Adsorption of boron on Si(111): Its effect on surface electronic states and reconstruction

Abstract

Adsorption of B induces a (VJxV3)/£30° reconstruction on Si(lll). By combining scanningtunneling-microscope topographs and spectra with first-principles calculations we are able to follow the different stages of B incorporation in the Si surface and the corresponding changes to the surface electronic states. We find that the thermodynamically stable configuration consists of a B substitutional atom directly below a Si adatom at a T* site. The stability of this configuration is due to the relief of subsurface strain by the short B-Si bonds and the passivation of the surface obtained through charge transfer from the Si adatom to the substitutional B.

Investigation of single boron acceptors at the cleaved Si:B(111) surface

“…In contrast, B at position 3 or 4 has to satisfy four bonds making a charge transfer from adjacent Si atoms very likely. Such an effect of the B substitutional site on the electronic structure has been reported for B deposited on Si (111) where B does indeed occupy immediate subsurface positions [11,12]. In addition, the Si-B bond length is about 12 % shorter than the Si-Si bond length mainly due to the smaller covalent radius of B compared to Si [12].…”

“…The most striking result is the strong reduction of the large peak observed on Si at +0.5 V. The corresponding unoccupied electronic states are located at the DB orbitals at position 2. Strong modifications of the STS spectra have also been reported for B deposited on Si (111) [11,12]. In the present case the reduction of the surface DOS above E F confirms the absence of a localized DB state at the B site and the effect of a missing orbital in the STM image at U = 0.4 − 0.6 V. Furthermore, the peak at −0.9 V representing the bottom of the occupied surface band is considerably shifted upward by ≈ 0.5 V at the B site.…”

“…Previous studies on the adsorption of B on Si (111) revealed different stages of B incorporation in the surface depending on coverage and thermal treatment [11,12] in contrast to other group III adsorbates [13,14]. For the cleaved Si:B (111) surface one might naively expect that apart from the change of the sign of the Coulomb potential the influence of the negatively ionized B acceptor on the electronic structure can be explained in a way similar to Si:P. However, we will show that unlike in Si:P, the DOS in Si:B is strongly modified at the acceptor site possibly due to the different electronic configuration of substitutional B in Si compared to P.…”

The thermal dissociation of decaborane on Si(111)-(7×7) and doping effects in the near surface region

“…The use of the more complex pentaborane (B 5 H 9 ) and decaborane (BloH 1 4 ) as molecular sources of boron, on the other hand, has been successful [3,[11][12][13]. Aside from the conventional approach of thermally dissociating boranes to yield boron deposition, alternatives such as photon [12,13] and electron-induced [15] dissociation have also been pursued with success.…”

A STM study on compared chemical reactivities of different Si(111) surfaces: copper growth and ferrocene adsorption

“…One major characteristic of the boron B/3 structure is that B atoms do not occupy a T4 adatom site as other group III elements [7][8][9], but sits in the 2nd layer of Si in a so-called S5 site [10][11][12][13] as shown in figure 1. This is a favourable situation for creating a b doped layer which might play an important role in atomic layer doping technology [14][15].…”