Amorphization from the quenched high-pressure phase in tetrahedrally-bonded materials

1. Phys. Chem. Solids Vol. 56. No. 3/4, pp. 559-562. 1995 Copyright 0 1995 Elwier Science Ltd Printed in Great Britain. All rights reserved 0022.3697/95 $9.50 + 0.00

AMORPHIZAT~ON FROM THE QUENCHED HIGH-PRESSURE PHASE IN TETRAHEDRALLY-BONDED MATERIALS K. TSUJI, Y. KATAYAMA, Y. YAMAMOTO, H. NOSAKA

H. KANDA

and

Department of Physics, Faculty of Science and Technology, Keio University, 3-14-t Hiyoshi. Yokohama 223, Japan Abstract-X-Ray diffraction of GaSb, GaAs, GaP and AlSb has been measured at various pressures up to 27 GPa and at temperatures down to 90 K by an energy dispersive method using synchrotron radiation. When pressure was released at low temperature, the high-pressure phase was quenched. The quenched phase showed amorphization when temperature was increased at constant pressure below 1GPa for GaSb. below 5 GPa for GaAs and below 3 GPa for AlSb, while it returned to the zinc-blende phase when the temperature was increased at pressures higher than these. Similar amorphization occurred when pressure was decreased at constant temperature below 270 K for GaSb. below 280 K for AISb. and below 300 K for Gap. These results are discussed in connection with the pressure dependence of potential barriers for the phase transitions by using a configuration-coordinate model. The effects of bonding and structural disorder on amorphization are also discussed in connection with phase transitions in other tetrahedrallybonded materials. Kqvwords: A. amorphous materials, A. semiconductors, C. high pressure, C. X-ray diffraction. D. phase transitions.

1. I~TRODU~IO~ Recentiy

many

phizations to obtain One

studies

on pressure-induced

amorphous

materials

pressure

above

quenched

Photon

Factory,

ground

thermodynamic

below

P,, The latter was reported

is amorphiz-

high-pressure for binary

resuits

were

dependence peaks gives

between

phase

transitions.

interesting

by using

The mixture

alloys

pressure

a con-

model @-IO]. The temperature

height

the two phases As the of the

to study

pounds which ionicity.

potential

amorphization

have different

barrier

depends AU, it is

in several

bonding

strength

comand

In this paper we examine the condition for amorphization from quenched high-pressure phases by measuring the X-ray diffraction of GaSb, GaAs, GaP and AiSb at high pressures using synchrotron radiations.

and low temperatures

marker

(NaCI

(pressure-transmitting :ethanoi)

He gas through

(BL-6C,)

suitable or KCI)

in a diamond

bellows.

at the

samples were for diffraction

of powdered

medium

to control the pressure temperatures [14].

and qfter-

before-

amorphization

magnet

fine powders

out

using synchrotron

KEK [14]. Crystalline

into

of the intensity of the diffraction information concerning the potential

barrier on the

analyzed

from a bending

measurement.

also occurs in elements

were carried

method

phase

methanol

figuration-coordinate

measurements

dispersive

radiation

from

f&8]. Similar amorphization

diffraction

the

P, [l-3] and another

the

X-Ray

by an energy

using high pressure.

ation

f9-I 31. These

amor-

have been made. There are two methods

is amorphization

transition

2. EXPERIMENTAL

sample and

was 4: 1

pressurized mixture

of

anvil cell, driven by

This apparatus continuously

allowed even

us

at low

3. RESULTS AND DISCUSSION

3.1. GaSh With

increasing

pressure

at 300 K, GaSb

trans-

forms into the p-tin phase at 7 GPa. During decompression, the high-pressure phase returns to the zinc-blende phase at about 3 GPa. On the other hand, when pressure is decreased at 100 K, the highpressure b-tin phase is quenched down to 0 GPa. The quenched high-pressure phase shows amorphization when its temperature is increased at 0.5 and 0.2 GPa.

K. TSUJI et a/.

560

When temperature is increased at 2.5 GPa, however, the quenched high-pressure phase returns to the zinc-blende phase at 280 K. With increasing temperature at 0.5 GPa, amorphization begins at 160 K and is completed at 300 K. The wide temperature width of the transition to the amorphous state for GaSb suggests that there is a broad distribution of AU which can arise from the structural disorder in the amorphous state as discussed in the case of Si [9, IO]. On the other hand the sharp transition at 280 K and 2.5 GPa from the quenched high-pressure phase to the zinc-blende phase for GaSb indicates a narrow distribution of AU. Similar amorphization was also observed when pressure was decreased at constant temperatures 250 and 270 K, while the phase transition to the zincblende phase was observed at 300 and 330 K, respectively. It is noted that the state after decompression depends on the paths in the P-T diagram. Figure 1 shows the X-ray diffraction pattern for amorphous GaSb obtained after heating of the quenched high-pressure phase (pressure-amorphized GaSb or P-a-GaSb). This pattern was obtained from the measured intensity by subtracting the scattering intensity of the diamond anvils. There are two broad peaks at Q = 1.9 8, and Q = 3.0 A. These values are the same as those for sputtered amorphous GaSb [ 151.To get information on its structural disorder, the X-ray diffraction was measured for P-a-GaSb at high pressures. Figure 2 shows examples of the diffraction pattern. The pressure dependence of the diffraction intensities of the zinc-blende phase (0) and of the P-tin phase (0) is shown in Fig. 3. At 4GPa, the diffraction peaks from the zinc-blende and the p-tin phases appear. The pressure is much lower than P,for crystalline GaSb. At 7 GPa, which is P,,the diffraction peaks from the zinc-blende phase disappear and

I

’

”

II

GaSb 28= 16 300K

10

20

Fig. 2. X-Ray diffraction pattern for P-a-GaSb with increasing pressure. F: fluorescence X-ray, 0: pressure marker, A: /?-tin phase, v: zinc-blende phase.

the intensity of the diffraction peak from the B-tin phase increases. Minomura et al. [15] reported a continuous change in the diffraction peaks with shifts in peak position in sputtered amorphous GaSb under pressure and crystallization was not observed up to 19 GPa. These differences in the pressure-induced structural change between the pressure-amorphized and sputtered amorphous GaSb suggest that the structural disorder is larger in P-a-GaSb.

’

GaSb 28 = 13.6’ OGPa 295K

GaSb 300K

1

0

. l

5

0.

L-4

2

0

0 l*. 0

.

oooo

.O” 0

I

.

00 IO

Pressure I GPa

Photon energy I keV Fig. I. Example of X-ray diffraction pattern Sharp peaks are diffraction from the pressure

30

Photon energy / keV

for P-a-GaSb. marker, NaCI.

Fig. 3. Intensities of the diffraction peak of zinc-blende structure (0) and b-tin structure (0) with increasing pressure for P-a-GaSb.

Amorphization

from the quenched high-pressure phase

3.2. GaAs When the temperature is increased at 5 GPa, amorphization from the quenched high-pressure phase occurs in GaAs from 140 to 260 I<. With decreasing pressure from 25 GPa at 300 K, the diffraction intensity from b-tin phase disappears at 10 GPa and several new diffraction peaks appear. Some peaks are diffraction from the zinc-blende phase. Peaks at d = 3.30 and 2.69 A at 10 GPa may be the diffraction peaks from a metastable crystalline phase. A transition from the metastable crystalline phase to the zinc-blende phase occurs at 5 GPa. At room temperature, amorphization during decompression from 115 GPa was reported by Vohra et al. [ 161. Partial amorphization during decompression from 22 GPa was studied by several diffraction and optical measurements by Besson et al. [17]. In the present study, however, the transition to the amorphous phase occurs at low temperature during heating at 5 GPa. 3.3. GaP We have measured the X-ray diffraction for GaP at several temperatures with decreasing pressure from 27GPa. Figure 4 shows the diffraction patterns for GaP with decreasing pressure at 130 K. At 6 GPa, the diffraction peaks from the p-tin phase disappear and a broad amorphous pattern is observed. Amorphization from the high-pressure phase was observed from 8 to 6 GPa at 90 K, from 11 to 6 GPa at 130 K, and from 17 to 14 GPa at 300 K. At 300 K, however, diffraction peaks from the zinc-blende phase were also observed. This result at room temperature is the same as that of Itie et al. [18]. They obtained EXAFS spectra for the recovered sample similar to that for

I

GaP

20 Photon energy I keV

Fig. 4. Some examples

of X-ray diffraction pattern (20 = 15 ,) for GaP with decreasing pressure at 130 K.

561

the normal amorphous sample, and also reported the results of electron diffraction and X-ray diffraction studies. Hu et al. 1191did not observe amorphization during decompression from 30 GPa. In our results, the transition pressure decreases with decreasing temperature. It suggests that AU decreases when pressure decreases from P, of the crystalline state. 3.4. AlSb At 300 K, AlSb undergoes phase transition to the p-tin phase at 8-10 GPa. With decreasing pressure, the high-pressure phase returns to the zinc-blende phase at 4-2GPa. On the other hand, the highpressure phase of AlSb with b-tin structure is quenched at 100 K when pressure is decreased. The quenched high-pressure phase shows amorphization when temperature is increased at 1.0, 2.0 and 2.5 GPa. When the amorphous phase is heated further, CrystaIiization to the zinc-blende phase occurs around 300 K. When temperature is increased at 3.5 GPa, however, the quenched high-pressure phase returns to the zinc-blende phase at about 300 K. Similar amorphization was also observed when pressure was decreased at 240 and 270 K, while phase transition to the zinc-blende phase was observed at 300 and 330 K. 3.5. Comparison between several III-V pounds and group IV semiconductors

com-

Analysis from a configuration-coordinate model suggests a difference in the pressure coefficient between AU to the amorphous state and that to the zinc-blende phase in the present III-V compounds. This causes the crossing of the AUs at a pressure P, and a temperature T,.Above P, or above T,, the phase transition to the zinc-blende phase occurs when temperature was increased or pressure was decreased, while below P, or below T, the transition is to the amorphous state. In Si and Ge. the crossing in AU occurs between the metastable crystalline phase and the amorphous phase [9, IO]. The value of AU to the diamond phase should be much higher than that to the metastabie crystalline phase and the amorphous phase. In GaP, P, is higher than 15GPa and 7”,is higher than 300 K. The high P, and a wide pressure region in the amorphization of GaP probably arise from its strong covalent bonds. The ionic character in III-V compounds should lower AU. In fact, T, values in GaSb (270 K), GaAs and AlSb (280 K) are lower than in Si or Ge. A large ionicity in the bonding nature should suppress the amo~hization in InAs and CdTe [7].

K. TSUJI et al.

562

Acknowledgement-This work has been performed under the approval of the Photon Factory Program Advisory Committee (Proposal Nos 94G1 I7 and 92-102).

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