Nuclear Instruments and Methods in Physics Research B 240 (2005) 105 110
www.elsevier.com/locate/nimb
Damage buildup and recovery in III V compound
semiconductors at low temperatures
a,b,* a a a
A. Turos , A. Stonert , L. Nowicki , R. Ratajczak ,
c c
E. Wendler , W. Wesch
a
Soltan Institute of Nuclear Studies, 05-400 Åšwierk/Otwock, Poland
b
Institute of Electronic Materials Technology, 01-919 Warsaw, ul. Wolczynska 133, Poland
c
Friedrich Schiller University, 07743 Jena, Max-Wien-Platz 1, Germany
Available online 1 August 2005
Abstract
Results are presented of the RBS/channeling study of the structural defect behavior in ion bombarded
InxGa1 xAsyP1 y (0 6 x, y 6 1) compounds at temperatures ranging from 15 K (LT) to 300 K (RT). Experiments con-
sisted of implantation with different ions to fluences ranging from 4 · 1013 to 5 · 1015 at./cm2 at different temperatures
followed by in situ RBS/channeling measurements. Successive measurements of LT implanted samples were performed
during warming up to RT.
Broad recovery stage beginning at 100 K for all compounds was revealed. It was attributed to the defect mobility in
the group III sublattice. Steep damage buildup up to amorphisation with increasing ion dose was observed. The defect
production efficiency is much higher at LT than at RT. The consequences of defect mobility at RT for ion implanted
semiconductor structures are discussed.
Ó 2005 Elsevier B.V. All rights reserved.
PACS: 61.80.Jh; 68.55.Jk; 68.55.Ln; 61.10.Nz
Keywords: III V semiconductor compounds; Defects; Ion implantation; RBS/channeling
1. Introduction
Modification of semiconductor properties by
ion implantation is a well-established technologi-
*
Corresponding author. Address: Institute of Electronic
cal process. For structures based on compound
Materials Technology, 01-919 Warsaw, ul. Wolczynska 133,
semiconductors it is used for introducing active
Poland. Tel.: [phone]; fax: [phone].
E-mail address: [e-mail] (A. Turos). doping, compositional mixing of quantum wells
0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.nimb.2005.06.097
106 A. Turos et al. / Nucl. Instr. and Meth. in Phys. Res. B 240 (2005) 105 110
and formation of isolation regions in electronic de- implantation at temperatures below 50 K and sub-
vices. Point defects and their complexes determine sequent warming up to RT. This process was mon-
optical and electrical properties of semiconduc- itored by in situ RBS/channeling measurements.
tors, diffusion of impurities as well as the recovery Since the main objective of this work was to eluci-
of crystalline lattice after ion bombardment and date the properties of point defects and their com-
subsequent annealing. plexes light ion bombardment was applied. Light
Broad recovery stage at low temperatures exists ions produce principally diluted binary collision
for III V semiconductor compounds [1 5]. It is cascades and are well suited for the study of simple
located between 100 K and 400 K and is attributed defects.
to the recombination or reconfiguration of a
variety of defects with different activation energy.
Thus, the investigation of thermally activated 2. Experimental
processes can be decisive for identification of de-
fects. On the other hand defect mobility at RT InxGa1 xAsyP1 y (0 6 x,y 6 1) binary, ternary
can lead to important effect transformation after and quaternary compound semiconductors were
RT implantation and subsequent storage. Hence, studied. Epitaxial layers of these compounds were
structure and distribution of radiation defects grown using the MOCVD technique in the Aix-
are of great scientific and technological interest tron AIX200RD reactor at the Institute of Elec-
and their reproducible control is crucial for elec- tronic Materials Technology, Warsaw on h100i
trical and structural properties of implanted semi-insulating GaAs and InP substrates. These
materials. were: InP, In0.53Ga0.47As, In0.82Ga0.18As0.52P0.48.
In this paper we review the results of the study Layers of such compositions are lattice matched
of defect buildup and recovery in arsenide and to InP substrates and consequently they are not
phosphide semiconductor compounds after ion strained due to the pseoudomorphic growth.
2000
Random
1500
10E12
4E12
1000
2E12
500
1E12
Virgin
0
600 800 1000 1200
Energy (keV)
Fig. 1. h100i aligned spectra measured in situ for InxGa1 xAsyP1 y (x = 0.82, y = 0.52) epitaxial layer before and after implantation
to different fluences of 150 keV N ions at 15 K. The spectra are labeled with fluences in 1013 at./cm2.
Yield
A. Turos et al. / Nucl. Instr. and Meth. in Phys. Res. B 240 (2005) 105 110 107
1.0
InGaAsP - 15 K
InGaAs -15 K
0.5
InP - 15 K
InGaAsP - RT
0.0
0 10 20 30 40 50 60 70 80
Fluence (1x1013 at/cm2)
Fig. 2. Damage buildup in different semiconductor compounds upon N-ion implantation at 15 K. Also shown is the similar curve for
InGaAsP measured after RT implantation.
1.2
1.0
0.8
0.6
InP
GaAs
0.4
InGaAs
After
InGaAsP
24 hr
0.2
0.0
0 100 200 300
Ta
(K)
Fig. 3. Defect recovery in various semiconductor compounds during warming from 15 K to up 295 K. The solid lines are drawn to
guide the eye.
Amorphous fraction
)
d
d
a
N (15K)/N (T
108 A. Turos et al. / Nucl. Instr. and Meth. in Phys. Res. B 240 (2005) 105 110
Experiments were carried out using the Romeo ple was stored for 10 min and then cooled
and Julia two beam facility at Institute of Solid down to 15 K where aligned RBS/c spectra
State Physics, FSU Jena. The beam delivered by were measured. Subsequently, the sample
the ion implanter Romeo were used to produce de- was warmed to the next preset temperature
fects, while the tandem accelerator Julia equipped and the whole procedure was repeated.
with a 3-axis goniometer was applied for in situ
ion-channeling (RBS/c) measurements. The exper- The evaluation of channeling data measured at
iments were carried out following two schemes: different temperatures requires consideration of
several usually neglected factors, like changes of
(i) Epitaxial layers were implanted to increasing thermal vibration amplitudes of crystal atoms
fluences of 150 keV N+ ions at two tempe- and defect production or removal by the analyzing
ratures (15 K 50 K) and RT until amorphi- beam. The Monte Carlo computer code McChasy
sation was attained; damage buildup was described in detail elsewhere [5] was used for the
monitored by in situ RBS/c measurements. purpose.
In order to avoid sample heating upon ion
implantation beam current density was kept
below 1 lA/cm2. 3. Results
(ii) Implanted at low temperatures epitaxial
layers were analyzed in situ by RBS/c with Fig. 1 shows the h100i aligned spectra for a Inx-
4
1.4 MeV He ions and stepwise warmed up Ga1 xAsyP1 y (x = 0.82, y = 0.52), epitaxial layer
to RT. At each selected temperature the sam- taken at 15 K prior to and after ion implantation
Random
Virgin
1E13 As/cm2 as implanted
3000
1E13 As/cm2 after 2 months at RT
1E12 As/cm2 as implanted
1E12 As/cm2 after 2 months at RT
2000
1000
0
400 500 600 700 800
Channel number
Fig. 4. Random and h100i aligned RBS spectra for InP single crystal prior and after 1.2 MeV As-ion implantation to different fluences
and after prolonged storage at RT.
Yield
A. Turos et al. / Nucl. Instr. and Meth. in Phys. Res. B 240 (2005) 105 110 109
to different fluences of 150 keV N ions. Typical to the further reduction of defect content. For
damage peak that forms upon ion implantation comparison similar recovery curve for GaAs is
is in this case composed of four peaks each corre- also plotted in Fig. 3.
sponding to a different sublattice. Damage profiles Defect mobility at RT has profound conse-
for each sublattice were calculated by fitting simu- quences on properties of ion implanted semicon-
lated spectra to the experimental ones yielding the ductor structures. Fig. 4 shows channeling
damage buildup curve shown in Fig. 2. There is a spectra for InP single crystal implanted in random
small difference in defect production efficiency at direction at RT to different fluences of 1.2 MeV As
LT between different In concentration containing ions. After prolonged storage at RT important
compounds. The damage ingrowth is much slower damage reduction was clearly visible. Damage
for RT ion implantation. Here again the difference depth profiles calculated from these spectra and
between the studied compounds is rather small. corresponding lattice strain profiles determined
Temperature dependence of defect production effi- by high resolution X-ray diffraction (HRXRD)
ciency is a strong indication that important defect [6] are shown in Fig. 5. One notes a strong corre-
transformations occur at temperatures below RT. lation between RBS/channeling and HRXRD
Fig. 3 shows damage recovery curve for samples data.
implanted at LT. For all studied compounds
broad recovery stage begins at approximately
100 K and extends above RT. Although our exper- 4. Discussion and conclusions
imental setup does not allow direct measurements
above RT the prolonged storage at RT after Despite considerable work in recent years the
warming up of a sample implanted at LT leads defect structure development in ion-irradiated
1E13 As/cm2 XRD as implanted
1E13 As/cm2 RBS/c as implanted
100 1E13 As/cm2 RBS/c after 6 months at RT
1000
1E13 As/cm2 XRD after 6 months at RT
80 800
60 600
40 400
20 200
0
0
0 200 400 600 800 1000
Depth (nm)
Fig. 5. Damage depth distribution for InP single crystal implanted with 1.2 MeV As ions to different fluences and the corresponding
strain profile for as implanted samples and after prolonged storage at RT. Note that the strain is negative, i.e. the implanted layer is
under tensile stress.
-
"
a/a (ppm)
Defect Concentration (at.%)
110 A. Turos et al. / Nucl. Instr. and Meth. in Phys. Res. B 240 (2005) 105 110
III V semiconductor compounds is not well recovery at low temperatures reveals much impor-
understood. Although ion bombardment processes tant differences: the fastest recovery was observed
in InP have been studied quite extensively over the for InGaAsP whereas it is slowest in InP. Conse-
last decade, there remains a lack of understanding quently the residual damage at RT amounts to
of the fundamental mechanism of dynamic anneal- 40% of the initial one as compared to 18% for
ing that controls the damage buildup, amorphisa- InGaAs. This is apparently related to the kind
tion and annealing in other In-based compounds. of formed defects which are unknown at the
There is a general agreement that high concentra- moment.
tions of Frenkel pairs can be frozen in during low The great mobility of group III interstitials has
temperature irradiations and that defects in the important consequences in the practice. Shelf stor-
two sublattices react independently. Those that an- age of ion implanted semiconductor structures,
neal below room temperature are related to the even the processed ones, can produce important
group III sublattice whereas the group V intersti- changes of their properties. Defect presence influ-
tials become mobile at approximately 500 K. Pos- ences directly the conductivity and defect induced
itron annihilation spectroscopy confirmed that the strain modifies the bandgap.
large annealing stage between 100 K and 300 K is
due to the mobility of In vacancies and their sub-
sequent recombination with In interstitials [7].
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