Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

1C/2002S2-002

Photoemission study of Sn films grown on an InSb(111)A surface
Daiyu KONDO1, Kazuyuki SAKAMOTO1*, Masahide SHIMA1, Wakaba TAKEYAMA1,Kenya NAKAMURA2, Kanta ONO3, Yoshitaka KASUKABE4, Masaharu OSHIMA2
1
Department of Physics, Tohoku University, Sendai, 980-8578, Japan2
Department of Applied Chemistry, The University of Tokyo, Tokyo, 113-0033, Japan
3
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan
4
Department of Electronic Engineering, Tohoku University, Sendai, 980-8578, JapanIntroduction
Thin films grown on III-V compound semiconductors
are quite interesting systems, due to their possibilities ofapplication such as high electron mobility transistors andsemiconductor laser devices. Sn film grown on InSb
surfaces is one of such systems. In contrast to bulk Sn,
which is known to show a semiconducting α phase with adiamond structure below 13.2 ˚C and a metallic β phasewith a tetragonal structure above this temperature, Sn filmgrown on an InSb(111) surface was reported to have an αphase even at room temperature [1,2]. Although theorigin of this difference was proposed to result from astrong chemical bonding between Sn and In atoms at theinterface [2], there is no strong evidence to confirm thismechanism so far. Since the understanding of the initial
growth process of an α-Sn film is essential tocomprehend the origin of the presence of an α phase even
above 13.2 ˚C, we have investigated the process using
high-resolution core-level spectroscopy.
Experimental details
The high-resolution photoemission measurements wereperformed at beamline BL-1C at the Photon Factory ofthe High Energy Accelerator Research Organization,
Tsukuba, Japan. An undoped InSb(111)A sample wascleaned by repeating Ar ion sputtering (500 eV) andannealing at 370 ˚C until a sharp 2x2 LEED pattern wasobserved. Sn adsorption was performed using an effusion
cell. All measurements were performed at room
temperature.
Results and discussion
Figure 1 shows the Sn coverage-dependent In 4d corelevel spectra. The spectrum of the InSb(111)A cleansurface is displayed in (a), and the Sn coverages are 0.25,
1.0, and 2.5 monolayer (ML) in (b)-(d). In order to obtain
information about the In 4d components that contribute to
the spectral shape, we have analyzed the spectra by astandard least-squares-fitting method using spin-orbit
split Voigt functions. The solid lines overlapping the datapoints (open circles) are the fitting results. Eachcomponent is indicated by different hatching. The numberof components and their binding energies were confirmedby measuring the spectra using different photon energies
and different photoelectron emission angles. The In 4d
core-level spectrum of the InSb(111) clean surface is well72

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reproduced using two components, B and S1. After the0.25 ML Sn adsorption, the intensity of S1 decreases, andtwo new components (S2 and S3) appear. At higher Sn
coverages, the intensities of both the S2 and S3components increase together with the decrease inintensity of S1. Taking the electronegativities of In, Sn,and Sb into account, the In-Sn bonding should be lessionic than the In-Sb bonding, and the charge state of In
atoms bonded to Sn atoms should be more negative thanthe charge state of In atoms in the bulk phase. This meansthat the binding energy of the 4d component of In atoms
bonded to Sn should be lower than that of the bulk
component within the initial state effect, and we therefore
attribute the S2 component to In atoms that bond directly
to Sn atoms at the interface. The observation of S2 at 0.25
ML indicates that Sn atoms do not adsorb preferably on
the In-vacancy sites of the InSb(111)A structure assuggested in the literature [2,3]. Further, the observationof the Sn-Sb and Sn-In bondings in the Sn 4d spectra at aSn coverage of 0.25 ML supports that Sn atoms adsorb
randomly on the InSb(111)A surface at the initial growth
process.

Figure 1; Sn coverage-dependent In 4d core-level spectra
References[1] R.F.C. Farrow et al., J. Crystal Growth 54, 507 (1981).
[2] T. Osaka et al., Phys. Rev. B 50, 7567 (1994).
[3] P. Fantini et al., Surf. Sci. 463, 174 (2000).
*sakamoto@surface.phys.tohoku.ac.jp