- Email: [email protected]
or Ge doping
ARTICLE IN PRESS
Materials Science in Semiconductor Processing 9 (2006) 257–260
Temperature dependence of Raman scattering in Si crystals with heavy B and/or Ge doping Xinming Huanga,, Kehui Wua, Mingwei Chena, Taishi Toshinorib, Keigo Hoshikawab, Shinji Koha, Satoshi Udaa a
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan Faculty of Education, Shinshu University, Nishinagano, Nagano 380-8544, Japan
b
Available online 10 February 2006
Abstract Raman backscattering measurements were carried out on Si crystals heavily doped with B and/or Ge over the temperature range from 123 to 573 K. It was found that the frequency of the qE0 optical phonon in the Si crystals decreased almost linearly with increasing temperature, and the temperature coefficient depended on the B concentration. On the other hand, the change in frequency with temperature was relatively insensitive to Ge doping in comparison with B doping. However, heavy B and Ge codoping in Si resulted in a relatively larger temperature coefficient than B doping with the same B concentration. r 2006 Elsevier Ltd. All rights reserved. Keywords: Si crystal; Heavy B and Ge codoping; Raman spectroscopy
1. Introduction Recently, a Czochralski (CZ) method without the Dash-neck [1] for growing a large and heavy dislocation-free Si crystal has been developed by using a heavily B- and Ge-codoped Si seed [2]. It was found that critical stress for dislocation generation in a Si crystal increased with B concentration, which was interpreted in terms of dislocation locking due to impurity segregation [3]. It was also found that heavy B and Ge codoping suppressed slip dislocation generation much more effectively than heavy B doping in a Si crystal with the same B concentration [4,5]. Corresponding author. Tel.: +81 22 215 2102; fax: +81 22 215 2101. E-mail address: [email protected] (X. Huang).
1369-8001/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.mssp.2006.01.050
On the other hand, Raman scattering as a powerful experimental method is frequently applied to investigate the interaction between an incident photon and an optical phonon in a Si crystal with heavy doping of impurities, including theoretical and experimental investigations. Cerdeira et al. [6,7] found that increasing the carrier concentration resulted in a marked decrease in frequency and considerable broadening of the optical phonon in heavily B-doped Si crystals, and they attributed the effects to the splitting of the valence band produced by the kE0 optical phonon. They also found that the decrease in frequency of Raman scattering at room temperature was different from that at 77 K, but no detailed temperature dependence was presented. Temperature dependence of Raman scattering in undoped Si was investigated by many researchers and they found that frequency shift
ARTICLE IN PRESS decreased with increasing temperature [8–11], but no doping effect was studied systematically. In the present work, Raman spectra on Si crystals heavily doped with B and/or Ge over the temperature range from 123 to 573 K were measured, and their temperature dependence was studied in detail. 2. Experimental Five-inch o1 0 04-oriented heavily B- doped, Ge-doped and B- and Ge-codoped dislocation-free Si wafers with a B concentration of 7.8 1017–2.1 1020 atoms/cm3, and a Ge concentration of 1.7 1019–5.3 1020 atoms/cm3 were processed from corresponding CZ-Si crystals. Some other Si wafers with light B doping were obtained with the same processes, as references. The lightly B-doped Si wafers had a B concentration of 1.0 1015 atoms/cm3. Raman scattering was carried out by a microRaman spectrometer (Renishaw, UK) with an He–Ne laser of 632.8 nm wavelength and about 1 mm spot size when using a 100 objective of the microscope on a square Si sample with about 5 5 mm2 cut from the Si wafers. The low laser power of 3 mW was used in the experiments in order to avoid possible influence caused by laser heating. Temperatures of the samples were controlled by a heating/cooling stage where liquid nitrogen (LN) was used as a cryogenic source and the temperatures were controlled by controlling heating power of a resistance heater located just around the samples. Temperatures of the samples were measured using a temperature sensor made of a Pt resistance with a measurement accuracy of 70.1 K. Resolution of the Raman shift in the measurements was 1.0 cm1. All the samples were measured for more than 3 times with the same experimental conditions. 3. Results and discussion Some typical Raman scattering spectra near the q ¼ 0 optical phonon of Si samples with different concentrations are shown in Figs. 1and 2. In Fig. 1, B concentration was 7 1018 atoms/cm3. Raman scattering spectra of the samples with a B concentration lower than that were almost the same as the spectra shown in Fig. 1. The peaks were very sharp, and all of them were almost symmetrical. Positions of the peaks shifted toward the lower frequency with increasing temperature. However, the Raman scattering spectra of the Si sample with a B concentra-
Raman Intensity (a.u.)
X. Huang et al. / Materials Science in Semiconductor Processing 9 (2006) 257–260
173K 223K 273K 323K 373K 423K 473K 523K 573K
400
450
500
550
600
Raman shift (cm-1) Fig. 1. Raman spectra at different temperatures in a heavily B-doped Si sample with a B concentration of 7 1018 atoms/cm3.
Raman Intensity (a.u.)
258
400
173K 198K 223K 248K 273K 299K 323K 348K 373K 398K 423K 448K 473K 498K 523K 548K 573K
450
500 -1 Raman shift (cm )
550
600
Fig. 2. Raman spectra at different temperatures in a heavily B-doped Si sample with a B concentration of 2.1 1020 atoms/cm3.
tion of 2.1 1020 atoms/cm3 were obviously different although the tendency of temperature dependence was similar, as shown in Fig. 2. The Fano–type continuous-discrete interference with broadening of the scattering peaks was observed [12], which was caused by the presence of high concentration of holes originating in heavy B doping.
ARTICLE IN PRESS X. Huang et al. / Materials Science in Semiconductor Processing 9 (2006) 257–260
Raman scattering spectra of a Si sample with a Ge concentration of 5.3 1020 atoms/cm3 which was much higher than the B concentration in the B-doped Si samples did not show any broadening behavior in the Raman scattering peaks. Ge is in the same IVb group as Si in the periodic table, thus Ge doping in Si itself would not generate any extra free carriers even with a very high doping level although heavy Ge doping would affect structure of energy band or band gap in Si, which will be discussed more detailedly later. Relationships between temperatures and the peak positions of the Raman scattering in Si with different B and/or Ge concentration are shown in Fig. 3. Generally, temperature dependence of Raman shift is explained by anharmonic phonon couplings, and it is proportional to reciprocal of temperature exponentially [11]. However, in the present temperature range, they decreased almost linearly with increasing temperature. In order to simplify the discussion, temperature dependence of the samples was fitted linearly. It is obvious that the temperature coefficient of Raman shift in Si depended on the impurity concentrations, and they increased obviously with increasing B concentration. However, only a relatively small temperature coefficient was obtained in the Ge-doped Si even though the Ge concentration was very high. Impurity in Si should have a direct effect on the frequency shift in Raman scattering because pho-
15
B = 1×10 18 B = 7 ×10 19 B = 7.8 ×10 20 B = 2.1 ×10 20 Ge = 5.3 ×10 19 19 B = 1 ×10 + Ge = 5.6 ×10
-1
Peak Position (cm )
525
520
515
510 100
y = 526.5 − 0.0215x y = 526.5 − 0.0217x y = 527.2 − 0.0250x y = 529.1 − 0.0315x y = 524.9 − 0.0204x y = 526.6 − 0.0227x 200
300
400
500
600
Temperature (K) Fig. 3. Temperature dependence of Raman shift in Si with heavy doping.
259
non frequency should be affected by the presence of the impurity itself although it was also theoretically and experimentally demonstrated that the effect on the frequency shift was dominated by free carrier contribution, as shown in the study of Cerdeira and Cardona [6]. Impurity can affect the phonon frequency through a change in the average atomic mass, which results in the frequency proportional to M1/2 [13], and a change in the average atomic volume, which should affect the frequency through the Gru¨neisen parameter. Temperature-insensitive direct impurity effect on the frequency shift in Raman scattering will be more detectable at a low temperature because free carrier concentration in Si and then its effect on Raman scattering will be decreased exponentially with decreasing temperature, especially at low temperature. Peak position of Raman shift would be about 523 cm1 at 123 K (by extrapolation) in Si with a B concentration lower than 1018 atoms/cm3, which was the same as that calculated by Cowley [8] or experimentally measured by Hart et al. [9], where undoped Si was investigated. However, a result that the frequency shift of about 522 cm1 in the Ge-doped Si was obtained at the same temperature, indicating that the direct impurity effect is easier to be observed at a relative low temperature and with an extremely low concentration of free carrier. Relationship between B concentration (corresponding to free carrier concentration) in Si and the temperature coefficients of Raman shift which were obtained from the results shown in Fig. 3 by considering that the peak positions decreased with temperature linearly, is shown in Fig. 4. The opened circles represent the results obtained from Si with heavy B doping, and the closed circle represents the result obtained from Si with heavy B and Ge codoping. The closed square represents the result obtained from Si with only heavy Ge doping. In the case of only heavy Ge doping, no electrical impurity was doped in the Si crystal. As shown in Fig. 4, temperature coefficient of the peak positions of Raman scattering in the heavily B-doped Si increased considerably with increasing B concentration, and it could be fitted numerically to be an exponential equation. The result of heavy Ge doping was obviously separate from the relationship of B doping, and temperature coefficient of the peak positions of Raman scattering in heavily Ge-doped Si was obviously lower than that of B-doped Si and even lower than that of lightly doped Si.
ARTICLE IN PRESS X. Huang et al. / Materials Science in Semiconductor Processing 9 (2006) 257–260
260
Temperature coefficient (cm-1/K)
0.040 Heavy B doping Heavy B and Ge codoping Heavy Ge codoping
0.030
temperature coefficient of the peak positions of Raman scattering in the Si with heavy B and Ge codoping by considering that the temperature coefficient increases with increasing B concentration, which is an important result of the present experiment, as mentioned above. 4. Conclusions
0.020
k = 0.0215exp(1.83e-21*C)
0.015 0
5 ×1019 1 ×1020 1.5 ×1020 2 ×1020 2.5 ×1020 B concentration (atoms/cm3)
Fig. 4. Relationship between the temperature coefficient of Raman shift and B concentration in Si with heavy doping.
Heavy B and Ge codoping resulted in a different effect on the temperature coefficient in comparison with heavy Ge doping or heavy B doping, as shown in Fig. 4. A relative larger temperature coefficient obtained from the Si samples with heavy B and Ge codoping could not be explained simply by algebraically adding the effect of Ge doping to B doping because an intermediate value should be obtained if that was the case. Although the Ge codoping in a Si crystal with about 1 at% only changed energy band or band gap of Si very slightly [14], Ge codoping would considerably decrease B acceptor level [15,16], corresponding to a decrease of activation energy of B ionization, which affected free carrier concentration in Si because free carrier concentration in a Si crystal is proportional to an exponential function of E A =kB T, where EA is the activation energy of B ionization, kB is the Boltzmann constant and T is the absolute temperature. The effect of Ge codoping on free carrier concentration would become much stronger with decreasing temperature. Some calculations were carried out as follows as a very rough estimation. For example, 1 at% Ge codoping in a Si crystal will result in about 1 meV decrease of activation energy, DEA, which will cause a relative increase of free carrier concentration to about 2.6 times at 123 K but almost the same at 573 K. Consequently, temperature dependence of free carrier concentration originating in B doping will become much larger due to B and Ge codoping in a Si crystal. The relative increase of free carrier concentration in Si due to B and Ge codoping would probably be responsible to the increase of
Raman backscattering measurements were carried out on Si crystals with heavy B and/or Ge doping over the temperature range from 123 to 573 K. The frequency of the qE0 optical phonon in the Si crystals decreased almost linearly with increasing temperature, and the temperature coefficient increased with increasing B concentration considerably. On the other hand, the change in frequency with temperature was relatively insensitive to Ge doping in comparison with B doping. However, B and Ge codoping in Si resulted in a relatively larger temperature coefficient with the same B concentration, which was interpreted from increase of free carrier concentration due to B and Ge codoping. Acknowledgment The authors acknowledge Silicon Technology Corporation for providing the Si wafers. References [1] Dash WC. J Appl Phys 1959;30:459. [2] Huang X, Taishi T, Yonenaga I, Hoshikawa K. Jpn J Appl Phys 2000;39:L1115. [3] Yonenaga I, Taishi T, Huang X, Hoshikawa K. J Appl Phys 2001;89:5788. [4] Yonenaga I, Taishi T, Huang X, Hoshikawa K. J Appl Phys 2003;93:265. [5] Huang X, Sato T, Nakanishi M, Taishi T, Hoshikawa K. Jpn J Appl Phys 2003;42:L1489. [6] Cerderia F, Cardona M. Phys Rev B 1972;5:1440. [7] Cerderia F, Fjeldly TA, Cardona M. Phys Rev B 1973;8:4734. [8] Cowley RA. J Phys (Paris) 1965;26:659. [9] Hart TR, Aggarwal RL, Lax B. Phys Rev B 1970;1:638. [10] Tsu R, Hernandez JG. Appl Phys Lett 1982;41:1016. [11] Menendez J, Cardona M. Phys Rev B 1984;29:2051. [12] Fano U. Phys Rev 1961;124:1866. [13] Klemens PG. Phys Rev 1966;148:845. [14] Penn C, Fromherz T, Bauer G. In: Kasper E, Lyutovich K, editors. Properties of silicon germanium and SiGe:carbon Emis datareviews series. UK: INSPEC; 2000. p. 125–34. [15] Buczko R. Solid State Commun 1995;93:367. [16] Gaworzewaki P, Tittelbach-Helmrich K, Penner U. J Appl Phys 1998;83:5258.
Materials Science in Semiconductor Processing 9 (2006) 257–260
Temperature dependence of Raman scattering in Si crystals with heavy B and/or Ge doping Xinming Huanga,, Kehui Wua, Mingwei Chena, Taishi Toshinorib, Keigo Hoshikawab, Shinji Koha, Satoshi Udaa a
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan Faculty of Education, Shinshu University, Nishinagano, Nagano 380-8544, Japan
b
Available online 10 February 2006
Abstract Raman backscattering measurements were carried out on Si crystals heavily doped with B and/or Ge over the temperature range from 123 to 573 K. It was found that the frequency of the qE0 optical phonon in the Si crystals decreased almost linearly with increasing temperature, and the temperature coefficient depended on the B concentration. On the other hand, the change in frequency with temperature was relatively insensitive to Ge doping in comparison with B doping. However, heavy B and Ge codoping in Si resulted in a relatively larger temperature coefficient than B doping with the same B concentration. r 2006 Elsevier Ltd. All rights reserved. Keywords: Si crystal; Heavy B and Ge codoping; Raman spectroscopy
1. Introduction Recently, a Czochralski (CZ) method without the Dash-neck [1] for growing a large and heavy dislocation-free Si crystal has been developed by using a heavily B- and Ge-codoped Si seed [2]. It was found that critical stress for dislocation generation in a Si crystal increased with B concentration, which was interpreted in terms of dislocation locking due to impurity segregation [3]. It was also found that heavy B and Ge codoping suppressed slip dislocation generation much more effectively than heavy B doping in a Si crystal with the same B concentration [4,5]. Corresponding author. Tel.: +81 22 215 2102; fax: +81 22 215 2101. E-mail address: [email protected] (X. Huang).
1369-8001/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.mssp.2006.01.050
On the other hand, Raman scattering as a powerful experimental method is frequently applied to investigate the interaction between an incident photon and an optical phonon in a Si crystal with heavy doping of impurities, including theoretical and experimental investigations. Cerdeira et al. [6,7] found that increasing the carrier concentration resulted in a marked decrease in frequency and considerable broadening of the optical phonon in heavily B-doped Si crystals, and they attributed the effects to the splitting of the valence band produced by the kE0 optical phonon. They also found that the decrease in frequency of Raman scattering at room temperature was different from that at 77 K, but no detailed temperature dependence was presented. Temperature dependence of Raman scattering in undoped Si was investigated by many researchers and they found that frequency shift
ARTICLE IN PRESS decreased with increasing temperature [8–11], but no doping effect was studied systematically. In the present work, Raman spectra on Si crystals heavily doped with B and/or Ge over the temperature range from 123 to 573 K were measured, and their temperature dependence was studied in detail. 2. Experimental Five-inch o1 0 04-oriented heavily B- doped, Ge-doped and B- and Ge-codoped dislocation-free Si wafers with a B concentration of 7.8 1017–2.1 1020 atoms/cm3, and a Ge concentration of 1.7 1019–5.3 1020 atoms/cm3 were processed from corresponding CZ-Si crystals. Some other Si wafers with light B doping were obtained with the same processes, as references. The lightly B-doped Si wafers had a B concentration of 1.0 1015 atoms/cm3. Raman scattering was carried out by a microRaman spectrometer (Renishaw, UK) with an He–Ne laser of 632.8 nm wavelength and about 1 mm spot size when using a 100 objective of the microscope on a square Si sample with about 5 5 mm2 cut from the Si wafers. The low laser power of 3 mW was used in the experiments in order to avoid possible influence caused by laser heating. Temperatures of the samples were controlled by a heating/cooling stage where liquid nitrogen (LN) was used as a cryogenic source and the temperatures were controlled by controlling heating power of a resistance heater located just around the samples. Temperatures of the samples were measured using a temperature sensor made of a Pt resistance with a measurement accuracy of 70.1 K. Resolution of the Raman shift in the measurements was 1.0 cm1. All the samples were measured for more than 3 times with the same experimental conditions. 3. Results and discussion Some typical Raman scattering spectra near the q ¼ 0 optical phonon of Si samples with different concentrations are shown in Figs. 1and 2. In Fig. 1, B concentration was 7 1018 atoms/cm3. Raman scattering spectra of the samples with a B concentration lower than that were almost the same as the spectra shown in Fig. 1. The peaks were very sharp, and all of them were almost symmetrical. Positions of the peaks shifted toward the lower frequency with increasing temperature. However, the Raman scattering spectra of the Si sample with a B concentra-
Raman Intensity (a.u.)
X. Huang et al. / Materials Science in Semiconductor Processing 9 (2006) 257–260
173K 223K 273K 323K 373K 423K 473K 523K 573K
400
450
500
550
600
Raman shift (cm-1) Fig. 1. Raman spectra at different temperatures in a heavily B-doped Si sample with a B concentration of 7 1018 atoms/cm3.
Raman Intensity (a.u.)
258
400
173K 198K 223K 248K 273K 299K 323K 348K 373K 398K 423K 448K 473K 498K 523K 548K 573K
450
500 -1 Raman shift (cm )
550
600
Fig. 2. Raman spectra at different temperatures in a heavily B-doped Si sample with a B concentration of 2.1 1020 atoms/cm3.
tion of 2.1 1020 atoms/cm3 were obviously different although the tendency of temperature dependence was similar, as shown in Fig. 2. The Fano–type continuous-discrete interference with broadening of the scattering peaks was observed [12], which was caused by the presence of high concentration of holes originating in heavy B doping.
ARTICLE IN PRESS X. Huang et al. / Materials Science in Semiconductor Processing 9 (2006) 257–260
Raman scattering spectra of a Si sample with a Ge concentration of 5.3 1020 atoms/cm3 which was much higher than the B concentration in the B-doped Si samples did not show any broadening behavior in the Raman scattering peaks. Ge is in the same IVb group as Si in the periodic table, thus Ge doping in Si itself would not generate any extra free carriers even with a very high doping level although heavy Ge doping would affect structure of energy band or band gap in Si, which will be discussed more detailedly later. Relationships between temperatures and the peak positions of the Raman scattering in Si with different B and/or Ge concentration are shown in Fig. 3. Generally, temperature dependence of Raman shift is explained by anharmonic phonon couplings, and it is proportional to reciprocal of temperature exponentially [11]. However, in the present temperature range, they decreased almost linearly with increasing temperature. In order to simplify the discussion, temperature dependence of the samples was fitted linearly. It is obvious that the temperature coefficient of Raman shift in Si depended on the impurity concentrations, and they increased obviously with increasing B concentration. However, only a relatively small temperature coefficient was obtained in the Ge-doped Si even though the Ge concentration was very high. Impurity in Si should have a direct effect on the frequency shift in Raman scattering because pho-
15
B = 1×10 18 B = 7 ×10 19 B = 7.8 ×10 20 B = 2.1 ×10 20 Ge = 5.3 ×10 19 19 B = 1 ×10 + Ge = 5.6 ×10
-1
Peak Position (cm )
525
520
515
510 100
y = 526.5 − 0.0215x y = 526.5 − 0.0217x y = 527.2 − 0.0250x y = 529.1 − 0.0315x y = 524.9 − 0.0204x y = 526.6 − 0.0227x 200
300
400
500
600
Temperature (K) Fig. 3. Temperature dependence of Raman shift in Si with heavy doping.
259
non frequency should be affected by the presence of the impurity itself although it was also theoretically and experimentally demonstrated that the effect on the frequency shift was dominated by free carrier contribution, as shown in the study of Cerdeira and Cardona [6]. Impurity can affect the phonon frequency through a change in the average atomic mass, which results in the frequency proportional to M1/2 [13], and a change in the average atomic volume, which should affect the frequency through the Gru¨neisen parameter. Temperature-insensitive direct impurity effect on the frequency shift in Raman scattering will be more detectable at a low temperature because free carrier concentration in Si and then its effect on Raman scattering will be decreased exponentially with decreasing temperature, especially at low temperature. Peak position of Raman shift would be about 523 cm1 at 123 K (by extrapolation) in Si with a B concentration lower than 1018 atoms/cm3, which was the same as that calculated by Cowley [8] or experimentally measured by Hart et al. [9], where undoped Si was investigated. However, a result that the frequency shift of about 522 cm1 in the Ge-doped Si was obtained at the same temperature, indicating that the direct impurity effect is easier to be observed at a relative low temperature and with an extremely low concentration of free carrier. Relationship between B concentration (corresponding to free carrier concentration) in Si and the temperature coefficients of Raman shift which were obtained from the results shown in Fig. 3 by considering that the peak positions decreased with temperature linearly, is shown in Fig. 4. The opened circles represent the results obtained from Si with heavy B doping, and the closed circle represents the result obtained from Si with heavy B and Ge codoping. The closed square represents the result obtained from Si with only heavy Ge doping. In the case of only heavy Ge doping, no electrical impurity was doped in the Si crystal. As shown in Fig. 4, temperature coefficient of the peak positions of Raman scattering in the heavily B-doped Si increased considerably with increasing B concentration, and it could be fitted numerically to be an exponential equation. The result of heavy Ge doping was obviously separate from the relationship of B doping, and temperature coefficient of the peak positions of Raman scattering in heavily Ge-doped Si was obviously lower than that of B-doped Si and even lower than that of lightly doped Si.
ARTICLE IN PRESS X. Huang et al. / Materials Science in Semiconductor Processing 9 (2006) 257–260
260
Temperature coefficient (cm-1/K)
0.040 Heavy B doping Heavy B and Ge codoping Heavy Ge codoping
0.030
temperature coefficient of the peak positions of Raman scattering in the Si with heavy B and Ge codoping by considering that the temperature coefficient increases with increasing B concentration, which is an important result of the present experiment, as mentioned above. 4. Conclusions
0.020
k = 0.0215exp(1.83e-21*C)
0.015 0
5 ×1019 1 ×1020 1.5 ×1020 2 ×1020 2.5 ×1020 B concentration (atoms/cm3)
Fig. 4. Relationship between the temperature coefficient of Raman shift and B concentration in Si with heavy doping.
Heavy B and Ge codoping resulted in a different effect on the temperature coefficient in comparison with heavy Ge doping or heavy B doping, as shown in Fig. 4. A relative larger temperature coefficient obtained from the Si samples with heavy B and Ge codoping could not be explained simply by algebraically adding the effect of Ge doping to B doping because an intermediate value should be obtained if that was the case. Although the Ge codoping in a Si crystal with about 1 at% only changed energy band or band gap of Si very slightly [14], Ge codoping would considerably decrease B acceptor level [15,16], corresponding to a decrease of activation energy of B ionization, which affected free carrier concentration in Si because free carrier concentration in a Si crystal is proportional to an exponential function of E A =kB T, where EA is the activation energy of B ionization, kB is the Boltzmann constant and T is the absolute temperature. The effect of Ge codoping on free carrier concentration would become much stronger with decreasing temperature. Some calculations were carried out as follows as a very rough estimation. For example, 1 at% Ge codoping in a Si crystal will result in about 1 meV decrease of activation energy, DEA, which will cause a relative increase of free carrier concentration to about 2.6 times at 123 K but almost the same at 573 K. Consequently, temperature dependence of free carrier concentration originating in B doping will become much larger due to B and Ge codoping in a Si crystal. The relative increase of free carrier concentration in Si due to B and Ge codoping would probably be responsible to the increase of
Raman backscattering measurements were carried out on Si crystals with heavy B and/or Ge doping over the temperature range from 123 to 573 K. The frequency of the qE0 optical phonon in the Si crystals decreased almost linearly with increasing temperature, and the temperature coefficient increased with increasing B concentration considerably. On the other hand, the change in frequency with temperature was relatively insensitive to Ge doping in comparison with B doping. However, B and Ge codoping in Si resulted in a relatively larger temperature coefficient with the same B concentration, which was interpreted from increase of free carrier concentration due to B and Ge codoping. Acknowledgment The authors acknowledge Silicon Technology Corporation for providing the Si wafers. References [1] Dash WC. J Appl Phys 1959;30:459. [2] Huang X, Taishi T, Yonenaga I, Hoshikawa K. Jpn J Appl Phys 2000;39:L1115. [3] Yonenaga I, Taishi T, Huang X, Hoshikawa K. J Appl Phys 2001;89:5788. [4] Yonenaga I, Taishi T, Huang X, Hoshikawa K. J Appl Phys 2003;93:265. [5] Huang X, Sato T, Nakanishi M, Taishi T, Hoshikawa K. Jpn J Appl Phys 2003;42:L1489. [6] Cerderia F, Cardona M. Phys Rev B 1972;5:1440. [7] Cerderia F, Fjeldly TA, Cardona M. Phys Rev B 1973;8:4734. [8] Cowley RA. J Phys (Paris) 1965;26:659. [9] Hart TR, Aggarwal RL, Lax B. Phys Rev B 1970;1:638. [10] Tsu R, Hernandez JG. Appl Phys Lett 1982;41:1016. [11] Menendez J, Cardona M. Phys Rev B 1984;29:2051. [12] Fano U. Phys Rev 1961;124:1866. [13] Klemens PG. Phys Rev 1966;148:845. [14] Penn C, Fromherz T, Bauer G. In: Kasper E, Lyutovich K, editors. Properties of silicon germanium and SiGe:carbon Emis datareviews series. UK: INSPEC; 2000. p. 125–34. [15] Buczko R. Solid State Commun 1995;93:367. [16] Gaworzewaki P, Tittelbach-Helmrich K, Penner U. J Appl Phys 1998;83:5258.