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Depth profiles of boron and hydrogen in boron-doped diamond films and related performance characteristics
Diamond and Related Materials 8 (1999) 1229–1233
Depth profiles of boron and hydrogen in boron-doped diamond films and related performance characteristics C. Liao a,1, Y. Wang b, *, S. Yang a a Department of Modern Physics, Lanzhou University, Lanzhou, Gansu Province, 730000, People’s Republic of China b Center for Interfacial Engineering, University of Minnesota, Minneapolis, MN 55455, USA Received 23 October 1998; accepted 23 January 1999
Abstract Depth profiles of boron and hydrogen in heavily, moderately, and lightly CVD boron-doped diamond films were determined by nuclear reaction analysis (NRA) and elastic recoil detection analysis (ERDA), respectively. The results indicate that the boron depth distribution in these films is uniform, whereas the hydrogen depth distribution shows a clear three-layer structure: the surface adsorption layer, the diffusion region, and the hydrogen-containing uniform matrix. The hydrogen content in the film increases with the boron-doping level, implying that the dangling bonds and CH bonds are accordingly increased in the films. Both the peak-to-base ratio near the Raman shift at 1332 cm−1 and the specific resistance of the films decreases with increasing boron-doping concentration. The effects of hydrogen profile and boron-doping concentration on these related performance characteristics are studied. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Boron-doped; Boron profile; Diamond film; Hydrogen profile
1. Introduction Chemical-vapor-deposited (CVD) diamond films are attracting interest due to the promising potential applications arising from their optical, electronic, thermal, and mechanical properties [1]. The advantages of diamond films, such as good thermal conductivity, wide bandgap, super hardness and infra-red transparency, offer a high potential for its use in high-temperature, high-frequency and high-power electronic devices. Thus, the production of good-quality semiconducting diamond films has become increasingly important. Boron is used to dope diamond and make it semiconductive because not only has it been extensively and successfully used to dope semiconductors, but it also has a high solubility in the diamond lattice and forms a substitutional acceptor level at about 0.37 eV, whereas other potential impurity dopants either have a low solubility or form a much deeper impurity level [2]. The performance characteristics of boron-doped diamond films have been studied by many research groups [3–9]. However, only a few papers measured the depth * Corresponding author. Fax: +1-612-626-7530. E-mail address: [email protected] ( Y. Wang) 1 Co-corresponding author.
profiles of boron in these films, mainly by the neutron depth profiling technique [10,11]. It is equally important that hydrogen plays a key role for preparing these films and thus affects the physical, electrical, and mechanical properties of the films. In other words, quantitative information on the concentration and depth distribution of hydrogen in the boron-doped diamond films is also required. As to our knowledge, the study on depth profiles of hydrogen in these films by ERDA has not yet been reported. In this paper, our investigation aims to determine the depth profiles of boron and hydrogen in boron-doped diamond films and to understand their effects on the performance characteristics of the films such as the Raman shift and specific resistance. Correlations among the boron-doping concentration, the hydrogen distribution, and the performance characteristics of the films are reported.
2. Methodology Boron-doped polycrystalline diamond films (PDFs) used in this study were grown on (100) silicon single crystal substrates by a hot filament CVD method [12]. A saturated solution of boron trioxide (B O ) powder 2 3 in methanol (CH OH ) was thinned with acetone 3
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C. Liao et al. / Diamond and Related Materials 8 (1999) 1229–1233
(C H CO), and the volatilized gas (reactant gas) from 2 6 this mixture, together with hydrogen gas (H ), was 2 introduced into the reactant chamber for synthesizing boron-doped-PDFs. The boron-doping concentration was controlled by the ratio of B/C in the reactant gas mixture. Scanning electron microscopy (SEM ) indicated that the films consist of grains roughly 2–5 mm in diameter, and the thickness of the films is approximately 10–15 mm. The PDF films used in this study were doped at different boron levels nominally: (1) heavily, (2) moderately, and (3) lightly doped. The boron depth profile was measured by a strong but broad nuclear resonance reaction 11B(p, a) 8Be at E = 660 keV with a convolup tion method to simulate the alpha spectra [13,14]. There is almost no background contribution to the a-spectra since no other higher Q value (p, a) reactions exist in the films. The analysis sensitivity is practically limited by the detector solid angle, the proton beam current, and the spectrum acquisition time. The analysis sensitivity for boron depth profile by this reaction in our experimental set-up is approximately 3 wt. ppm, which is necessary for detecting boron in our lightly borondoped film. The possible analysis depth in diamond films is approximately 3 mm. However, the depth resolution is relatively poor, ~600 nm at the diamond film, due to the very broad width of the nuclear reaction. A much better depth resolution (~50 nm) may be achieved using a narrow nuclear resonance reaction 11B(p, a)8Be at a lower energy of E =163 keV provided that p a significant reduction in both the maximum analysis depth (~400 nm) and the analysis sensitivity for boron depth profiling (~0.5 wt.%) is acceptable [13,14]. The hydrogen depth profiles in these films were measured by elastic recoil detection analysis ( ERDA) with a convolution method to simulate the recoil proton spectra induced by 3-MeV 4He ions [15,16 ]. It is difficult to determine the hydrogen background level because a natural hydrogen adsorption layer exists on practically all solid surfaces. However, if hydrogen in this adsorption layer is considered to be part of the analysis sample, the hydrogen measurement by ERDA is essentially background-free since the other heavier recoils and the scattering helium particles from the film matrix are completely filtered out by a ranger foil that is placed in front of the detector. Therefore, as in the boron analysis, the hydrogen analysis sensitivity by ERDA is also limited by the feasibility of the detector solid angle, the helium beam current, and/or the spectrum acquisition time. The analysis sensitivity of the ERDA in our configuration is approximately 0.1 at.%, sufficient for hydrogen depth profile measurements in these films. The possible analysis depth is about 1 mm in diamond films. Experimental determination of the hydrogen depth resolution by ERDA is very difficult. However, after the convolution calculation in our case [15,16 ], the surface
adsorption layer is clearly separated from the diffusion region. This implies that the surface depth resolution of the ERDA in our case is at least the thickness of the hydrogen adsorption layer, i.e. less than 50 nm. A small beam current (~3 nA) and a small amount of charge (<5 mC ) were used during each spectrum acquisition to ensure that the beam-induced hydrogen loss or hydrogen mobility is negligible.
3. Results and discussion Fig. 1 shows the measured (circles) and simulated (solid lines) a-spectra for (a) heavily, (b) moderately, and (c) lightly boron-doped PDFs. The corresponding boron depth profiles used to generate the simulated spectra in Fig. 1 are uniform within the depth detection limit (~3 mm) of the technique, as shown in Fig. 2. The corresponding boron-doping concentrations for different doping levels are approximately (a) 2.3×1020 at. cm−3, (b) 4.2×1018 at. cm−3, and (c) 4.4×1017 at. cm−3, respectively. These results conform with the speculation by previous research groups that the depth profiles of boron in p-type polycrystalline diamond films are uniform. Fig. 3 shows the measured (circles) and simulated (solid lines) proton spectra for (a) heavily, (b) moderately, and (c) lightly boron-doped PDFs. The corre-
Fig. 1. Measured (circles) and simulated (solid lines) a-spectra using NRA for (a) heavily, (b) moderately, and (c) lightly boron-doped polycrystalline diamond films.
C. Liao et al. / Diamond and Related Materials 8 (1999) 1229–1233
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Fig. 2. Boron depth profiles used to generate the simulated spectra in Fig. 1, indicating a uniform boron distribution.
Fig. 4. Hydrogen depth profiles used to generate the simulated spectra in Fig. 3, indicating a clear three-layer hydrogen structure.
Fig. 3. Measured (circles) and simulated (solid lines) proton spectra using ERDA for (a) heavily, (b) moderately, and (c) lightly borondoped polycrystalline diamond films.
sponding hydrogen depth profiles used to generate the simulated spectra in Fig. 3 are shown in Fig. 4. Fig. 4 indicates that the hydrogen depth profiles in these borondoped diamond films have a clear three-layer structure: the layer of surface adsorption, the diffusion region, and the hydrogen-containing matrix. It is also shown in
Fig. 4 that the hydrogen concentration, especially in the surface adsorption layer, increases with boron-doping concentration. To understand how the boron-doping concentration and hydrogen profile affect the performance of these diamond films, their Raman shift and specific resistance were determined. The Raman spectra obtained from these diamond films are shown in Fig. 5. A strong and sharp scattering peak observed near 1332 cm−1 in Fig. 5 suggests that these boron-doped diamond films still have a good quality of undoped CVD diamond films. However, the increase in fluorescence scattering background in the Raman spectra with the boron-doping concentration indicates the gradual degradation in diamond microstructure in these films. The ratio of the peak to base (P/B) near 1332 cm−1 decreases with increasing boron-doping concentration, as shown in Fig. 6(a). The specific resistance of these boron-doped films at room temperature is measured to be approximately: (a) 1×102 V · cm (heavily boron-doped); (b) 1×104 V · cm (moderately boron-doped ); and (c) 3×105 V · cm ( lightly boron-doped). The specific resistance (SR) and the hydrogen concentration of the surface adsorption
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C. Liao et al. / Diamond and Related Materials 8 (1999) 1229–1233
Fig. 5. Raman spectra from CVD diamond films doped with different boron concentrations: (a) 2.3×1020 at. cm−3; (b) 4.2×1018 at. cm−3; and (c) 4.4×1017 at. cm−3. The peak-to-base ratio at 1332 cm−1 is almost inversely proportional to the boron-doping concentration.
layer as a function of boron-doping concentration are shown in Fig. 6(b) and (c). Fig. 6 shows that the surface hydrogen concentration increases, while the specific resistance decreases with increasing the boron-doping concentration. The increase of hydrogen concentration as increasing the boron-doping concentration introduces more CH bonds and dangling bonds, which in turn decreases the peak-to-base ratio of the scattering peak near 1332 cm−1. The increase in boron-doping concentration introduces more electronic energy states between the wide energy gap of the diamond films, thus decreasing the specific resistance of the films.
4. Conclusion In summary, the boron and hydrogen depth profiles obtained by NRA and ERDA are valuable for the study
Fig. 6. Peak-to-base ratio (P/B) near 1332 cm−1, specific resistance (SR) and surface hydrogen concentration in boron-doped diamond films as a function of boron-doping concentration.
of boron-doped CVD diamond films. The depth profiles of boron in these diamond films are found to be reasonably uniform, which conforms to the speculated uniform boron distribution by previous researchers. The hydrogen depth profiles in these films show a clear threelayer structure: the hydrogen surface adsorption layer, the hydrogen diffusion region, and the hydrogen-containing film matrix. Whereas the hydrogen concentration is increased with increasing the boron-doping concentration, the specific resistance and the peak-to-base ratio of the Raman Shift at 1332 cm−1 are both decreased. For our heavily boron-doped diamond film, its specific resistance is reduced down to a level (102 cm · V) that is already suitable for semiconducting device fabrications, but the undesirable change in the microstructure of the film indicated by Raman spectra will affect the desirable physical and mechanical properties of the film. Further
C. Liao et al. / Diamond and Related Materials 8 (1999) 1229–1233
research is needed to find a compromising solution to the dilemma.
References [1] G.Sh. Gildenblat, S.A. Grot, A. Badzian, Proc. IEEE 79 (1991) 647 and references therein. [2] J.W. Glesener, Appl. Phys. Lett. 63 (1993) 767. [3] N. Fujimori, New Diamond 2 (1986) 10. [4] G.Sh. Gildenblat, S.A. Grot, C.R. Wronski, A.R. Bazian, T. Badzian, R. Messier, Appl. Phys. Lett. 53 (1988) 586. [5] L.S. Pan, D.R. Kania, P. Pianetta, O.N. Landen, Appl. Phys. Lett. 57 (1990) 623. [6 ] K. Nishmura, K. Das, J.T. Glass, J. Appl. Phys. 69 (1991) 3142. [7] K. Zhang, J.G. Guo, Y.F. Yao, R. Wang, G.M. Chen, W.K. Zhou, S. Yu, Appl. Phys. 56 (1993) 425.
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[8] M. Werner, O. Dorsch, H.U. Baerwind, E. Obermeier, L. Hase, W. Seifert, A. Ringhandt, C. Johnston, S. Romani, H. Bishop, P.R. Chalker, Appl. Phys. Lett. 64 (1994) 595. [9] R.J. Zhang, S.T. Lee, Y.W. Lam, Diamond Relat. Mater. 5 (1996) 1288. [10] G.P. Lamaze, R.G. Downing, L. Pilione, A. Badzian, T. Badzian, Appl. Surf. Sci. 65/66 (1993) 587. [11] G.P. Lamaze, R.G. Downing, Proc. Int. Workshop on Semiconductor Characterization: Present and Future Needs, AIP Press, Woodbury, NY, 1996, pp. 351–355. [12] F.Q. Zhang, N.P. Zhang, E.Q. Xie, B. Yang, Y.H. Yang, G.H. Chen, X.L. Jiang, Thin Solid Films 216 (1992) 279. [13] C.G. Liao, H. Jiang, Y.Q. Wang, Z.H. Zheng, Nucl. Instrum. Meth. B 95 (1995) 97. [14] C.G. Liao, Y.Q. Wang, S.S. Yang, Nucl. Instrum. Meth. A 422 (1999) 863. [15] Y.Q. Wang, C.G. Liao, S.S. Yang, Z.H. Zheng, Nucl. Instrum. Meth. B 47 (1990) 427. [16 ] C.G. Liao, Y.Q. Wang, S.S. Yang, X.M. Chen, Vacuum, submitted.
Depth profiles of boron and hydrogen in boron-doped diamond films and related performance characteristics C. Liao a,1, Y. Wang b, *, S. Yang a a Department of Modern Physics, Lanzhou University, Lanzhou, Gansu Province, 730000, People’s Republic of China b Center for Interfacial Engineering, University of Minnesota, Minneapolis, MN 55455, USA Received 23 October 1998; accepted 23 January 1999
Abstract Depth profiles of boron and hydrogen in heavily, moderately, and lightly CVD boron-doped diamond films were determined by nuclear reaction analysis (NRA) and elastic recoil detection analysis (ERDA), respectively. The results indicate that the boron depth distribution in these films is uniform, whereas the hydrogen depth distribution shows a clear three-layer structure: the surface adsorption layer, the diffusion region, and the hydrogen-containing uniform matrix. The hydrogen content in the film increases with the boron-doping level, implying that the dangling bonds and CH bonds are accordingly increased in the films. Both the peak-to-base ratio near the Raman shift at 1332 cm−1 and the specific resistance of the films decreases with increasing boron-doping concentration. The effects of hydrogen profile and boron-doping concentration on these related performance characteristics are studied. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Boron-doped; Boron profile; Diamond film; Hydrogen profile
1. Introduction Chemical-vapor-deposited (CVD) diamond films are attracting interest due to the promising potential applications arising from their optical, electronic, thermal, and mechanical properties [1]. The advantages of diamond films, such as good thermal conductivity, wide bandgap, super hardness and infra-red transparency, offer a high potential for its use in high-temperature, high-frequency and high-power electronic devices. Thus, the production of good-quality semiconducting diamond films has become increasingly important. Boron is used to dope diamond and make it semiconductive because not only has it been extensively and successfully used to dope semiconductors, but it also has a high solubility in the diamond lattice and forms a substitutional acceptor level at about 0.37 eV, whereas other potential impurity dopants either have a low solubility or form a much deeper impurity level [2]. The performance characteristics of boron-doped diamond films have been studied by many research groups [3–9]. However, only a few papers measured the depth * Corresponding author. Fax: +1-612-626-7530. E-mail address: [email protected] ( Y. Wang) 1 Co-corresponding author.
profiles of boron in these films, mainly by the neutron depth profiling technique [10,11]. It is equally important that hydrogen plays a key role for preparing these films and thus affects the physical, electrical, and mechanical properties of the films. In other words, quantitative information on the concentration and depth distribution of hydrogen in the boron-doped diamond films is also required. As to our knowledge, the study on depth profiles of hydrogen in these films by ERDA has not yet been reported. In this paper, our investigation aims to determine the depth profiles of boron and hydrogen in boron-doped diamond films and to understand their effects on the performance characteristics of the films such as the Raman shift and specific resistance. Correlations among the boron-doping concentration, the hydrogen distribution, and the performance characteristics of the films are reported.
2. Methodology Boron-doped polycrystalline diamond films (PDFs) used in this study were grown on (100) silicon single crystal substrates by a hot filament CVD method [12]. A saturated solution of boron trioxide (B O ) powder 2 3 in methanol (CH OH ) was thinned with acetone 3
0925-9635/99/$ – see front matter © 1999 Elsevier Science S.A. All rights reserved. PII: S0 9 2 5- 9 6 3 5 ( 9 9 ) 0 0 12 7 - 2
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C. Liao et al. / Diamond and Related Materials 8 (1999) 1229–1233
(C H CO), and the volatilized gas (reactant gas) from 2 6 this mixture, together with hydrogen gas (H ), was 2 introduced into the reactant chamber for synthesizing boron-doped-PDFs. The boron-doping concentration was controlled by the ratio of B/C in the reactant gas mixture. Scanning electron microscopy (SEM ) indicated that the films consist of grains roughly 2–5 mm in diameter, and the thickness of the films is approximately 10–15 mm. The PDF films used in this study were doped at different boron levels nominally: (1) heavily, (2) moderately, and (3) lightly doped. The boron depth profile was measured by a strong but broad nuclear resonance reaction 11B(p, a) 8Be at E = 660 keV with a convolup tion method to simulate the alpha spectra [13,14]. There is almost no background contribution to the a-spectra since no other higher Q value (p, a) reactions exist in the films. The analysis sensitivity is practically limited by the detector solid angle, the proton beam current, and the spectrum acquisition time. The analysis sensitivity for boron depth profile by this reaction in our experimental set-up is approximately 3 wt. ppm, which is necessary for detecting boron in our lightly borondoped film. The possible analysis depth in diamond films is approximately 3 mm. However, the depth resolution is relatively poor, ~600 nm at the diamond film, due to the very broad width of the nuclear reaction. A much better depth resolution (~50 nm) may be achieved using a narrow nuclear resonance reaction 11B(p, a)8Be at a lower energy of E =163 keV provided that p a significant reduction in both the maximum analysis depth (~400 nm) and the analysis sensitivity for boron depth profiling (~0.5 wt.%) is acceptable [13,14]. The hydrogen depth profiles in these films were measured by elastic recoil detection analysis ( ERDA) with a convolution method to simulate the recoil proton spectra induced by 3-MeV 4He ions [15,16 ]. It is difficult to determine the hydrogen background level because a natural hydrogen adsorption layer exists on practically all solid surfaces. However, if hydrogen in this adsorption layer is considered to be part of the analysis sample, the hydrogen measurement by ERDA is essentially background-free since the other heavier recoils and the scattering helium particles from the film matrix are completely filtered out by a ranger foil that is placed in front of the detector. Therefore, as in the boron analysis, the hydrogen analysis sensitivity by ERDA is also limited by the feasibility of the detector solid angle, the helium beam current, and/or the spectrum acquisition time. The analysis sensitivity of the ERDA in our configuration is approximately 0.1 at.%, sufficient for hydrogen depth profile measurements in these films. The possible analysis depth is about 1 mm in diamond films. Experimental determination of the hydrogen depth resolution by ERDA is very difficult. However, after the convolution calculation in our case [15,16 ], the surface
adsorption layer is clearly separated from the diffusion region. This implies that the surface depth resolution of the ERDA in our case is at least the thickness of the hydrogen adsorption layer, i.e. less than 50 nm. A small beam current (~3 nA) and a small amount of charge (<5 mC ) were used during each spectrum acquisition to ensure that the beam-induced hydrogen loss or hydrogen mobility is negligible.
3. Results and discussion Fig. 1 shows the measured (circles) and simulated (solid lines) a-spectra for (a) heavily, (b) moderately, and (c) lightly boron-doped PDFs. The corresponding boron depth profiles used to generate the simulated spectra in Fig. 1 are uniform within the depth detection limit (~3 mm) of the technique, as shown in Fig. 2. The corresponding boron-doping concentrations for different doping levels are approximately (a) 2.3×1020 at. cm−3, (b) 4.2×1018 at. cm−3, and (c) 4.4×1017 at. cm−3, respectively. These results conform with the speculation by previous research groups that the depth profiles of boron in p-type polycrystalline diamond films are uniform. Fig. 3 shows the measured (circles) and simulated (solid lines) proton spectra for (a) heavily, (b) moderately, and (c) lightly boron-doped PDFs. The corre-
Fig. 1. Measured (circles) and simulated (solid lines) a-spectra using NRA for (a) heavily, (b) moderately, and (c) lightly boron-doped polycrystalline diamond films.
C. Liao et al. / Diamond and Related Materials 8 (1999) 1229–1233
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Fig. 2. Boron depth profiles used to generate the simulated spectra in Fig. 1, indicating a uniform boron distribution.
Fig. 4. Hydrogen depth profiles used to generate the simulated spectra in Fig. 3, indicating a clear three-layer hydrogen structure.
Fig. 3. Measured (circles) and simulated (solid lines) proton spectra using ERDA for (a) heavily, (b) moderately, and (c) lightly borondoped polycrystalline diamond films.
sponding hydrogen depth profiles used to generate the simulated spectra in Fig. 3 are shown in Fig. 4. Fig. 4 indicates that the hydrogen depth profiles in these borondoped diamond films have a clear three-layer structure: the layer of surface adsorption, the diffusion region, and the hydrogen-containing matrix. It is also shown in
Fig. 4 that the hydrogen concentration, especially in the surface adsorption layer, increases with boron-doping concentration. To understand how the boron-doping concentration and hydrogen profile affect the performance of these diamond films, their Raman shift and specific resistance were determined. The Raman spectra obtained from these diamond films are shown in Fig. 5. A strong and sharp scattering peak observed near 1332 cm−1 in Fig. 5 suggests that these boron-doped diamond films still have a good quality of undoped CVD diamond films. However, the increase in fluorescence scattering background in the Raman spectra with the boron-doping concentration indicates the gradual degradation in diamond microstructure in these films. The ratio of the peak to base (P/B) near 1332 cm−1 decreases with increasing boron-doping concentration, as shown in Fig. 6(a). The specific resistance of these boron-doped films at room temperature is measured to be approximately: (a) 1×102 V · cm (heavily boron-doped); (b) 1×104 V · cm (moderately boron-doped ); and (c) 3×105 V · cm ( lightly boron-doped). The specific resistance (SR) and the hydrogen concentration of the surface adsorption
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C. Liao et al. / Diamond and Related Materials 8 (1999) 1229–1233
Fig. 5. Raman spectra from CVD diamond films doped with different boron concentrations: (a) 2.3×1020 at. cm−3; (b) 4.2×1018 at. cm−3; and (c) 4.4×1017 at. cm−3. The peak-to-base ratio at 1332 cm−1 is almost inversely proportional to the boron-doping concentration.
layer as a function of boron-doping concentration are shown in Fig. 6(b) and (c). Fig. 6 shows that the surface hydrogen concentration increases, while the specific resistance decreases with increasing the boron-doping concentration. The increase of hydrogen concentration as increasing the boron-doping concentration introduces more CH bonds and dangling bonds, which in turn decreases the peak-to-base ratio of the scattering peak near 1332 cm−1. The increase in boron-doping concentration introduces more electronic energy states between the wide energy gap of the diamond films, thus decreasing the specific resistance of the films.
4. Conclusion In summary, the boron and hydrogen depth profiles obtained by NRA and ERDA are valuable for the study
Fig. 6. Peak-to-base ratio (P/B) near 1332 cm−1, specific resistance (SR) and surface hydrogen concentration in boron-doped diamond films as a function of boron-doping concentration.
of boron-doped CVD diamond films. The depth profiles of boron in these diamond films are found to be reasonably uniform, which conforms to the speculated uniform boron distribution by previous researchers. The hydrogen depth profiles in these films show a clear threelayer structure: the hydrogen surface adsorption layer, the hydrogen diffusion region, and the hydrogen-containing film matrix. Whereas the hydrogen concentration is increased with increasing the boron-doping concentration, the specific resistance and the peak-to-base ratio of the Raman Shift at 1332 cm−1 are both decreased. For our heavily boron-doped diamond film, its specific resistance is reduced down to a level (102 cm · V) that is already suitable for semiconducting device fabrications, but the undesirable change in the microstructure of the film indicated by Raman spectra will affect the desirable physical and mechanical properties of the film. Further
C. Liao et al. / Diamond and Related Materials 8 (1999) 1229–1233
research is needed to find a compromising solution to the dilemma.
References [1] G.Sh. Gildenblat, S.A. Grot, A. Badzian, Proc. IEEE 79 (1991) 647 and references therein. [2] J.W. Glesener, Appl. Phys. Lett. 63 (1993) 767. [3] N. Fujimori, New Diamond 2 (1986) 10. [4] G.Sh. Gildenblat, S.A. Grot, C.R. Wronski, A.R. Bazian, T. Badzian, R. Messier, Appl. Phys. Lett. 53 (1988) 586. [5] L.S. Pan, D.R. Kania, P. Pianetta, O.N. Landen, Appl. Phys. Lett. 57 (1990) 623. [6 ] K. Nishmura, K. Das, J.T. Glass, J. Appl. Phys. 69 (1991) 3142. [7] K. Zhang, J.G. Guo, Y.F. Yao, R. Wang, G.M. Chen, W.K. Zhou, S. Yu, Appl. Phys. 56 (1993) 425.
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[8] M. Werner, O. Dorsch, H.U. Baerwind, E. Obermeier, L. Hase, W. Seifert, A. Ringhandt, C. Johnston, S. Romani, H. Bishop, P.R. Chalker, Appl. Phys. Lett. 64 (1994) 595. [9] R.J. Zhang, S.T. Lee, Y.W. Lam, Diamond Relat. Mater. 5 (1996) 1288. [10] G.P. Lamaze, R.G. Downing, L. Pilione, A. Badzian, T. Badzian, Appl. Surf. Sci. 65/66 (1993) 587. [11] G.P. Lamaze, R.G. Downing, Proc. Int. Workshop on Semiconductor Characterization: Present and Future Needs, AIP Press, Woodbury, NY, 1996, pp. 351–355. [12] F.Q. Zhang, N.P. Zhang, E.Q. Xie, B. Yang, Y.H. Yang, G.H. Chen, X.L. Jiang, Thin Solid Films 216 (1992) 279. [13] C.G. Liao, H. Jiang, Y.Q. Wang, Z.H. Zheng, Nucl. Instrum. Meth. B 95 (1995) 97. [14] C.G. Liao, Y.Q. Wang, S.S. Yang, Nucl. Instrum. Meth. A 422 (1999) 863. [15] Y.Q. Wang, C.G. Liao, S.S. Yang, Z.H. Zheng, Nucl. Instrum. Meth. B 47 (1990) 427. [16 ] C.G. Liao, Y.Q. Wang, S.S. Yang, X.M. Chen, Vacuum, submitted.