Initial growth of Bi films on a Si(111) substrate: Two phases of √3 × √3 low-energy-electron-diffraction pattern and their geometric structures

Abstract

The ordering of Bi on a Si(111)-7&&7 surface was studied as a function of overlayer coverage and deposition conditions using low-energy electron diff'raction (LEED) and Auger electron spectroscopy.We observed a one-third-monolayer and a saturated one-monolayer phase. Both phases displayed identical J3XJ3-R30' LEED symmetries. LEED intensity data were used to differentiate between the two phases and to determine a quantitative atomic geometry via a thorough dynamical LEED analysis.The structural characterization of column-III and -V elements deposited on semiconductor substrates continues to be a major subject of study. This interest is driven in part by the desire to improve III-V epitaxy on silicon for application to the manufacture of microelectronics. ' The Si(111)surface is one of the most thoroughly studied substrates. It is known that atomic reconstruction occurs for the free surface of Si(111) and that this reconstruction can be significantly modified by the presence of adatom impurities even at trace, submonolayer concentration. The physical origin of surface reconstruction can be understood as a minimization of the surface free energy.The Si(111)-1x 1 surface with all atoms located at their ideal bulk positions is not realized since it would have too many energetically costly dangling bonds. The 2X 1 and 7X7 reconstructions are stabilized electronically by the removal of surface dangling bonds, leading to a subtle change in the surface atomic geometry. The introduction of covalently bonded adatoms introduces an additional term in the surface free energy, that passivates the surface dangling bonds. Column-III (Al, Ga, In) adatoms generally induce a J3x J3-R30' (called J3Xv 3 hereafter) reconstruction on the Si(111) surface by bonding at the T4 site directly above second-layer Si atoms. The column-V metal As, on the other hand, stabilizes a 1 x 1 surface cell by substituting for the topmost (absent) Si atom. One might expect As-like reconstructions to occur upon adsorbing other column-V elements such as Sb and Bi. Instead, both Sb and Bi adatoms induce a J3XJ3 structure; no well-ordered 1 x 1 structure has been reported. Recent x-ray-diff'raction and scanning-tunnel microscope (STM) studies show that the J3XJ3 reconstruction involves adatom trimers at each 43 x J3 site, at one monolayer (ML) coverage.This trirner model disagrees with the model of 3 -ML saturated coverage proposed earlier by Kawazu et al. However, x-ray-diffraction results are ambiguous with respect to a 180 rotation of the Si(111) surface. ' Therefore, the atomic configuration responsible for the J3XJ3 reconstruction on an atomic scale has not been determined. In this paper, we present results from low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) studies which show that two distinct phases form the v3X&3 superlattice in the Bi/Si(111) system. The Bi coverage necessary for the completion of each phase was determined to be about -, ' and 1 ML and the substrate temperatures corresponding to each phase are -360 C an...

Controlling the effective mass of quantum well states in Pb/Si(111) by interface engineering

“…1(e). From previous studies it is known that Bi has two √ 3 superlattice phases on Si(111) which form depending on the initial coverage and the annealing process 18 . The α-phase forms at T > 640 K with 1 3 ML coverage in substrate units (1 ML = 7.83 × 10 14 atoms/cm 2 ) whereas the denser β-phase forms for temperatures below 640 K and has a coverage of 1 ML.…”

Optimized Ge nanowire arrays on Si by modified surfactant mediated epitaxy

“…[14][15][16] This is associated with a significant surface mass transport of Si, because 0.24 ML of Si atoms are released as a result of the lifting of the 7 ϫ 7 surface reconstruction. 17 Performing the termination in a standard way at substrate temperature T s = 500°C and terminating with a Bi flux F Bi = 0.7 ML/ min for Ϸ10 min results in a need to incorporate 0.24 ML Si at the surface step edges in a relatively short time.…”

“…[14][15][16] This is associated with a significant surface mass transport of Si, because 0.24 ML of Si atoms are released as a result of the PHYSICAL REVIEW B 75, 241309͑R͒ ͑2007͒…”

Observation of Multi-Step Ordering of Bi Adsorbed on the Si(111)7*7 Structure by RHEED and STM

“…Bi was deposited onto the substrate held at constant temperatures at a deposition rate of 0.1 ML/min. The coverage (ML) and deposition rate was calibrated in-situ by observing the completion of the Si(111)β-√ 3× √ 3-Bi phase [24] in the RHEED pattern. During the Bi deposition onto the Si(111)7 × 7 clean surface, the RHEED pattern in the incident azimuth was recorded continuously by a CCD camera to monitor the changes of the surface structures.…”