Observation of substitutional and interstitial phosphorus on clean $\mathrm{Si}(100)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ with scanning tunneling microscopy

Observation of substitutional and interstitial phosphorus on clean $Si (100) − (2 \times 1)$ with scanning tunneling microscopy

Geoffrey W. Brown, Blas P. Uberuaga, Holger Grube, Marilyn E. Hawley, Steven R. Schofield, Neil J. Curson, Michelle Y. Simmons, and Robert G. Clark

Phys. Rev. B 72, 195323 – Published 14 November 2005

Abstract

We have used scanning tunneling microscopy to identify phosphorus that is present at the clean silicon $(100) − (2 \times 1)$ surface as a result of the thermal cycling necessary for preparation of samples cut from heavily doped wafers. Substitutional phosphorus is observed in top layer sites as buckled $Si − P$ heterodimers. We also observe a second type of feature that appears as a single depressed dimer site. Within this site, the atoms appear as a pair of protrusions in the empty states and a single protrusion in the filled states. These properties are not consistent with known adsorbate signatures or previously reported observations of $P − P$ dimers on the $(100) − (2 \times 1)$ surface. The lack of other impurity sources suggests that they are due to either phosphorus or silicon. The symmetry of the features and their magnitude are consistent with one of those elements residing in an interstitial site just below the top layer of atoms. To identify the type of interstitial, we performed density functional theory calculations for both phosphorus and silicon located below a surface dimer. The resulting charge density plots and simulated STM images are consistent with interstitial phosphorus and not interstitial silicon.

Received 3 June 2005

DOI:https://doi.org/10.1103/PhysRevB.72.195323

Authors & Affiliations

Geoffrey W. Brown^*, Blas P. Uberuaga, Holger Grube, and Marilyn E. Hawley

Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

Steven R. Schofield^†, Neil J. Curson, Michelle Y. Simmons, and Robert G. Clark

Centre for Quantum Computer Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia

^*Electronic address: geoffb@lanl.gov
^†Now at School of Mathematical and Physical Sciences, University of Newcastle, Callaghan, NSW 2308, Australia.

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Vol. 72, Iss. 19 — 15 November 2005

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Figure 1
Filled-state image of a $Si (100) − (2 \times 1)$ surface prepared with the standard flash-anneal technique on a sample cut from a highly doped wafer. Stress due to phosphorus near the surface leads to the vacancy line defects. Several phosphorus-induced features are visible in the clean areas. The image was acquired at $- 1.25 V$ sample bias and $400 pA$ tunnel current. The image area is $350 Å \times 350 Å$ .Reuse & Permissions
Figure 2
(a) Filled- and (b) empty-state images of the same area on a $Si (100) − (2 \times 1)$ surface prepared with the standard flash to $\sim 1250 ° C$ and a $30 \min$ postanneal at $\sim 900 ° C$ . The vacancy line defects have diminished due to desorption of phosphorus. The circles mark remaining features that appear to be phosphorus induced. The tunneling conditions were $- 1.2 V$ for the filled states, $+ 1.2 V$ for empty states and $150 pA$ tunnel current in both cases. The image area is $250 Å \times 250 Å$ .Reuse & Permissions
Figure 3
(a) Filled- and (b) empty-state images from a highly doped sample with one of the “bright” features marked by the circle. A $C$ type defect combined with a vacancy is directly below it in the image. The asymmetric dimer and its neighboring structure are consistent with previous observations of $Si − P$ heterodimers. The tunneling conditions were $- 1.4 V$ for the filled states, $+ 1.2 V$ for empty states, and $150 pA$ tunnel current in both cases. The image area is $120 Å \times 120 Å$ .Reuse & Permissions
Figure 4
(a) Filled- and (b) empty-state images of one of the “dark” features observed on the highly doped samples. The tunneling conditions were $- 1.4 V$ for the filled states, $+ 1.0 V$ for empty states, and $150 pA$ tunnel current in both cases. The image area is $120 Å \times 120 Å$ .Reuse & Permissions
Figure 5
Schematic diagrams of stable interstitial positions with respect to the surface dimer. The top surface (lower diagram) and side views (upper diagrams) are shown. The empty circles are top layer atoms in dimer rows. The black circles are subsurface atoms whose size diminishes with increasing depth. The gray circles indicate the two possible stable interstitial phosphorus positions. For interstitial silicon, the gray circles would be slightly closer together.Reuse & Permissions
Figure 6
(Left) Simulated filled-state STM image with phosphorus interstitial located below the center surface dimer. (Right) Simulated filled-state STM image with silicon interstitial located below the center surface dimer. In each case, the charge density was averaged over both possible stable interstitial positions before the STM image was generated.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Observation of substitutional and interstitial phosphorus on clean $Si (100) − (2 \times 1)$ with scanning tunneling microscopy

Geoffrey W. Brown, Blas P. Uberuaga, Holger Grube, Marilyn E. Hawley, Steven R. Schofield, Neil J. Curson, Michelle Y. Simmons, and Robert G. Clark

Phys. Rev. B 72, 195323 – Published 14 November 2005

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Physical Review B

covering condensed matter and materials physics

Observation of substitutional and interstitial phosphorus on clean Si(100)−(2×1) with scanning tunneling microscopy

Geoffrey W. Brown, Blas P. Uberuaga, Holger Grube, Marilyn E. Hawley, Steven R. Schofield, Neil J. Curson, Michelle Y. Simmons, and Robert G. Clark

Phys. Rev. B 72, 195323 – Published 14 November 2005

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Observation of substitutional and interstitial phosphorus on clean $Si (100) − (2 \times 1)$ with scanning tunneling microscopy