Electrical transport in a two-dimensional electron and hole gas on a $\text{Si}(001)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface

Electrical transport in a two-dimensional electron and hole gas on a $Si (001) − (2 \times 1)$ surface

Hassan Raza, Tehseen Z. Raza, and Edwin C. Kan

Phys. Rev. B 78, 193401 – Published 6 November 2008

Abstract

$Si (001) − (2 \times 1)$ surface is one of the many two-dimensional systems of scientific and applied interest. Due to its asymmetric dimer reconstruction, transport through this surface can be considered in two distinct directions, i.e., along and perpendicular to the paired dimer rows. We calculate the zero-bias conductance of these surface states under flatband condition and find that conduction along the dimer row direction is significant due to strong orbital hybridization. Additionally, we find that the surface conductance is orders of magnitude higher than the bulk conductance close to the band edges for the unpassivated surface at room temperature. Thus, we propose that the transport through these surface states may be the dominant conduction mechanisms in the recently reported scanning tunneling microscopy of silicon nanomembranes. The zero-bias conductance is also calculated for the weakly interacting dangling-bond wires along and perpendicular to the dimer row direction and similar trends are obtained. The extended Hückel theory is used for the electronic structure calculations.

Received 1 April 2008

DOI:https://doi.org/10.1103/PhysRevB.78.193401

Authors & Affiliations

Hassan Raza¹, Tehseen Z. Raza², and Edwin C. Kan¹

¹School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA
²School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA

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Vol. 78, Iss. 19 — 15 November 2008

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Figure 1
(Color online) Ball and stick models. Unpassivated paired AD surface and hydrogenated symmetric dimer surface. Top four layers, represented by ‡, are relaxed due to surface reconstruction. Bottom 12 layers, represented by †, are bulk layers. The back surface is hydrogenated to eliminate any inadvertent DB induced states. The top Si atom of the AD surface is shaded as black and the bottom Si atom is shaded as gray. The atoms below the first monolayer of Si surface are represented by white circles. The direction parallel to the dimer row is referred to as $[\bar{1} 10]$ , whereas the one perpendicular to the dimer row is labeled as [110]. Atomic coordinates for these structures are discussed and reported in Ref. 6. Atomic visualization is done using GAUSSVIEW (Ref. 9).Reuse & Permissions
Figure 2
(Color online) Transmission calculations for models I, II, and III. Hydrogenated Si(001) surface (model I) gives bulk Si band gap of 1.18 eV. Unpassivated Si(001) surface (model II) gives large transmission in the dangling-bond row direction $([\bar{1} 10])$ for both the $π^{*}$ and the $π$ states because the dimer atoms on which these states are localized are $3.84 Å$ apart. Transmission through the paired dangling-bond (model III) wire along the dangling-bond row direction, is about half of that in model II due to half of the total dangling-bond states per unit transverse length.Reuse & Permissions
Figure 3
(Color online) Transmission calculations for models IV and V. For model IV, the transmission through Si surface states in the direction perpendicular to dimer row direction ([110]) is smaller than the one along the dimer row direction (model II) due to the reduced hybridization between surface states—DB atoms being $7.68 Å$ apart. The conclusion for the DB wire, for which the transmission is calculated perpendicular to dimer row direction (model V), is the same.Reuse & Permissions
Figure 4
(Color online) Zero-bias conductance under flatband condition. For model I (hydrogenated surface with transport in the dimer row direction), the conductance decreases exponentially inside the band gap due to Fermi tail. Close to the band edge, the zero-bias conductance is orders of magnitude higher for model II (unpassivated surface with transport in dimer row direction) than that of model I. The zero-bias conductance for model III (DB wire with transport in dimer row direction) follows the same trend as that of model II with some quantitative differences. The zero-bias conductance for the $π^{*}$ states of model IV (unpassivated surface with transport perpendicular to the dimer row direction) is 2 orders of magnitude higher and less than 1 order of magnitude higher than that of model V (DB wire with transport perpendicular to the dimer row direction) inside the band gap.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Electrical transport in a two-dimensional electron and hole gas on a $Si (001) − (2 \times 1)$ surface

Hassan Raza, Tehseen Z. Raza, and Edwin C. Kan

Phys. Rev. B 78, 193401 – Published 6 November 2008

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Physical Review B

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Electrical transport in a two-dimensional electron and hole gas on a Si(001)−(2×1) surface

Hassan Raza, Tehseen Z. Raza, and Edwin C. Kan

Phys. Rev. B 78, 193401 – Published 6 November 2008

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Electrical transport in a two-dimensional electron and hole gas on a $Si (001) − (2 \times 1)$ surface