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Investigation of the Plasticity of InP as a Function of Temperature
E. Le Bourhis, A. Zozime, A. Rivière, C. Vermeulin
To cite this version:
E. Le Bourhis, A. Zozime, A. Rivière, C. Vermeulin. Investigation of the Plasticity of InP as a Function of Temperature. Journal de Physique III, EDP Sciences, 1995, 5 (11), pp.1795-1801.
�10.1051/jp3:1995226�. �jpa-00249415�
Classification Ph~vsics Abstracts
07.80 61.70J 62.20F
Investigation of the Plasticity of InP as a Function of Temperature
E. Le Bourhis(*), A. Zozime, A. RiviAre and C. Vermeulin
C.N.R-S.~ Laboratoire de Physique des MatAriaux, I Place A. Briand. 92195 Meudon cedex, France
(Received 20 December 1994, revised 17 February1995~ accepted 10 April 1995)
Rdsumd. Des Achantillons de phosphure d'indium monocristallin non dopA ont AtA dAformAs
par compression uniaxiale suivant une direction < ool > h vitesse de dAformation constante sur une gamme de tempAratures allant de 300 °C (o,43 Tf h 700 °C (0,72 Tf ). Les cissions h la limite
Alastique dAterminAes sont comparAes avec celles rapportAes dans la littArature. La microscopie Alectronique h balayage en mode cathodoluminescent, ainsi que la microscopie Alectronique en
transmission ont AtA utilisAes pour Atudier la1nicrostructure des Achantillons dAformAs. Dans
aucun cas du micromaclage n'a AtA observA.
Abstract. Compression tests at constant strain rate were performed on < 001 > oriented
single crystals of undoped indium phosphide, in the temperature range 300 °C (0.43 Tm) to 700 °C (0.72 Tm). Critical resolved shear stresses are compared with those reported in the liter-
ature. Scanning electron microscopy in the cathodoluminescence mode and transmission electron
microscopy were used to investigate the deformed sample microstructure. No microtwinning was
observed.
1. Introduction
There is a great number of investigations on the mechanical properties of semiconductors.
The results are useful in improving the handling of materials during device processing (crystal growth, thermal treatment.. and in understanding the basic mechanisms of deformation.
Silicon~ germanium and also compound semiconductors (GaAs) have been studied in detail
as reviewed by Rabier and George ill. The less well-known III-V compound semiconductor, Indium Phosphide becomes brittle at low temperatures (T < 300 °C-400 °C) so it is difficult to deform it without pre-deformation [2,3j. However an investigation at temperatures within
[460 °C. 670 °Cj, without pre-deformation was done many years ago for two sample orientations
< 001 > and < 123 > [4j. In order to complete this study and test new industrial single crystals (Crismatec Inpact), we have deformed samples of undoped InP along a < 001 > direction and
investigated the influence of the temperature from 300 °C to 700 °C on their microstructure.
(*) also at UniversitA Evry Val d'Essonne Bld des Coquibus, 91025 Evry, France
1796 JOURNAL DE PHYSIQUE III N°11
2. Experimental Techniques
2.I. SAMPLE PREPARATION. Parallelepiped compression samples were cut from an un-
doped InP ingot with carrier concentration n
= 5 x 10~~ cm~~ and
an Etch-Pit Density (E.P.D.) about 10~ cm~~ The size
was 5.0 mm x 2.5 mm x 2.5 mm, with the < 001 >
compression axis and side faces along (110). Specimens were mechanically polished with a 2 pm diamond paste. The < 001 > orientation was chosen because it keeps the specimens
symetrical during the deformation; four (1ii ) slip planes are equally stressed, each containing
two <110 > slip directions.
2.2. DEFORMATION CONDITIONS. Deformation tests were performed on an Instron machine
under an atmosphere of argon. The strain rate I was 10~~ s~~ The resolved shear stress
T was calculated from T
= la with # = 0.41 the Schmid factor and a the stress applied to the
sample. The strain 5 was taken as the ratio
~~
where lo is the initial length of the sample and lo
~hl the length variation during the deformation test. Two types of TIE) curves were obtained.
When a peak appeared at the yield point, the Critical Resolved Shear Stress (C.R.S.S.) T~ was
taken at the onset of yielding. When no peak appeared, T~ was taken at the intersection of the
extrapolated "elastic" and plastic stages.
2.3. OBSERVATION OF THE SAMPLES. For cathodoluminescence (C.L.) observations, the
(110) lateral faces of the specimens were mechanically and chemically polished with 1%
bromine-methanol solution. For Transmission Electron Microscopy (T.E.M.) observations, foils
were cut in the middle of the samples parallel to a (111) plane. They were mechanically and
chemically thinned with the same bromine-methanol solution until sufficiently thin to transmit the electron beam.
3. Results and Discussion
3. I. DEFORMATION TESTS. On the T(5) curves, two deformation stages could be observed:
a pseudo-elastic stage followed by a plastic stage (Fig. 1). We did not attempt to obtain a
correct elastic behaviour because of the drawbacks of the compression test [5j. Two types of
curves were obtained at yielding. For the highest deformation temperatures, the deformation
progressively changed from elastic to plastic behaviour, whereas at the lower temperatures a
peak was observed. At the lower temperatures, the yield drop is an usual observation in the deformation of semiconductor crystals iii. Note that at 300 °C, the samples were brittle; the deformation was inhomogeneous and cracks appeared.
The stress to be applied on the sample increased greatly when the temperature was decreased
[Fig. 1). Around 600 °C, the stress strain curve that we obtained is similar to the results which Brown et al. obtained for the same strain rate [4j.
The C-R-S-S- determined from the TIE) curves are given in Table I. A plot of the C-R-S-S-
against the reciprocal of the temperature shows that the deformation is thermionically activated
(Fig. 2). When compared to other authors, our determinations of the critical resolved shear
stress are larger especially at high temperatures although we used a lower strain rate. The
results of Azzaz et al. [6j for a compression axis also parallel to the < 001 > direction are close
to ours, for specimens pre-deformed at 500 °C. In the other investigations [2,8,9j, undoped InP
samples were deformed along a < 123 > direction so that only one slip system was activated
during the first stage, also called the easy stage (Tab. II). In the present case the sample
was deformed along a < 001 > direction so that multiple slip was activated and dislocation
45
40
j~
$ ~~
i 30 f? 25
I 20
j 15 b)
I lo
i~
o
0 05 1.5 2 2.5 3 35
Strain (%)
Fig. I. Resolved shear stress as a function of the strain for undoped InP, for a strain rate I
10~~ s~~ and the temperatures T = 300 °C (Curve a), T =
= 400 °C (Curve b), T
= 500 °C (Curve c)
and T
= 600 °C (Curve d).
Table I. Critical resolved shear stress
as a function of the temperature for undoped InP m
our experimental conditions.
C-R-S-S.
563 26
667 12.5
681 10.5
761 7
773 4
778 6.2
869 4.8
875 3.8
973 3.4
interactions led to parabolic stress strain curves at high temperature and to higher critical resolved shear stresses. A similar observation was made in GaAs [7j.
The activation energy of the deformation Q could be determined using the relation T
=
Ai~/"
exp
~
,
n comes from the microscopic behavior of the deformed sample. Our deter-
nkT mination of ~
is rather close to that deduced from the results of Azzaz et al. [6j with the
n
same sample orientation and lower than the other authors who deformed the specimen along
1798 JOURNAL DE PHYSIQUE III N°11
ioo
i$-~
$
~i
f . ourwork
~
# ° Gall et al.
fu 10
~
. Mbller et al.
$nz O Siethoff et al.
o ~
i °
. ' Azzaz et al.
~ ~a
.j / ~
'C .o
LJ .
0,8 1,2 1,4 1,6 1,8 2 2,2
103/T (K-1)
Fig. 2- Critical resolved shear stress as a function of the reciprocal temperature for undoped InP
for different authors.
Table II. Activation energies of the deformation and experimental conditions given by dif- ferent authors for undoped InP.
Authors n
our work 0.25 300-700 10-5 <001>
Azzaz et al. 0.26 200-500 10"5 <001>
MUller et al. 0.33 600-800 10~ <123>
Gall et al. 0. 34 300-65 0 10"4 <123>
Siethoffet al. 0.53 540-780 2 x 10~ <123>
a < 123 > direction (Tab. II). Such discrepencies may be attributed to the change of the deformation axis, that is to say the difference between multiple slip and single slip. When
compared to reference [9j their
~
is even twice as high as our determination. Such difference
n
may be due to some differences between the material used. It is well known that impurities influence the mechanical behavior of semiconductors and in particular that of InP [11.
3.2. MICROSTRUCTURE OF THE DEFORMED SAMPLES. Visual observation of the (110)
faces of the deformed samples revealed slip lines parallel to two < 112 > directions (Fig. 3).
They correspond to intersections between the (110) faces and the different (ii1) slip planes.
When the temperature was increased, slip lines were less visible but more numerous, which
means that the samples were more uniformly deformed.
C-L- micrograph of the (110) faces show straight dark lines (Fig. 4a) corresponding to the steps of Figure 3. Dark lines correspond to high densities of dislocations which are non
a)
I <ooi>
lmm lmm
Fig. 3. Optical views of undoped InP samples after deformation with a strain rate I = 10~~ s~~,
at 400 °C for a strain E
= 2$io, a) and at 500 °C for a strain
E = 2.5%~ b).
~ <001> '~ &) "~~~ b)
[, ~
~:@'
l' ~~~_
~'
h~_~if
~
i.
so
~ ci d~
50 pm 10
Fig. 4. C-L- micrographs of undoped InP after deformation with a strain rate I = 10~~ s~~~ at 400 °C for a strain
E = 2% a) and b), at 500 °C for
a strain E
= 2.5% c) and d). (At low magnification,
the light collection is not homogeneous~ giving a clear area in the center of the micrograph.)
1800 JOURNAL DE PHYSIQUE III N°11
/ , ,1.
,j
g
,
i' 2 P"
Fig- 5- T-E-M- micrographs of (iii) plane of undoped InP after deformation with a strain rate
I
= 10~~ s~~, at 400 °C for a strain E
= 2% a) and at 500 °C for
a strain
E = 2.5% b) with a < 220 >
type diffraction vector g.
radiative in indium phosphide. At high magnification, dislocation polygonisation becomes visible (Fig.4b). At higher deformation temperature, the straight lines are hardly seen (Fig. 4c)
and polygonization becomes prominent (Fig. 4d). C-L- observations of samples deformed at 600 °C and 700 °C confirm the formation of a cell structure at 2-3ilo strain. ~vhen the samples were deformed at 400 °C the cell structure was not so homogeneous. Large parts of the samples were less deformed; there are no dark spots and lines in such areas on the
micrograph (Fig. 4a). The cells are formed at small strains because we deformed the samples
along a < 001 > direction, multiple slip being activated and interacting to form such cell walls.
When the samples are deformed along a < 123 > direction, an intermediate microstructure exists [10, iii. The cell structure appears when a secondary glide system is activated at high
strains.
On T-E-M- micrographs of ( ii1) planes cell walls are observed along at least two < 110 >
directions (Fig. 5) which means that multiple slip has occurred. In such walls the dislocation density was too high to be measured. In the cell interior, the dislocation density is much lower than in the walls. We never observed twins or microtwins in agreement with [2,10j but in
contrast to observation in reference [4j. Twinning may be related to impurity level, as shown
at low temperature (T < 300 °C) by Azzaz et al. [12j. The specimen of Brown et al. [4j are
nominally pure, but may have been contaminated, although the comparison of their mechanical data with ours give no indication of hardening around 600 °C.
4. Conclusion
The absence of twinning at high temperatures of deformed samples does not explain its oc-
curence during Czochralski crystal growth. The determination of the critical resolved shear
stress at different temperatures shows that the deformation is thermionically activated. The
C.R.S.S. is larger for multiple slip orientation than that for single slip, due to dislocation inter- action. The C-R-S-S- values are consistant with the microscopic shear stress deduced from the
equilibrium dislocation configurations observed in InP deformed by microindentation [13,14j.
Acknowledgments
We are grateful to G. Jacob (Crismatec Inpact, PlombiAre, France) for providing the InP
samples and to J. Castaing for useful suggestions on the work.
References
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