We have employed the plane-wave pseudopotential method, within the density functional scheme, to study the structural and electronic properties of the clean cleaved (110) surface of BSb, a hard semiconductor [1] with a cation of small size with no p core electrons.
The clear picture of the BSb(110) surface
relaxation is that the top layer Sb atoms move out of the surface and
B atoms move inwards, resulting in a layer tilt of 26.5°. This picture is similar to other III-V’s but contrasts with III-nitrides, which are characterized by a much smaller tilt angle. The location and number of surface states on BSb(110) is similar to that obtained for other III-V(110) surfaces.
The structural and electronic results are used in conjunction with a linear response
approach based on density functional perturbation theory [2] to calculate localized phonon modes on this surface. Three surface phonon peaks have been identified, with energies 40 meV, 60 meV and 85 meV. It is found that phonon modes on BSb(110) exhibit at least two important differences with phonon modes on other III-V(110) surfaces. Firstly, the highest surface optical phonon branch lies well
above from the projected bulk phonon spectrum.
Secondly, in contrast to a previously established observation that localized gap surface
phonon modes lie just above the edge of the bulk acoustic bands and
below the optic bulk phonon edge for III-V(110) surfaces with
larger anionic mass [3], we find that
localized gap phonon branches on BSb(110) are well separated from
bulk phonons. These differences can be related to
the smaller ionicity of BSb.
[1] D. Touat, M. Ferhat and A. Zaoui, J. Phys.:Condens. Matter 18 (2006) 3647.
[2] S. Baroni, S. de Gironcoli, A. Dal. Corso and P. Giannozzi, Rev. Mod. Phys. 73 (2001) 515.
[3] H. M. Tütüncü and G. P. Srivastava, Phys. Rev. B 59 (1999) 4925.
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