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p-Si structures
Nuclear Instruments and Methods in Physics Research B 173 (2001) 299±303
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4 MeV electron irradiation eect on electroluminesencence from Au/SiO2 /p-Si and Au/Si-rich SiO2 /p-Si structures G.Z. Ran a, W.C. Qin a, Z.C. Ma c, W.H. Zong c, G.G. Qin b
a,b,*
a Department of Physics, Peking University, Beijing 100871, People's Republic of China International Center for Materials Physics, Academia Sinica, Shenyang 110015, People's Republic of China c National Key Laboratory for ASIC, HSRI, Shijiazhuang 050051, People's Republic of China
Received 2 May 2000; received in revised form 18 July 2000
Abstract The eects of 4 MeV electron irradiation on electroluminescence (EL) from Au=SiO2 =p-Si and Au/Si-rich SiO2 /p-Si structures are reported. The SiO2 and Si-rich SiO2 ®lms were deposited on p-Si wafers using the magnetron sputtering technique and then processed by rapid thermal annealing (RTA) at a series of temperatures. The Au=SiO2 =p-Si and Au/ Si-rich SiO2 /p-Si structures were irradiated by electrons with an energy of 4 Mev and a dose rate of 8:5 1012 cmÿ2 sÿ1 . EL intensities of the two structures as functions of the RTA temperature and electron irradiation time have been studied. For the Au=SiO2 =p-Si structure with SiO2 /p-Si annealed at 900°C, the EL intensity increased to a maximum in electron irradiation for 20 s, which is larger than that before irradiation by a factor of 3. These experimental results have been discussed. Ó 2001 Elsevier Science B.V. All rights reserved.
1. Introduction In recent years, visible electroluminescence (EL) from Si-based structures, e.g., porous Si [1±6], native silicon oxide (NSO) [7±10] and Si-rich SiO2 (SRSO) [11±13] on Si substrates, has been studied intensely because of a promising prospect in optoelectronics applications. However, the EL eciency and stability of the Si-based structures cannot yet meet the requirements of the practical use, and their EL mechanisms wait to be revealed further. In this paper, we study the irradiation *
Corresponding author. Fax: +86-10-627-51615. E-mail address: [email protected] (G.G. Qin).
eect of 4 MeV electrons on EL from Au=SiO2 =p-Si and Au/Si-rich SiO2 /p-Si structures. One goal of the study is to investigate their abilities in anti-irradiation; another is to explore a new way to enhance EL eciency, and the third goal is to reveal further their EL mechanisms.
2. Experiment The substrates used were (100)-oriented, 6±9 X cm p-type Si wafers. The thin SiO2 and SRSO ®lms were deposited using the magnetron sputtering technique. A Si±SiO2 composite target with an area ratio of Si to SiO2 around 20% was employed
0168-583X/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 0 ) 0 0 3 8 2 - 7
300
G.Z. Ran et al. / Nucl. Instr. and Meth. in Phys. Res. B 173 (2001) 299±303
in depositing the SRSO ®lms. The thicknesses of the SRSO and SiO2 ®lms, controlled by depositing time, were all around 12 nm. Then some SiO2 /p-Si and SRSO/p-Si samples were treated by rapid thermal annealing (RTA) in N2 at 700°C, 800°C, 900°C and 1000°C, respectively, and the others were unannealed. Later ohmic contacts on the backs of all the p-Si wafers were formed by evaporating thin Al ®lms and alloying at 530°C for 7 min in N2 . Finally, semitransparent Au ®lms were evaporated onto the SiO2 /p-Si and SRSO/pSi as electrodes to form the Au=SiO2 =p-Si and Au/ SRSO/p-Si structures. Electron irradiation was carried out at room temperature in air using electron linear accelerator with an electron energy of 4 MeV and a dose rate of 8:5 1012 cmÿ2 sÿ1 . The irradiation time was in a range of 10±240 s. All the EL measurements before and after electron irradiation were carried out under a bias of 8 V. In the following text, `the Au/SiO2 (or SRSO)/p-Si structure annealed' always means `the Au/SiO2 (or SRSO)/p-Si structure rapid thermally annealed before depositing Au', and `the structure irradiated' always means `the structure irradiated by 4 MeV electrons after depositing Au'.
3. Results All the Au=SiO2 =p-Si and Au/SRSO/p-Si samples have good rectifying junction behavior. Fig. 1 shows I±V characteristics of the two structures annealed at 800°C and irradiated for a series of times. Under forward biases, the currents decreased a little with increasing irradiation time when the irradiation time is less than 40 s. However, the currents changed neither with the forward bias when irradiation time is over 40 s, nor with the reverse bias from the beginning of irradiation. Fig. 1 also indicates that the current of the Au/SRSO/pSi structure was larger than those of the Au=SiO2 =p-Si structure under an identical bias. Quite strong visible EL from the two unirradiated structures could be observed under a forward bias of 8 V; under a reverse bias, however, no EL could be observed. EL spectra of the Au=SiO2 = p-Si sample annealed at 800°C and irradiated for a
Fig. 1. I±V characteristics of (a) the Au=SiO2 =p-Si and (b) the Au/SRSO/p-Si structures both annealed at 800°C and irradiated by 4 Mev electrons for 0, 10, 20 and 40 s.
series of times are shown in Fig. 2. The EL peak before irradiation was located at 640 nm. When the irradiation time was less than 20 s, EL intensity increased with increasing irradiation time, and became two times of that before irradiation when irradiation time is up to 20 s. When irradiation time was 40 s, the EL intensity began to decrease. After irradiation for 120 and 240 s, the EL intensities decreased, respectively, to a half and one-third of that before irradiation. Fig. 3 shows how the EL spectra of an Au/ SRSO/p-Si sample annealed at 800°C was changed with irradiation time. The EL peak was located at 620 nm before electron irradiation. EL intensity increased by a factor of larger than 2 after 20 s irradiation and EL spectra changed obviously, but with the peak wavelength remained a constant. After irradiation for 120 and 240 s, the EL intensities decreased, respectively, to one third and one ®fth of that before irradiation. Comparing Fig. 2 with Fig. 3, we found that the EL from the
G.Z. Ran et al. / Nucl. Instr. and Meth. in Phys. Res. B 173 (2001) 299±303
Fig. 2. EL spectra of the Au=SiO2 =p-Si structure annealed at 800 C and irradiated by 4 MeV electrons for 0, 10, 20, 40, 60, 120 and 240 s.
Au=SiO2 =p-Si structure has a higher ability in anti-irradiation than that from the Au/SRSO/p-Si structure. We also studied how the RTA temperature for the SiO2 /p-Si and SRSO/p-Si in¯uences irradiation eects of the Au=SiO2 =p-Si and Au/SRSO/p-Si structures. Fig. 4(a) shows the EL intensities of the Au=SiO2 =p-Si samples unirradiated and irradiated for 20 and 40 s as functions of the RTA temperature. As seen clearly, the EL intensities increased evidently after 20 s irradiation, but decreased after 40 s irradiation for each RTA temperature. Figs. 4(a) and (b) indicate that for the Au=SiO2 =p-Si and Au/SRSO/p-Si structures 900°C and 800°C are, respectively, the optimal annealing temperatures for the EL intensity enhancement after 20 or 40 s irradiation.
4. Discussion For the Au=SiO2 =p-Si structure, electrons from the Au electrode and holes from the p-Si substrate
301
Fig. 3. EL spectra of the Au/SRSO/p-Si structure annealed at 800°C and irradiated by 4 MeV electrons for 0, 10, 20, 40, 60, 120 and 240 s.
tunnel directly into luminescence centers (LCs, defects or impurities) in the SiO2 layers and then recombine there to give rise to EL. But for the Au/ SRSO/p-Si structures, the case is more complicated due to the existence of the nanometer Si particles (NSPs) in the SiO2 layer. DiMaria et al. [11] suggested the quantum con®nement (QC) model, which claimed that EL from the structure mainly originated from the NSPs in SiO2 , while the peak position of EL was determined by the NSP sizes. However, based on the experimental results reported above and in [12,13] etc., we consider that even in the Au/SRSO/p-Si structure, EL originates mainly from the LCs. The fact that the EL intensity increased to a maximum without changing the EL peak position in electron irradiation for 20 s is dicult to be explained by the QC model, because electron irradiation always induces nonradiative centers and intents to decrease the EL intensity, it is hard to imagine that electron irradiation can induce a great deal new NSPs with the same sizes as the original ones and thus enlarge the EL peak
302
G.Z. Ran et al. / Nucl. Instr. and Meth. in Phys. Res. B 173 (2001) 299±303
process. A similar reason can explain the fact that the EL intensity increased most in 20 s electron irradiation for the Au/SRSO/p-Si sample annealed at 800°C. 5. Conclusion
Fig. 4. The EL intensities of (a) the Au=SiO2 =p-Si and (b) the Au/SRSO/p-Si structures irradiated for 0, 20 and 40 s as functions of the RTA temperature.
without changing its position. If we suppose that EL is mainly from the LCs in the SiO2 and the SRSO, it is easy to explain qualitatively the experimental results as follows. Many papers have reported that irradiation can induce radiative defects into the SiO2 and SRSO ®lms besides nonradiative defects [14±17]. The fact that the EL intensities increased and EL spectra changed due to electron irradiation for time in a range of 10±40 s indicates that some types of LCs had been produced in the SiO2 and SRSO ®lms in the irradiation process and their eect on EL surpasses the eect of generation of nonradiative defects during electron irradiation for such a short time. The reason for the EL intensity enhancement due to electron irradiation attaining a maximum for the Au=SiO2 =p-Si sample annealed at 900°C was probably that RTA at such a temperature generated the greatest amount of precursors in the SiO2 ®lms, which turned into LCs in the irradiation
In summary, we have studied the eects of 4 MeV electron irradiation on EL from the Au=SiO2 =p-Si and Au/SRSO/p-Si structures. The dose rate was 8:5 1012 cmÿ2 sÿ1 . Their EL spectra changed and EL intensities increased after electron irradiation less than 40 s. After 20 s electron irradiation for the Au=SiO2 =p-Si sample annealed at 900 , the EL intensity increased by a factor of 3, and for the Au/SRSO/p-Si sample annealed at 800°C, it increased by a factor of more than 2. When electron irradiation time is over 40 s, the EL intensity decreased. The reason for the EL intensity increase after electron irradiation for less than 40 s is that LCs had been induced in the SiO2 and SRSO ®lms, and its eect on EL intensity surpasses the eect of generation of nonradiative centers. Acknowledgements This work was supported by the National Natural Science Foundation of China. References [1] A. Ritcher, P. Steiner, F. Kozlowski, W. Lang, IEEE Electron Device Lett. 12 (1991) 691. [2] N. Koshida, H. Koyama, Appl. Phys. Lett. 60 (1992) 347. [3] B. Gelloz, T. Nakagawa, N. Koshida, Appl. Phys. Lett. 73 (1998) 2021. [4] K.D. Hirschman, L. Tsybeskov, S.P. Duttagupta, P.M. Fauchet, Nature 384 (1996) 338. [5] J. Linnros, N. Lallic, Appl. Phys. Lett. 66 (1995) 3048. [6] S. Lazarouk, P. Jaguiro, S. Katsouba, G. Mashini, S. La Monica, G. Maiello, A. Ferrari, Appl. Phys. Lett. 68 (12) (1996) 1646. [7] G.G. Qin, Y.M. Huang, B.Q. Zong, L. Zhang, B.R. Zhang, Superlattices Microstruct. 16 (1994) 387. [8] G.F. Bai, Y.Q. Wang, Z.C. Ma, W.H. Zong, G.G. Qin, J. Phys.: Condens. Matter 10 (1998) L717. [9] Y.Q. Wang, T.P. Zhao, J. Liu, G.G. Qin, Appl. Phys. Lett. 74 (15) (1999) 3815.
G.Z. Ran et al. / Nucl. Instr. and Meth. in Phys. Res. B 173 (2001) 299±303 [10] J. Yuan, D. Haneman, J. Appl. Phys. 86 (4) (1999) 2358. [11] D.J. DiMaria, J.R. Kirtley, E.J. Pakulis, D.W. Dong, T.S. Kuan, F.L. Pesavento, T.N. Theis, J.A. Cutro, S.D. Brorson, J. Appl. Phys. 56 (1984) 401. [12] G.G. Qin, A.P. Li, B.R. Zhang, B.C. Li, J. Appl. Phys. 78 (1995) 2006. [13] G.G. Qin, A.P. Li, Y.X. Zhang, Phys. Rev. B 54 (16) (1996) R11122.
303
[14] S.Y. Ma, B.R. Zhang, G.G. Qin, Z.C. Ma, W.H. Zong, X.T. Meng, Mater. Res. Bull. 32 (7) (1997) 1427. [15] C.M. Gee, M. Kastner, in: G. Lucovsky, S.T. Pantelides, F.L. Galeener (Eds.), The Physics of MOS Insulators, Pergamon, New York, 1980, p. 132. [16] H. Nishikawa, E. Watanabe, D. Ito, Y. Sakurai, K. Nagasawa, Y. Ohki, J. Appl. Phys. 80 (1996) 3513. [17] Y. Sakurai, K. Nagasawa, J. Appl. Phys. 86 (3) (1999).
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4 MeV electron irradiation eect on electroluminesencence from Au/SiO2 /p-Si and Au/Si-rich SiO2 /p-Si structures G.Z. Ran a, W.C. Qin a, Z.C. Ma c, W.H. Zong c, G.G. Qin b
a,b,*
a Department of Physics, Peking University, Beijing 100871, People's Republic of China International Center for Materials Physics, Academia Sinica, Shenyang 110015, People's Republic of China c National Key Laboratory for ASIC, HSRI, Shijiazhuang 050051, People's Republic of China
Received 2 May 2000; received in revised form 18 July 2000
Abstract The eects of 4 MeV electron irradiation on electroluminescence (EL) from Au=SiO2 =p-Si and Au/Si-rich SiO2 /p-Si structures are reported. The SiO2 and Si-rich SiO2 ®lms were deposited on p-Si wafers using the magnetron sputtering technique and then processed by rapid thermal annealing (RTA) at a series of temperatures. The Au=SiO2 =p-Si and Au/ Si-rich SiO2 /p-Si structures were irradiated by electrons with an energy of 4 Mev and a dose rate of 8:5 1012 cmÿ2 sÿ1 . EL intensities of the two structures as functions of the RTA temperature and electron irradiation time have been studied. For the Au=SiO2 =p-Si structure with SiO2 /p-Si annealed at 900°C, the EL intensity increased to a maximum in electron irradiation for 20 s, which is larger than that before irradiation by a factor of 3. These experimental results have been discussed. Ó 2001 Elsevier Science B.V. All rights reserved.
1. Introduction In recent years, visible electroluminescence (EL) from Si-based structures, e.g., porous Si [1±6], native silicon oxide (NSO) [7±10] and Si-rich SiO2 (SRSO) [11±13] on Si substrates, has been studied intensely because of a promising prospect in optoelectronics applications. However, the EL eciency and stability of the Si-based structures cannot yet meet the requirements of the practical use, and their EL mechanisms wait to be revealed further. In this paper, we study the irradiation *
Corresponding author. Fax: +86-10-627-51615. E-mail address: [email protected] (G.G. Qin).
eect of 4 MeV electrons on EL from Au=SiO2 =p-Si and Au/Si-rich SiO2 /p-Si structures. One goal of the study is to investigate their abilities in anti-irradiation; another is to explore a new way to enhance EL eciency, and the third goal is to reveal further their EL mechanisms.
2. Experiment The substrates used were (100)-oriented, 6±9 X cm p-type Si wafers. The thin SiO2 and SRSO ®lms were deposited using the magnetron sputtering technique. A Si±SiO2 composite target with an area ratio of Si to SiO2 around 20% was employed
0168-583X/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 0 ) 0 0 3 8 2 - 7
300
G.Z. Ran et al. / Nucl. Instr. and Meth. in Phys. Res. B 173 (2001) 299±303
in depositing the SRSO ®lms. The thicknesses of the SRSO and SiO2 ®lms, controlled by depositing time, were all around 12 nm. Then some SiO2 /p-Si and SRSO/p-Si samples were treated by rapid thermal annealing (RTA) in N2 at 700°C, 800°C, 900°C and 1000°C, respectively, and the others were unannealed. Later ohmic contacts on the backs of all the p-Si wafers were formed by evaporating thin Al ®lms and alloying at 530°C for 7 min in N2 . Finally, semitransparent Au ®lms were evaporated onto the SiO2 /p-Si and SRSO/pSi as electrodes to form the Au=SiO2 =p-Si and Au/ SRSO/p-Si structures. Electron irradiation was carried out at room temperature in air using electron linear accelerator with an electron energy of 4 MeV and a dose rate of 8:5 1012 cmÿ2 sÿ1 . The irradiation time was in a range of 10±240 s. All the EL measurements before and after electron irradiation were carried out under a bias of 8 V. In the following text, `the Au/SiO2 (or SRSO)/p-Si structure annealed' always means `the Au/SiO2 (or SRSO)/p-Si structure rapid thermally annealed before depositing Au', and `the structure irradiated' always means `the structure irradiated by 4 MeV electrons after depositing Au'.
3. Results All the Au=SiO2 =p-Si and Au/SRSO/p-Si samples have good rectifying junction behavior. Fig. 1 shows I±V characteristics of the two structures annealed at 800°C and irradiated for a series of times. Under forward biases, the currents decreased a little with increasing irradiation time when the irradiation time is less than 40 s. However, the currents changed neither with the forward bias when irradiation time is over 40 s, nor with the reverse bias from the beginning of irradiation. Fig. 1 also indicates that the current of the Au/SRSO/pSi structure was larger than those of the Au=SiO2 =p-Si structure under an identical bias. Quite strong visible EL from the two unirradiated structures could be observed under a forward bias of 8 V; under a reverse bias, however, no EL could be observed. EL spectra of the Au=SiO2 = p-Si sample annealed at 800°C and irradiated for a
Fig. 1. I±V characteristics of (a) the Au=SiO2 =p-Si and (b) the Au/SRSO/p-Si structures both annealed at 800°C and irradiated by 4 Mev electrons for 0, 10, 20 and 40 s.
series of times are shown in Fig. 2. The EL peak before irradiation was located at 640 nm. When the irradiation time was less than 20 s, EL intensity increased with increasing irradiation time, and became two times of that before irradiation when irradiation time is up to 20 s. When irradiation time was 40 s, the EL intensity began to decrease. After irradiation for 120 and 240 s, the EL intensities decreased, respectively, to a half and one-third of that before irradiation. Fig. 3 shows how the EL spectra of an Au/ SRSO/p-Si sample annealed at 800°C was changed with irradiation time. The EL peak was located at 620 nm before electron irradiation. EL intensity increased by a factor of larger than 2 after 20 s irradiation and EL spectra changed obviously, but with the peak wavelength remained a constant. After irradiation for 120 and 240 s, the EL intensities decreased, respectively, to one third and one ®fth of that before irradiation. Comparing Fig. 2 with Fig. 3, we found that the EL from the
G.Z. Ran et al. / Nucl. Instr. and Meth. in Phys. Res. B 173 (2001) 299±303
Fig. 2. EL spectra of the Au=SiO2 =p-Si structure annealed at 800 C and irradiated by 4 MeV electrons for 0, 10, 20, 40, 60, 120 and 240 s.
Au=SiO2 =p-Si structure has a higher ability in anti-irradiation than that from the Au/SRSO/p-Si structure. We also studied how the RTA temperature for the SiO2 /p-Si and SRSO/p-Si in¯uences irradiation eects of the Au=SiO2 =p-Si and Au/SRSO/p-Si structures. Fig. 4(a) shows the EL intensities of the Au=SiO2 =p-Si samples unirradiated and irradiated for 20 and 40 s as functions of the RTA temperature. As seen clearly, the EL intensities increased evidently after 20 s irradiation, but decreased after 40 s irradiation for each RTA temperature. Figs. 4(a) and (b) indicate that for the Au=SiO2 =p-Si and Au/SRSO/p-Si structures 900°C and 800°C are, respectively, the optimal annealing temperatures for the EL intensity enhancement after 20 or 40 s irradiation.
4. Discussion For the Au=SiO2 =p-Si structure, electrons from the Au electrode and holes from the p-Si substrate
301
Fig. 3. EL spectra of the Au/SRSO/p-Si structure annealed at 800°C and irradiated by 4 MeV electrons for 0, 10, 20, 40, 60, 120 and 240 s.
tunnel directly into luminescence centers (LCs, defects or impurities) in the SiO2 layers and then recombine there to give rise to EL. But for the Au/ SRSO/p-Si structures, the case is more complicated due to the existence of the nanometer Si particles (NSPs) in the SiO2 layer. DiMaria et al. [11] suggested the quantum con®nement (QC) model, which claimed that EL from the structure mainly originated from the NSPs in SiO2 , while the peak position of EL was determined by the NSP sizes. However, based on the experimental results reported above and in [12,13] etc., we consider that even in the Au/SRSO/p-Si structure, EL originates mainly from the LCs. The fact that the EL intensity increased to a maximum without changing the EL peak position in electron irradiation for 20 s is dicult to be explained by the QC model, because electron irradiation always induces nonradiative centers and intents to decrease the EL intensity, it is hard to imagine that electron irradiation can induce a great deal new NSPs with the same sizes as the original ones and thus enlarge the EL peak
302
G.Z. Ran et al. / Nucl. Instr. and Meth. in Phys. Res. B 173 (2001) 299±303
process. A similar reason can explain the fact that the EL intensity increased most in 20 s electron irradiation for the Au/SRSO/p-Si sample annealed at 800°C. 5. Conclusion
Fig. 4. The EL intensities of (a) the Au=SiO2 =p-Si and (b) the Au/SRSO/p-Si structures irradiated for 0, 20 and 40 s as functions of the RTA temperature.
without changing its position. If we suppose that EL is mainly from the LCs in the SiO2 and the SRSO, it is easy to explain qualitatively the experimental results as follows. Many papers have reported that irradiation can induce radiative defects into the SiO2 and SRSO ®lms besides nonradiative defects [14±17]. The fact that the EL intensities increased and EL spectra changed due to electron irradiation for time in a range of 10±40 s indicates that some types of LCs had been produced in the SiO2 and SRSO ®lms in the irradiation process and their eect on EL surpasses the eect of generation of nonradiative defects during electron irradiation for such a short time. The reason for the EL intensity enhancement due to electron irradiation attaining a maximum for the Au=SiO2 =p-Si sample annealed at 900°C was probably that RTA at such a temperature generated the greatest amount of precursors in the SiO2 ®lms, which turned into LCs in the irradiation
In summary, we have studied the eects of 4 MeV electron irradiation on EL from the Au=SiO2 =p-Si and Au/SRSO/p-Si structures. The dose rate was 8:5 1012 cmÿ2 sÿ1 . Their EL spectra changed and EL intensities increased after electron irradiation less than 40 s. After 20 s electron irradiation for the Au=SiO2 =p-Si sample annealed at 900 , the EL intensity increased by a factor of 3, and for the Au/SRSO/p-Si sample annealed at 800°C, it increased by a factor of more than 2. When electron irradiation time is over 40 s, the EL intensity decreased. The reason for the EL intensity increase after electron irradiation for less than 40 s is that LCs had been induced in the SiO2 and SRSO ®lms, and its eect on EL intensity surpasses the eect of generation of nonradiative centers. Acknowledgements This work was supported by the National Natural Science Foundation of China. References [1] A. Ritcher, P. Steiner, F. Kozlowski, W. Lang, IEEE Electron Device Lett. 12 (1991) 691. [2] N. Koshida, H. Koyama, Appl. Phys. Lett. 60 (1992) 347. [3] B. Gelloz, T. Nakagawa, N. Koshida, Appl. Phys. Lett. 73 (1998) 2021. [4] K.D. Hirschman, L. Tsybeskov, S.P. Duttagupta, P.M. Fauchet, Nature 384 (1996) 338. [5] J. Linnros, N. Lallic, Appl. Phys. Lett. 66 (1995) 3048. [6] S. Lazarouk, P. Jaguiro, S. Katsouba, G. Mashini, S. La Monica, G. Maiello, A. Ferrari, Appl. Phys. Lett. 68 (12) (1996) 1646. [7] G.G. Qin, Y.M. Huang, B.Q. Zong, L. Zhang, B.R. Zhang, Superlattices Microstruct. 16 (1994) 387. [8] G.F. Bai, Y.Q. Wang, Z.C. Ma, W.H. Zong, G.G. Qin, J. Phys.: Condens. Matter 10 (1998) L717. [9] Y.Q. Wang, T.P. Zhao, J. Liu, G.G. Qin, Appl. Phys. Lett. 74 (15) (1999) 3815.
G.Z. Ran et al. / Nucl. Instr. and Meth. in Phys. Res. B 173 (2001) 299±303 [10] J. Yuan, D. Haneman, J. Appl. Phys. 86 (4) (1999) 2358. [11] D.J. DiMaria, J.R. Kirtley, E.J. Pakulis, D.W. Dong, T.S. Kuan, F.L. Pesavento, T.N. Theis, J.A. Cutro, S.D. Brorson, J. Appl. Phys. 56 (1984) 401. [12] G.G. Qin, A.P. Li, B.R. Zhang, B.C. Li, J. Appl. Phys. 78 (1995) 2006. [13] G.G. Qin, A.P. Li, Y.X. Zhang, Phys. Rev. B 54 (16) (1996) R11122.
303
[14] S.Y. Ma, B.R. Zhang, G.G. Qin, Z.C. Ma, W.H. Zong, X.T. Meng, Mater. Res. Bull. 32 (7) (1997) 1427. [15] C.M. Gee, M. Kastner, in: G. Lucovsky, S.T. Pantelides, F.L. Galeener (Eds.), The Physics of MOS Insulators, Pergamon, New York, 1980, p. 132. [16] H. Nishikawa, E. Watanabe, D. Ito, Y. Sakurai, K. Nagasawa, Y. Ohki, J. Appl. Phys. 80 (1996) 3513. [17] Y. Sakurai, K. Nagasawa, J. Appl. Phys. 86 (3) (1999).