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Hall probe Cdx Hg1-x Te for use in magnetic investigations of Nb3Sn superconducting layers
Hall probe Cdx Hgl-xTe for use in magnetic investigations of Nb3Sn superconducting layers
Simpkins showed that semiconductor layers of InAs and InSb are more suitable for use as magnetic field sensors in liquid helium 7. The objective of the study described in this Paper was to develop a Hall probe Cd~Hgl_~Te (x = 0.175) which is useful in magnetic measurements of superconducting Nb3Sn materials in the temperature range 4.218.5 K.
Hall p r o b e m a n u f a c t u r e
B.A. GTowacki* and S.A. Ignatowicz' I n s t i t u t e of F u n d a m e n t a l E l e c t r o t e c h n i c s and E l e c t r o t e c h n o l o g y , pl. G r u n w a l d z k i 13, 50-377 Wroetaw, Poland tTele-Radio Research Institute, ul. Ratuszova 11, 03-450 Warszawa, Poland Received 2 June 1986; revised 27 November 1986
The critical temperature of a superconducting Nb3Sn layer has been measured by repulsion of magnetic flux as a function of temperature, using a Hall probe. Hall probes of an active semiconductor film, CdxHgl-xTe (x = 0.175), have been made by thermal evaporation in a vacuum. The chemical composition of the CdxHgl-xTe thin films have been determined by spectrophotometric analysis. The Hall probes have been characterized by electric measurements over a temperature range of 4.2-18.5 K in a magnetic field. The probes are particulary suitable for magnetic measurements of superconducting Nb3Sn layers at low temperatures.
Keywords: NbaSn; superconductors; semiconductors; Hall probes Magnetic field measurements of superconductors is a necessary part of the development of superconducting material technology ~-4. If attempting to obtain information about magnetic field distribution or changes in superconducting materials associated with magnetic fields, it is essential to use a magnetic field sensor in the range of liquid helium temperature. This sensor must fulfil certain conditions: independence of sensitivity in thermal cycling from 300 to 4.2 K; linear function of sensor signal v e r s u s magnetic field; independence of sensor signal v e r s u s temperature in the range 4.2-20 K. Various sensors used for the measurement of magnetoresistance and the Hall effect have been developed from bismuth but this approach has limitations 5"~. Magnetoresistance is a non-linear function of the magnetic field and the Hall constant of bismuth is relatively low and strongly temperature dependent. Also, large changes in the sensitivity of bismuth sensors occur upon thermal cycling as well as instability in the Hall voltage while the sensor remains at a constant temperature in liquid helium.
*Present address: Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK 0011-2275/87/030162-03 $03.00 © 1987 Butterworth & Co (Publishers) Ltd 162
Cryogenics 1987 Vol 27 March
The Hall probe under consideration was manufactured by evaporation of an active semiconductor film and the gold leads onto a cleaved mica plate of thickness 40-50 tam. Semiconductor CdxHgl_xTe (x -- 0.175) thin films designed for the probes were obtained by the method of simple thermal evaporation 8'1°,14. The films were deposited by thermal evaporation of the single crystal Cd.,. Hgl_xTe (x = 0.175) bulk material in a standard vacuum apparatus. During the evaporation process the pressure, p, was (3-9) x 10 -5 Torr and the source temperature, Tv, was increased gradually from 600 to 780°C. Films of thickness d = 1.3 tam were condensed on the mica substrates at the temperature T~ = 125°C. After deposition the films underwent two heat treatments: in mercury vapour (at T = 280°C) and in an argon atmosphere (at T = 120°C). The heat treatment was carried out inside a glass enclosure in which the substrates with deposited thin films were placed in a heater above a mercury-filled crucible, and a stream of argon was blown through the enclosure. The treatment in mercury vapour recrystallizes the films and complements the mercury insufficiency. After treatment in mercury vapour the films did not have stable electrical parameters, and a second additional heat treatment using only an argon atmosphere (with no mercury in the crucible) was applied. This treatment removed the weakly bound mercury atoms (on the film surface and at grain boundaries) and thus stabilizes the electrical properties and parameters of the films. The chemical composition of the Cd~Hg~_xTe bulk material and deposited thin films was determined by spectrophotometric analysis, which, for these films, gave an error of < + 0.2%1~ The above method of simple thermal evaporation, followed by a subsequent heat treatment, produces strictly stoichiometric coarse crystalline CdxHg~_xTe(x < 0.3) films, which have electrical properties that are the same as those of the bulk material ~'9"14. For example, CdxHg,_, Te(x = 0.175) thin films designed for the Hall probes under consideration have the following parameters: Hall mobility, ~tH = (1-1.4) x 104 cm 2 V -l s-I; Hall coefficient, Rrt = 50-90 cm 3 °C-J; and resistivity, p = (5-7) x 10 -3 ~ cm. Cd~Hgj_xTe(x < 0.3) films manufactured by the method of simple thermal evaporation have also found application in the production of other modern thin-film galvanomagnetic devices lj'13"14.
Probe characteristics and discussion For all measurements the Hall probe was supplied with a
Research and technical note
¥ (VA"T")
UH (mV)
70 m
4.'/5
Om
Om
O.
--
'~O
60
0
I
I
I
I
I
I
1
2
3
4
5
6
THERMAL
50
CYCLE
Figure 1 Change of U H at T = 4.2 K and 0.5 T as a result of thermal cycling of the CdxHgl_xTe Hall probe from 300 to 4.2 K
40 I
0 stable control current, I¢ = 0.2 mA. Such a small value of 1~ is required because of the necessity to keep the influence of heating or magnetic flux generated by the Hall probe on the superconductor to a minimum. (In some magnetic measurements of superconducting materials the Hall probe must be in direct contact with the superconductor and in this case current, I~, flow through the Hall probe produces a magnetic field and can result in perturbation of the field being measured.) In some of the Hall probes slight asymmetry of the Hall voltage was noticed, and for such Hall probes, compensation for the asymmetry was achieved by adjustment of the electronic circuit ~5. To check the change of the Hall sensitivity, y, resulting from thermal cycling of the probe from 300 to 4.2 K, the sensor was rapidly cooled down and then UH at B = 0.5 T and 4.2 K was measured. The results presented in Figure I show that UH is independent of thermal cycling from 300 to 4.2 K. Hall voltage of the probe as a function of magnetic field intensity for 4.2 and 18.5 K is shown in Figure 2. UH versus B monotonically increases and is independent of temperature over the whole range from 4.2 to 18.5 K, which is a very important fact in the measurement of superconducting materials. The Hall sensitivity as a function of B (shown in Figure 3) decreases monotonically. Only in two field regions, 0-25 mT and 0.4-2 T, are the changes of Hall probe sensitivity, y, almost linear as a function of B. The largest change in ? versus B (dy/dB = 500 V A - I T -2) appears in the range 0-25 mT, whereas in the range 0.4--2 T the change in y versus B is small (dy/dB = 5 V A - 1T - 2 ). One has to account for the dependence of y on B during the measurement of superconducting magnetic properties. The relationship between UH versus
UH (mV)
4
s.s" .s"
3
.s"
2
~,./s
s
I"
s s s s s "p s S ' S ' S
1 .~.s" ,.s
0
I
I
0.t
0.2
,
'
0.3
'
0.4
Figure 2 Hall voltage of the CdxHgl-~Te probe as a function of magnetic field for: . . . . 4.2 K; ~ , 18.5 K
0.5
I
I
1
1.5
2
-"(T)
Figure 3 Change of sensitivity, y, as a function of B
B or y versus B must be taken into account to obtain correct results. A p p l i c a t i o n : m e a s u r e m e n t of critical t e m p e r a t u r e , To of N b ~ S n s u p e r c o n d u c t i n g layers From the discussion presented in the previous section, useful applications of thin film Hall probe CdxHgl_xTe in the measurement of change of the trapped magnetic flux in an Nb3Sn tape superconductor as a function of temperature are evident. The Nb3Sn layer in tape form used for the measurements was obtained by a liquid diffusion process 16J7 in which tin atoms from the Cu80%Sn solution diffused to the Nb1.5%Zr substrate in tape form (width 1 x 10-2m), forming the Nb3Sn layer on both sides of the substrate. The sample formed as a circular disc (diameter 0.8 x 10-2m) of the Nb3Sn tape. It is a well-known fact that grain boundaries in a Nb3Sn superconductor act as pinning centres for the magnetic flux lines ~8"19. From previous research on Nb3Sn layers it follows that inside the Nb3Sn grains, Z r O 2 precipitates are present which are also magnetic flux pinning centres 2°'2~. The establishing of the trapped flux in the superconductor was carried out by placing the flat Nb3Sn disc in an axial magnetic field of 12 mT at a temperature > To. The sample is cooled down to 4.2 K while the applied magnetic field remained constant, and finally the applied field was reduced to zero. In the experiment the Hall probe was placed on the central part of the Nb3Sn disc, as shown in Figure 4. UH, which is proportional to the trapped flux, was measured as a function of increasing temperature. The result is presented in Figure 4. From this measurement the critical temperature, T¢, of the Nb3Sn can be defined as the temperature at which all magnetic flux pinned by the pinning centres leave the sample. This situation occurs when the superconducting state of Nb3Sn changes to the normal state. The critical temperature of the measured Nb3Sn layer deduced from the UH versus Trelationship is 16.6 K. However, using the resistive technique, T¢ of the same sample, defined as the midpoint of the resistive transition 22 (see Figure 5) is equal to 17.5 K 23. The resistive transition appeared at a higher temperature than the trapped flux transition and became sharper. The
C r y o g e n i c s 1987 V o l 27 M a r c h
163
Research and technical note
B (mT) 12 RR
'1'
!/Hall m
°
.b,S
6
Probe
. . . . . . ; . . . . . .l
b L,J
I
(J Z
i 3
(/) (/1 I,M iv
0 : " 4. .5 . 6. 7. .8 . 9. 10 . .11. 12. 13 . 14 lS 16 17 T (K) Rgure 4 Change in trapped magnetic flux of the Nb3Sn superconductor as a function of temperature
above difference in the measurements of the Tc(A Tc 1 K) values are connected to the difference in behaviour of the physical quantity in the techniques used. The resistive transition reveals that the best superconducting path exists along the sample and T~ takes its highest value. The trapped flux transition is very sensitive to the pinning of flux lines in the volume of the sample, which leads to local changes in the critical parameters as a function of T in the layer investigated. In our experiments some reduction of the measured magnetic flux level can arise which is related to the finite dimensions of the Hall probe used. We suggest, however, that in spite of the above reduction of T valueg, flux trapping measurements give useful information about the phase composition in Nb3Sn tape form superconductors24
References 1 2 3 4 5 6
164
Suenaga, M. and Clark, A.F. Filamentary A-15 Superconductors Plenum Press, New York, USA (1980) Foner, S. and Schwartz, B.B. Superconductor Materials Science Plenum Press, New York, USA (1980) GI0wadd, B.A. and Zaleski, A. In~ynieria Materia~owa (1985) 2 43 Hlasnik, I. Elektrotechnicki Casopis (1877) 28 547 Shift'man, C.A. Rev Sci lnstrum (1962) 33 206 Roshon, D.D. Rev Sci lnstrum (1962) 33 201
Cryogenics 1987 Vol 27 March
o
,4
""
,
.
'
'
15 16 17 18 19
T()-X-
Figure 5 Change in resistance of the NbsSn superconductor as a function of temperature
7 8 9 10 11
Simpkins, J.E. Rev Sci lnstrum (1968) 39 570 lgnatowicz, S.A. Thin Solid Films (1970) 6 299 Piotrowska, A. Thin Solid Films (1974) 24 143 Ignatowicz, S.A. Thin Solid Films (1976) 32 81 lgnatowicz, S.A., Dajna, A., Goliger, Z., Mikulko, A. and Piotrowska, A. Thin Solid Films (1976) 36 399 12 Marczenko, Z. Spectrophotometric Determination of Elements Ellis Horwood, Chichester, UK (1976) 13 Chorally, M., lgnstowicz, $.A. and Kobenza, A. Elektronika (1981) 22 6 14 Ignatowiez, S.A. and Kobenza, A. Semiconductor Thin Films of A 11B vl Compounds Ellis Horwood, Chichester, UK, in print 15 Gl6wacki,B.A. Senate Report, Technical University of Wroclaw, Poland (1985) 16 G~waeki, B.A. ln~ynieria Materi~owa (1985) 3 86 17 Cdbwaeki, B.A. and Chojean, J. Phys Stat Sol a (1983) 80 K93 18 Suenaga, M. and Jansen, W. Appl Phys Lett (1983) 43 791 19 Gi~warki, B.A. J Mater Sci Left (1985) 4 389 20 GlOwarki, B.A. and Horobiowski, M. Phys Stat Sol A (1985) 89 K13 21 Scanlan,R., Fietz, W. and Koch, E. J Appl Phys (1975) 46 2244 22 Powell,R.L. and Clark, A.F. Cryogenics (1978)18 137 23 GI6warki, B.A. DSc Institute of Low Temperature and Structure Research, Polish Academy of Science, Wroclaw, Poland (1983) 24 Glowaeki, B.A. to be published
Simpkins showed that semiconductor layers of InAs and InSb are more suitable for use as magnetic field sensors in liquid helium 7. The objective of the study described in this Paper was to develop a Hall probe Cd~Hgl_~Te (x = 0.175) which is useful in magnetic measurements of superconducting Nb3Sn materials in the temperature range 4.218.5 K.
Hall p r o b e m a n u f a c t u r e
B.A. GTowacki* and S.A. Ignatowicz' I n s t i t u t e of F u n d a m e n t a l E l e c t r o t e c h n i c s and E l e c t r o t e c h n o l o g y , pl. G r u n w a l d z k i 13, 50-377 Wroetaw, Poland tTele-Radio Research Institute, ul. Ratuszova 11, 03-450 Warszawa, Poland Received 2 June 1986; revised 27 November 1986
The critical temperature of a superconducting Nb3Sn layer has been measured by repulsion of magnetic flux as a function of temperature, using a Hall probe. Hall probes of an active semiconductor film, CdxHgl-xTe (x = 0.175), have been made by thermal evaporation in a vacuum. The chemical composition of the CdxHgl-xTe thin films have been determined by spectrophotometric analysis. The Hall probes have been characterized by electric measurements over a temperature range of 4.2-18.5 K in a magnetic field. The probes are particulary suitable for magnetic measurements of superconducting Nb3Sn layers at low temperatures.
Keywords: NbaSn; superconductors; semiconductors; Hall probes Magnetic field measurements of superconductors is a necessary part of the development of superconducting material technology ~-4. If attempting to obtain information about magnetic field distribution or changes in superconducting materials associated with magnetic fields, it is essential to use a magnetic field sensor in the range of liquid helium temperature. This sensor must fulfil certain conditions: independence of sensitivity in thermal cycling from 300 to 4.2 K; linear function of sensor signal v e r s u s magnetic field; independence of sensor signal v e r s u s temperature in the range 4.2-20 K. Various sensors used for the measurement of magnetoresistance and the Hall effect have been developed from bismuth but this approach has limitations 5"~. Magnetoresistance is a non-linear function of the magnetic field and the Hall constant of bismuth is relatively low and strongly temperature dependent. Also, large changes in the sensitivity of bismuth sensors occur upon thermal cycling as well as instability in the Hall voltage while the sensor remains at a constant temperature in liquid helium.
*Present address: Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK 0011-2275/87/030162-03 $03.00 © 1987 Butterworth & Co (Publishers) Ltd 162
Cryogenics 1987 Vol 27 March
The Hall probe under consideration was manufactured by evaporation of an active semiconductor film and the gold leads onto a cleaved mica plate of thickness 40-50 tam. Semiconductor CdxHgl_xTe (x -- 0.175) thin films designed for the probes were obtained by the method of simple thermal evaporation 8'1°,14. The films were deposited by thermal evaporation of the single crystal Cd.,. Hgl_xTe (x = 0.175) bulk material in a standard vacuum apparatus. During the evaporation process the pressure, p, was (3-9) x 10 -5 Torr and the source temperature, Tv, was increased gradually from 600 to 780°C. Films of thickness d = 1.3 tam were condensed on the mica substrates at the temperature T~ = 125°C. After deposition the films underwent two heat treatments: in mercury vapour (at T = 280°C) and in an argon atmosphere (at T = 120°C). The heat treatment was carried out inside a glass enclosure in which the substrates with deposited thin films were placed in a heater above a mercury-filled crucible, and a stream of argon was blown through the enclosure. The treatment in mercury vapour recrystallizes the films and complements the mercury insufficiency. After treatment in mercury vapour the films did not have stable electrical parameters, and a second additional heat treatment using only an argon atmosphere (with no mercury in the crucible) was applied. This treatment removed the weakly bound mercury atoms (on the film surface and at grain boundaries) and thus stabilizes the electrical properties and parameters of the films. The chemical composition of the Cd~Hg~_xTe bulk material and deposited thin films was determined by spectrophotometric analysis, which, for these films, gave an error of < + 0.2%1~ The above method of simple thermal evaporation, followed by a subsequent heat treatment, produces strictly stoichiometric coarse crystalline CdxHg~_xTe(x < 0.3) films, which have electrical properties that are the same as those of the bulk material ~'9"14. For example, CdxHg,_, Te(x = 0.175) thin films designed for the Hall probes under consideration have the following parameters: Hall mobility, ~tH = (1-1.4) x 104 cm 2 V -l s-I; Hall coefficient, Rrt = 50-90 cm 3 °C-J; and resistivity, p = (5-7) x 10 -3 ~ cm. Cd~Hgj_xTe(x < 0.3) films manufactured by the method of simple thermal evaporation have also found application in the production of other modern thin-film galvanomagnetic devices lj'13"14.
Probe characteristics and discussion For all measurements the Hall probe was supplied with a
Research and technical note
¥ (VA"T")
UH (mV)
70 m
4.'/5
Om
Om
O.
--
'~O
60
0
I
I
I
I
I
I
1
2
3
4
5
6
THERMAL
50
CYCLE
Figure 1 Change of U H at T = 4.2 K and 0.5 T as a result of thermal cycling of the CdxHgl_xTe Hall probe from 300 to 4.2 K
40 I
0 stable control current, I¢ = 0.2 mA. Such a small value of 1~ is required because of the necessity to keep the influence of heating or magnetic flux generated by the Hall probe on the superconductor to a minimum. (In some magnetic measurements of superconducting materials the Hall probe must be in direct contact with the superconductor and in this case current, I~, flow through the Hall probe produces a magnetic field and can result in perturbation of the field being measured.) In some of the Hall probes slight asymmetry of the Hall voltage was noticed, and for such Hall probes, compensation for the asymmetry was achieved by adjustment of the electronic circuit ~5. To check the change of the Hall sensitivity, y, resulting from thermal cycling of the probe from 300 to 4.2 K, the sensor was rapidly cooled down and then UH at B = 0.5 T and 4.2 K was measured. The results presented in Figure I show that UH is independent of thermal cycling from 300 to 4.2 K. Hall voltage of the probe as a function of magnetic field intensity for 4.2 and 18.5 K is shown in Figure 2. UH versus B monotonically increases and is independent of temperature over the whole range from 4.2 to 18.5 K, which is a very important fact in the measurement of superconducting materials. The Hall sensitivity as a function of B (shown in Figure 3) decreases monotonically. Only in two field regions, 0-25 mT and 0.4-2 T, are the changes of Hall probe sensitivity, y, almost linear as a function of B. The largest change in ? versus B (dy/dB = 500 V A - I T -2) appears in the range 0-25 mT, whereas in the range 0.4--2 T the change in y versus B is small (dy/dB = 5 V A - 1T - 2 ). One has to account for the dependence of y on B during the measurement of superconducting magnetic properties. The relationship between UH versus
UH (mV)
4
s.s" .s"
3
.s"
2
~,./s
s
I"
s s s s s "p s S ' S ' S
1 .~.s" ,.s
0
I
I
0.t
0.2
,
'
0.3
'
0.4
Figure 2 Hall voltage of the CdxHgl-~Te probe as a function of magnetic field for: . . . . 4.2 K; ~ , 18.5 K
0.5
I
I
1
1.5
2
-"(T)
Figure 3 Change of sensitivity, y, as a function of B
B or y versus B must be taken into account to obtain correct results. A p p l i c a t i o n : m e a s u r e m e n t of critical t e m p e r a t u r e , To of N b ~ S n s u p e r c o n d u c t i n g layers From the discussion presented in the previous section, useful applications of thin film Hall probe CdxHgl_xTe in the measurement of change of the trapped magnetic flux in an Nb3Sn tape superconductor as a function of temperature are evident. The Nb3Sn layer in tape form used for the measurements was obtained by a liquid diffusion process 16J7 in which tin atoms from the Cu80%Sn solution diffused to the Nb1.5%Zr substrate in tape form (width 1 x 10-2m), forming the Nb3Sn layer on both sides of the substrate. The sample formed as a circular disc (diameter 0.8 x 10-2m) of the Nb3Sn tape. It is a well-known fact that grain boundaries in a Nb3Sn superconductor act as pinning centres for the magnetic flux lines ~8"19. From previous research on Nb3Sn layers it follows that inside the Nb3Sn grains, Z r O 2 precipitates are present which are also magnetic flux pinning centres 2°'2~. The establishing of the trapped flux in the superconductor was carried out by placing the flat Nb3Sn disc in an axial magnetic field of 12 mT at a temperature > To. The sample is cooled down to 4.2 K while the applied magnetic field remained constant, and finally the applied field was reduced to zero. In the experiment the Hall probe was placed on the central part of the Nb3Sn disc, as shown in Figure 4. UH, which is proportional to the trapped flux, was measured as a function of increasing temperature. The result is presented in Figure 4. From this measurement the critical temperature, T¢, of the Nb3Sn can be defined as the temperature at which all magnetic flux pinned by the pinning centres leave the sample. This situation occurs when the superconducting state of Nb3Sn changes to the normal state. The critical temperature of the measured Nb3Sn layer deduced from the UH versus Trelationship is 16.6 K. However, using the resistive technique, T¢ of the same sample, defined as the midpoint of the resistive transition 22 (see Figure 5) is equal to 17.5 K 23. The resistive transition appeared at a higher temperature than the trapped flux transition and became sharper. The
C r y o g e n i c s 1987 V o l 27 M a r c h
163
Research and technical note
B (mT) 12 RR
'1'
!/Hall m
°
.b,S
6
Probe
. . . . . . ; . . . . . .l
b L,J
I
(J Z
i 3
(/) (/1 I,M iv
0 : " 4. .5 . 6. 7. .8 . 9. 10 . .11. 12. 13 . 14 lS 16 17 T (K) Rgure 4 Change in trapped magnetic flux of the Nb3Sn superconductor as a function of temperature
above difference in the measurements of the Tc(A Tc 1 K) values are connected to the difference in behaviour of the physical quantity in the techniques used. The resistive transition reveals that the best superconducting path exists along the sample and T~ takes its highest value. The trapped flux transition is very sensitive to the pinning of flux lines in the volume of the sample, which leads to local changes in the critical parameters as a function of T in the layer investigated. In our experiments some reduction of the measured magnetic flux level can arise which is related to the finite dimensions of the Hall probe used. We suggest, however, that in spite of the above reduction of T valueg, flux trapping measurements give useful information about the phase composition in Nb3Sn tape form superconductors24
References 1 2 3 4 5 6
164
Suenaga, M. and Clark, A.F. Filamentary A-15 Superconductors Plenum Press, New York, USA (1980) Foner, S. and Schwartz, B.B. Superconductor Materials Science Plenum Press, New York, USA (1980) GI0wadd, B.A. and Zaleski, A. In~ynieria Materia~owa (1985) 2 43 Hlasnik, I. Elektrotechnicki Casopis (1877) 28 547 Shift'man, C.A. Rev Sci lnstrum (1962) 33 206 Roshon, D.D. Rev Sci lnstrum (1962) 33 201
Cryogenics 1987 Vol 27 March
o
,4
""
,
.
'
'
15 16 17 18 19
T()-X-
Figure 5 Change in resistance of the NbsSn superconductor as a function of temperature
7 8 9 10 11
Simpkins, J.E. Rev Sci lnstrum (1968) 39 570 lgnatowicz, S.A. Thin Solid Films (1970) 6 299 Piotrowska, A. Thin Solid Films (1974) 24 143 Ignatowicz, S.A. Thin Solid Films (1976) 32 81 lgnatowicz, S.A., Dajna, A., Goliger, Z., Mikulko, A. and Piotrowska, A. Thin Solid Films (1976) 36 399 12 Marczenko, Z. Spectrophotometric Determination of Elements Ellis Horwood, Chichester, UK (1976) 13 Chorally, M., lgnstowicz, $.A. and Kobenza, A. Elektronika (1981) 22 6 14 Ignatowiez, S.A. and Kobenza, A. Semiconductor Thin Films of A 11B vl Compounds Ellis Horwood, Chichester, UK, in print 15 Gl6wacki,B.A. Senate Report, Technical University of Wroclaw, Poland (1985) 16 G~waeki, B.A. ln~ynieria Materi~owa (1985) 3 86 17 Cdbwaeki, B.A. and Chojean, J. Phys Stat Sol a (1983) 80 K93 18 Suenaga, M. and Jansen, W. Appl Phys Lett (1983) 43 791 19 Gi~warki, B.A. J Mater Sci Left (1985) 4 389 20 GlOwarki, B.A. and Horobiowski, M. Phys Stat Sol A (1985) 89 K13 21 Scanlan,R., Fietz, W. and Koch, E. J Appl Phys (1975) 46 2244 22 Powell,R.L. and Clark, A.F. Cryogenics (1978)18 137 23 GI6warki, B.A. DSc Institute of Low Temperature and Structure Research, Polish Academy of Science, Wroclaw, Poland (1983) 24 Glowaeki, B.A. to be published