Ferromagnetic interaction between spins in amorphous SiGe films

Solid State Communications, Vol. 23, pp. 901—903, 1977. Pergamon Press. Printed in Great Britain.

FERROMAGNETIC INTERACTION BETWEEN SPINS IN AMORPHOUS Si—Ce FILMS S. Hasegawa, S. Yazaki and T. Shimizu Department of Electronics,

Faculty of Technology, Kanazawa University,

(Received

Kanazawa 920, Japan

20 June 1977 by W. Sasaki)

Temperature dependence of the ESR signal intensity in amorphous Si—Ce films annealed at various temperatures is investigated. As a result, it is found that spins undergo a ferromagnetic interaction and the Curie—Weiss 0 in the relation x — C/(T—O) distributes between 40 and 135 K. The ferromagnetic behavior suggests that spins are inhomogeneously distributed and closely located together.

In amorphous Si—Ge films prepared by rf—

hol-ler in a proper ratio to fabricate the Si

50Ge50

sputtering, the large ESR signal due to dangling

alloy. Two species of samples (No. 1 and No. 2)

bonds has been observed, 1,2 and it has been found

were fabricated with a Varian FP—21 sputtering

that the dc conductivity o in the temperature range 2—4 T 300 K is Consistent with the Mott relation, 4). c(T) = ~ ~pE-(T0/T)~’ The temperature dependence of the ESR signal

system at the present laboratory and with that at —~

C

___________________________________

7 6

-

>,

intensity I

has been investigated on a non— 8 5-8 annealed amorphous Si or Ge (a—Si or a—Ge),

-

but there has not been such an investigation ~ amorphous Si—Ge. Generally, the dependence of I a obeys the following Curie law or Curie—Weiss law,

C

AMORPHOUS Si—Ge . 1-virgin ~

1—200

~

1—500

•

1— 500L

° A °

or

I I~ 8

lIT (Curie), l/(T — 0) (Curie-Weiss).

(2) (3)

2

—

(3) (0

1

—

=

/

2—virgin 2—450 2-550

/

II

/7 /7

3

It has been found that the dependence in a—Si is 5,6 fitted to equation (2) or equation (3) (0 = —1.3 K),7 and that in a—Ge is fitted to equation 30 K).8 Furthermore, in Si sample im—

7

-

~

~

/~C•

planted with Ne+ and Ar+ ions at doses of 2 to 3 x 1017 cm2, the dependence has also been found

0

present paper, the dependence of I

S

0

100

I 200

I

I 300

MEASUREMENT TEMPERATURE(K)

to obey the Curie-Weiss law (0 ~ 140 K).9 In the on measurement

temperature is investigated on amorphous Si—Ge

Fig.

films with thickness of about I i’m. This result is Compared with the measurement temperature de—

1.

Reciprocal ESR signal intensity I/Is versus measurement temperature for amorphous Si—Ge samples (No. 1; 1 vir— gin, 1—200 and 1—500) annealed at room temperature, 200 and 500°C, respectiv— ely. and samples (No. 2; 2—virgin,

pendence of a Carried out previously by the present authors,2 and the nature of dangling bonds

2—450 and 2—550) annealed at room temperature, 450 and 550°C, respectively. The sample denoted by 1—5001. is 1—500

responsible for ESR is investigated. The amorphous Si—Ge films were deposited on

left in air atmosphere for about two months.

thermally grown Si0 2 substrates by rf—sputtering from Si and Ge targets. The Si and Ge targets were

Faculty of Coordinated Sciences of Tokyo Institute

P doped Si single crystal with a resistivity of

of Technology, respectively. The composition ratio

4

of the sample No. 1 was analyzed with X-ray micro—

‘~

6 £2 cm and highly pure polycrystalline Ge,

respectively, and were set together on the target

analyzer, and the concentration of Si atoms in the 901

902

FERROMAGNETIC INTERACTION BETWEEN SPINS IN AMORPHOUS FILMS

Table

1. The

spin

denaity and 0 for var’tou8 ecvnples 3)

Sample

0 (K)

Spin density (cm x x x x

1—virgin 1-200 1—500 l—500L

~5 ~ 2.2 1.8

2—virgin 2—450 2—550

~2 x io19 a) 4.3 x 1019 4.3 x 1019

l0~ a) 1018 a) 1019

6 x 1019

a—Gee

6 x 1019

implanted Si

e)

120 “ 15O~ 120 ~ 135

io19

a—Si~

implanted si~

Vol. 23, No. 12

76 75 40

30

dose; 2 to 3 x l017/cm2 energy; 50 key

~ 140

dose; < l0~/cm 2 energyT ~. 50 key

a) Spin density and 0 are obtained from the behavior of below about 200 K. b) See refs. 5—7 and also see Fig. 2. c)See ref. 8. d) See ref. 9. e) See refs. 10, 11.

sample was 57

+

5 at%. That of the sample No. 2

temperature region used. The model to explain the

was not analyzed. The Sf0 2 substrates were set on

temperature dependence for group 1 is not clear

water—cooled substrate holder. The deposition rate

at present, but the behavior may be expressed by

was about 330 A/mm. The annealing was carried out

the summation of several Curie—Weiss terms with

in nitrogen atmosphere, and the annealing time

different values of 0. Table 1 summarizes the spin

for each stage was 10 mm. The ESR apparatus is

density and 0 for various samples.

an X—band spectrometer (JEOL PE3X)

.

The ESE signal

The temperature dependences of I~in these

was measured between 140 and 300 K, and at a micro—

two groups agree well with those of

wave input power of 1 mW at which a saturation

bending at about 200 K seen for the temperature

behavior can not be observed,

dependence of I~in group 1 can also be seen for

An ESR signal with Lorentzian lineshape and + 2 C was observed for samples 2 annealed at various temperatures to 650 ‘C. The 9—value was found to approachupfrom the average

0,

i.e.

the

that of a in group 1, and that of ~ in

with linewidth of 34

group 2 is(1)) well conformed to Mott relation equation over the temperature region used

of the 9—values 2.0055 for a—Si and 2.02 for a—Ge

dependence of I

(125 to 300 K).2 The measurement temperature in a—Si annealed in N

to 2.020 for a—Ge with the increase of annealing

or 112 2 at various temperatures is shown in fig. 2 for

temperature.2 The linewidth and the g—value do not

comparison. The a—Si samples were produced under

change with measurement temperature.

a similar sputtering condition as that in

8

Figure 1 shows 1/18 versus measurement temper-

amorphous Si—Ge sample. The temperature dependence

ature in samples (No. 1; 1—virgin, 1—200 and 1-500)

of I~in all samples is found to obey the Curie

annealed at room temperature, 200 and 500 ‘C,

law in Contrast with that in amorphous Si—Ge.

respectively, and in samples (No. 2; 2—virgin,

In a Curie—Weiss paramagnet, the magnitude of

2—450 and 2—550) annealed at room temperature, 450

the ferromagnetic spin exchange interaction

and 550 ‘C, respectively. Here, the sample denoted

proportional to 0, and the values of 0 are dis-

by l—500L is 1—500 left in air atmosphere for

tributed between 40 and 135 K in samples annealed

about two months. As shown in Fig. 1, it is found

above 450 ‘C as seen in Fig. 1. This value of J is

that the temperature dependence in samples annealed

strongly dependent upon the distance between spins.

J is

below 200 ‘C (group 1) can not be iitted to equation This fact suggests that the considerchly stronger (2) or (3), but that in samples annealed above 450 ferromagnetic interaction exists between spins in ‘C (group 2) obeys the Curie—Weiss law over the

amorphous Si—Ge than in a—Si and a—Ge. Owing to

Vol. 23, No. 12

FERROMAGNETIC INTERACTION BETWEEN SPINS IN AMORPHOUS FILMS

10

tively large value of ~

a—Si • virgin -

.0 -

but that in Si implanted

with p+ or Ne+ ions at ion—doses below 1015 cm —2 10,11

-

~ 8 I-

903

620N ° 500H °800H

obeys the Curie law. 2) The temperature dependence of I 8 in a—Si with 19 —3 spin densit~, of 4 ~ 6 x 10 cm prepared by

•

•

$

. law (see Fig. 2 and Table 1),

5—7

and that of 3 obeys evaporation in a—Ge with or spin sputtering density of roughly 6 x 1019 obeys cmthe Curie the Curie—Weiss law with relatively small value

6-

of 0 (30 K).8 On the other hand, in amorphous $

C

Si—Ge (1—500), that of I~obeys the Curie—Weiss

/~

law with relatively although the spin density large value is relatively of 0 (135low K) (2.2 x 1019 cm —3 ) as seen in Fig. 1 and Table 1. This speculation for spin distribution is 2 consistent with the model proposed to explain

2—

0

I

0

I

100

I

I

200

the behaviors of ~ and the 9—value as follows: In samples (No. 1) annealed above about 300 ‘C

I

300

(group 2), it has been suggested that the inhomo—

MEASUREMENT TEMPERATURE( K) Fig. 2.

Reciprocal ESR signal intensity 1/1~ versus measurement temperature for a—Si samples annealed at room temperature (virgin), at 620°Cin N 2 (620N), and at 500 and 800°Cin H2 (500H and 800H), respectively,

the following results and discussions, this ferro—

geneous distribution of Si and Ge atoms exists, and that most of the spins exist in Ge—rich region with relatively higher spin density.2 Accordingly, the temperature dependence of I

in these samples 6

is considered to be well conformed to the Curie— Weiss law over the temperature range used as shown in Fig. 1.

magnetic behavior should originate from the inhomo— geneous distribution of spins with the very high

Ackno~led~ementsThe authors wish to thank Dr.

local spin density. 1) The temperature dependence of I8 in Si implanted

M. Suhara for the use of the ESS spectrometer at Faculty of Science of Kanazawa University and Dr.

with Ne+2)or obeys Ar+ ions high ion—doses (2 to 3 x the at Curie—Weiss law with rela— 1017 cm

H. Ishiwara for Institute the use ofof the sputtering appa— ratus at Tokyo Technology.

REFERENCES KUMSDA M., JIN1~0Y. and SHIMIZL’ T., Phys. stat. sal. (b) 81, No. 1 (1977). HASEGAWA S., YAZAKI S. and SHIMIZIJ T., (to be published). HAI2SER 3. J., Phys. Rev. B8, 3817 (1973). PAUL D. K. and MITRA S. S., Phys. Rev. Letters 31, 1000 (1973). HASEGAWA S. and YAZAXI S., Solid State Convnun. 23, 41 (1977). THOMAS P. A. and KAPLA} D., AlP Conf. Proc. No. 32 p. 85. Williamsburg (1976). BRODSKY M. H. and TITLE R. S., AIR Conf. Proc. No. 32 p. 97. Williamsburg (1976). ARIZUMI T., YOSHIDA A. and SA.JI K., Proc. 6th mt. Conf. on Amorphous and Liquid Semiconductors p. 1065. Garmisch—Patenkirchen (1973). 9. KNOKHLOV A. F. and PAVLOV P. V., Zh. Eskp. and Tear. Fiz. Pis’ma (USSR) 24, 238 (1976). 10. MURAKANI K., MASUDA K., GAMO K. and NAIIBA S., Japan. J. appi. Phys. 12, T~oi(1973). 11. HASEGAWA S., ICHIDA K. and SHIMIZU T., (unpublished). 1. 2. 3. 4. 5. 6. 7. 8.