Journal ofNon-CrystallineSolids North-tlolland, Amslcrdam
&96(1987)
525
THERMAL AND LASER-INDUCED Lisong
Hou,
Shanghai P.O.Box
525 - 532
Donghong
PHASE CHANGES OF Te-Se-M(H=In,Sn,Sb)
GU and
Fuxi
THIN
FILMS
CAN
Institute of Optics and Fine 8211, Shanghai, P.R.China
Elechanics,
Academia
Sinica
Results of rapid(laser-induced) and slow(therma1) phase-change studies on Te-Se-H(M=In,Sn,Sb) thin films are reported. When the amorphous-to-crystalline phase transitions take place, the surface resistivity exhibits a sudden drop of 3 to 4 orders of magnitude and the reflectivity increases by more than 30% relatively. The crystallization temperatures of the films studied are all between 100 and 200°C depending upon the film composition. Only when the laser power and pulse duration are within certain ranges can the phase changes be induced. The mechanisms of thermal and laser-induced phase changes are compared and discussed. 1.
INTRODUCTION
Since the laser-induced ductor films were first number of studies which have been as reversible
amorpj-nus-to-crystalline observed by J. Feinleib
have been performed concentrating receiving wider and wider attention
optical
information
is the instability of overcome this difficulty, Te and their
its
influences
on the
microscopy(TDI) The crystallization
mined by measuring the of some elements added peratures were also
were used
results films.
investigated. to induce
of
In and Pb results
behavior
of the
alloys
were
also been given to the to Te-based al10ys~~'~.
exp-
on thermal and laser-induced phase changes X-ray diffraction (XRD) analysis and transwere
employed to examine the occurrence temperatures of these films were
surface resistivity to Te and Te-based Besides heat amorphous-to-crystalline
in
a great on Te-based alloys they can be used
media 2-b. A major limitation of Te room temperature. In order to such as Se, Ge and As were added to
efforts have in addition
films. It is shown that the crystallization are all between 100 and 200°C depending tion
mainly because
of semicon-
at
crystallization
on-going materials
In this paper we present Te-Se-EI(H=In,Sn,Sb) thin
mission electron phase transition.
storage
amorphous state various elements
investigated7*8. Fleanwhile. loration of new phase-change of
phase changes and S.R. Ovshinskyl,
significant
peratures of Te-Se and Te-Se-% films power and pulse duration are properly 0022-3093/87/%03.50 OElsevier SciencePublishen (North-Holland Physics Publishing Division)
change during alloys on their treatment,
upon
decrease
B.V.
heating. The effects crystallization tem-
He-Ne and argon lasers phase transitions of the
temperatures the film
respectively. selected,
of deter-
in
of the composition. the
Only can
the
films
studied The addi-
crystallization when the
ternlaser
amorphous-to-crystal-
526
Hou Lisong
lization cuss
phase
of
of Te - Se - A{ (M = In.Sn.SI?)
be induced.
thermal
and
In
an attempt
addition,
laser-induced
/hit1 /ilnrr
phase
is
made to
dis-
transitions.
EXPERIMENTAL The
chemical
Te-Se-In
were while
Starting
with
cut
for
in to
others
only purity
4-5N
air
film
of
or quenched targets
are
listed
evaporation
in and
table
1.
The
RF-sputtering
by RF-sputtering. were in
the in
of
samples
vacuum
end melted
rotation
obtain
the
by both
of
ampoule
constant
was cooled then
the
glass
of
deposited
elements
a quartz
900°C
compositions
films
techniques,
in
Phase changes
transition
mechanisms
2.
et al. /
mixed
ampoule
water.
desired
in
desired
atomic
a high-frequency for
The
at
least
resulting
shapes
for
ratio,
heating 10h. cake
Then
in
sputtering
sealed
furnace
at
the
the
ampoule
ampoule
and broken
was
pieces
evaporation.
Table 1. Compositions, temperatures of the Sample NO.
Quartz strates Torr
and
a 5x10-5
deposition methods films studied
Composition (at%)
glass for
thin
the
coupons films.
the
substrates
Torr
vacuum
of The
crystallization
Deposition method
2 mm thick
and
background
were
and
was used
and
Evaporation
120
Sputtering
134
Sputtering
160
Sputtering
150
Sputtering
200
Sputtering
175
Sputtering
150
Sputtering
108
23 mm in
pressure
cooled
with the
Crystallization temperature
for
liquid
substrates
diameter
were
evaporation
N2.
For
were
("C)
used
is
the
sputtering
cooled
as sub-
below
lob6 process
by a semiconduc-
or refregirator. XRD patterns meter
using
JlW2OOCX tances
with
were
Cubline(l54 transmission increasing
taken
with
a Rigaku
pm) and Ni-filter. electron temperature
microscope. were
Geierflex-D/MAX-RA
X-ray
TED patterns Variations measured
using
were of the
diffracto-
obtained
electrical equipment
with resisdeveloped
a
Hou Lisong et al. / Phme changes of Te-Se-
in our laboratory A CW argon ion
at a rate laser(488
and the A static
discs using He-Ne used to study the of the films. sample surface Reflectivity
irradiation tester for
3.
erns
is
The 8 mm
time optical
is
The focused spot on the is 1.5,um in diameter. curves(400-1000 nm) of
9 UV/VIS/NIR
phase trana Perkin-Elmer
spectrophotometer.
RESULTS 3.1. Examination It
52-l
laser(633 run) was also phase-change behavior
the films before and after sition were measured with Lambda
thin films
of 5 K/min. nm, 2 watts)
was used to irradiate the films. beam spot on the sample surface in diameter 5 minutes.
M (M = In.Sn,Sb)
of film
structure
is shown by the TED and XRll pattthat the states of the as-deposited
films depend strongly on the preparation conditions. Films deposited without substrate-cooling while those
were deposited
(b)
found crystalline with substrate-
cooling are amorphous. show the TED patterns
Fig.1 (a) and of TeTOSe2+3
(b)
films deposited by evaporation without and with substrate-cooling respectively. The diffuse the film is implies talline
halo in (b) in amorphous
the presence spherulites
indicates that state while (a)
of some polycrysin the film. Heating
film (b) to 2OO'C made the diffraction pattern become sharp rings suggesting the occurrence of crystallization in film,
as shown
in fig.1
(c).
patterns depicted in fig.2 conclusion as fig.1 does. 3.2 Change in electrical Figs. dependence
3 and 4 show of
the
the
electrical
(cl the
The XRD lead
to same
resistance temperature resistance
FIGURE 1 TED patterns of Te70Se271n3 films evaporated (a): without cooling, (b): with cooling. (c) is obtained by heating film (b) to 2OOY. of various for
each
resistance
films. film drop
It
there of
can
be seen
exists 3-4
orders
that
a sudden of mag-
nitude at a certain XRD analyses have temperature We call it (Tc). table
temperature. proved that
crystallization crystallization
TED and this
at
Se (a)
takes place. temperature
Tc of various films 1. All of them are
are given in between 100°C
and 200°C. 2 A
It is well known that Te spontaneously crystallizes at room temperaturell. The addition of Se to Te results in 40
large increase of T, because the partial replacement of Te by Se leads to a Te-Se chain structure so that the increases by about 2 orders
30
10
20
2d(degree)
viscosity of magnitude.
Another effect of Se is the supression of oxidation of Te and thereby the increase in addition
the chemical durability of Sn and Sb to Te-Se
known to crosslink the increase the stability phase13. fective
(b)
12. The alloys is
Te-Se chains and of the amorphous
In this respect, Sn is more efthan Sb as is implied by figs. 3
and 4. On the
-1 other
hand,
we can
also
see
from fig. 3 that the addition of In to a Te-Se alloy gives rise to a considerable decrease in T, as compared Sb. The low melting point may be responsible 4 reveals that in
with increasing considered to be
due to the more metallic One may also notice TeyOSe2yIn3 differences
tivity
Fig. system
characteristics from fig. 3 that
films deposited in composition
by different and thickness
3.3
Change
Great
interest has been concentrated because the use of chalcogenide
I 20
I 10
GIGURE 2 of evaporated without cooling,
TeyOSe2yIn3 (b): with
30 28(degree)
with Sn and of In(156'C)
for this effect. the Te-Se-Sn-Pb
T, decreases remarkably amount of Pb. This is
1 40
XRD patterns films. (a):
cooling,
1:
as-deposit-d, 2: heated to
2OOOC. of Pb than Sn. different T, values methods. between
are
obtained
This may be due to the the films.
for
the
small
in reflectivity on the effect of phase change on reflecalloys for reversible optical storage is
529
Hou Lisong er al. / Phase changes o/ Te - Se - M (M = I,1,Sn. Sh) thin films
60 8-
30 '"1
, 1
1
,,:,,.2,7I.,, Te70Se271"3
,
,
I
I
,
I
,
I
I
I
,
,
60 450 40
120
80
160
Temperature FIGURE dependence of samples
Temperature resistance table 1)
200
240
2
40
("C)
30
3 of electrical 1,2,3 and 4 (see
I
31
,
400 a
600
I
40
I
I
80
160
Temperature Temperature resistance table I) on the
FIGURE dependence of samples change
of
flectivity of the films T, and due to irradiation
200
1000
(nm)
FIGURE 5 Increase in film reflectivity due to heating and Ar-laser irradiation 1: as-deposited films (amorphous) 2: heated films (crystallized) 3: Ar-laser irradiated films (crystallized)
1
120
,
800
Wavelength
I
based
Te,&T"1:4,
240
("C) 4 of electrical 5,6,7 and 8 (see their
optical
properties.
due to heating at by the Ar-laser.
Fig.
temperatures As a result
5 shows
the
higher
than
of heating
increase the the
in rerespective
reflecti-
530
vity
Hou L.isong et al. / Plme
of
all
the
as-deposited
out the wavelength tion, however, is
changes of Te - Se - M (M = In. .%I. Sb) thin JYms
films
increases
by more
than
30% relatively
throgh-
region. The increase in reflectivity due to Ar-laser irradianot so significant as that due to heating. This indicates that
the
laser is not effective enough to induce full phase transition of the materials. In order to establish the reversibility of the amorphous-to-crystalline phase transition, the Ar-laser-irradiated films were further irradiated by a He-Ne laser (10 laser(633 conclusion
mW, 1~~s) and the reflectivity run). The results are shown that
the
films
have
good
of some films and additional
at the wavelength of He-Ne which we can come to the
reversibility
of phase
as-deposited He-Ne laser
(Rl), irradiated
transition.
Ar(R3)
R1 W
R2 W
R3 (%)
2
30
40
29
5
33
44
28
7
37
46
36
Sample
Fig.
was measured table 2, from
reasonably
Table 2. Reflectivities laser-irradiated (R2)
films tivity
in
6 shows and He-Ne exhibits
No.
the
results
of the
interaction
laser beam focued onto the detectable to considerable
the
amorphous
Te7OSe27In3
region the
2 the reflecoccurrence of
amorphous-to-crystalline a level slightly
higher
the film material reflectivity can is expected that
on the irradiated spots. In region 3, however, no change in be detected suggesting that no phase transition takes place. with high power and short duration in this region crystalline-
to-amorphous
phase
1 Pulse
transition, than that
between
film surface. In increase indicating
transition
10 duration
will
100
while in region 1 the of the substrate implying
occur
resulting
reflectivity drops to the burnning-out of
in decrease
in reflectivity.
1000
9s)
FIGURE 6 Relationship between laser power,pulse duration and irradiation results region 1: burnning-out, region 2: reflectivity up, region 3: no change
FIGURE 7 Reflection microscopic photographs the crystallized and burnned-out irradiated by He-Ne laser beam
of spots
It
Hou Lisong et 01. / Phase changes of Te - SC- M (M = In.Sn,Sh)
HOWETIX
our
(
films
are
already
crystalline-to-amorphous microscopic photographs out spots tively. 4.
in amorphous
states,
transition to take of the crystallized
(white-and-black)
corresponding
thus it is impossible for the Fig. 7 shows the reflection (fully white) and the burnned-
place. spots to regions
2 and
cation furnace
known that there exists states of a material.
fig.
6 respec-
of energy or light
an energy barrier between the amorphous and This energy barrier can be overcome by appli-
from a number of sources. For example, exposure by a laser beam of sufficient
tallization of amorphous states as was performed in To achieve a crystalline-to-amorphous transition, spots above give
on the film the melting rise
must point
to a large
treatment
This
can
and sufficiently impossible to induce
short this
process
this work. energy delivered
rate.
without
attendant
duration transition
special
rate
must
be met.
This
T,
process
of a laser
Tg
8. In this solid state
case, the process.
If the process(curve
melting-quenching 1 in fig.
recording lization
beam
intensity and sufficiently as depicted by curve 2 in transition
is
long fig.
--
II , ------
--
---
---
2
3 --
--
FIGURE 8 Schematic illustration of amophiting and crystallization processes
the
should melting
-
-Time amorphizing 8) is used for
operations because thorough erase can not may be proposed for erase (crystallization) In this
-------
1
storage,
8.
is to be achieved to its Tc would
k
lization approach duration than the
1
techniques.
transition temperature
I
a
and the solid state crystalprocess for erase in optical signal
pulse
it-
be accomplished heat treatment
of proper duration,
by a laser
as is shown by curve by the conventional
quenching
kind
of phase transition can both by the conventional and by exposure
to the
increase to a level be established to
be accomplished
On the other hand, if a amorphous-to-crystalline energy at least sufficient to increase the material be needed. Moreover, conditions favoring a low cooling
heat treatment in a energy can cause crys-
be sufficient to cause a temperature of the material snd conditions must
quenching
sufficient intensity fig. 8. But it is
heat
fig.
1 in
DISCUSSION
It is crystalline
of in
531
thin films
quality
approach,
will
a laser
deteriorate
pulse
be used to ensure the point of the material
after
of
proper
repeated
amorphizing-crystal-
be achieved. Therefore, as is shown by curve intensity
and reasonably
acquirement of a little higher and a sufficiently low cooling
another 3 in long
temperature rate and to
avoid
burnning-out
research There general, lization
of the
film
material.
In this
work is expected. are several factors which determine a material with compound composition tendency while a material with high
If a material longer time
has high to crystallize.
viscosity near its In addition,
respect,
the crystallization will exhibite melting point
melting
and crystalline The influences
density states can also affect the growth of In and Pb on the crystallization
in
work
the
present
Investigations their chemical
may be the
careful
compromising
and deep-goiing
behavior14. In a higher crystalhas high T, as well.
temperature,
it
will
trsults
of these
are continuing in our laboratory and physical properties and capability
factors.
on these systems to study as optical storage media.
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R.J.
et
al.
Davis
N. Sato
Van Uijien,
Von Gutfeld
12) M. Terao, 13)
P.H.
14)
PI. Chen,
Solid
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