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Y. CORDIER,
1,3 P. MISKA,
1 and D. FERRE2
1.—Institut d’Electronique et de Microélectronique du Nord, U.M.R.-C.N.R.S 8520,
Avenue Poincaré, Université de Lille 1, BP 69, 59652 Villeneuve d’Ascq Cedex, France.
2.—Laboratoire Structure et Propriétés de l’Etat Solide, URA 234, Université de Lille 1,
59650 Villeneuve d’Ascq, France. 3.—e-mail: yvon.cordier@iemn.univ-lille1.fr
InAs islands self-assembled on InAlAs layers lattice mismatched on GaAs
substrates have been grown by molecular beam epitaxy. Both pseudomorphic
and metamorphic InAlAs buffer layers were used as a template to investigate the
effects of strain relaxation on the formation of the islands. The effect of alloy
composition in the metamorphic templates is shown on the density and the shape
of the islands. The present observations confirms the reduction of surface mass
transport due to aluminum in the buffer layers.
Key words: Molecular beam epitaxy, RHEED, atomic force microscopy,
self-assembled islands, lattice mismatch, pseudomorphic,
metamorphic, cross-hatch

(Received August 1, 2000; accepted January 25, 2001)
INTRODUCTION
The self-organization of InAs islands is a powerful
tool for the realization of devices based on quantum
dots.
1,2 The way in which the two dimensional (2D)
wetting layer becomes three dimensional (3D) and
rearranges into islands involves strain as well as
surface diffusion.
3,4 Furthermore, in the case of a
matrix lattice mismatched to the substrate, other
aspects like surface roughness (steps), strain, and
composition modulations have to be investigated. In
this work, we have compared InAs islands grown on
(001) GaAs substrates and on thin pseudomorphic
(PM) or thick composition graded strain relaxed meta-
morphic (MM) InAlAs layers used as a template. The
layers were grown by molecular beam epitaxy and
reflective high-energy electron diffraction (RHEED)
pattern evolutions were recorded to study the transi-
tion from 2D to 3D growth mode. Atomic force micros-
copy (AFM) has been used to investigate the nucle-
ation sites of the InAs islands and to measure the
density as well as the vertical and lateral extension of
these islands.
COMPARISON OF InAs ISLANDS
GROWN ON PSEUDOMORPHIC AND
ON METAMORPHIC InAlAs BUFFERS
A first set of samples has been grown by gas source
molecular beam epitaxy (GSMBE) using cracked ar-
sine and standard effusion cells for elements III, on
2-inch epiready semi-insulating (001) GaAs substrates.
After thermal desorption of the oxide, a GaAs buffer
layer was grown at 580°C to restore surface smooth-
ness. InAs layers were grown at 500°C; the growth
rate of InAs was set to 0.37 monolayer (ML) per
second and the AsH3 flux was maintained at about
1 sccm to obtain arsenic stabilized conditions. Three
kinds of samples were grown. In the first one, InAs
was grown directly on the GaAs buffer layer. The
second type of sample consists of a 3 nm thick pseudo-
morphic InAlAs with indium molar fraction of 33%
prior to the deposition of InAs. In the third type of
sample, a 0.7 µm thick InAlAs metamorphic buffer
with a graded composition profile was grown at 400°C
prior to the realization of the InAs islands; in this
layer the indium molar fraction is graded from 1% to
33% to relax the mismatch strain with the GaAs
substrate and to achieve efficient dislocation filter-
ing.