- Email: [email protected]
Effect of high pressure annealing on electrical properties of nitrogen and germanium doped silicon
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 253 (2006) 214–216 www.elsevier.com/locate/nimb
Effect of high pressure annealing on electrical properties of nitrogen and germanium doped silicon W. Jung a
a,*
, A. Misiuk a, D. Yang
b
Institute of Electron Technology, Al. Lotniko´w 32/46, 02-668 Warsaw, Poland b Zhejiang University, Hangzhou 310027, PR China Available online 7 November 2006
Abstract The effect of annealing at 720–920 K under enhanced pressure (up to 1.4 GPa) in argon ambient on electrical properties of the surface layer of the Czochralski and Float zone grown nitrogen doped silicon (doping level 1 · 1014–5 · 1015 cm 3) and Czochralski grown germanium doped silicon (doping level 7 · 1017 cm 3) was investigated by electrical C–V, I–V and admittance methods. The decrease in electron concentration was observed in nitrogen doped Czochralski grown silicon annealed under normal pressure at 720 K. The stress induced increase in electron concentration was observed in nitrogen doped Czochralski grown silicon independently on nitrogen doping level in the range 1 · 1014–5 · 1014 cm 3. No dependence of electron concentration on hydrostatic pressure was observed in nitrogen doped Float zone silicon even for high doping level of 5 · 1015 cm 3. Germanium doped silicon indicated the strongly enhanced creation of thermal donors if processed at 1.1 GPa. The observed effects can be explained as a result of the oxygen–nitrogen complexes in nitrogen doped silicon and the pressure stimulated creation of thermal donors both in nitrogen and germanium doped silicon. 2006 Elsevier B.V. All rights reserved. PACS: 61.72.Tt Keywords: Nitrogen doped silicon; Germanium doped silicon; High pressure annealing
1. Introduction Nitrogen or germanium doped silicon is now considered for the next generation of high performance electronic devices [1]. Nitrogen in silicon can stimulate oxygen precipitation to improve internal gettering, while germanium doped silicon indicates enhanced carrier mobility; its band gap can be tuned within 0.8–1.12 eV. SiGe single crystals are used in photodetectors, solar cells and other electronic and photonic devices. During single crystal growing by Czochralski method a large number of oxygen and carbon atoms are incorporated into the crystal due to chemical reaction between melt and quartz crucible. It is well known that oxygen related centres are responsible for the formation of thermal donors. It is also known that germanium *
Corresponding author. Tel.: +48 22 548 7784; fax: +48 22 847 0631. E-mail address: [email protected] (W. Jung).
0168-583X/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.10.056
doping induce silicon lattice extension, so annealing under compressive stress should change the surface layer properties. This paper presents our investigation of the electrical properties of surface layer of nitrogen and germanium doped Czochralski grown silicon subjected to high pressure annealing. 2. Experimental Nitrogen and germanium doped silicon was used as initial crystal. Phosphorus doped n-type Czochralski grown silicon (Cz–Si) wafers, <1 1 1> oriented with resistivity of about 28 X cm and 0.5 X cm were additionally doped with nitrogen (doping level in the range 1–2 · 1014 cm 3) and denoted as CzSi:N. Phosphorus doped n-type Float zone silicon (Fz–Si) wafers, <1 0 0> oriented with resistivity of about 43 X cm were additionally doped with nitrogen (doping level in the range 5 · 1014–5 · 1015 cm 3) and denoted
W. Jung et al. / Nucl. Instr. and Meth. in Phys. Res. B 253 (2006) 214–216
3. Experimental results and discussion The admittance measurements of nitrogen and germanium doped samples have not shown any peaks on all loss tangent plots so only shallow state are present in the investigated samples. That means that annealing under even high hydrostatic pressure do not introduce deep levels. Greater values of loss tangent observed for samples subjected to highest hydrostatic pressure may result from structural defects formed due to oxygen precipitation [4]. Carrier concentrations calculated from C–V measurements of Hg–Si Schottky junction for nitrogen doped Cz–Si subjected to different temperature–pressure conditions are presented in Figs. 1 and 2 for lower and higher initial doping, respectively. Some results for Cz–Si without nitrogen doping are also shown in Fig. 1 for comparison. It is evident from the Figs. 1 and 2, that the annealing under hydrostatic pressure enhances the thermal donors creation and the thermal donor generation does not depend on nitrogen doping. The influence of nitrogen doping on thermal donor suppression can be seen only for annealing under normal pressure and is caused by formation of nitrogen–oxygen complexes [5]. Thermal donors generation saturates at the pressure of about 1 GPa in the case of higher initial doping as presented in Fig. 2. This saturation may be caused by faster oxygen precipitation and decreased nuclei formation
16
Electron concentration [cm-3]
10
15
10
As grown CzSi Nitrogen doped as grown CzSi CzSi annealed at 720 K, 10 h Nitrogen doped CzSi annealed at 720 K, 10 h
14
10
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Hydrostatic pressure [GPa] Fig. 1. Electron concentration in the nitrogen doped Cz–Si with resistivity 28 X cm as a function of hydrostatic pressure.
18
10
Electron concentration [cm-3]
as FzSi:N. Boron doped p-type Cz–Si wafers, <1 0 0> oriented with resistivity of about 80 X cm and phosphorus doped n-type Cz–Si wafers, <1 1 1> oriented with resistivity of about 8 X cm were additionally doped with germanium (doping level about 7 · 1017 cm 3) and denoted as CzSip:Ge and CzSin:Ge. The initial oxygen concentration was determined by Fourier transform infrared spectroscopy (FTIR) from the absorption band at 1107 cm 1 with a calibration factor of 3.14 · 1017 atom/cm 3 and the oxygen concentration was about 8 · 1017 cm 3, <1 · 1016 cm 3 and 6.5 · 1017 cm 3 for CzSi:N, FzSi:N and germanium doped samples, respectively. Nitrogen doped samples CzSi:N and FzSi:N were annealed at temperature of 720 K in argon ambient for 10 h for several different pressure values up to 1.45 GPa. P-type germanium doped samples, CzSip:Ge were annealed at temperature of 720 K and 920 K in argon ambient for 10 h for several different pressure values up to 1 GPa and the n-type germanium doped samples CzSin:Ge were subjected to annealing at the temperature range 620–1000 K under hydrostatic pressure of 1.1 GPa. The prepared samples were studied by electrical measurements of C–V, I–V and admittance characteristics of Schottky barrier junction. Hg–Si (mercury probe, nondestructive testing). The admittance characteristics were performed in the frequency range of 100 Hz–2 MHz. Carrier concentration near the interface silicon – Schottky barrier, has been determined from 1/C2(V) plot, while the concentration profiles has been obtained by numerical analysis of C–V characteristics of Schottky barrier Hg–Si [2,3].
215
17
10
As grown CzSi Nitrogen doped CzSi annealed at 720 K, 10 h 16
10
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Hydrostatic pressure [GPa] Fig. 2. Electron concentration in the nitrogen doped Cz–Si with resistivity 0.5 X cm versus hydrostatic pressure.
for thermal donors generation. The annealing of nitrogen doped Float zone samples (nitrogen doping level 5 · 1014–5 · 1015 cm 3) at 720 K under hydrostatic pressure up to 1.1 GPa does not generate any thermal donors and confirms, that thermal donors generation depends only on oxygen concentration. There are two kinds of explanation of this phenomena in literature. One of them says that an effect of HP can be explained as an activation of structural inhomogeneities creating nuclei for thermal donors formation and preventing them from dissolution with rising temperature [6]. The other one points out that the enhanced formation of thermal donors under high pressure is due to increasing diffusivity of oxygen atoms [7]. Carrier concentrations calculated from C–V measurements of Hg– Si Schottky junction for germanium doped Cz–Si subjected to different temperature–pressure conditions are presented
216
W. Jung et al. / Nucl. Instr. and Meth. in Phys. Res. B 253 (2006) 214–216
observed (see Fig. 3) but no hydrostatic pressure dependence is noticed, contrarily to standard Cz–Si in which small dependence of new donors generation on hydrostatic pressure is reported [9]. Temperature dependence of thermal and new donors creation in germanium doped silicon annealed under hydrostatic pressure of 1.1 GPa for 10 h is presented in Fig. 4. Enhanced thermal donors generation starts at 670 K and reaches the maximum at temperatures 720–745 K. At temperatures above 770 K thermal donors are get annihilated, and at temperatures above 870 K new donors are formed but with much lower concentration.
15
Carrier concentration [cm-3]
10
14
4x10
Germanium doped Si As grown, p type 720 K, 10 h, n type 920 K, 10 h, n type
4. Conclusions
14
10
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Hydrostatic pressure [GPa] Fig. 3. Electron concentration in the germanium doped Cz–Si, sample CzSip:Ge versus hydrostatic pressure.
Electron concentration [cm-3]
3x1015
1015
High pressure annealing of nitrogen doped Cz–Si at 720 K results in enhanced formation of thermal donors and the thermal donor generation does not depend on nitrogen doping, but is caused by increased diffusivity of oxygen atoms or high pressure stimulated embryos for thermal donors creation. The effect of hydrostatic pressure on thermal donors creation in germanium doped samples is similar to nitrogen doped samples. Concentration of thermal donors depends on oxygen concentration in standard and both nitrogen and germanium doped silicon. Acknowledgement
4x1014
Germanium doped Si 1.1 GPa, 10 h
This work was supported in part by the Grant No. 3 T11B 052 27 of the Polish State Committee for Scientific Research. References
1014 600 650 700 750 800 850 900 950 1000
Temperature [K] Fig. 4. Electron concentration in the germanium doped Cz–Si, sample CzSin:Ge versus annealing temperature under hydrostatic pressure of 1.1 GPa.
in Fig. 3, sample CzSip:Ge and Fig. 4, sample CzSin:Ge. The effect of hydrostatic pressure on thermal donors creation in germanium doped samples is similar to nitrogen doped samples, but to lesser extent due to lower oxygen concentration. Cz–Si annealing at 920 K results in generation of new donors (ND) and annihilation of thermal donors [8]. In the case of germanium-doped Cz–Si generation of new donors at temperature of 920 K is also
[1] D. Yang, Phys. Stat. Sol. (a) 202 (2005) 931. [2] W. Jung, K. Klima, Prace ITE 9 (1982) 12. [3] J. Kiszkurno, W. Jung, Proceedings of the 6th Symposium of Microcomputer and Microprocessor Application (1989) 25. [4] Y.X. Li, H.Y. Guo, B.D. Liu, T.J. Liu, Q.Y. Hao, C.C. Liu, D.R. Yang, D.L. Que, J. Cryst. Growth 253 (2003) 6. [5] A. Misiuk, B. Surma, Deren Yang, A. Shalimov, J. Phys.: Condens. Mater. 16 (2004) 473. [6] A. Misiuk, W. Jung, B. Surma, J. Jun, M. Rozental, Solid State Phen. 57–58 (1997) 393. [7] V.V. Emtsev, B.A. Andreev, V.Yu. Davydov, D.S. Poloskin, G.A. Oganesyan, D.I. Kryzhkov, V.B. Shmagin, V.V. Emtsev Jr., A. Misiuk, C.A. Londos, Physica B 340–342 (2003) 769. [8] Xu Jin, Deren Yang, Duanlin Que, A. Misiuk, Physica B 339 (2003) 204. [9] V.V. Emtsev, B.A. Andreev, A. Misiuk, W. Jung, K. Schmalz, Appl. Phys. Lett. 71 (1997) 264.
Nuclear Instruments and Methods in Physics Research B 253 (2006) 214–216 www.elsevier.com/locate/nimb
Effect of high pressure annealing on electrical properties of nitrogen and germanium doped silicon W. Jung a
a,*
, A. Misiuk a, D. Yang
b
Institute of Electron Technology, Al. Lotniko´w 32/46, 02-668 Warsaw, Poland b Zhejiang University, Hangzhou 310027, PR China Available online 7 November 2006
Abstract The effect of annealing at 720–920 K under enhanced pressure (up to 1.4 GPa) in argon ambient on electrical properties of the surface layer of the Czochralski and Float zone grown nitrogen doped silicon (doping level 1 · 1014–5 · 1015 cm 3) and Czochralski grown germanium doped silicon (doping level 7 · 1017 cm 3) was investigated by electrical C–V, I–V and admittance methods. The decrease in electron concentration was observed in nitrogen doped Czochralski grown silicon annealed under normal pressure at 720 K. The stress induced increase in electron concentration was observed in nitrogen doped Czochralski grown silicon independently on nitrogen doping level in the range 1 · 1014–5 · 1014 cm 3. No dependence of electron concentration on hydrostatic pressure was observed in nitrogen doped Float zone silicon even for high doping level of 5 · 1015 cm 3. Germanium doped silicon indicated the strongly enhanced creation of thermal donors if processed at 1.1 GPa. The observed effects can be explained as a result of the oxygen–nitrogen complexes in nitrogen doped silicon and the pressure stimulated creation of thermal donors both in nitrogen and germanium doped silicon. 2006 Elsevier B.V. All rights reserved. PACS: 61.72.Tt Keywords: Nitrogen doped silicon; Germanium doped silicon; High pressure annealing
1. Introduction Nitrogen or germanium doped silicon is now considered for the next generation of high performance electronic devices [1]. Nitrogen in silicon can stimulate oxygen precipitation to improve internal gettering, while germanium doped silicon indicates enhanced carrier mobility; its band gap can be tuned within 0.8–1.12 eV. SiGe single crystals are used in photodetectors, solar cells and other electronic and photonic devices. During single crystal growing by Czochralski method a large number of oxygen and carbon atoms are incorporated into the crystal due to chemical reaction between melt and quartz crucible. It is well known that oxygen related centres are responsible for the formation of thermal donors. It is also known that germanium *
Corresponding author. Tel.: +48 22 548 7784; fax: +48 22 847 0631. E-mail address: [email protected] (W. Jung).
0168-583X/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.10.056
doping induce silicon lattice extension, so annealing under compressive stress should change the surface layer properties. This paper presents our investigation of the electrical properties of surface layer of nitrogen and germanium doped Czochralski grown silicon subjected to high pressure annealing. 2. Experimental Nitrogen and germanium doped silicon was used as initial crystal. Phosphorus doped n-type Czochralski grown silicon (Cz–Si) wafers, <1 1 1> oriented with resistivity of about 28 X cm and 0.5 X cm were additionally doped with nitrogen (doping level in the range 1–2 · 1014 cm 3) and denoted as CzSi:N. Phosphorus doped n-type Float zone silicon (Fz–Si) wafers, <1 0 0> oriented with resistivity of about 43 X cm were additionally doped with nitrogen (doping level in the range 5 · 1014–5 · 1015 cm 3) and denoted
W. Jung et al. / Nucl. Instr. and Meth. in Phys. Res. B 253 (2006) 214–216
3. Experimental results and discussion The admittance measurements of nitrogen and germanium doped samples have not shown any peaks on all loss tangent plots so only shallow state are present in the investigated samples. That means that annealing under even high hydrostatic pressure do not introduce deep levels. Greater values of loss tangent observed for samples subjected to highest hydrostatic pressure may result from structural defects formed due to oxygen precipitation [4]. Carrier concentrations calculated from C–V measurements of Hg–Si Schottky junction for nitrogen doped Cz–Si subjected to different temperature–pressure conditions are presented in Figs. 1 and 2 for lower and higher initial doping, respectively. Some results for Cz–Si without nitrogen doping are also shown in Fig. 1 for comparison. It is evident from the Figs. 1 and 2, that the annealing under hydrostatic pressure enhances the thermal donors creation and the thermal donor generation does not depend on nitrogen doping. The influence of nitrogen doping on thermal donor suppression can be seen only for annealing under normal pressure and is caused by formation of nitrogen–oxygen complexes [5]. Thermal donors generation saturates at the pressure of about 1 GPa in the case of higher initial doping as presented in Fig. 2. This saturation may be caused by faster oxygen precipitation and decreased nuclei formation
16
Electron concentration [cm-3]
10
15
10
As grown CzSi Nitrogen doped as grown CzSi CzSi annealed at 720 K, 10 h Nitrogen doped CzSi annealed at 720 K, 10 h
14
10
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Hydrostatic pressure [GPa] Fig. 1. Electron concentration in the nitrogen doped Cz–Si with resistivity 28 X cm as a function of hydrostatic pressure.
18
10
Electron concentration [cm-3]
as FzSi:N. Boron doped p-type Cz–Si wafers, <1 0 0> oriented with resistivity of about 80 X cm and phosphorus doped n-type Cz–Si wafers, <1 1 1> oriented with resistivity of about 8 X cm were additionally doped with germanium (doping level about 7 · 1017 cm 3) and denoted as CzSip:Ge and CzSin:Ge. The initial oxygen concentration was determined by Fourier transform infrared spectroscopy (FTIR) from the absorption band at 1107 cm 1 with a calibration factor of 3.14 · 1017 atom/cm 3 and the oxygen concentration was about 8 · 1017 cm 3, <1 · 1016 cm 3 and 6.5 · 1017 cm 3 for CzSi:N, FzSi:N and germanium doped samples, respectively. Nitrogen doped samples CzSi:N and FzSi:N were annealed at temperature of 720 K in argon ambient for 10 h for several different pressure values up to 1.45 GPa. P-type germanium doped samples, CzSip:Ge were annealed at temperature of 720 K and 920 K in argon ambient for 10 h for several different pressure values up to 1 GPa and the n-type germanium doped samples CzSin:Ge were subjected to annealing at the temperature range 620–1000 K under hydrostatic pressure of 1.1 GPa. The prepared samples were studied by electrical measurements of C–V, I–V and admittance characteristics of Schottky barrier junction. Hg–Si (mercury probe, nondestructive testing). The admittance characteristics were performed in the frequency range of 100 Hz–2 MHz. Carrier concentration near the interface silicon – Schottky barrier, has been determined from 1/C2(V) plot, while the concentration profiles has been obtained by numerical analysis of C–V characteristics of Schottky barrier Hg–Si [2,3].
215
17
10
As grown CzSi Nitrogen doped CzSi annealed at 720 K, 10 h 16
10
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Hydrostatic pressure [GPa] Fig. 2. Electron concentration in the nitrogen doped Cz–Si with resistivity 0.5 X cm versus hydrostatic pressure.
for thermal donors generation. The annealing of nitrogen doped Float zone samples (nitrogen doping level 5 · 1014–5 · 1015 cm 3) at 720 K under hydrostatic pressure up to 1.1 GPa does not generate any thermal donors and confirms, that thermal donors generation depends only on oxygen concentration. There are two kinds of explanation of this phenomena in literature. One of them says that an effect of HP can be explained as an activation of structural inhomogeneities creating nuclei for thermal donors formation and preventing them from dissolution with rising temperature [6]. The other one points out that the enhanced formation of thermal donors under high pressure is due to increasing diffusivity of oxygen atoms [7]. Carrier concentrations calculated from C–V measurements of Hg– Si Schottky junction for germanium doped Cz–Si subjected to different temperature–pressure conditions are presented
216
W. Jung et al. / Nucl. Instr. and Meth. in Phys. Res. B 253 (2006) 214–216
observed (see Fig. 3) but no hydrostatic pressure dependence is noticed, contrarily to standard Cz–Si in which small dependence of new donors generation on hydrostatic pressure is reported [9]. Temperature dependence of thermal and new donors creation in germanium doped silicon annealed under hydrostatic pressure of 1.1 GPa for 10 h is presented in Fig. 4. Enhanced thermal donors generation starts at 670 K and reaches the maximum at temperatures 720–745 K. At temperatures above 770 K thermal donors are get annihilated, and at temperatures above 870 K new donors are formed but with much lower concentration.
15
Carrier concentration [cm-3]
10
14
4x10
Germanium doped Si As grown, p type 720 K, 10 h, n type 920 K, 10 h, n type
4. Conclusions
14
10
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Hydrostatic pressure [GPa] Fig. 3. Electron concentration in the germanium doped Cz–Si, sample CzSip:Ge versus hydrostatic pressure.
Electron concentration [cm-3]
3x1015
1015
High pressure annealing of nitrogen doped Cz–Si at 720 K results in enhanced formation of thermal donors and the thermal donor generation does not depend on nitrogen doping, but is caused by increased diffusivity of oxygen atoms or high pressure stimulated embryos for thermal donors creation. The effect of hydrostatic pressure on thermal donors creation in germanium doped samples is similar to nitrogen doped samples. Concentration of thermal donors depends on oxygen concentration in standard and both nitrogen and germanium doped silicon. Acknowledgement
4x1014
Germanium doped Si 1.1 GPa, 10 h
This work was supported in part by the Grant No. 3 T11B 052 27 of the Polish State Committee for Scientific Research. References
1014 600 650 700 750 800 850 900 950 1000
Temperature [K] Fig. 4. Electron concentration in the germanium doped Cz–Si, sample CzSin:Ge versus annealing temperature under hydrostatic pressure of 1.1 GPa.
in Fig. 3, sample CzSip:Ge and Fig. 4, sample CzSin:Ge. The effect of hydrostatic pressure on thermal donors creation in germanium doped samples is similar to nitrogen doped samples, but to lesser extent due to lower oxygen concentration. Cz–Si annealing at 920 K results in generation of new donors (ND) and annihilation of thermal donors [8]. In the case of germanium-doped Cz–Si generation of new donors at temperature of 920 K is also
[1] D. Yang, Phys. Stat. Sol. (a) 202 (2005) 931. [2] W. Jung, K. Klima, Prace ITE 9 (1982) 12. [3] J. Kiszkurno, W. Jung, Proceedings of the 6th Symposium of Microcomputer and Microprocessor Application (1989) 25. [4] Y.X. Li, H.Y. Guo, B.D. Liu, T.J. Liu, Q.Y. Hao, C.C. Liu, D.R. Yang, D.L. Que, J. Cryst. Growth 253 (2003) 6. [5] A. Misiuk, B. Surma, Deren Yang, A. Shalimov, J. Phys.: Condens. Mater. 16 (2004) 473. [6] A. Misiuk, W. Jung, B. Surma, J. Jun, M. Rozental, Solid State Phen. 57–58 (1997) 393. [7] V.V. Emtsev, B.A. Andreev, V.Yu. Davydov, D.S. Poloskin, G.A. Oganesyan, D.I. Kryzhkov, V.B. Shmagin, V.V. Emtsev Jr., A. Misiuk, C.A. Londos, Physica B 340–342 (2003) 769. [8] Xu Jin, Deren Yang, Duanlin Que, A. Misiuk, Physica B 339 (2003) 204. [9] V.V. Emtsev, B.A. Andreev, A. Misiuk, W. Jung, K. Schmalz, Appl. Phys. Lett. 71 (1997) 264.