Structure of the InSb„ 111… A - „ 2 ) 2 )… - R 30° surface and its dynamical formation processes
Masayasu Nishizawa and Toyoaki Eguchi
Department of Materials Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169, Japan
Tetsuya Misima and Jun Nakamura
Kagami Memorial Laboratory for Materials Science and Technology, Waseda University, Nishiwaseda, Shinjuku-ku, Tokyo 169, Japan
Toshiaki Osaka
Department of Materials Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169, Japan
and Kagami Memorial Laboratory for Materials Science and Technology, Waseda University, Nishiwaseda, Shinjuku-ku,
Tokyo 169, Japan
Received 10 September 1997
We have studied the structure of the InSb(111) A -(2 )2 ))- R 30° surface and how it is transformed from
the original 22 surface under Sb-rich conditions, by using scanning tunneling microscopy, Auger electron
spectroscopy, and reflection high-energy electron diffraction. In the 2) structure a Sb trimer settles its center
on the In vacancy site of the 22 surface, and the three In atoms are further missing from it. These missing
In atoms are consumed in a way that, while Sb is deposited onto the 22 surface at 230 °C, the 2) surface
grows along a direction normal to the step edge, increasing the terrace area and causing the step edge to
become ragged. S0163-18299801808-6
The 111 A , B surfaces of InSb are polar and, change
their reconstructed structures with temperature and composi-
tion. One of these polar surfaces, (111) A , exhibits two types
of reconstructions: 22 and (2 )2 ))- R 30°.
1,2
The
22-reconstructed surface has an In-vacancy buckling
structure, in which 0.25 ML of In is missing at the outermost
surface. This structure, determined by Bohr et al. using
grazing-incidence x-ray diffraction,
3
was confirmed by trans-
mission electron diffraction
4
and angle-resolved photoelec-
tron spectroscopy.
5,6
The 22 reconstruction is trans-
formed to the 2) reconstruction in temperatures ranging
from 250 to 310 °C under more Sb-rich conditions than the
homoepitaxial growth conditions for the InSb111A-
22 system.
1
Most recently, we reported that the 2) re-
construction appears purely and solely in the narrow tem-
perature range between 200 and 215 °C, beyond which it
begins to coexist with the 22.
7
However, details associ-
ated with the Sb-stabilized 2) surface have not yet been
investigated.
In this paper, we report on the surface structure and
stoichiometry of InSb(111) A -(2 )2 ))- R 30°, and also
on its dynamical surface processes. In evaluating such sur-
face features, we used scanning tunneling microscopy
STM, Auger electron spectroscopy AES, and reflection
high-energy electron diffraction RHEED.
Experiments were performed using an ultrahigh-vacuum
UHV system equipped with a scanning tunneling micro-
scope and a molecular-beam epitaxy MBE unit and a
RHEED apparatus. The ultimate pressure was less than
1.010
-10
Torr, and the pressure during evaporation was
below 2 10
-9
Torr.
Before being loaded into the load lock chamber, the
InSb(111) A substrate nondoped was rinsed in ethanol, and
etched in a lactic-acid–nitric-acid 10:1 solution for 10 min.
After being outgassed at 350 °C for 6 h, the substrate was
transferred to the STM chamber for the following cleaning
procedures: The native oxide was removed from the sub-
strate surface by heating at 410 °C with an impingement of
Sb
4
molecules at 6.610
14
molecules/cm
2
min correspond-
ing to 1.2 ML/min. Homoepitaxial growth of InSb was
performed on the surface at 320 °C with present fluxes of In
1
1 ML/min and Sb
4
0.75 ML/min. The In
1
and Sb
4
beam
sources were a W basket and a Knudsen-type Mo crucible,
respectively. The evaporation rate was monitored with a
quartz-crystal microbalance. Such treatments gave us a sharp
RHEED pattern which stemmed from the InSb111A-
22 surface. Subsequently, in order to prepare the 2)-
reconstructed surface, a flux of Sb
4
was impinged onto the
22 surface at 200 °C for 4 min at a rate of 0.1 ML/min,
FIG. 1. Empty-state STM image taken from where the
InSb(111) A -(2 )2 ))- R 30° area coexists with the 22. The
inset is a magnified STM image of the 22-reconstructed area in
which the 22 unit cell is outlined with white lines.
PHYSICAL REVIEW B 15 MARCH 1998-I VOLUME 57, NUMBER 11
57 0163-1829/98/5711/63174/$15.00 6317 © 1998 The American Physical Society