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Effect of high hydrostatic pressure on the electrophysical properties of doped silicon crystals and devices based on them
Solid-State
Pergamon
0038-l 101(94)00098-0
Electronics Vol. 38. No. 3, pp. 693-695. 1995 Copyright c 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038-l lOI/ $9.50 + 0.00
EFFECT OF HIGH HYDROSTATIC PRESSURE ON THE ELECTROPHYSICAL PROPERTIES OF DOPED SILICON CRYSTALS AND DEVICES BASED ON THEM S. Z. ZAINABIDINOV, Physics
Department,
P. I. BARANSKIY, I. N. KARIMOV, KH. KH. KARIMBERDIEV
Tashkent
State University,
(Received 22 November Abstract-This paper presents pressure on the electrophysical the dependence of the specific in a dynamic regime has a capacitance characteristics of be due to the dissociation of
1993;
Vuzgorodok, in revised
form
Tashkent, 3 May
A. R. TURAEV and 700095,
Uzbekistan
1994)
results obtained by an experimental study of the effect of hydrostatic properties of silicon crystals and corresponding structures. It is shown that resistance of n-Si(Ni) and n-Si(Gd) samples on the pressure measured nonmonotonic character. Changes in the current-voltage and currentSchottky diodes, made by using the above silicon monocrystals. appear to impurity precipitates owing to the effect of external pressure.
INTRODUaION
Studying the influence of hydrostatic pressure and special doping on the processes of defect-impurity interaction in semiconductors is one of the matters of current interest for the making of modern semiconductor devices. Despite publication of a number of papers devoted to studying the mechanisms of defect formation under external pressure and the nature of non-equilibrium defect states, the mechanisms of emergence of equilibrium defects and their nature have not yet been established. At the same time the investigations carried out show that these residual defects play an important role in fixing the properties of semiconductor materials and devices made on their basis. One of the objects convenient for an experimental study of residual effects of the influence of external pressure in semiconductors is monocrystal Si, containing precipitates of impurity atoms[l]. As shown in [2], hydrostatic pressure on silicon, containing precipitates of Ni atoms, results in a change of the state of the precipitates; therefore the electrophysical properties of the material can thus be modified. This paper presents results of a study of the effect of hydrostatic pressure on the electrophysical properties of silicon doped by Ni (or Cd) and of corresponding devices.
of _ 150 K/s. The concentration of oxygen and impurity (Ni) was (2-3) x 10” and 5 x 1017cm-3, respectively. There were about lo* dislocations per cm’. Electric activity of Gd doping atoms, introduced into the Si monocrystals by melting, was caused by their thermal treatment within a temperature range from 1073 to 1273 K. The Toroid method[3] was applied to measure the specific resistance under external pressure within the 0 < P < 1.2 x IO9Pa interval. To determine the influence of external pressure on the properties of diodes made on the basis of Si with Ni or Gd impurities, Au-n-Si(Ni) and Au-nSi(Gd) Schottky diode have been fabricated. The capacitance-voltage characteristics of the structures under external pressure were measured with a method described in [4] by using an LG-16 setup in dynamic and static regime in the pressure range of cl.2 x lo9 Pa. This pressure range was limited by the setup. DISCUSSION
The experiments carried out showed that the p (P) dependence, measured on the n-Si(Ni) samples when the external pressure was increasing from 0 to 6 x 10'Pa, has a nonmonotonic, uneven character, increasing up to 3.6 x IO9Pa and slowly decreasing for P 2 3.6 x IO9Pa [solid curve of Fig. I(a)]. However, reducing P from 6 x IO9Pa down to atmospheric pressure turns out to give rise to a monotonic increase, though uneven, in p up to a value which is almost 15 times higher than the initial one [see the dashed curve of Fig. l(a)]. A similar dependence of p (P ) within the mentioned pressure interval has also been observed in experiments with samples made of n-Si(Ad) (the corresponding curves are not presented here).
EXPERIMENTAL
For experimental research Czochralski grown samples of n-type silicon mono crystals having [I 1I] orientation were used. Initial n-Si samples with a specific resistance p = 20 R. cm have been doped by Ni diffusion at 1523 K, followed by cooling at a rate 693
S. Z. Zainabidinov et al.
694 3 (a) I
2
4
P [lo* Pa] 2.0
6
a
-cl WI
1 @I (b)
1.5
.l-
,,,,i-.
P
IlO8 Pal
Fig. 1. Dependence p (P) (a) on increasing P (solid curve) and decreasing P (dashed curve) and J,(P ) (b) for Au-nSi(Ni) Schottky diodes at U = const. The investigation carried out on the diode structures showed that the current-voltage characteristics measured in two directions undergo noticeable changes beginning at P z 10’ Pa. Figure l(b) presents a typical dependence of the n-Si(Ni) diode current on the pressure P at U = 2V = const. The curve has clear extrema at P,,, = 3 x lo* Pa and diode P m,n= 6 x 10’ Pa, while for the n-Si(Gd) structure similar extrema Jn,, = J,(P) are located at P,,, = 1.5 x lo8 Pa and P,,,,, = 4 x 10’ Pa, respectively (the corresponding curve is not presented). The main parameters of structures made with material under study were obtained by using the method described in [2]. So, for instance, the capacitance-voltage characteristics for the Au-n-Si(Ni) Schottky diodes, measured before pressure [curve 1, Fig. 2(a)] and after a pressure of P = 1.2 x IO9Pa has been applied [curve 2, Fig. 2(a)], enabled us to calculate the profile of doping impurities [see the curves 1 and 2 of Fig. 2(b), respectively] by using common techniques[rl,S]. As seen from Fig. 2, the effect of external pressure reduces significantly the capacitance of the diode structures within the range of the voltages applied. The essential change of the impurity distribution profiles under the influence of external pressure is well illustrated by the curves 1 and 2 where Fig. 2(b) has been obtained
I
I
I
I
2
4
6
I 8
h Ml Fig. 2. C-V characteristics (a) and doping impurity distribution profile in Au-n-Si(Ni) Schottky diodes: I-
before external pressure; 2-after external pressure at P = 1.2 x IO9Pa.
before and after the effect of P = 1.2 x IO9Pa, respectively. The concentration of impurity precipitates, emerging in introducing Ni and Gd into silicon, is known from [l] to be much higher for a surface layer than for the bulk, and the external pressure causes the dissociation of the precipitates[l,2]. An increase in the concentration of acceptor impurities (Ni and Gd) due to precipitate dissociation under pressure should increase the degree of crystal compensation, if the crystals have an n-type conductivity in the initial state. It is this effect that has been observed in the experiments carried out.
The influence of external pressure on the Au-nSi(Ni) and Au-n-Si(Gd) structures, containing Ni and Gd impurities in silicon in the form of complexes, stimulates the dissociation of those complexes. This causes the emergence of electrically active impurity centres, providing an increase in Si crystal compensation, if the crystals have an n-type conductivity in the initial state.
Effect of high hydrostatic pressure on silicon crystals REFERENCES
I. S. Z. Zainabidinov, A. R. Turaev, V. I. Fistul and M. D. Khodzaev, Fiz. Tech. Poluprov. 23, 2118 (1989) [Sm. Phys. Semiccmd. 23, 1311 (1989)]. 2. S. Z. Zainabidinov and V. 1. Fistul, Fiz. Tekh. Poluprov. 21, 766 (1987). (In Russian)
695
L. G. Khvostansev, L. E. Vereshagin and A. P. Novicov, High Temp. High Press. 9, 631 (1977). 4. V. M. Koleshko and G. L. Kaplan, in Review in Electronic Technic, Her. 3, issue 2 (465). Mikroelectronika, Moscow (1977). (In Russian) 5. A. S. Berman, Capasitive Methods for Semiconductor Studies. Izd. Nauka, Moscow (1972). (In Russian) 3.
Pergamon
0038-l 101(94)00098-0
Electronics Vol. 38. No. 3, pp. 693-695. 1995 Copyright c 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038-l lOI/ $9.50 + 0.00
EFFECT OF HIGH HYDROSTATIC PRESSURE ON THE ELECTROPHYSICAL PROPERTIES OF DOPED SILICON CRYSTALS AND DEVICES BASED ON THEM S. Z. ZAINABIDINOV, Physics
Department,
P. I. BARANSKIY, I. N. KARIMOV, KH. KH. KARIMBERDIEV
Tashkent
State University,
(Received 22 November Abstract-This paper presents pressure on the electrophysical the dependence of the specific in a dynamic regime has a capacitance characteristics of be due to the dissociation of
1993;
Vuzgorodok, in revised
form
Tashkent, 3 May
A. R. TURAEV and 700095,
Uzbekistan
1994)
results obtained by an experimental study of the effect of hydrostatic properties of silicon crystals and corresponding structures. It is shown that resistance of n-Si(Ni) and n-Si(Gd) samples on the pressure measured nonmonotonic character. Changes in the current-voltage and currentSchottky diodes, made by using the above silicon monocrystals. appear to impurity precipitates owing to the effect of external pressure.
INTRODUaION
Studying the influence of hydrostatic pressure and special doping on the processes of defect-impurity interaction in semiconductors is one of the matters of current interest for the making of modern semiconductor devices. Despite publication of a number of papers devoted to studying the mechanisms of defect formation under external pressure and the nature of non-equilibrium defect states, the mechanisms of emergence of equilibrium defects and their nature have not yet been established. At the same time the investigations carried out show that these residual defects play an important role in fixing the properties of semiconductor materials and devices made on their basis. One of the objects convenient for an experimental study of residual effects of the influence of external pressure in semiconductors is monocrystal Si, containing precipitates of impurity atoms[l]. As shown in [2], hydrostatic pressure on silicon, containing precipitates of Ni atoms, results in a change of the state of the precipitates; therefore the electrophysical properties of the material can thus be modified. This paper presents results of a study of the effect of hydrostatic pressure on the electrophysical properties of silicon doped by Ni (or Cd) and of corresponding devices.
of _ 150 K/s. The concentration of oxygen and impurity (Ni) was (2-3) x 10” and 5 x 1017cm-3, respectively. There were about lo* dislocations per cm’. Electric activity of Gd doping atoms, introduced into the Si monocrystals by melting, was caused by their thermal treatment within a temperature range from 1073 to 1273 K. The Toroid method[3] was applied to measure the specific resistance under external pressure within the 0 < P < 1.2 x IO9Pa interval. To determine the influence of external pressure on the properties of diodes made on the basis of Si with Ni or Gd impurities, Au-n-Si(Ni) and Au-nSi(Gd) Schottky diode have been fabricated. The capacitance-voltage characteristics of the structures under external pressure were measured with a method described in [4] by using an LG-16 setup in dynamic and static regime in the pressure range of cl.2 x lo9 Pa. This pressure range was limited by the setup. DISCUSSION
The experiments carried out showed that the p (P) dependence, measured on the n-Si(Ni) samples when the external pressure was increasing from 0 to 6 x 10'Pa, has a nonmonotonic, uneven character, increasing up to 3.6 x IO9Pa and slowly decreasing for P 2 3.6 x IO9Pa [solid curve of Fig. I(a)]. However, reducing P from 6 x IO9Pa down to atmospheric pressure turns out to give rise to a monotonic increase, though uneven, in p up to a value which is almost 15 times higher than the initial one [see the dashed curve of Fig. l(a)]. A similar dependence of p (P ) within the mentioned pressure interval has also been observed in experiments with samples made of n-Si(Ad) (the corresponding curves are not presented here).
EXPERIMENTAL
For experimental research Czochralski grown samples of n-type silicon mono crystals having [I 1I] orientation were used. Initial n-Si samples with a specific resistance p = 20 R. cm have been doped by Ni diffusion at 1523 K, followed by cooling at a rate 693
S. Z. Zainabidinov et al.
694 3 (a) I
2
4
P [lo* Pa] 2.0
6
a
-cl WI
1 @I (b)
1.5
.l-
,,,,i-.
P
IlO8 Pal
Fig. 1. Dependence p (P) (a) on increasing P (solid curve) and decreasing P (dashed curve) and J,(P ) (b) for Au-nSi(Ni) Schottky diodes at U = const. The investigation carried out on the diode structures showed that the current-voltage characteristics measured in two directions undergo noticeable changes beginning at P z 10’ Pa. Figure l(b) presents a typical dependence of the n-Si(Ni) diode current on the pressure P at U = 2V = const. The curve has clear extrema at P,,, = 3 x lo* Pa and diode P m,n= 6 x 10’ Pa, while for the n-Si(Gd) structure similar extrema Jn,, = J,(P) are located at P,,, = 1.5 x lo8 Pa and P,,,,, = 4 x 10’ Pa, respectively (the corresponding curve is not presented). The main parameters of structures made with material under study were obtained by using the method described in [2]. So, for instance, the capacitance-voltage characteristics for the Au-n-Si(Ni) Schottky diodes, measured before pressure [curve 1, Fig. 2(a)] and after a pressure of P = 1.2 x IO9Pa has been applied [curve 2, Fig. 2(a)], enabled us to calculate the profile of doping impurities [see the curves 1 and 2 of Fig. 2(b), respectively] by using common techniques[rl,S]. As seen from Fig. 2, the effect of external pressure reduces significantly the capacitance of the diode structures within the range of the voltages applied. The essential change of the impurity distribution profiles under the influence of external pressure is well illustrated by the curves 1 and 2 where Fig. 2(b) has been obtained
I
I
I
I
2
4
6
I 8
h Ml Fig. 2. C-V characteristics (a) and doping impurity distribution profile in Au-n-Si(Ni) Schottky diodes: I-
before external pressure; 2-after external pressure at P = 1.2 x IO9Pa.
before and after the effect of P = 1.2 x IO9Pa, respectively. The concentration of impurity precipitates, emerging in introducing Ni and Gd into silicon, is known from [l] to be much higher for a surface layer than for the bulk, and the external pressure causes the dissociation of the precipitates[l,2]. An increase in the concentration of acceptor impurities (Ni and Gd) due to precipitate dissociation under pressure should increase the degree of crystal compensation, if the crystals have an n-type conductivity in the initial state. It is this effect that has been observed in the experiments carried out.
The influence of external pressure on the Au-nSi(Ni) and Au-n-Si(Gd) structures, containing Ni and Gd impurities in silicon in the form of complexes, stimulates the dissociation of those complexes. This causes the emergence of electrically active impurity centres, providing an increase in Si crystal compensation, if the crystals have an n-type conductivity in the initial state.
Effect of high hydrostatic pressure on silicon crystals REFERENCES
I. S. Z. Zainabidinov, A. R. Turaev, V. I. Fistul and M. D. Khodzaev, Fiz. Tech. Poluprov. 23, 2118 (1989) [Sm. Phys. Semiccmd. 23, 1311 (1989)]. 2. S. Z. Zainabidinov and V. 1. Fistul, Fiz. Tekh. Poluprov. 21, 766 (1987). (In Russian)
695
L. G. Khvostansev, L. E. Vereshagin and A. P. Novicov, High Temp. High Press. 9, 631 (1977). 4. V. M. Koleshko and G. L. Kaplan, in Review in Electronic Technic, Her. 3, issue 2 (465). Mikroelectronika, Moscow (1977). (In Russian) 5. A. S. Berman, Capasitive Methods for Semiconductor Studies. Izd. Nauka, Moscow (1972). (In Russian) 3.