Thermal and laser-induced phase changes of Te-Se-M(M=In,Sn,Sb) thin films

Thermal and laser-induced phase changes of Te-Se-M(M=In,Sn,Sb) thin films

Journal ofNon-CrystallineSolids North-tlolland, Amslcrdam &96(1987) 525 THERMAL AND LASER-INDUCED Lisong Hou, Shanghai P.O.Box 525 - 532 Dongho...

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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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Feinleib,

J. deNeufville

2) R.J.

Von Gutfeld,

Appl.

3) A.W.

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K.A.

R.J.

et

al.

Davis

N. Sato

Van Uijien,

Von Gutfeld

12) M. Terao, 13)

P.H.

14)

PI. Chen,

Solid

Gaskell, K.A.

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132.

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