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Disordering of InGaAs/GaAs strained
quantum well structures induced by
rare gas ion implantation
Sergio Pellegrino, C. Pignataro, Manuela Caldironi, M.
Dellagiovanna, F. Vidimari, et al.
Sergio Pellegrino, C. Pignataro, Manuela Caldironi, M. Dellagiovanna, F.
Vidimari, Alberto Carnera, A. Gasparotto, "Disordering of InGaAs/GaAs
strained quantum well structures induced by rare gas ion implantation," Proc.
SPIE 2150, Design, Simulation, and Fabrication of Optoelectronic Devices
and Circuits, (2 May 1994); doi: 10.1117/12.175013
Event: OE/LASE '94, 1994, Los Angeles, CA, United States
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Disorderixig of InGaAs/GaAs Strained Quantum Well structures
induced by rare gases ion implantation
S .Pellegrino, C.Pignataro,M.Caldironi,M.Dellagiovanna, F .Vidimari
Alcatel-Telettra Research Center
via Trento 30, 20059 Vimercate (Mi), Italy
A .
Camera,
A .
Gasparotto
Universita' di Padova, Dipartimento di Fisica
via Marzolo 8, 35131 Padova, Italy
.
Abstract
In this work we have investigated the effect of various
implantation schemes on In (0 .
2)
GaAs/GaAs/A1GaA5 Single Quantum
Well, where the implanted species are Argon and Helium, with doses
in the range lEl2 to lEl4 at/cmA2, at energy spanning 270-400 KeV
and 30 to 50 KeV for Ar and He, respectively.Repetitive annealing
processes were carried out between 735 and 870 °C and the
interdiffusion was deduced by photoluminescence measurements.
A maximum of 20 nm shift from He ion implanted Quantum Well with
an high degree of reconstruction has been recorded, thus allowing
the application of this disordering scheme for the realization of
optoelectronic devices.
Introduction
Quantum Well
(QW)
structures based on 111-V compound
semiconductors show a remarkable stability respect to constituents
interdiffusion.
Typical measured diffusion coefficients at 800 °C for GaAs based
Quantum Wells lie arount lE-l8 cmA2/s, leading to diffusion length
in the nanometers range for usual thermal treatments.
The QW constituents interdiffusion results in a blue-shift of the
electronic transitions induced by the potential profile variation
and a net decrease of the concentration of the diffusing
constituents (Indium in this case) at the center of the Well.
On the other hand, for device application it is highly desiderable
to introduce local variations in the bandgap of the Quantum Wells,
and
with
this
technique
sophisticated
structures
like
nanostructures [1], lasers integrated with saturable absorbers
[2], and others have been realized.
Several techniques have been exploited in order to reduce the
thermal stability of the Quantum Well structures, like diffusion
induced disordering, impurity free vacancy diffusion, thermal
interdiffusion, laser induced intermixing, ion implantation.
The use of ion implantation is particularly interesting since it
can have a good lateral definition, the applicability of focussed
ion beam allows for the definition of sub-micrometer structures
38
/SPIE Vol. 2150
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and might be performed with non-doping elements, thus retaining
the original doping profile of the epitaxial structure.Till now
most of the work was done on A1GaA5/GaAs QW's.Recently the
InGaAs/GaAs system was emerging for its high potential use in
Optoelectronics, where very low threshold lasers [3] ,
very
high
frequency modulation [4] and high power [5] devices have been
demonstrated.
Experimental
The samples used for intermixing experiments were 7.5 nm
In(O.18)GaAs Single Quantum Wells surrounded either by GaAs or by
layers of AlGaAs with Al content varying from 2O to 5O&, and
grown by Low Pressure Metal Organic Chemical Vapor Deposition (LP-
MOCVD).
As
for the first case, or samples (I) ,
the
Quantum Well was grown
on (100) ,
2
deg off toward (110) GaAs substrates and located at
190 nm from the surface.
The second kind of structures, or samples (II) comprises 1.2
microns of Al(O.5)GaAs, 70 nm of Al(O.2)GaAs, 6 nm GaAs spacer
symmetrical to the Quantum Well, 70 nm of Al(O.2)GaAs and 100 nm
of Al(O.5)GaAs.
The structure was then terminated for protection with a 50 nm GaAs
capping layer.The precise structural
parameters have been
extracted by Transmission Electron Microscopy (TEM) measurements.
The implantation experiments were performed with a 200 KeV Ion
Implanter at room temperature, and the samples were tilted 10°
respect to the beam axis in order to avoid channeling effects.
The implanted species were Argon and Helium, the energy ranged
270-400 KeV for Ar and 30-50 Key for He and the doses swept lEl2-
lEl4 at/cm"2.
The implantation current density was kept as low as 50 nA/cm'2 in
order to avoid the effects of dynamical annealing [61, which have
been verified by a series of implantation experiments at high
current density of 5 ,uA/cm2, as shown for comparison with a low
current implant in figure 1.It is clearly shown how the maximum
strain is higher for the implantation at low current density,
since the angular separation of the furthest prominent oscillation
from the substrate peak is higher in this later case.
SPIE Vol. 2150/39
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Figure 1:X-Ray Rocking curve of an Argon implanted GaAs substrate
at the dose of 1E14 at/cm'2; implantation current density f or:
curve a) 5 pA/cm2
curve b) 50 nA/cm2
Reconstruction of the damage profile
The implantation process induces crystallographic damage,
which can be detected by X-Ray Diffraction (XRD) techniques. The
recorded rocking curves are very sensitive to strain profiles
which,
in case of ion implanted GaAs are positive and
perpendicular to the growth surface.The strain was found to be
proportional to the density of deposited energy
[7] ,
with
significant nonlinearities at high implantation doses.
The strain profiles were obtained by iteractive fitting with a
dynamical model of diffraction, using vacancy and interstitial
distribution of the implanted layers, derived from TRIM-90 code
[8], as initial guess of a trial and error procedure.
The damage profile was considered to be linearly related to the
strain distribution, and in the calculation the implanted region
is divided in thin lamellae uniformly strained.
A reasonably good agreement was usually obtained with
five to
seven slides, where no significant change was noticed decreasing
the discretization step.
In figure 2 we show a measured and simulated rocking curve f or an
Argon implanted GaAs layer at a dose of lEl4 at/cm2 and 270 KeV
energy.
The calculated curve
resemble quite closely the
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