. We demonstrate that Ge atoms move by exchange diffusion with (1) adsorbed monomers and (2) individual constituent atoms of adsorbed dimers. Our observations are consistent with recent density-functional theory calculations, which give the atomistic pathways and energetic barriers for both exchange mechanisms. We find that neither adsorbed monomers nor dimers can diffuse more than a few nanometers between exchange events, illustrating how Ge diffusion and intermixing are intimately coupled at the nanoscale on the Si(100) surface.
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Affiliation(s)
- E Bussmann
- Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
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2
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Paul N, Filimonov S, Cherepanov V, Cakmak M, Voigtländer B. Identification of Ge/Si intermixing processes at the Bi/Ge/Si(111) surface. PHYSICAL REVIEW LETTERS 2007; 98:166104. [PMID: 17501435 DOI: 10.1103/physrevlett.98.166104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2007] [Indexed: 05/15/2023]
Abstract
The chemical contrast between Si and Ge obtained by scanning tunneling microscopy on Bi-covered Si(111) surfaces is used as a tool to identify two vertical Ge/Si intermixing processes. During annealing of an initially pure Ge monolayer on Si, the intermixing is confined to the first two layers approaching a 50% Ge concentration in each layer. During epitaxial growth, a growth front induced intermixing process acting at step edges is observed. Because of the open atomic structure at the step edges, relative to the terraces, a lower activation barrier for intermixing at the step edge, compared to the terrace, is observed.
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Affiliation(s)
- Neelima Paul
- Institute of Bio- and Nanosystems (IBN 3), and cni - Center of Nanoelectronic Systems for Information Technology, Research Center Jülich, 52425 Jülich, Germany
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Li Q, Tok ES, Zhang J, Kang HC. Reassessment of the molecular mechanisms for H2 thermal desorption pathways from Si(1-x)Gex(001)-(2x1) surfaces. J Chem Phys 2007; 126:044706. [PMID: 17286498 DOI: 10.1063/1.2432114] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
One of the aims of temperature-programmed desorption experiments is to facilitate identification of molecular pathways for desorption. The authors provide a rigorous assessment of the difficulty of doing this for H(2)/Si((1-x))Ge(x)(100)-(2x1). An extensive series of density functional calculations using both cluster and slab methods is performed. The resulting desorption barriers are used to compute thermal desorption spectra. A mean-field approximation is used to treat the populations of the various adsites present on the surface. The authors find a number of significant results. First, slab and cluster calculations do not appear to predict consistent differences in desorption barriers between intradimer and interdimer channels. Second, they find that a germanium atom affects the desorption barrier significantly only if it is present at the adsite. A germanium atom adjacent to an adsite or in the second layer influences the desorption barrier negligibly. Both cluster and slab calculations consistently predict a decrease of approximately 0.3-0.4 eV per germanium atom at the adsite. Third, current analysis of thermal desorption spectra in the literature, although yielding good fits to experimental data, is not rigorous. The authors' calculated spectra can be fitted rather well by assuming, as in current analysis of experimental data, three independent second-order channels, even though the underlying molecular pathways used to calculate the spectra are considerably different. Fourth, the authors' results highlight the importance of treating the rearrangement of hydrogen and germanium atoms at the surface during the thermal desorption process. This is generally not taken into account in kinetics modeling of desorption spectra.
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Affiliation(s)
- Qiang Li
- Department of Chemistry, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore
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Hannon JB, Copel M, Stumpf R, Reuter MC, Tromp RM. Critical role of surface steps in the alloying of Ge on Si(001). PHYSICAL REVIEW LETTERS 2004; 92:216104. [PMID: 15245297 DOI: 10.1103/physrevlett.92.216104] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2004] [Indexed: 05/24/2023]
Abstract
Using low-energy electron microscopy, we show that intermixing of Ge on Si(001) during growth is enhanced on stepped surfaces and is hindered on terraces where step flow does not occur. On large terraces we have identified a dramatic and unanticipated structural rearrangement that facilitates intermixing: Pairs of steps spontaneously form and migrate over the surface, leaving alloyed regions in their wake. The driving force for step formation is the entropy gain associated with the enhanced intermixing of Ge.
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Affiliation(s)
- J B Hannon
- IBM Research Division, T.J. Watson Research Center, Yorktown Heights, New York 10598, USA
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5
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Mui C, Bent SF, Musgrave CB. A Density Functional Theory Study on the Effect of Ge Alloying on Hydrogen Desorption from SiGe Alloy Surfaces. J Phys Chem B 2004; 108:6336-50. [DOI: 10.1021/jp037948a] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Collin Mui
- Department of Chemical Engineering, Stanford University, Stanford California 94305
| | - Stacey F. Bent
- Department of Chemical Engineering, Stanford University, Stanford California 94305
| | - Charles B. Musgrave
- Departments of Chemical Engineering and Materials Science and Engineering, Stanford University, Stanford California 94305
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Tok ES, Ong SW, Kang HC. Hydrogen desorption kinetics from the Si(1−x)Gex(100)-(2×1) surface. J Chem Phys 2004; 120:5424-31. [PMID: 15267416 DOI: 10.1063/1.1645510] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We study the influence of germanium atoms upon molecular hydrogen desorption energetics using density functional cluster calculations. A three-dimer cluster is used to model the Si((1-x))Ge(x)(100)-(2x1) surface. The relative stabilities of the various monohydride and clean surface configurations are computed. We also compute the energy barriers for desorption from silicon, germanium, and mixed dimers with various neighboring configurations of silicon and germanium atoms. Our results indicate that there are two desorption channels from mixed dimers, one with an energy barrier close to that for desorption from germanium dimers and one with an energy barrier close to that for desorption from silicon dimers. Coupled with the preferential formation of mixed dimers over silicon or germanium dimers on the surface, our results suggest that the low barrier mixed dimer channel plays an important role in hydrogen desorption from silicon-germanium surfaces. A simple kinetics model is used to show that reasonable thermal desorption spectra result from incorporating this channel into the mechanism for hydrogen desorption. Our results help to resolve the discrepancy between the surface germanium coverage found from thermal desorption spectra analysis, and the results of composition measurements using photoemission experiments. We also find from our cluster calculations that germanium dimers exert little influence upon the hydrogen desorption barriers of neighboring silicon or germanium dimers. However, a relatively larger effect upon the desorption barrier is observed in our calculations when germanium atoms are present in the second layer.
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Affiliation(s)
- E S Tok
- Department of Materials Science, National University of Singapore, 10 Science Drive 4, Singapore 117543
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Kao YH, Kim S, Soo YL. Nondestructive Characterization of Nanostructure in Layered Materials Using Synchrotron Radiation. INTERNATIONAL JOURNAL OF NANOSCIENCE 2003. [DOI: 10.1142/s0219581x03001115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
This paper presents a brief review of nondestructive methods useful for the general purpose of characterizing nanostructure in layered materials using x-rays from synchrotron radiation. By way of examples, some practical applications of these methods to the study of layered systems of recent technological interest are demonstrated.
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Affiliation(s)
- Y. H. Kao
- Department of Physics, State University of New York at Buffalo, Amherst, NY 14260, USA
| | - S. Kim
- Department of Physics, State University of New York at Buffalo, Amherst, NY 14260, USA
| | - Y. L. Soo
- Department of Physics, State University of New York at Buffalo, Amherst, NY 14260, USA
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Lin DS, Wu JL, Pan SY, Chiang TC. Atomistics of Ge deposition on Si(100) by atomic layer epitaxy. PHYSICAL REVIEW LETTERS 2003; 90:046102. [PMID: 12570436 DOI: 10.1103/physrevlett.90.046102] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2002] [Indexed: 05/24/2023]
Abstract
Chlorine termination of mixed Ge/Si(100) surfaces substantially enhances the contrast between Ge and Si sites in scanning tunneling microscopy observations. This finding enables a detailed investigation of the spatial distribution of Ge atoms deposited on Si(100) by atomic layer epitaxy. The results are corroborated by photoemission measurements aided by an unusually large chemical shift between Cl adsorbed on Si and Ge. Adsorbate-substrate atomic exchange during growth is shown to be important. The resulting interface is thus graded, but characterized by a very short length scale of about one monolayer.
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Affiliation(s)
- D S Lin
- Institute of Physics, National Chiao-Tung University, 1001 Ta-Hsueh Road, Hsinchu 300, Taiwan, Republic of China
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Qin XR, Swartzentruber BS, Lagally MG. Scanning tunneling microscopy identification of atomic-scale intermixing on Si(100) at submonolayer Ge coverages. PHYSICAL REVIEW LETTERS 2000; 84:4645-4648. [PMID: 10990761 DOI: 10.1103/physrevlett.84.4645] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2000] [Indexed: 05/23/2023]
Abstract
The positions of Ge atoms intermixed in the Si(100) surface at very low concentration are identified using empty-state imaging in scanning tunneling microscopy. A measurable degree of place exchange occurs at temperatures as low as 330 K. Contrary to earlier conclusions, good differentiation between Si atoms and Ge atoms can be achieved by proper imaging conditions.
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Affiliation(s)
- XR Qin
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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Uberuaga BP, Leskovar M, Smith AP, Jonsson H, Olmstead M. Diffusion of Ge below the Si(100) surface: theory and experiment. PHYSICAL REVIEW LETTERS 2000; 84:2441-2444. [PMID: 11018905 DOI: 10.1103/physrevlett.84.2441] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/1999] [Indexed: 05/23/2023]
Abstract
We have studied diffusion of Ge into subsurface layers of Si(100). Auger electron diffraction measurements show Ge in the fourth layer after submonolayer growth at temperatures as low as 500 degrees C. Density functional theory predictions of equilibrium Ge subsurface distributions are consistent with the measurements. We identify a surprisingly low energy pathway resulting from low interstitial formation energy in the third and fourth layers. Doping significantly affects the formation energy, suggesting that n-type doping may lead to sharper Si/Ge interfaces.
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Affiliation(s)
- BP Uberuaga
- Department of Physics, Box 351560, University of Washington, Seattle, Washington 98195-1560 and Department of Chemistry, Box 351700, University of Washington, Seattle, Washington 98195-1700, USA
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11
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Mui C, Bent SF, Musgrave CB. A Theoretical Study of the Structure and Thermochemistry of 1,3-Butadiene on the Ge/Si(100)-2 × 1 Surface. J Phys Chem A 1999. [DOI: 10.1021/jp991797n] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Collin Mui
- Department of Chemical Engineering, Stanford University, Stanford, California 94305-5025
| | - Stacey F. Bent
- Department of Chemical Engineering, Stanford University, Stanford, California 94305-5025
| | - Charles B. Musgrave
- Departments of Chemical Engineering and Materials Science and Engineering, Stanford University, Stanford, California 94305-5025
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12
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Liu F, Wu F, Lagally MG. Effect of Strain on Structure and Morphology of Ultrathin Ge Films on Si(001). Chem Rev 1997; 97:1045-1062. [PMID: 11851440 DOI: 10.1021/cr9600722] [Citation(s) in RCA: 125] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Feng Liu
- University of Wisconsin-Madison, Madison, Wisconsin 53706
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13
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Lin DS, Huang KH, Pi TW, Wu RT. Coverage-dependent thermal reactions of digermane on Si(100)-(2 x 1). PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 54:16958-16964. [PMID: 9985825 DOI: 10.1103/physrevb.54.16958] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Falta J, Schmidt T, Hille A, Materlik G. Surfactant adsorption site and growth mechanism of Ge- on Ga-terminated Si(111). PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 54:R17288-R17291. [PMID: 9985939 DOI: 10.1103/physrevb.54.r17288] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Goldoni A, Modesti S, Dhanak VR, Sancrotti M, Santoni A. Evidence for three surface components in the 3d core-level photoemission spectra of Ge(100)-(2 x 1) surface. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 54:11340-11345. [PMID: 9984922 DOI: 10.1103/physrevb.54.11340] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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16
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Katayama M, Nakayama T, Aono M, McConville CF. Influence of surfactant coverage on epitaxial growth of Ge on Si(001). PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 54:8600-8604. [PMID: 9984537 DOI: 10.1103/physrevb.54.8600] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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17
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Liu F, Lagally MG. Interplay of stress, structure, and stoichiometry in Ge-covered Si(001). PHYSICAL REVIEW LETTERS 1996; 76:3156-3159. [PMID: 10060889 DOI: 10.1103/physrevlett.76.3156] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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