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1
Growth Behavior of Ge Quantum Dots on the
Nano-sized Si(111) surface bounded by the (100)
facets

• S.-S. Ferng and D.-S. Lin
• Institute of Physics, National Chiao-Tung
  University, Hsinchu 300, Taiwan

This paper is published at Nanotechnology 17,
5207 ( 2006) as a front cover page featured
article.
Introduction
Method

• The strain-driven self-organized growth of
  three-dimensional quantum-dot (QD) nanostructure
  in semiconductor heteroepitaxy has attracted much
  attention .
• Nanoscale-sized surface in the form of mesa or
  ridges on patterned substrates offer
  opportunities not only for novel growth-control
  engineering, but also fundamental understanding
  of the size-dependent crystal growth phenomena
  during the formation of QDs. .
• The studies of the Ge QD growth on the windows
  or mesas have been largely conducted on the (100)
  plane of silicon. Few literatures discussed the
  effect of the Ge growth on the nano-sized (111)
  plane.

• Microscopy Commercial AFM operated in the
  tapping mode.
• Sample Prepared

Anisotropic etching 20 KOH IPA (51) at room
temperature UHVCVD 650?, 20 and 100 sec
Ge2H4
5 sccm
2D arrays of 36 µm2 rectangular mesas and 11
µm2 negative pyramid.
Results

• The formation of well-confined (111) surfaces

• Ge dots on (100) planes derivative AFM image

20 sec
Profiles and slop angles of Si mesa sidewall vs.
etching depth
Etching depth 120 nm
300 nm
500 nm
The Ge dots on the (100) plane
average radius average height
20 sec 28 nm 10.6 nm
100 sec 30 nm 15.2 nm
(111)
(100)
(100)
5 µm 5 µm
100 sec
Ge dot
Etching depth 80 nm
970 nm
150 nm
420 nm
the (111) facets become well-defined as the
etching depth is larger than 80 nm.
5.5 µm 5.5 µm

• Ge dots on (111) planes

Conclusions
The effective chemical potential for Ge adatoms
on the (111) facet is smaller than that on the
(100) facet, leading to the effective adatom flux
from (111) to (100).
20 sec
100 sec
W111 150 nm
W111 100 nm
µ100
µ111
lt
(100)
400 nm 400 nm
W111 180 nm
W111 370 nm
(111)
(100)
(100)
(111)
The volumes distribution and the thickness of Ge
on the (111) planes with different width.
(100)
W111 530 nm
Acknowledgements
W111 610 nm
Tsung-Hsi YANG Microelectronics and Information
Systems Research Center, National Chiao Tung
University, Hsinchu 300, Taiwan Guangli
LUO National Nano Device Laboratories, No. 26,
Prosperity Road 1, Science-base Industrial Park,
Taiwan 300, R.O.C.
(100)
(111)
(100)
W111 1190 nm
Nuclei-free bands (the denuded zone ) clearly
observed on both edge of the (111) facets, as an
example marked in blue dash line.
References
A. Bruce, Joyce, et al. Quantum Dots
Fundamentals, Applications, and Frontiers, NATO
science series. 190 (Springer, Dordrecht, 2005)
and reference therein.
The boundaries between (111) and (100) planes
denuded zone The boundaries between (111)
facets denuded zone