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X-ray diffraction, Raman, and photoacoustic studies of ZnTe nanocrystals
K. Ersching,1,a兲C. E. M. Campos,1J. C. de Lima,1T. A. Grandi,1S. M. Souza,2
D. L. da Silva,2and P. S. Pizani3
1Departamento de Física, Universidade Federal de Santa Catarina, Campus Trindade,
88040-900 Florianópolis, Santa Catarina, Brazil
2Departamento de Engenharia Mecânica, Universidade Federal de Santa Catarina, Campus Universitário
Trindade, S/N, C.P. 476, 88040-900 Florianópolis, Santa Catarina, Brazil
3Departamento de Física, Universidade Federal de São Carlos, 13565-905 São Carlos, São Paulo, Brazil
共Received 8 October 2008; accepted 23 May 2009; published online 26 June 2009兲
Nanocrystalline ZnTe was prepared by mechanical alloying. X-ray diffraction 共XRD兲, energy
dispersive spectroscopy, Raman spectroscopy, and photoacoustic absorption spectroscopy
techniques were used to study the structural, chemical, optical, and thermal properties of the
as-milled powder. An annealing of the mechanical alloyed sample at 590 °C for 6 h was done to
investigate the optical properties in a defect-free sample 共close to bulk form兲. The main crystalline
phase formed was the zinc-blende ZnTe, but residual trigonal tellurium and hexagonal ZnO phases
were also observed for both as-milled and annealed samples. The structural parameters, phase
fractions, average crystallite sizes, and microstrains of all crystalline phases were obtained from
Rietveld analyses of the X-ray patterns. Raman results corroborate the XRD results, showing the
longitudinal optical phonons of ZnTe 共even at third order兲and those modes of trigonal Te.
Nonradiative surface recombination and thermal bending heat transfer mechanisms were proposed
from photoacoustic analysis. An increase in effective thermal diffusivity coefficient was observed
after annealing and the carrier diffusion coefficient, the surface recombination velocity, and the
recombination time parameters remained the same. © 2009 American Institute of Physics.
关DOI: 10.1063/1.3155887兴
I. INTRODUCTION
ZnTe is an interesting II–VI semiconductor material due
to its wide band gap 共⬃2.26 eV at room temperature兲. Ac-
cording to the phase diagram,1it crystallizes only in a cubic
zinc-blende 共ZB兲structure. This material is promising for
application in high efficiency light-emitting diodes and laser
diodes operating in the green spectral region, X-ray detec-
tors, and solar cells. It is also being used as devices of light
sources in television projectors and for signal transmission.2,3
Different techniques have been used to prepare ZnTe alloys,
such as electrodeposition,4solvothermal process,5,6thermal
evaporation,7molecular beam epitaxy,8and radio-frequency
sputtering.9
Recently Campos et al.10 produced ZnTe nanocrystals by
mechanical alloying 共MA兲and characterized them with
X-ray diffraction 共XRD兲and differential scanning calorim-
etry techniques. It was concluded that the majority ZB-ZnTe
phase remains stable after annealing, but its phase fraction
was reduced while the minority phase fractions 共trigonal tel-
lurium and hexagonal ZnO兲increased.
In the present article, the reproducibility of the ZnTe
nanocrystal production was verified. This new batch was
used to study thermo-optical properties of the ZnTe nano-
crystals with different techniques, such as Raman spectros-
copy and photoacoustic absorption spectroscopy.
II. EXPERIMENTAL PROCEDURE
In order to test the reproducibility of the MA process, the
same experimental procedure reported in Ref. 10 to produce
the ZnTe alloy was adopted. However, in this article we used
a PanAlytical XPert Pro diffractometer 共with Cu K
␣
radia-
tion兲to analyze the starting powders and the as-milled and
annealed ZnTe samples.
Energy dispersive spectroscopy 共EDS兲analysis of the
as-milled and the annealed ZnTe samples were performed in
a JEOL JSM-6390LV scanning electron microscope
equipped with NORAN X-ray microanalysis system Six. The
main results for the as-milled sample were 17.5⫾0.5 at. %
of Zn, 54⫾2 at. %of Te, and 23.0⫾0.8 at. %of O 共al-
though it is commonly overestimated for powder samples兲.
For the annealed one the results showed 23.4⫾0.6 at. %of
Zn, 56⫾2 at. %of Te, and 20.9⫾0.8 at. %of O. This fluc-
tuation from the equiatomic Zn–Te ratio can be associated
with 共i兲gluing of some fraction of Zn on the vial walls
and/or 共ii兲Te-rich interfacial component.
The Raman spectra were collected in backscattering ge-
ometry with a 5145 Å line 共2.41 eV兲of Ar+laser as excita-
tion wavelength. The samples were kept under room tem-
perature. The laser power used in the experiments was about
0.8 mW to minimize heating and consequent changes in the
crystalline state, amorphization, or oxidation of the samples.
The beam diameter on the sample was about 2
m using a
50⫻objective in the Raman microprobe. Jobin-Yvon
T64000 spectrometer was used for recording the spectra. The
liquid nitrogen cooled charge couple device detector was em-
ployed to detect the Raman signals. An acceptable signal to
a兲Electronic mail: kleb85@hotmail.com.
JOURNAL OF APPLIED PHYSICS 105, 123532 共2009兲
0021-8979/2009/105共12兲/123532/6/$25.00 © 2009 American Institute of Physics105, 123532-1
noise ratio was achieved with at least five scans and accu-
mulation times up to 2 min. The Lorentzian fitting was used
to obtain mainly the peak positions. The calibration of the
instrument was done using the 521.6 cm−1 Raman line of a
silicon wafer.
The photoacoustic absorption spectroscopy 共PAS兲mea-
surements were performed on a home-made system with an
open photoacoustic cell configuration.11 The system consists
of a 250 W quartz-tungsten-halogen lamp, a Bentham 605
current power supply, a water lens, a Perkin–Elmer light
chopper 共model 197兲, an electret microphone, a lock-in am-
plifier, and a computer in order to record the PAS signal
共amplitude and phase兲as a function of the modulation fre-
quency 共f兲. The samples for PAS measurements were pre-
pared by compressing at the same pressure the as-milled and
the annealed ZnTe powders to form tiny circular pellets, 10
mm in diameter, with thicknesses 共ls兲of 500 and 465
m,
respectively. Considering the thicknesses of our samples and
the thermal diffusivity 共
␣
兲reported by Kishore et al.12 for the
ZnTe polycrystalline 共
␣
=0.18 cm2/s at room temperature
and
␣
=0.22 cm2/s after annealing at 200 °C to room tem-
perature兲, the characteristic frequencies13 共fc=
␣
/
ls
2兲of 23
and 32 Hz were obtained for the as-milled and annealed
ZnTe samples, respectively. Thus, the PAS data presented
here were acquired between 10 and 270 Hz in order to
achieve a thermally thick regime. To improve the statistics of
PAS measurements, three scans were performed for the as-
milled sample and five scans for the annealed one. The ther-
mal diffusivity parameter is extremely dependent on the al-
loy composition and its microstructure,14 as well as its
processing conditions.11 To analyze the PAS data the theory
shown in Ref. 13 was used.
III. RESULTS
A. X-ray diffraction measurements
Figure 1shows the XRD patterns of the starting powders
tellurium 共c-Te兲and zinc 共c-Zn兲, as well as the patterns of
the as-milled and annealed ZnTe samples. In order to obtain
the structural parameters of these samples, all the patterns
were submitted to the Rietveld analysis 共Ref. 15兲via GSAS.16
The starting model used in the refinements was based on
information given in the ICSD database.17 All the results
discussed along this section are summarized in Table I.
The most intense peaks in the c-Te pattern are attributed
to the trigonal Te phase 共ICSD Card No. 76150兲. The minor-
ity peaks observed at about 26.2°, 29.9°, 37.4°, 48.6°, and
55.3° 共see crosses in Fig. 1兲are attributed to the tetragonal
␣
-TeO2phase 共ICSD Card No. 27515兲. The best fitting ob-
tained by the Rietveld analysis showed weighted phase frac-
tions of 79.33共8兲wt % for the trigonal Te and 20.7共2兲wt %
for the tetragonal
␣
-TeO2.
In the c-Zn pattern the most intense peaks are attributed
to the hexagonal Zn phase 共ICSD Card No. 52259兲and the
peaks observed at about 31.8°, 34.4°, 36.4°, 47.6°, 56.6°, and
62.9° 共open circles in Fig. 1兲are attributed to the minority
hexagonal ZnO phase 共ICSD Card No. 82029兲. The weighted
phase fractions for the hexagonal Zn and ZnO were
83.632共1兲and 16.4共3兲wt %, respectively.
For the as-milled sample the most intense peaks are at-
tributed to the cubic ZB-ZnTe phase 共ICSD Card No.
41984兲. The minority peaks at about 22.9°, 27.5°, and 38.2°
2
positions are attributed to the trigonal Te phase and those
at about 31.7°, 34.4°, and 36.3° 2
positions to the hexagonal
ZnO phase. The weighted phase fractions for the cubic ZB-
ZnTe, trigonal Te, and hexagonal ZnO were 77.28共4兲,
11.54共9兲, and 11.2共2兲wt %, respectively. All the peaks seen
in this XRD pattern are enlarged, indicating the presence of a
nanometric structure. The structural refinement by the Ri-
etveld method was made by applying the profile function
modified Thompson–Cox–Hasting pseudo-Voigt that takes
into account the particle size broadening by Scherrer and it
also uses the microstrain broadening description.18 The peak
linewidths fitted on the XRD pattern were used to obtain the
average size of the crystallites 共L兲and microstrain 共
兲by the
formalism shown in Ref. 16, taking into account the instru-
mental broadening measured with Y2O3standard sample.
The values obtained for L共and
兲were L=145 Å 共
=1.96%兲for the cubic ZB-ZnTe, L=138 Å 共
=2.04%兲for
the trigonal Te, and L=258 Å 共
=0.42%兲for the hexagonal
ZnO phases.
The XRD pattern of the annealed sample shows the
same features of the as-milled sample, however, the peak
intensities increased and the linewidths substantially re-
duced, indicating crystallinity improvement and growth in
average crystallite sizes. The best fitting from the XRD Ri-
etveld analysis gives weighted phase fractions of 69.30共6兲,
16.4共2兲, and 14.3共2兲wt % for the cubic ZB-ZnTe, trigonal
Te, and hexagonal ZnO phases, respectively. It is interesting
to notice that the tetragonal
␣
-TeO2phase was not identified
20 40 60 80 10
0
difference
difference
annealed
Intensity (arb. units)
2
θ
θθ
θ
(de
g
ree)
/7 c-Te
c-Zn
/3
as-milled
/5
FIG. 1. XRD patterns of the c-Te, c-Zn, as well as the as-milled and an-
nealed ZnTe samples overlapped with their respective Rietveld fittings. The
gray lines represent the difference between the theoretical and experimental
data. The symbols represent the main peak positions of the trigonal Te 共兩兲,
tetragonal
␣
-TeO2共+兲, hexagonal Zn 共쎲兲, hexagonal ZnO 共䊊兲, and cubic
ZB-ZnTe 共䉮兲phases, respectively.
123532-2 Ersching et al. J. Appl. Phys. 105, 123532 共2009兲
either in the as-milled or in the annealed samples; the phase
fraction of the hexagonal ZnO for both as-milled and an-
nealed samples is also smaller than that observed for the
c-Zn one. The values obtained for L共and
兲were L
=1107 Å 共
=0.11%兲for the cubic ZB-ZnTe, L=561 Å
共
=0.48%兲for the trigonal Te, and L=587 Å 共
=0.36%兲
for the hexagonal ZnO phases. It can be observed that the L
value obtained for the cubic ZB-ZnTe phase in the annealed
sample is in submicrometer scale. According to Cullity,19 the
Scherrer formalism can be used to calculate crystallite sizes
of the order of 2000 Å only in very good experimental con-
ditions. Thus, the Lvalue obtained for the cubic ZB-ZnTe
phase in the annealed sample indicates that considerable
grain growth occurred for this phase.
Comparing the results from Table Iwith the results from
the previous article,10 one can notice slight differences,
which are attributed to better resolution provided by the
PanAlytical XPert Pro diffractometer and to the using of a
standard sample 共instrumental broadening兲. Thus, we assume
that the MA method is quite reproducible.
B. Raman spectroscopy measurements
Figure 2shows the Raman spectra of the as-milled and
annealed ZnTe samples, as well as the c-Te spectrum sample
as a reference. The Raman spectrum of the c-Te sample
shows three pronounced lines located at low-frequency re-
gion 共⬍200 cm−1兲and at about 645 cm−1 共in the high-
frequency region, see inset of Fig. 2兲. Other small Raman
lines can be seen at 62 and 95 cm−1 and around 400 cm−1.
The Lorentzian fitting procedure of the c-Te Raman spec-
trum was guided by the XRD analysis and its result is shown
in Table II. From this table one can see that all the Raman
active modes of trigonal Te 共Refs. 20 and 21兲were identified
TABLE I. Structural parameters derived from Rietveld analyses of XRD patterns of the as-milled and annealed ZnTe samples using program package GSAS.
as-milled annealed
RBragg;
2共wRp兲0.08; 1.55 共11.7%兲0.07; 2.02 共13.4%兲
ZB-ZnTe 共F-43m兲, cubic Cell parameter 共Å兲6.1056共2兲6.103 68共3兲
Uiso 共Å2兲共x;y;z兲
Zn 0.0310共7兲共0; 0; 0兲0.0162共5兲共0; 0; 0兲
Te 0.0201共2兲共
1
4;1
4;1
4兲0.0122共2兲共
1
4;1
4;1
4兲
共g/cm3兲5.632 5.637
L共Å兲145 1107
共%兲1.96 0.11
wt % 77.28共4兲69.30共6兲
Te 共P3121兲, trigonal
Cell parameter 共Å兲
a4.4777共9兲4.4733共2兲
c5.916共2兲5.9100共4兲
Uiso 共Å2兲共x;y;z兲0.0148共6兲共0.260共2兲;0;1/3兲0.0221共8兲共0.2600共6兲;0;1/3兲
共g/cm3兲6.188 6.206
L共Å兲138 561
共%兲2.04 0.48
wt % 11.54共9兲16.4共2兲
ZnO 共P63mc兲, hexagonal
Cell parameter 共Å兲
a3.2535共5兲3.2507共2兲
c5.217共2兲5.2025共4兲
Uiso 共Å2兲共x;y;z兲
Zn 0.027共2兲共2/3; 1/3; 0兲0.007共2兲共2/3; 1/3; 0兲
O 0.013共9兲共2/3; 1/3; 0.579共5兲兲 0.033共8兲共2/3; 1/3; 0.605共4兲兲
共g/cm3兲5.651 5.677
L共Å兲258 587
共%兲0.42 0.36
wt % 11.2共2兲14.3共2兲
50 100 150 200 250 300 35
0
LO
annealed
c-Te
LO
as-milled
Intensity
(
arb. units
)
Raman Shiff
(
cm-1
)
400 480 560 640
3LO
2LO
FIG. 2. Raman spectra of the c-Te, as-milled, and annealed ZnTe samples
overlapped with their respective Lorentzian fittings. The inset shows the
same Raman spectra in frequency region between 350 and 700 cm−1.
123532-3 Ersching et al. J. Appl. Phys. 105, 123532 共2009兲
in this spectrum, but those related to the
␣
-TeO2ones22 were
only partially satisfied by the fitting. This may be due to poor
crystallinity and/or strain conditions imposed by the majority
crystalline phase over the minority
␣
-TeO2one.
The spectrum of the as-milled sample shows a weak line
at about 96 cm−1 and two intense ones between 110 and
150 cm−1. In frequency region between 200 and 400 cm−1
there are one intense line near 200 cm−1 and another weak
and broad one near 275 cm−1. For high frequencies
共⬎400 cm−1兲, two weak lines can be seen 共inset of Fig. 2兲.
The spectrum of the annealed sample shows basically the
same features observed in the as-milled sample, except for
two lines at about 80 and 235 cm−1. The Lorentzian fitting
procedure was guided by the previous XRD analysis and the
results from the best fitting for both as-milled and annealed
samples are shown in Table II. From this table one can see
that the Raman active modes of trigonal Te 共Refs. 20 and 21兲
共except the line 174 cm−1兲and ZB-ZnTe 共Refs. 23 and 26兲
共except the line 182 cm−1, the TO mode兲were identified in
the spectra for both as-milled and annealed ZnTe samples. It
can also be observed that the fitted lines assigned as 161 and
273 cm−1 for the as-milled sample and 151, 236, and
276 cm−1 for the annealed sample were attributed neither to
the trigonal Te nor to the ZB-ZnTe phases. Maybe these lines
are related to some kind of minority phases not detected by
the XRD measurements. Raman active modes of the hexago-
nal ZnO phase27 共observed in the XRD patterns兲were not
identified.
C. PAS measurements
Figure 3shows the plots of log PAS amplitude versus
log f共a兲and PAS phase versus f共b兲for both as-milled 共open
squares兲and annealed 共crossed circles兲ZnTe samples. The
signal amplitude increased by 35% and the phase increased
by 28% at 11 Hz after annealing. Figure 3共a兲shows changes
in the PAS amplitude between 20 and 30 Hz. Notice that
characteristic modulation frequencies fccalculated for both
samples are in this frequency range. The PAS amplitude of
the as-milled sample shows a modulation frequency depen-
dence of the type ⬇f−1.03 between 55 and 145 Hz, which is
characteristic of nonradiative surface recombination, ther-
moelastic bending, or thermal dilation heat transfer
mechanism,13,28 and for the annealed sample dependences
f−1.05 and f−1.06 were observed for 48–70 and 125–165 Hz
ranges, respectively. The thermal dilation process produces a
constant PAS phase 共equal to ⫺90°兲and Fig. 3共b兲shows that
the PAS phase varies with frequency, which discards this
heat transfer mechanism. On the other hand, the expression
for the phase corresponding to the thermoelastic bending
mechanism, described by Eq. 共1兲, was fitted on the ⌽ph 共ra-
dians兲versus fplot in the modulation frequency range from
95 to 145 Hz,
TABLE II. Frequency of active Raman lines detected for the c-Te, as-milled,andannealed ZnTe samples.
Frequency of active Raman lines in cm−1 共mode symmetry assignment兲
c-Te as-milled annealed TeaZnTeb
␣
-TeO2cZnOd
64.5 62 共B1兲
¯82 82 共A2兲
95 96 96 97 共E兲99
121 121 共E兲
124.8 125 127 123 共A1兲¯
143.4 143 144 141 共E兲¯
152 151 152 共A1兲
157 161 157 共B2兲
171 174 共2E兲174 共E兲
180 179 共B1兲
¯182ⴱ共TO兲¯
¯206.6 207.2 210 共LO兲¯
230 236 210 共E兲, 218 and 235 共B1兲
271 273 259 共A2兲
280 276 281 共B2兲
297 297 共E兲
394 315 共A2兲, 330 and 349 共E兲, 392 共A1兲382
409.5 411.3 420 共2LO兲¯414
417 415 共B2兲439
592 575 共A2兲, 592 共B1兲574
613.7 615.7 630 共3LO兲¯580
642 642 共E兲
649 649 共A1兲
680
769 共E兲, 786 共B2兲
aReferences 20 and 21.
bReference 23–26.
cReference 22.
dReference 27.
123532-4 Ersching et al. J. Appl. Phys. 105, 123532 共2009兲
⌽ph =⌽0+ tan−1
冋
1
a冑f−1
册
,共1兲
where a=ls共
/
␣
兲2. From this fit an effective
␣
=0.152 cm2/s was obtained for the as-milled sample. This
value is 16.7% smaller than that at room temperature re-
ported by Kishore et al.12 and agrees quite well with that
共0.150 cm2/s兲theoretically calculated considering the
weighted phase fractions 共Table I兲and their respective ther-
mal diffusivity coefficients reported in the literature 关
␣
ZnTe
=0.18,12
␣
Te=0.019 cm2/s,29 and
␣
ZnO=0.080 cm2/s共Ref.
30兲兴. The equation for the phase corresponding to the nonra-
diative surface recombination mechanism, described by Eq.
共2兲, was fitted on the ⌽ph versus fplot in the modulation
frequency range from 55 to 95 Hz,
⌽ph =
2+ tan−1
冋
共bD/v兲共
eff +1兲
共bD/v兲共1−
eff兲−1−共
eff兲2
册
,共2兲
where
eff=
共D/
␣
−1兲,b=ls共
f/
␣
兲1/2, and
=2
fand
is
the relaxation time, Dis the carrier diffusion coefficient, and
vis the surface recombination velocity. From this fitting,
where the thermal diffusivity value of
␣
=0.152 cm2/s pre-
viously obtained was fixed, D,v, and
parameters were
determined and are listed in Table III. Good fittings of the
thermoelastic bending 关Eq. 共1兲兴and nonradiative surface re-
combination 关Eq. 共2兲兴mechanisms were not achieved inside
the modulation frequency range from 55 to 95 Hz and from
95 to 145 Hz, respectively, excluding their predominance in
these ranges.
For the annealed sample, the equations for the phase
corresponding to the nonradiative surface recombination and
thermoelastic bending mechanisms were fitted on the ⌽ph
共radians兲versus fplot in the modulation frequency ranges of
48–70 and 125–165 Hz, respectively. For these fittings the
values previously obtained were used as initial values and
␣
,
D,v, and
parameters were determined 共see Table III兲. The
theoretical weighted
␣
value for the annealed sample was
0.167 cm2/s, which agrees with that obtained in this work
and it is 24% smaller than that reported by Kishore et al.12
after successive heating and cooling to room temperature.
Those workers measured an
␣
value for the annealed sample
greater than that measured for the as-prepared one. In this
work the same behavior is observed. We have attributed the
difference between our values and those measured by
Kishore et al.12 to the presence of spurious trigonal Te and
hexagonal ZnO phases in our samples. Aleksiejunas et al.2
reported a value of D=11.1 cm2/s for the ZnTe alloy, which
agrees quite well with the values found in this work for both
as-milled and annealed ZnTe samples. Unfortunately, we did
not find in the literature values for the vand
parameters for
the ZnTe alloy, however, the vand
fitted values are of the
same order of semiconductor materials.
Figure 3also shows that the frequency ranges of nonra-
diative surface recombination and thermoelastic bending
mechanisms are separated for the annealed sample. This
separation can be attributed to structural relaxation 共grain
growth and elimination of defects present in both crystalline
and interfacial components兲promoted by annealing, as sug-
gested by the XRD measurements. The increase in the ther-
mal diffusivity value with annealing also seems to be related
to the structural relaxation. The coexistence of the three crys-
talline phases showed by XRD induces lattice mismatching,
originating empty spaces 共such as pores兲that favor a tem-
perature gradient inside the samples. This temperature gradi-
ent may be responsible for the thermoelastic bending process
observed for both samples.
IV. CONCLUSIONS
In this work XRD, EDS, Raman, and PAS techniques
were used to investigate structural, chemical, optical, and
thermal properties of the as-milled and annealed ZnTe
samples and the main conclusions are as follows:
10 100
102
103
0 50 100 150 200 250
0
1
2
3
f-1.05
f-1.06
f-1.03
PA
S
amplitude
(
µ
µ
µ
µ
V
)
Modulation Frequenc
y
(Hz)
(a)
(b)
PAS phase (radian)
Modulation Frequency (Hz)
FIG. 3. 共a兲Log of PAS amplitude vs log of modulation frequency and 共b兲
PAS phase vs modulation frequency for both as-milled 共open squares兲and
annealed 共crossed circles兲samples. The gray and black solid lines represent
the best theoretical fittings 共Ref. 13兲for both as-milled and annealed
samples, respectively.
TABLE III. Thermal diffusivity 共
␣
兲, diffusion coefficient 共D兲, surface re-
combination velocity 共v兲, and relaxation time 共
兲obtained for the as-milled
and annealed ZnTe samples.
As milled Annealed
ls共
m兲500 465
␣
共cm2/s兲0.152/0.150a0.167/0.167a
D共cm2/s兲10.3 11.6
v共cm/s兲42.5 38.7
共
s兲7.3 10.0
a
␣
values obtained from theoretical weighted calculation.
123532-5 Ersching et al. J. Appl. Phys. 105, 123532 共2009兲
• MA process is reproducible when the same experimen-
tal procedures are used.
• After a few hours of milling it is possible to obtain
relatively pure ZB-ZnTe phase.
• Raman measurements show the optical phonons of
ZB-ZnTe up to third order and confirm the nonreacted
Te identified in XRD measurements for both as-milled
and annealed ZnTe samples.
• PAS measurements showed nonradiative surface re-
combination and thermal bending heat transfer mecha-
nisms for both as-milled and annealed ZnTe samples.
• The experimental effective thermal diffusivity of the
as-milled and annealed ZnTe samples agrees with that
obtained from simple 共weighted兲theoretical calcula-
tions. An increase in the effective thermal diffusivity
was observed after annealing.
ACKNOWLEDGMENTS
The authors wish to thank the Brazilian agencies
CAPES, CNPq, and FAPESC for their financial support. We
also thank the Laboratório Central de Microscopia Eletrônica
共LCME-UFSC兲staff for EDS measurements.
1TAPP, Version 2.2, E. S. Microwave, Inc., Wade Court, Hamilton, OH.
2R. Aleksiejunas, T. Malinauskas, M. Sudzius, K. Jarasiunas, N. Lovergine,
M. Traversa, P. Prete, A. M. Mancini, and T. Asahi, Proceedings of the
Tenth European Workshop on MOVPE, Lecce, Italy, 8–11 June 2003 共un-
published兲.
3W. S. Kuhn, A. Lusson, B. Qu Hen, C. Grattepain, H. Dumont, O. Goro-
chov, S. Bauer, K. Wolf, M. Wörz, T. Reisinger, A. Rosenauer, H. P.
Wagner, H. Stanzl, and W. Gebhardt, Prog. Cryst. Growth Charact. Mater.
31,119共1995兲.
4T. Ishizaki, T. Ohtomo, and A. Fuwa, J. Phys. D 37,255共2004兲.
5Y. D. Li, D. Yi, and Z. Y. Yu, Adv. Mater. 共Weinheim, Ger.兲11, 847
共1999兲.
6J. Du, L. Xu, G. Zou, L. Chai, and Y. Qian, J. Cryst. Growth 291, 183
共2006兲.
7A. K. S. Aqili, Z. Ali, and A. Maqsood, Appl. Surf. Sci. 167,1共2000兲.
8R. L. Gunshor, L. A. Koladziejski, N. Otsuka, and S. Dutta, Surf. Sci. 174,
522 共1986兲.
9H. Bellakhder, A. Outzourhit, and E. L. Ameziane, Thin Solid Films 382,
30 共2001兲.
10C. E. M. Campos, J. C. de Lima, T. A. Grandi, and H. Höhn, J. Non-Cryst.
Solids 354,3503共2008兲.
11J. C. de Lima, N. Cella, L. C. M. Miranda, C. An Chying, A. H. Franzan,
and N. F. Leite, Phys. Rev. B 46, 14186 共1992兲.
12V. Kishore, R. Sharma, V. K. Saraswat, N. S. Saxena, K. Sharma, and T. P.
Sharma, Appl. Therm. Eng. 27, 1552 共2007兲.
13S. M. Souza, D. M. Trichês, J. C. de Lima, T. A. Grandi, and C. E. M.
Campos, J. Appl. Phys. 102, 063523 共2007兲.
14G. Ziegler and D. P. H. Hasselman, J. Mater. Sci. 16, 495 共1981兲.
15H. M. Rietveld, J. Appl. Crystallogr. 2,65共1969兲.
16A.C. Larson and R.B. Von Dreele, “General structure analysis system
共GSAS兲,” Los Alamos National Laboratory Report No. LAUR 86-748,
2000.
17Inorganic Crystal Structure Database 共ICSD兲, Fachinformationszentrum
Karlsruhe, Germany and the U.S. Department of Commerce on behalf of
the United States, 2007.
18P. W. Stephens, J. Appl. Crystallogr. 32, 281 共1999兲.
19B. D. Cullity, Elements of X-Ray Diffraction 共Addison-Wesley, Reading,
MA, 1978兲, p. 285.
20B. K. Rai, H. D. Bist, R. S. Katiyar, K.-T. Chen, and A. Burger, J. Appl.
Phys. 80, 477 共1996兲.
21J. B. Renucci, Ph.D. thesis, Université Paul Sabatie, 1974.
22A. P. Mirgorodsky, T. Merle-Méjean, J.-C. Champarnaud, P. Thomas, and
B. Frit, J. Phys. Chem. Solids 61, 501 共2000兲.
23M. Scagliotti, M. Jouanne, and M. Balkanski, Phys. Rev. B 31,5343
共1985兲.
24S. Hayashi, H. Sanda, M. Agata, and K. Yamamoto, Phys. Rev. B 40, 5544
共1989兲.
25S. Perkowitz, L. S. Kim, Z. C. Feng, and P. Becla, Phys. Rev. B 42, 1455
共1990兲.
26R. L. Schmidt, B. D. McCombe, and M. Cardona, Phys. Rev. B 11,746
共1975兲.
27F. Decremps, J. Pellicer-Porres, A. M. Saitta, J. C. Chervin, and A. Polian,
Phys. Rev. B 65, 092101 共2002兲.
28G. Rousset, F. Lepoutre, and L. Bertrand, J. Appl. Phys. 54,2383共1983兲.
29K. Tsigaridis, Periodic Table of Elements, available at http://
atlas.chemistry.uoc.gr/ptoe.
30X.-D. Xu, D. Ma, S.-Y. Zhang, A.-H. Luo, and W. Kiyotaka, Chin. Phys.
Lett. 25, 176 共2008兲.
123532-6 Ersching et al. J. Appl. Phys. 105, 123532 共2009兲
