Dimer Pairing on the C-Alloyed Si(001) Surface

Leifeld, O.; Grützmacher, D.; Müller, Bert; Kern, Klaus; Kaxiras, Efthimios; Kelires, P. C.

doi:10.1103/physrevlett.82.972

Cited by 72 publications

(49 citation statements)

References 14 publications

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“…From our first-principles calculations, we found that the geometrical features of the Si-Si dimers in all 12 cells are essentially the same. Surface C is invisible, or shows up as a missing Si atom, in STM experiments [16]. This implies that one cannot distinguish, using standard microscopy, between pure Si(100) or Si(100) with vacancies, and a configuration with C in the third layer; the only criterion is the long-range order and the change of the reconstruction.…”

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Thermodynamics of C Incorporation on Si(100) fromab initioCalculations

2001

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We study the thermodynamics of C incorporation on Si(100), a system where strain and chemical effects are both important. Our analysis is based on first-principles atomistic calculations to obtain the important lowest energy structures, and a classical effective Hamiltonian which is employed to represent the long-range strain effects and incorporate the thermodynamic aspects. We determine the equilibrium phase diagram in temperature and C chemical potential, which allows us to predict the mesoscopic structure of the system that should be observed under experimentally relevant conditions.PACS numbers: 61.66. Dk, 68.35.Rh, 68.35.Bs Carbon-enriched silicon systems are the focus of current interest as candidates for a material with tailored electronic properties, which is compatible with wellestablished silicon technology. The tetravalent nature and large band gap in the diamond structure make carbon an ideal candidate for incorporation in Si. However, the solubility of C in Si under thermodynamic equilibrium is extremely low (≈ 10 −5 ) due to the huge mismatch in bond length (35%) and bond energy (60%) between C and Si. Non-equilibrium methods, such as molecular beam epitaxy (MBE), that exploit the higher atomic mobility on surfaces, can be used to overcome this obstacle and enhance solubility [1]. As predicted theoretically by Tersoff[2], C solubility is enhanced by several orders of magnitude near the Si(100) surface, especially in subsurface layers. Osten et al.[3] confirmed experimentally this prediction and observed that C atoms diffuse to subsurface layers above a certain temperature. This finding opened new possibilities for growth of C-rich metastable structures.The enhanced solubility near the surface has important consequences. The large tensile strain associated with C incorporation in Si has proven a very powerful tool in device engineering: a small amount of C can compensate the Ge-induced tension in pseudomorphic SiGe layers [4,5,6] , and can also suppress dopant outdiffusion. This idea was recently implemented in a novel heterojunction bipolar transistor [7]. Another interesting effect [8,9] produced by C incorporation on the Si(100) surface is an unusual change of the surface periodicity after deposition of even a small amount of C (≈ 1 8 of a mono-layer (ML)): the well-known c(2 × 4) or p(2 × 2) reconstructions of the pure Si surface change to a c(4 × 4) pattern. This is clearly visible in several LEED experiments after ethylene exposure [10,11], or MBE [8].The microscopic features of C incorporation in Si are rather well understood. Previous work by the authors [12,13,14] revealed an oscillatory C profile driven by the competition between two factors: the tendency of C atoms to occupy favorable sites which are determined by the reconstruction strain field, and the preferential arrangement of C atoms at certain distances which minimizes the lattice elastic energy. The profile is characterized by enhancement of C content in the first and third layer, depletion in the second and an exponential red...

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“…Guided by previous work, [2,12,13,16] we can establish a set of rules which should be obeyed by low energy configurations of the CSi(100) system, namely:…”

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Thermodynamics of C Incorporation on Si(100) fromab initioCalculations

2001

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“…This was reproduced by Sakamoto et al, 2 and later Müller et al 3 reported that this reconstruction also appeared when a clean Si͑100͒ surface was annealed in vacuum. It turns out that this reconstruction has been formed with a wealth of methods; Si deposition, 1,2,4,5 C deposition, [6][7][8][9][10][11] Ge deposition, 12 H exposure, [13][14][15][16][17][18][19] C 2 H 4 and C 2 H 2 treatment, 20-24 SiH 4 /Si 2 H 6 growth, [25][26][27][28][29] annealing in vacuum, 3,[30][31][32][33][34][35][36] B deposition, [37][38][39] and O or S treatment. [40][41][42] Several models for the reconstruction have been proposed: Pandey's -bonded defect model, 30,43 missing dimer, 9,13 parallel ad-dimer, 15 and mixed ad-dimer 15 models, and it has been debated whether it is a pure Si reconstruction or if it contains any foreign species.…”

Section: Introductionmentioning

confidence: 99%

“…There were some Auger electron spectroscopy ͑AES͒ investigations reporting a clean surface 27,30,42 while others reported traces of C present on the surface. 13,6 In recent years most investigations seem to support the idea that the reconstruction is C related [7][8][9]19,22,24 and there have been some attempts to estimate the carbon concentration. 6,7,9,20,22 Some have argued for reconstruction models containing an integer number of C atoms per unit cell while others claim that subsurface C and/or surface C produces the reconstruction indirectly-by strain or otherwise.…”

Section: Introductionmentioning

confidence: 99%

STM study of the C-inducedSi(100)−c(4×4)reconstruction

et al. 2002

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We report a direct and reliable way to produce the Si͑100͒-c(4ϫ4) reconstruction by submonolayer deposition from a SiC source and subsequent annealing. Auger electron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy ͑STM͒ investigations reveal that a C amount equivalent to 0.07 monolayers ͑ML's͒ is sufficient to obtain full coverage of the c(4ϫ4)reconstruction. A deposition of 0.035 ML's C produces a c(4ϫ4)coverage of only 19%, indicating that C is not only present in the c(4ϫ4)areas, but also in the 2ϫ1 areas. There is not enough C to make it a regular part of the c(4ϫ4) reconstruction and we therefore conclude that the c(4ϫ4) reconstruction is strain induced. We find that a combination of the mixed ad-dimer and buckled ad-dimer models explains all main features observed in the STM images. Images of freshly prepared c(4ϫ4) surfaces exhibit a decoration of approximately 50% of the unit cells, which is attributed to perpendicular ad-dimers. Long exposures (Ͼ20 h) to the UHV background gas quench these features and the c(4ϫ4) reconstruction appears as if more homogeneous.

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“…In the first stage carbonization of a Si(100) surface, 2 × n (6 ≤ n ≤ 12) [27,28] and c(4 × 4) [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] reconstructions have been reported. However, similar 2 × n [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] and c(4 × 4) reconstructions have been reported without carbonization.…”

Section: Introductionmentioning

confidence: 99%

Initial-Stage Structural Change of Si(100) Surface Induced by Exposure to Ethylene Gas and Annealing

Takami¹,

Kusaka

Kusunoki

2006

e-J. Surf. Sci. Nanotech.

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The initial stage of the structural change in a clean Si(100)-2 × 1 surface induced by annealing at 640• C and exposure to ethylene gas was studied by reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). The RHEED pattern included SiC spots and STM images revealed SiC particles on the surface, which confirmed the carbonization of the Si surface. At a different area of the same sample, the RHEED pattern showed both twice the periodicity of surface spots which indicates a flat surface region and transmitted bulk Si spots which indicates the initial stage of voids. The STM images of the flat region showed a 2 × n (6 ≤ n ≤ 12) reconstruction. The topography of the 2 × n STM image depended on the bias voltage. The 2 × n reconstruction was clearly induced by carbon impurities; STM images were similar to those in previous studies in which structures were formed by various kinds of impurities or contaminations.

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Dimer Pairing on the C-Alloyed Si(001) Surface

Cited by 72 publications

References 14 publications

Thermodynamics of C Incorporation on Si(100) fromab initioCalculations

Thermodynamics of C Incorporation on Si(100) fromab initioCalculations

STM study of the C-inducedSi(100)−c(4×4)reconstruction

Initial-Stage Structural Change of Si(100) Surface Induced by Exposure to Ethylene Gas and Annealing

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