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Vapor phase transport of cadmium telluride
162
Journal of Crystal Growth 24/25 (1974) 162—165 © North-Holland Publishing Co.
VAPOR PHASE TRANSPORT OF CADMIUM TELLURIDE KENZO IGAK[ and KATSUMI MOCHIZUKE
Department of Materials Science, School of Engineering, Tohoku University, Aoba, Aramaki, Sendai, Japan Cadmium telluride crystals were grown by the sublimation method under an independently-controlled partial pressure of one of the constituent elements. A reservoir chamber at one end of the closed quartz tube is used to control the partial pressure. When the partial pressure in the reservoir chamber is high, the transport rate is strongly dependent on the partial pressure; proportional to the (—3/2)th power of Te 2 partial pressure for the tellurium reservoir or proportional to the (—3)rd power of Cd partial pressure for the cadmium reservoir. In these cases the transport rate depends upon the average temperature gradient and is known to be rate-determined by the diffusion process in the vapor phase. With decreasing partial pressure in the reservoir, the transport rate becomes independent of partial pressure but is determined by the temperature difference between the source chamber and the growth chamber. Furthermore, it is found to be proportional to the surface area of the source specimen or to the condensation area. In these cases either the evaporation or the condensation process is rate-determining.
1. Introduction
stoichiometric proportion, each with a purity of 6-nines,
Single crystals of the il—VI semiconducting cornpound2)cadmium canphase3’4), be grown because either from the or fromtelluride the vapor of the melt” relatively low melting point and moderate equilibrium vapor pressures of the constituent elements5’6). Prior’s method7), of static vapor phase crystal growth, is unique in that it makes possible the growth of a crystal under controlled partial pressure of one of the constituent elements using a reservoir at one end of a closed tube, in the present study, Prior’s method was employed in order to obtain a reproducible growth rateand to grow crystals with controlled deviation from stoichiometry. The transport rate is usually a complicated function of many factors. In this study, efforts were made to distinguish the contribution from each factor experimentally. in order to clarify the transport mechanism, the transport rate was measured as a function of the following independently-regulated parameters: the source temperature T~,the temperature difference AT and the distance AX between the source and growth chambers, the partial pressure of one of the constituent elements, estimated from the reservoir temperature, the surface area of the source specimen S~and the condensation area S~.
were weighed and introduced into a carbon-coated quartz tube of 8 flushed mm diam. x 200times mm. with The argon tube was first evacuated, several of 4-nines purity and finally sealed off under a vacuum of about iO~ Torr. Polycrystalline specimens prepared by gradually raising the temperature and melting at 1100 °Cwere vacuum-sealed anew into another carboncoated quartz tube, and single-crystalline specimens were obtained by the Bridgman method. These singlecrystalline specimens were cleaved into disc shapes and, after heat treating under a fixed cadmium or tellurium partial pressure, they were used as the source specimens for the transport experiment. The standard dimensions of the source specimens were 7 mm in diameter and 3 mm in thickness. These procedures, which define precisely the surface area and the heat treatment of the source specimen, were adopted in order to eliminate effects which might be caused by a difference in the surface area or in the history of the source specimen in obtaining a reproducible growth rate. Source specimens in powder form might cause a different degree of supersaturation depending upon the particle size even under otherwise identical experimental conditions. 2.2. VAPoR PHASE TRANSPORT UNDER CONTROLLED
2. Experimental procedures
The schematic construction of the electric furnace and an example of the temperature profile used to grow
2.1.
PARTIAL PRESSURE
PREPARATION OF THE SOURCE SPECIMEN
cadmium telluride through the vapor phase are shown in fig. 1.
About 0.1 mole of cadmium and tellurium in ill
—
5
163
VAPOR PHASE TRANSPORT OF CADMIUM TELLURIDE
f4I ~.,.,
I
L~’
~~,j’~iscm
04U~0~m
.,
AT1IIC
io2.
_I_
~-:—~
/
£_7.
\~$7~6t
N 1k 200 Fig. 1. Schematic construction of the electric furnace and an example of temperature profile for vapor phase transportation. (a) source chamber; (b) reservoir chamber; (c) growth chamber; (d), (e) auxiliary heater; (f), (g) alumel-chromel thermocouple; (h), (i) main heater.
10~2
10~
1(10
101
102
P~2(Torr)
Fig. 2. Transported quantity after 1 hr as a function of Te2 partial pressure for several source temperatues with fixed AT (10 °C) and AX (4.0 cm). Vertical bar indicates the estimated error.
The fused quartz tube consisted of: (a) the source chamber, (b) the reservoir containing one of the pure constituent elements, cadmium or tellurium and (c) the growth chamber with a flat end window for easy observation. The tube was vacuum sealed in the same way as previously described. The growth chamber was carefully baked out before introducing the tube into the furnace in order to clean the inner wall and to avoid spurious nucleation. The growth chamber with a flat end also served to keep a fixed condensation area when growing alarge crystal. The partial pressure ofthe constituent element was controlled by regulating the reservoir temperature TR and the partial pressure in the transport chamber was assumed 8) to be by at determined the reservoir the equilibrium pressure temperature. Aftervapor the vapor phase transport the tube was water-quenched and the crystals grown in the
As seen from fig. 2, there exist three different regions. (1) In the cases of high partial pressures of Te2 the transported quantity was found to be proportional to time and the transport rate was proportional to the ——th power of Te2 partial pressure. This region is designated as Region I. (2) For intermediate partial pressures of Te2, the transport rate was found to be proportional to the —~th power of Te2 partial pressure. This region is designated as Region II. (3) For low partial pressures of Te2, the transport rate was a little scattered but was found to be independent of partial pressure. This region is designated as Region III.The range of partial pressures covered by Region II is wide at low I’~ temperatures, butbecomes narrow and finally disappears at the higher T 0 temperatures. The growth chamber were weighed to calculate the tran- arrows in fig. 2 show the values of FTc2 corresponding sport rate. Experiments were performed under con- to minimum total pressure in the transport tube. ditions coveringthe following ranges, (i) T0: 7 16—876 °C Region III is known to cover the pressure range lower regulated with an accuracy of ±2 °C,(ii) AT: 2—40 °C than this value. The scattering of the data in Region III with accuracy of ±0.5 °C, (iii) AX: 20—70 mm, (iv) is known to be caused by differences in sample history. 2, (vi) S~: When samples, previously heat-treated under the same 0.13—0.95 cm2. Torr, (v) S~:0.10—1.93 cm conditions as the transport experiment, were used as ~TC2 10~l0 source specimens, the highest transport rate was ob3. Experimental results and discussion tamed and showed no dependence upon the partial The transport rate was first studied as a function of
pressure of Te 2. The transport rate in this region was known to depend only on AT and not on AX, as shown in fig. 3. This behaviour suggested that the surface reaction might rate-determine the transportation. The transport rate was next studied as a function of S~and S~.The
the partial pressure of the constituent element. Fig. 2 shows the transported quantity after one hour as a function of Te2 partial pressure for three T~temperatures with fixed AT and AX for the case of the tellurium reservoir, III
—
5
164
K. IGAKI AND K. MOCHIZUKI 24
1s76t
20
TR,380’C
rate was found to be proportional to the average
/
a
/
~‘16
temperature in this region, in agreement with thegradient assumedAT/AX transport mechanism.
~
Similar transport experiments were also performed
12
/
8 4
5
10
15 20 25 30 M Ic) Fig. 3. Relation between transport rate and AT in Region III. (o) AX = 2.0 cm; (x) AX= 4.0 cm; (~)AX= 6.0 cm.
condensation area S~,was regulated by changing the inner diameter of the growth chamber. At relatively low T0 temperatures, S~,had no effect on the transportation. The transport rate was found to be proportional to S~,not only in Region III but also in Region II, as shown in fig. 4. At high T0 temperatures, however, the surface area of the source specimen S~had a serious effect on the transport rate. It is known that the rate-determining step in Regions III and II is the surface reaction: evaporation for high T0 temperature and condensation for low T~temperatures. The transport behaviour in the transition T0 temperature range is not yet clear, A transport rate proportional to the 4th power of the Te2 partial pressure, observed in Region I, is similar to the tendency already reported by tendency previous 4’910) and this workers on Il—VI compounds is explained by assuming that the rate-determining process is diffusion in the vapor phase. The transport
for the case of the cadmium reservoir and the following two different regions were observed. (4) For low partial pressures of Cd, the transport rate was independent of the partial pressure. This region is designated as Region III’. (5) For high partial pressures of Cd, the transport rate was found to be proportional to the 3rd power —
.
.
.
of the Cd partial pressure. This region is designated as Region I. Transport behaviour in Region I’ is quite similar to that in Region land is known to be explained by assuming that the rate-determining process is diffusion in the vapor phase. The rate-determining step in Region iii’ for high T~ temperatures is known to be the evaporation process. Fig. 5 shows the temperature dependence of the electrical conductivity of crystals grown under controlled partial pressure. Crystals grown with appreciable growth rates are always p-type. The electrical conductivity at room temperature as a function of Te2 partial pressure is shown in the right portion of fig. 6.
—
______________________
:~
Ts,876’C(Te) TR,
a
______
~,
6o2t
o
55d~C
~
~25
~\
T
/~T~z~c
/%
0\~\\
10
~O
0.2
ck4
0.6
Q~
1
-7 ____________________________
Sc(cm2)
1C 3 6 3/T( K -1 Fig. 5. Temperature dependenceoftheelectricalconductivityof i0 the crystals grown under controlled partial pressure.
in Region III and Region (~)T~=rate 716and °C,TR = 500°C(II); Fig. 4. Relation betweenII.transport condensation area (x), (C) T, = 716 °C,TR = 380°C (III).
III
—
5
VAPOR PHASE TRANSPORT OF CADMIUM TELLURIDE
iuI ________________________________________________ ~ Ts,876C(Te)
~8 ~
directly through the vapor phase was abandoned. Figs 5. and 6 show that the electrical conductivity of the grown crystals depends upon the growth conditions. Even though disturbing effects from unregulated defects or impurities are observed, vapor phase growth
A Prrin(87(C) B PmIn(798t)
°Ts,870 (Cd) ~T~798~(Te)
-1
10
\
~
I
B
under controlled partial pressure is confirmed to be anddeviation efficacious for stoichiometry. obtaining crystals having anecessary controlled from
A
10
Ca
4.
10
I 1o-~
10-4
1o-~ 10-2 P1e2(Torr)
10-1
100
6.
101
102
The transport rate through the vapor phase was io~ precisely studied by independently regulating the experimental parameters. Depending upon the rate-
Electrical conductivity at room temperature as a funcof Te 2 partial pressure. Right portion is of as grown p-type specimen and left portion is of specimen converted to n-type after heat treating in cadmium vapor,
tion
Conclusion
0
~106
Fig.
165
determining process, diffusion in the vapor phase or surface reaction, regions with different behaviours were clearly observed and identified. Further efforts will be necessary to apply the present information to the case of dynamic transportation or to develop it for application to ternary compounds.
Results for crystals grown with a cadmium reservoir 1~Te
are also shown, converting ~Cd into 2 by using the reported dissociation constant of cadmium telluride at the temperature T0. The results shown in the left portion of fig. 6 are the electrical conductivity at room temperature after heat treating the crystals at 800 °Cunder nearly saturated cadmium pressure. In spite of the differences in growth conditions, specimens became n-type with high conductivity after this cadmium treatment. Direct vapor phase growth of n-type specimens with high conductivities was found difficult. By extrapolating the cadmium partial pressure dependence of the transport rate, the time neccessary for growing n-type crystals with appreciable size was estimated to be several years and the attempt to grow n-type specimens
III
References 1) D. de Nobel, Philips Res. Rept. 14 (1959) 361. 2) R. Triboulet and Y. Marfaing, J. Electrochem. Soc. 120 3) 4) 5) 6)
(1973) 1260. R. Höschl T. Lynch, Phys.Phys. 33 (1962) P. andJ.~.Appi. Koñák, Status1009. Solidi 9 (1965) 167. M. R. Lorenz, J. Phys. Chem. Solids 23 (1962) 939. R. F. Brebrick and A. J. Strauss, J. Phys. Chem. Solids 25
1441. J. Electrochem. Soc. 108 (1961) 82. 7) (1964) A. C. Prior, 8) A. N. Nesmeyanov, Vapor Pressure of the Chemical Elements (Elsevier, Amsterdam, 1963). 9) T. Kiyosawa, K. Igaki and N. Ohashi, Trans. Japan Inst. Metals 13 (1972) 248. 10) M. Toyama, Japan. J. Appi. Phys. 5 (1966) 1204.
—
5
Journal of Crystal Growth 24/25 (1974) 162—165 © North-Holland Publishing Co.
VAPOR PHASE TRANSPORT OF CADMIUM TELLURIDE KENZO IGAK[ and KATSUMI MOCHIZUKE
Department of Materials Science, School of Engineering, Tohoku University, Aoba, Aramaki, Sendai, Japan Cadmium telluride crystals were grown by the sublimation method under an independently-controlled partial pressure of one of the constituent elements. A reservoir chamber at one end of the closed quartz tube is used to control the partial pressure. When the partial pressure in the reservoir chamber is high, the transport rate is strongly dependent on the partial pressure; proportional to the (—3/2)th power of Te 2 partial pressure for the tellurium reservoir or proportional to the (—3)rd power of Cd partial pressure for the cadmium reservoir. In these cases the transport rate depends upon the average temperature gradient and is known to be rate-determined by the diffusion process in the vapor phase. With decreasing partial pressure in the reservoir, the transport rate becomes independent of partial pressure but is determined by the temperature difference between the source chamber and the growth chamber. Furthermore, it is found to be proportional to the surface area of the source specimen or to the condensation area. In these cases either the evaporation or the condensation process is rate-determining.
1. Introduction
stoichiometric proportion, each with a purity of 6-nines,
Single crystals of the il—VI semiconducting cornpound2)cadmium canphase3’4), be grown because either from the or fromtelluride the vapor of the melt” relatively low melting point and moderate equilibrium vapor pressures of the constituent elements5’6). Prior’s method7), of static vapor phase crystal growth, is unique in that it makes possible the growth of a crystal under controlled partial pressure of one of the constituent elements using a reservoir at one end of a closed tube, in the present study, Prior’s method was employed in order to obtain a reproducible growth rateand to grow crystals with controlled deviation from stoichiometry. The transport rate is usually a complicated function of many factors. In this study, efforts were made to distinguish the contribution from each factor experimentally. in order to clarify the transport mechanism, the transport rate was measured as a function of the following independently-regulated parameters: the source temperature T~,the temperature difference AT and the distance AX between the source and growth chambers, the partial pressure of one of the constituent elements, estimated from the reservoir temperature, the surface area of the source specimen S~and the condensation area S~.
were weighed and introduced into a carbon-coated quartz tube of 8 flushed mm diam. x 200times mm. with The argon tube was first evacuated, several of 4-nines purity and finally sealed off under a vacuum of about iO~ Torr. Polycrystalline specimens prepared by gradually raising the temperature and melting at 1100 °Cwere vacuum-sealed anew into another carboncoated quartz tube, and single-crystalline specimens were obtained by the Bridgman method. These singlecrystalline specimens were cleaved into disc shapes and, after heat treating under a fixed cadmium or tellurium partial pressure, they were used as the source specimens for the transport experiment. The standard dimensions of the source specimens were 7 mm in diameter and 3 mm in thickness. These procedures, which define precisely the surface area and the heat treatment of the source specimen, were adopted in order to eliminate effects which might be caused by a difference in the surface area or in the history of the source specimen in obtaining a reproducible growth rate. Source specimens in powder form might cause a different degree of supersaturation depending upon the particle size even under otherwise identical experimental conditions. 2.2. VAPoR PHASE TRANSPORT UNDER CONTROLLED
2. Experimental procedures
The schematic construction of the electric furnace and an example of the temperature profile used to grow
2.1.
PARTIAL PRESSURE
PREPARATION OF THE SOURCE SPECIMEN
cadmium telluride through the vapor phase are shown in fig. 1.
About 0.1 mole of cadmium and tellurium in ill
—
5
163
VAPOR PHASE TRANSPORT OF CADMIUM TELLURIDE
f4I ~.,.,
I
L~’
~~,j’~iscm
04U~0~m
.,
AT1IIC
io2.
_I_
~-:—~
/
£_7.
\~$7~6t
N 1k 200 Fig. 1. Schematic construction of the electric furnace and an example of temperature profile for vapor phase transportation. (a) source chamber; (b) reservoir chamber; (c) growth chamber; (d), (e) auxiliary heater; (f), (g) alumel-chromel thermocouple; (h), (i) main heater.
10~2
10~
1(10
101
102
P~2(Torr)
Fig. 2. Transported quantity after 1 hr as a function of Te2 partial pressure for several source temperatues with fixed AT (10 °C) and AX (4.0 cm). Vertical bar indicates the estimated error.
The fused quartz tube consisted of: (a) the source chamber, (b) the reservoir containing one of the pure constituent elements, cadmium or tellurium and (c) the growth chamber with a flat end window for easy observation. The tube was vacuum sealed in the same way as previously described. The growth chamber was carefully baked out before introducing the tube into the furnace in order to clean the inner wall and to avoid spurious nucleation. The growth chamber with a flat end also served to keep a fixed condensation area when growing alarge crystal. The partial pressure ofthe constituent element was controlled by regulating the reservoir temperature TR and the partial pressure in the transport chamber was assumed 8) to be by at determined the reservoir the equilibrium pressure temperature. Aftervapor the vapor phase transport the tube was water-quenched and the crystals grown in the
As seen from fig. 2, there exist three different regions. (1) In the cases of high partial pressures of Te2 the transported quantity was found to be proportional to time and the transport rate was proportional to the ——th power of Te2 partial pressure. This region is designated as Region I. (2) For intermediate partial pressures of Te2, the transport rate was found to be proportional to the —~th power of Te2 partial pressure. This region is designated as Region II. (3) For low partial pressures of Te2, the transport rate was a little scattered but was found to be independent of partial pressure. This region is designated as Region III.The range of partial pressures covered by Region II is wide at low I’~ temperatures, butbecomes narrow and finally disappears at the higher T 0 temperatures. The growth chamber were weighed to calculate the tran- arrows in fig. 2 show the values of FTc2 corresponding sport rate. Experiments were performed under con- to minimum total pressure in the transport tube. ditions coveringthe following ranges, (i) T0: 7 16—876 °C Region III is known to cover the pressure range lower regulated with an accuracy of ±2 °C,(ii) AT: 2—40 °C than this value. The scattering of the data in Region III with accuracy of ±0.5 °C, (iii) AX: 20—70 mm, (iv) is known to be caused by differences in sample history. 2, (vi) S~: When samples, previously heat-treated under the same 0.13—0.95 cm2. Torr, (v) S~:0.10—1.93 cm conditions as the transport experiment, were used as ~TC2 10~l0 source specimens, the highest transport rate was ob3. Experimental results and discussion tamed and showed no dependence upon the partial The transport rate was first studied as a function of
pressure of Te 2. The transport rate in this region was known to depend only on AT and not on AX, as shown in fig. 3. This behaviour suggested that the surface reaction might rate-determine the transportation. The transport rate was next studied as a function of S~and S~.The
the partial pressure of the constituent element. Fig. 2 shows the transported quantity after one hour as a function of Te2 partial pressure for three T~temperatures with fixed AT and AX for the case of the tellurium reservoir, III
—
5
164
K. IGAKI AND K. MOCHIZUKI 24
1s76t
20
TR,380’C
rate was found to be proportional to the average
/
a
/
~‘16
temperature in this region, in agreement with thegradient assumedAT/AX transport mechanism.
~
Similar transport experiments were also performed
12
/
8 4
5
10
15 20 25 30 M Ic) Fig. 3. Relation between transport rate and AT in Region III. (o) AX = 2.0 cm; (x) AX= 4.0 cm; (~)AX= 6.0 cm.
condensation area S~,was regulated by changing the inner diameter of the growth chamber. At relatively low T0 temperatures, S~,had no effect on the transportation. The transport rate was found to be proportional to S~,not only in Region III but also in Region II, as shown in fig. 4. At high T0 temperatures, however, the surface area of the source specimen S~had a serious effect on the transport rate. It is known that the rate-determining step in Regions III and II is the surface reaction: evaporation for high T0 temperature and condensation for low T~temperatures. The transport behaviour in the transition T0 temperature range is not yet clear, A transport rate proportional to the 4th power of the Te2 partial pressure, observed in Region I, is similar to the tendency already reported by tendency previous 4’910) and this workers on Il—VI compounds is explained by assuming that the rate-determining process is diffusion in the vapor phase. The transport
for the case of the cadmium reservoir and the following two different regions were observed. (4) For low partial pressures of Cd, the transport rate was independent of the partial pressure. This region is designated as Region III’. (5) For high partial pressures of Cd, the transport rate was found to be proportional to the 3rd power —
.
.
.
of the Cd partial pressure. This region is designated as Region I. Transport behaviour in Region I’ is quite similar to that in Region land is known to be explained by assuming that the rate-determining process is diffusion in the vapor phase. The rate-determining step in Region iii’ for high T~ temperatures is known to be the evaporation process. Fig. 5 shows the temperature dependence of the electrical conductivity of crystals grown under controlled partial pressure. Crystals grown with appreciable growth rates are always p-type. The electrical conductivity at room temperature as a function of Te2 partial pressure is shown in the right portion of fig. 6.
—
______________________
:~
Ts,876’C(Te) TR,
a
______
~,
6o2t
o
55d~C
~
~25
~\
T
/~T~z~c
/%
0\~\\
10
~O
0.2
ck4
0.6
Q~
1
-7 ____________________________
Sc(cm2)
1C 3 6 3/T( K -1 Fig. 5. Temperature dependenceoftheelectricalconductivityof i0 the crystals grown under controlled partial pressure.
in Region III and Region (~)T~=rate 716and °C,TR = 500°C(II); Fig. 4. Relation betweenII.transport condensation area (x), (C) T, = 716 °C,TR = 380°C (III).
III
—
5
VAPOR PHASE TRANSPORT OF CADMIUM TELLURIDE
iuI ________________________________________________ ~ Ts,876C(Te)
~8 ~
directly through the vapor phase was abandoned. Figs 5. and 6 show that the electrical conductivity of the grown crystals depends upon the growth conditions. Even though disturbing effects from unregulated defects or impurities are observed, vapor phase growth
A Prrin(87(C) B PmIn(798t)
°Ts,870 (Cd) ~T~798~(Te)
-1
10
\
~
I
B
under controlled partial pressure is confirmed to be anddeviation efficacious for stoichiometry. obtaining crystals having anecessary controlled from
A
10
Ca
4.
10
I 1o-~
10-4
1o-~ 10-2 P1e2(Torr)
10-1
100
6.
101
102
The transport rate through the vapor phase was io~ precisely studied by independently regulating the experimental parameters. Depending upon the rate-
Electrical conductivity at room temperature as a funcof Te 2 partial pressure. Right portion is of as grown p-type specimen and left portion is of specimen converted to n-type after heat treating in cadmium vapor,
tion
Conclusion
0
~106
Fig.
165
determining process, diffusion in the vapor phase or surface reaction, regions with different behaviours were clearly observed and identified. Further efforts will be necessary to apply the present information to the case of dynamic transportation or to develop it for application to ternary compounds.
Results for crystals grown with a cadmium reservoir 1~Te
are also shown, converting ~Cd into 2 by using the reported dissociation constant of cadmium telluride at the temperature T0. The results shown in the left portion of fig. 6 are the electrical conductivity at room temperature after heat treating the crystals at 800 °Cunder nearly saturated cadmium pressure. In spite of the differences in growth conditions, specimens became n-type with high conductivity after this cadmium treatment. Direct vapor phase growth of n-type specimens with high conductivities was found difficult. By extrapolating the cadmium partial pressure dependence of the transport rate, the time neccessary for growing n-type crystals with appreciable size was estimated to be several years and the attempt to grow n-type specimens
III
References 1) D. de Nobel, Philips Res. Rept. 14 (1959) 361. 2) R. Triboulet and Y. Marfaing, J. Electrochem. Soc. 120 3) 4) 5) 6)
(1973) 1260. R. Höschl T. Lynch, Phys.Phys. 33 (1962) P. andJ.~.Appi. Koñák, Status1009. Solidi 9 (1965) 167. M. R. Lorenz, J. Phys. Chem. Solids 23 (1962) 939. R. F. Brebrick and A. J. Strauss, J. Phys. Chem. Solids 25
1441. J. Electrochem. Soc. 108 (1961) 82. 7) (1964) A. C. Prior, 8) A. N. Nesmeyanov, Vapor Pressure of the Chemical Elements (Elsevier, Amsterdam, 1963). 9) T. Kiyosawa, K. Igaki and N. Ohashi, Trans. Japan Inst. Metals 13 (1972) 248. 10) M. Toyama, Japan. J. Appi. Phys. 5 (1966) 1204.
—
5