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Deep level properties of erbium implanted epitaxially grown SiGe
Nuclear Instruments and Methods in Physics Research B 148 (1999) 523±527
Deep level properties of erbium implanted epitaxially grown SiGe M. Mamor a, F.D. Auret a,*, S.A. Goodman a, J. Brink a, M. Hayes a, F. Meyer b, A. Vantomme c, G. Langouche c, P.N.K. Deenapanray d b
a Physics Department, University of Pretoria, Pretoria 0002, South Africa Institut dÕElectronique Fondamentale, CNRS URA 22, Bat 220, Universit e Paris Sud, 91405 Orsay cedex, France c Physics Department, Catholic University of Leuven, Belgium d Department of Electronic Materials Engineering, Australian National University, Canberra, Australia
Abstract We have used deep-level transient spectroscopy (DLTS) in an investigation of the electronic properties of defects introduced in n-Si0:96 Ge0:04 during 180 keV erbium ion implantation (¯uence 1 ´ 1010 cmÿ2 ). Five defects with discrete energy levels, ranging from 0.17 to 0.59 eV below the conduction band, were introduced during Er ion implantation. These defects are compared to those introduced during He-ion etching and alpha particle irradiation. By comparing the DLTS spectra and DLTS signatures, it was noted that certain defects (Eer3, Eer4 and Eer5) are only observed in the Er implanted SiGe. Photoluminescence in the 1.54 lm region due to the erbium implantation in Si0:96 Ge0:04 was observed after a thermal treatment at 900°C for 30 s. Ó 1999 Published by Elsevier Science B.V. All rights reserved. PACS: 68.35.Dv; 68.55.Ln; 61.72.Tt; 61.80.Jh Keywords: SiGe; Erbium implantation; Schottky diodes; DLTS; PL
1. Introduction Ion implantation in compound semiconductors is particularly attractive due to its many promising applications in integrated devices [1,2]. Recently rare-earth erbium (Er) in semiconductors has received much attention due to its potential applications in optoelectronics [3]. This combination of erbium as dopant atoms incorporated into semiconductors provides a system which exhibits a
* Corresponding author. Tel.: +27 12 420 2684; fax: +27 12 362 5288; e-mail: [email protected]
temperature stable luminescence wavelength at about 1.54 lm which is nearly independent of the speci®c semiconductor host. This speci®c wavelength corresponds to the minimum absorption window of optical ®bres and is thus of great interest for optical communication technology. Previously, Si:Er light emitting diodes (LEDs) have been demonstrated [4]. The optical activity of Er in Si has recently received a lot of attention [5±8]. However, the low solubility of optically active Er and the long radiative lifetime, result in a luminescence yield that is moderate at low temperatures. This implies that devices operating at room temperature have insucient emission. It has been
0168-583X/98/$ ± see front matter Ó 1999 Published by Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 8 ) 0 0 6 9 3 - 4
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M. Mamor et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 523±527
reported that the band gap energy of the host semiconductor is an important parameter to change the energy transfer eciency [9]. In a SiGebased host, we can change the band-gap energy and thus change the energy transfer. The SiGe can also be integrated with the Si easily. If we want to realize an Er-doped semiconductor laser on Si, it is very likely that we will have to dope Er in a quantum well structure such as Si/SiGe:Er/Si. Previously, the photoluminescence [10] and electroluminescence [11] of Er in SiGe have been reported. The usual way of incorporating erbium in SiGe is in situ doping during growth or via implantation. Ion implantation is a suitable technique to dope Si with high concentration and high eciency. With ion implantation, the quality of the crystal is impaired and several kinds of defects are generated. Therefore, for application in semiconductor devices, it is necessary to investigate the defect levels existing in Er implanted samples. Our study of Si0:96 Ge0:04 :Er forms part of a systematic study of SiGe with dierent Ge-content. Very few investigations on deep level states in Er doped Si have been reported in the literature [6,12] and to the knowledge of the authors, there has been no report on electrically active deep levels in Er doped SiGe. This paper reports the results from a deep level transient spectroscopy (DLTS) study of defects introduced by Er implantation of n-type Si0:96 Ge0:04 at 300 K. In order to investigate the physical origin of these defect, we have compared their electronic properties to those introduced during 5.4 MeV alpha particle irradiation and 1 keV helium-ion etching. 2. Experimental details In the experiment we used Si0:96 Ge0:04 layers which were grown by chemical vapor deposition (CVD) on a lightly doped (4±6 ´ 1016 cmÿ3 ) Si buer layer grown on an n -Si substrate. The thickness of the Si0:96 Ge0:04 epilayer was 500 nm. Since this thickness was smaller than its critical thickness, the epilayer was strained [13]. From Xray diraction measurements, it was con®rmed that there was no lattice relaxation in the n-Si0:96 Ge0:04
epilayers. The carrier density of the epitaxial SiGe layers as determined by capacitance voltage (C±V) measurements was uniform and was 8 ´ 1016 ± 1 ´ 1017 cmÿ3 . Erbium-doped SiGe samples were obtained by implanting Er into the Si0:96 Ge0:04 epilayers at 300 K. In order to have a shallow Er layer, the implantation energy was 180 keV with a dose of 1 ´ 1010 cmÿ2 . The projected implant range is approximately 80 nm as inferred from the TRIM program. After implantation a set of samples were annealed in a rapid thermal processor under nitrogen ¯ux at a temperature of 900°C for 30 s. Circular Pd contacts, 0.77 mm in diameter and 200 nm thick, were deposited onto the SiGe epilayers, through a contact metal mask by resistive evaporation. For control, purposes SBDs were also formed on a chemically cleaned sample which was not exposed to Er ions. The erbium implantation induced defects in the Si1ÿx Gex epilayer were characterized by deep-level transient spectroscopy (DLTS) [14] using a lock-in ampli®er (LIA) based system. The energy level (Et ) in the band gap and apparent capture cross section (ra ) of the defects were determined from Arrhenius plots of ln (T2 /e) versus 1/T. Photoluminescence measurements were performed using the 514.5 nm line of a 100 mW Ar ion laser at focused to a spot of 0.2 ´ 0.5 mm2 . The infrared luminescence was observed with 0.64 m grating monochromator equipped with a liquid nitrogen cooled germanium detector. 3. Results and discussion Curves (a) in Fig. 1 (solid line) show DLTS spectra obtained from 180 keV Er implanted nSi0:96 Ge0:04 to a ¯uence of 1 ´ 1010 ions/cm2 . The DLTS spectrum from the control sample (not shown here), indicated that no defects with peaks between 40 and 300 K are present in detectable concentrations. Five prominent defects (Eer1± Eer5) were introduced in the band gap of SiGe. Defects are identi®ed in the form, where ``E'' denotes an electron trap and ``er'' stands for an Er implantation related defect. The levels of Eer1, Eer3 and Eer5 are located at EC )0.17 eV,
M. Mamor et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 523±527
Fig. 1. DLTS spectra of n-Si0:96 Ge0:04 after 180 keV Er implantation to a ¯uence of 1 ´ 1010 ions/cm2 (curve a), He-ion etching (curve b) and alpha particle irradiation (curve c). All spectra were recorded at a lock-in ampli®er frequency of 46 Hz, a quiescent reverse bias (Vr ) of 0.5 V and a forward bias (Vp ) of 0.8 V.
EC )0.37 eV and EC )0.59 eV, respectively. Some of the defect levels have already been reported for Si:Er [6±8], but have not been observed in Si implanted with other ions. We demonstrate this by comparing the defects created by Er implantation to those detected in the same material after high (5.4 MeV) energy alpha irradiation and low (1 keV) energy He-ion etching. The measured DLTS spectra for the high energy alpha irradiation and low energy He-ion etching are depicted as a solid line (curve b) and dashed-dot line (curve c) in Fig. 1 respectively. By comparing the three DLTS spectra of Fig. 1, we believe that the defects Eer1 and Eer2 are similar to EHe2 and EHe3 detected after He-ion etching, respectively. It can therefore be concluded that the defects (Eer3, Eer4 and Eer5) are only observed in the Er implanted SiGe. Arrhenius plots of the DLTS ``signatures'' after Er-implantation and He-ion etching are depicted in Fig. 2. This ®gure shows also a comparison of the Arrhenuis plots of the thermal emission rate of primary defects introduced in n-type Si [15] after alpha particle irradiation, most of which the structure is known, i.e., (the two charge states of =± ±=0 the divacancy (V2 and V2 ) and the vacancy±
525
Fig. 2. Arrhenius plots of defects detected in n-SiGe after 180 keV Er implantation to a ¯uence of 1 ´ 1010 ions/cm2 and Heion etching of the same material. The data points of the two charge state of the divacancy and the vacancy-phosphorous complex are also shown for comparison.
phosphorous complex (V±P)). From this ®gure, we believe there is no similarity between the Er induced defects Eer3 and Eer5 and the He-ion etching induced defects and primary defects. A comparison of the DLTS ``signatures'' of these defects detected after Er implantation with those of He-ions etching and alpha particle irradiation of the same material is reported in Table 1. DLTS depth pro®ling was performed by recording spectra at ®xed Vr but incrementing Vp in small steps from one scan to the next. The approach of Zohta et al. [16] was then used to obtain the defect concentration as a function of depth below the interface for Eer1(0.17 eV) and Eer5(0.59 eV) detected in n-Si0:96 Ge0:04 . From this study it is noted, that the defect Eer1 has the same pro®le shape as Eer5, however, it has a slightly lower concentration. The concentrations of Eer1 and Eer5, 60 nm below semiconductor surface are 7 0.2 ´ 1014 cmÿ3 and 3.2 0.2 ´ 1015 cmÿ3 , respectively. Eer1 and Eer2 were observed up to a depth of 180 and 140 nm from the metal-semiconductor surface, respectively. It is believed that interstitials and vacancies created in the Er damaged ``near surface'' region diuse into the material forming pairs and complexes. As mentioned above one set of the implanted samples was annealed in a rapid thermal processor
526
M. Mamor et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 523±527
Table 1 DLTS ``signatures'' of defects introduced during 180 keV Er implantation, 1 keV He-ion etching and 5.4 MeV alpha-particle irradiation of n-type Si1ÿx Gex (x 0.04) Defect label
Et (eV)
ra ´ 10ÿ16 (cm2 )
Tpeak (K) at 46 Hz
Eer1 Eer2 Eer3 Eer4 Eer5
0.17 ± 0.37 ± 0.59
1.7 ± 34 ± 210
100 ± 193 ± 260
EHe1 EHe2 EHe3 EHe4 EHe5 EHe6
0.11 ± 0.19 0.28 0.36 0.52
0.09 ± 3.6 1.7 3.7 4.7
75 ± 108 157 193 267
EA1 EA2 EA3
0.24 0.44 0.44
2.3 7.6 0.07
136 226 274
under nitrogen ¯ux at a temperature of 900°C for 30 s. DLTS spectrum obtained from this sample is shown in Fig. 3 and revealed that most of the defects have been eliminated. It has been shown [8, 12] that the annealing treatment of Er:Si reduces the defect concentration and most of them disappear after annealing at 900°C. At this high temperature it is possible that there is removal of such Er-defects which implies an improvement of the lattice. The photoluminescence spectrum of the annealed sample is also shown in Fig. 3 and the emission peak at 1.54 lm is clearly visible. The presence of a luminescence signal after thermal annealing could be due to a reduction in the concentration of the nonradiative paths correlated to the removal of defects during annealing. Because Eer1±Eer5 were not present after annealing, these results indicate that none of the defects (Eer1± Eer5) could be considered optically active centers. It has been reported that in the presence of oxygen [12], a new defect related to an Er±O complex at EC )0.15 eV was observed which is responsible for the increased Er luminescence eciency. We did not detect this defect in the present DLTS study, due to the low concentration of oxygen in our samples. The thermal annealing properties of erbium co-implanted with oxygen will be discussed in a forthcoming paper.
4. Summary and conclusion Erbium implantation induced defects in strained, epitaxial n-type Si1ÿx Gex (x 0.04) layers have been investigated by DLTS. From this study it is evident that ion implanted Er in n-SiGe introduced ®ve discrete level electron traps in the
Fig. 3. DLTS spectrum of n-Si0:96 Ge0:04 after annealing at 900°C for 30 s. The inset shows the PL spectrum of the annealed sample recorded at 12 K.
M. Mamor et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 523±527
band gap. From a comparison of the DLTS ``signatures'' of our work and reported work, we have shown that three of these defects are the same as those detected in Er:Si after thermal annealing. When comparing the DLTS signature of defects to those introduced during He-ion etching and alpha particle irradiation of the same material, it was noted that certain defects (Eer3, Eer4 and Eer5) are only observed in the Er implanted SiGe and were not the same as those detected during He-ion etching or alpha particle irradiation. The photoluminescence characteristics were also studied and characteristic Er-related photoluminescence was observed in the 1.54 lm region. Acknowledgements We acknowledge the ®nancial assistance of the Foundation for Research Development. References [1] T.E. Haynes, R. Morton, S.S. Lau, Appl. Phys. Lett. 64 (1994) 991. [2] A. Okubo, S. Fukatsu, Y. Shiraki, Appl. Phys. Lett. 65 (1994) 2522.
527
[3] S. Coa, A. Polman, R.N. Schwartz (Eds.), Rare earth doped semiconductors II, Mater. Res. Soc. Symp. Proc. 422 (1996). [4] H. Ennen, G. Pomrenke, A. Axmann, K. Eisele, W. Haydl, J. Schneider, Appl. Phys. Lett. 46 (1985) 381. [5] J. Michel, J.L. Benton, R.F. Ferrante, D.C. Jacobson, D.J. Eaglesham, E.A. Fitzgerald, Y.H. Xie, J.M. Poate, L.C. Kimerling, J. Appl. Phys. 70 (1991) 2672. [6] J.L. Benton, J. Michel, L.C. Kimerling, D.C. Jacobson, Y.H. Xie, D.J. Eaglesham, J.M. Poate, J. Appl. Phys. 70 (1991) 2667. [7] S. Coa, G. Franzo, F. Priolo, A. Polman, R. Serna, Phys. Rev. B 49 (1994) 16313. [8] H. Przybylinska, W. Jantsch, Yu. Suprun-Belevitch, M. Stepikhova, L. Palmetshofer, G. Hendorfer, A. Kozanecki, R.J. Wilson, B.J. Sealy, Phys. Rev. B 54 (1996) 2532. [9] A. Taguchi, M. Taniguchi, K. Takhei, Appl. Phys. Lett. 60 (1992) 965. [10] M.Q. Huda, A.R. Peaker, J.H. Evans, D.C. Houghton, W.P. Gillin, Electronics Letters 33 (1997) 1182. [11] S.J. Chang, D.K. Nayak, Y. Shiraki, J. Appl. Phys. 83 (1998) 1426. [12] S. Libertino, S. Coa, G. Franzo, F. Priolo, J. Appl. Phys. 78 (1995) 3867. [13] R. People, J.C. Bean, Appl. Phys. Lett. 47 (1985) 322. [14] D.V. Lang, J. Appl. Phys. 45 (1974) 3014. [15] F.D. Auret, P.N.K. Deenapanray, S.G. Goodman, W.E. Meyer, G. Myburg, J. Appl. Phys. 83 (1998) 5576. [16] Y. Zohta, M.O. Watanabe, J. Appl. Phys. 53 (1982) 1809.
Deep level properties of erbium implanted epitaxially grown SiGe M. Mamor a, F.D. Auret a,*, S.A. Goodman a, J. Brink a, M. Hayes a, F. Meyer b, A. Vantomme c, G. Langouche c, P.N.K. Deenapanray d b
a Physics Department, University of Pretoria, Pretoria 0002, South Africa Institut dÕElectronique Fondamentale, CNRS URA 22, Bat 220, Universit e Paris Sud, 91405 Orsay cedex, France c Physics Department, Catholic University of Leuven, Belgium d Department of Electronic Materials Engineering, Australian National University, Canberra, Australia
Abstract We have used deep-level transient spectroscopy (DLTS) in an investigation of the electronic properties of defects introduced in n-Si0:96 Ge0:04 during 180 keV erbium ion implantation (¯uence 1 ´ 1010 cmÿ2 ). Five defects with discrete energy levels, ranging from 0.17 to 0.59 eV below the conduction band, were introduced during Er ion implantation. These defects are compared to those introduced during He-ion etching and alpha particle irradiation. By comparing the DLTS spectra and DLTS signatures, it was noted that certain defects (Eer3, Eer4 and Eer5) are only observed in the Er implanted SiGe. Photoluminescence in the 1.54 lm region due to the erbium implantation in Si0:96 Ge0:04 was observed after a thermal treatment at 900°C for 30 s. Ó 1999 Published by Elsevier Science B.V. All rights reserved. PACS: 68.35.Dv; 68.55.Ln; 61.72.Tt; 61.80.Jh Keywords: SiGe; Erbium implantation; Schottky diodes; DLTS; PL
1. Introduction Ion implantation in compound semiconductors is particularly attractive due to its many promising applications in integrated devices [1,2]. Recently rare-earth erbium (Er) in semiconductors has received much attention due to its potential applications in optoelectronics [3]. This combination of erbium as dopant atoms incorporated into semiconductors provides a system which exhibits a
* Corresponding author. Tel.: +27 12 420 2684; fax: +27 12 362 5288; e-mail: [email protected]
temperature stable luminescence wavelength at about 1.54 lm which is nearly independent of the speci®c semiconductor host. This speci®c wavelength corresponds to the minimum absorption window of optical ®bres and is thus of great interest for optical communication technology. Previously, Si:Er light emitting diodes (LEDs) have been demonstrated [4]. The optical activity of Er in Si has recently received a lot of attention [5±8]. However, the low solubility of optically active Er and the long radiative lifetime, result in a luminescence yield that is moderate at low temperatures. This implies that devices operating at room temperature have insucient emission. It has been
0168-583X/98/$ ± see front matter Ó 1999 Published by Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 8 ) 0 0 6 9 3 - 4
524
M. Mamor et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 523±527
reported that the band gap energy of the host semiconductor is an important parameter to change the energy transfer eciency [9]. In a SiGebased host, we can change the band-gap energy and thus change the energy transfer. The SiGe can also be integrated with the Si easily. If we want to realize an Er-doped semiconductor laser on Si, it is very likely that we will have to dope Er in a quantum well structure such as Si/SiGe:Er/Si. Previously, the photoluminescence [10] and electroluminescence [11] of Er in SiGe have been reported. The usual way of incorporating erbium in SiGe is in situ doping during growth or via implantation. Ion implantation is a suitable technique to dope Si with high concentration and high eciency. With ion implantation, the quality of the crystal is impaired and several kinds of defects are generated. Therefore, for application in semiconductor devices, it is necessary to investigate the defect levels existing in Er implanted samples. Our study of Si0:96 Ge0:04 :Er forms part of a systematic study of SiGe with dierent Ge-content. Very few investigations on deep level states in Er doped Si have been reported in the literature [6,12] and to the knowledge of the authors, there has been no report on electrically active deep levels in Er doped SiGe. This paper reports the results from a deep level transient spectroscopy (DLTS) study of defects introduced by Er implantation of n-type Si0:96 Ge0:04 at 300 K. In order to investigate the physical origin of these defect, we have compared their electronic properties to those introduced during 5.4 MeV alpha particle irradiation and 1 keV helium-ion etching. 2. Experimental details In the experiment we used Si0:96 Ge0:04 layers which were grown by chemical vapor deposition (CVD) on a lightly doped (4±6 ´ 1016 cmÿ3 ) Si buer layer grown on an n -Si substrate. The thickness of the Si0:96 Ge0:04 epilayer was 500 nm. Since this thickness was smaller than its critical thickness, the epilayer was strained [13]. From Xray diraction measurements, it was con®rmed that there was no lattice relaxation in the n-Si0:96 Ge0:04
epilayers. The carrier density of the epitaxial SiGe layers as determined by capacitance voltage (C±V) measurements was uniform and was 8 ´ 1016 ± 1 ´ 1017 cmÿ3 . Erbium-doped SiGe samples were obtained by implanting Er into the Si0:96 Ge0:04 epilayers at 300 K. In order to have a shallow Er layer, the implantation energy was 180 keV with a dose of 1 ´ 1010 cmÿ2 . The projected implant range is approximately 80 nm as inferred from the TRIM program. After implantation a set of samples were annealed in a rapid thermal processor under nitrogen ¯ux at a temperature of 900°C for 30 s. Circular Pd contacts, 0.77 mm in diameter and 200 nm thick, were deposited onto the SiGe epilayers, through a contact metal mask by resistive evaporation. For control, purposes SBDs were also formed on a chemically cleaned sample which was not exposed to Er ions. The erbium implantation induced defects in the Si1ÿx Gex epilayer were characterized by deep-level transient spectroscopy (DLTS) [14] using a lock-in ampli®er (LIA) based system. The energy level (Et ) in the band gap and apparent capture cross section (ra ) of the defects were determined from Arrhenius plots of ln (T2 /e) versus 1/T. Photoluminescence measurements were performed using the 514.5 nm line of a 100 mW Ar ion laser at focused to a spot of 0.2 ´ 0.5 mm2 . The infrared luminescence was observed with 0.64 m grating monochromator equipped with a liquid nitrogen cooled germanium detector. 3. Results and discussion Curves (a) in Fig. 1 (solid line) show DLTS spectra obtained from 180 keV Er implanted nSi0:96 Ge0:04 to a ¯uence of 1 ´ 1010 ions/cm2 . The DLTS spectrum from the control sample (not shown here), indicated that no defects with peaks between 40 and 300 K are present in detectable concentrations. Five prominent defects (Eer1± Eer5) were introduced in the band gap of SiGe. Defects are identi®ed in the form, where ``E'' denotes an electron trap and ``er'' stands for an Er implantation related defect. The levels of Eer1, Eer3 and Eer5 are located at EC )0.17 eV,
M. Mamor et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 523±527
Fig. 1. DLTS spectra of n-Si0:96 Ge0:04 after 180 keV Er implantation to a ¯uence of 1 ´ 1010 ions/cm2 (curve a), He-ion etching (curve b) and alpha particle irradiation (curve c). All spectra were recorded at a lock-in ampli®er frequency of 46 Hz, a quiescent reverse bias (Vr ) of 0.5 V and a forward bias (Vp ) of 0.8 V.
EC )0.37 eV and EC )0.59 eV, respectively. Some of the defect levels have already been reported for Si:Er [6±8], but have not been observed in Si implanted with other ions. We demonstrate this by comparing the defects created by Er implantation to those detected in the same material after high (5.4 MeV) energy alpha irradiation and low (1 keV) energy He-ion etching. The measured DLTS spectra for the high energy alpha irradiation and low energy He-ion etching are depicted as a solid line (curve b) and dashed-dot line (curve c) in Fig. 1 respectively. By comparing the three DLTS spectra of Fig. 1, we believe that the defects Eer1 and Eer2 are similar to EHe2 and EHe3 detected after He-ion etching, respectively. It can therefore be concluded that the defects (Eer3, Eer4 and Eer5) are only observed in the Er implanted SiGe. Arrhenius plots of the DLTS ``signatures'' after Er-implantation and He-ion etching are depicted in Fig. 2. This ®gure shows also a comparison of the Arrhenuis plots of the thermal emission rate of primary defects introduced in n-type Si [15] after alpha particle irradiation, most of which the structure is known, i.e., (the two charge states of =± ±=0 the divacancy (V2 and V2 ) and the vacancy±
525
Fig. 2. Arrhenius plots of defects detected in n-SiGe after 180 keV Er implantation to a ¯uence of 1 ´ 1010 ions/cm2 and Heion etching of the same material. The data points of the two charge state of the divacancy and the vacancy-phosphorous complex are also shown for comparison.
phosphorous complex (V±P)). From this ®gure, we believe there is no similarity between the Er induced defects Eer3 and Eer5 and the He-ion etching induced defects and primary defects. A comparison of the DLTS ``signatures'' of these defects detected after Er implantation with those of He-ions etching and alpha particle irradiation of the same material is reported in Table 1. DLTS depth pro®ling was performed by recording spectra at ®xed Vr but incrementing Vp in small steps from one scan to the next. The approach of Zohta et al. [16] was then used to obtain the defect concentration as a function of depth below the interface for Eer1(0.17 eV) and Eer5(0.59 eV) detected in n-Si0:96 Ge0:04 . From this study it is noted, that the defect Eer1 has the same pro®le shape as Eer5, however, it has a slightly lower concentration. The concentrations of Eer1 and Eer5, 60 nm below semiconductor surface are 7 0.2 ´ 1014 cmÿ3 and 3.2 0.2 ´ 1015 cmÿ3 , respectively. Eer1 and Eer2 were observed up to a depth of 180 and 140 nm from the metal-semiconductor surface, respectively. It is believed that interstitials and vacancies created in the Er damaged ``near surface'' region diuse into the material forming pairs and complexes. As mentioned above one set of the implanted samples was annealed in a rapid thermal processor
526
M. Mamor et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 523±527
Table 1 DLTS ``signatures'' of defects introduced during 180 keV Er implantation, 1 keV He-ion etching and 5.4 MeV alpha-particle irradiation of n-type Si1ÿx Gex (x 0.04) Defect label
Et (eV)
ra ´ 10ÿ16 (cm2 )
Tpeak (K) at 46 Hz
Eer1 Eer2 Eer3 Eer4 Eer5
0.17 ± 0.37 ± 0.59
1.7 ± 34 ± 210
100 ± 193 ± 260
EHe1 EHe2 EHe3 EHe4 EHe5 EHe6
0.11 ± 0.19 0.28 0.36 0.52
0.09 ± 3.6 1.7 3.7 4.7
75 ± 108 157 193 267
EA1 EA2 EA3
0.24 0.44 0.44
2.3 7.6 0.07
136 226 274
under nitrogen ¯ux at a temperature of 900°C for 30 s. DLTS spectrum obtained from this sample is shown in Fig. 3 and revealed that most of the defects have been eliminated. It has been shown [8, 12] that the annealing treatment of Er:Si reduces the defect concentration and most of them disappear after annealing at 900°C. At this high temperature it is possible that there is removal of such Er-defects which implies an improvement of the lattice. The photoluminescence spectrum of the annealed sample is also shown in Fig. 3 and the emission peak at 1.54 lm is clearly visible. The presence of a luminescence signal after thermal annealing could be due to a reduction in the concentration of the nonradiative paths correlated to the removal of defects during annealing. Because Eer1±Eer5 were not present after annealing, these results indicate that none of the defects (Eer1± Eer5) could be considered optically active centers. It has been reported that in the presence of oxygen [12], a new defect related to an Er±O complex at EC )0.15 eV was observed which is responsible for the increased Er luminescence eciency. We did not detect this defect in the present DLTS study, due to the low concentration of oxygen in our samples. The thermal annealing properties of erbium co-implanted with oxygen will be discussed in a forthcoming paper.
4. Summary and conclusion Erbium implantation induced defects in strained, epitaxial n-type Si1ÿx Gex (x 0.04) layers have been investigated by DLTS. From this study it is evident that ion implanted Er in n-SiGe introduced ®ve discrete level electron traps in the
Fig. 3. DLTS spectrum of n-Si0:96 Ge0:04 after annealing at 900°C for 30 s. The inset shows the PL spectrum of the annealed sample recorded at 12 K.
M. Mamor et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 523±527
band gap. From a comparison of the DLTS ``signatures'' of our work and reported work, we have shown that three of these defects are the same as those detected in Er:Si after thermal annealing. When comparing the DLTS signature of defects to those introduced during He-ion etching and alpha particle irradiation of the same material, it was noted that certain defects (Eer3, Eer4 and Eer5) are only observed in the Er implanted SiGe and were not the same as those detected during He-ion etching or alpha particle irradiation. The photoluminescence characteristics were also studied and characteristic Er-related photoluminescence was observed in the 1.54 lm region. Acknowledgements We acknowledge the ®nancial assistance of the Foundation for Research Development. References [1] T.E. Haynes, R. Morton, S.S. Lau, Appl. Phys. Lett. 64 (1994) 991. [2] A. Okubo, S. Fukatsu, Y. Shiraki, Appl. Phys. Lett. 65 (1994) 2522.
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[3] S. Coa, A. Polman, R.N. Schwartz (Eds.), Rare earth doped semiconductors II, Mater. Res. Soc. Symp. Proc. 422 (1996). [4] H. Ennen, G. Pomrenke, A. Axmann, K. Eisele, W. Haydl, J. Schneider, Appl. Phys. Lett. 46 (1985) 381. [5] J. Michel, J.L. Benton, R.F. Ferrante, D.C. Jacobson, D.J. Eaglesham, E.A. Fitzgerald, Y.H. Xie, J.M. Poate, L.C. Kimerling, J. Appl. Phys. 70 (1991) 2672. [6] J.L. Benton, J. Michel, L.C. Kimerling, D.C. Jacobson, Y.H. Xie, D.J. Eaglesham, J.M. Poate, J. Appl. Phys. 70 (1991) 2667. [7] S. Coa, G. Franzo, F. Priolo, A. Polman, R. Serna, Phys. Rev. B 49 (1994) 16313. [8] H. Przybylinska, W. Jantsch, Yu. Suprun-Belevitch, M. Stepikhova, L. Palmetshofer, G. Hendorfer, A. Kozanecki, R.J. Wilson, B.J. Sealy, Phys. Rev. B 54 (1996) 2532. [9] A. Taguchi, M. Taniguchi, K. Takhei, Appl. Phys. Lett. 60 (1992) 965. [10] M.Q. Huda, A.R. Peaker, J.H. Evans, D.C. Houghton, W.P. Gillin, Electronics Letters 33 (1997) 1182. [11] S.J. Chang, D.K. Nayak, Y. Shiraki, J. Appl. Phys. 83 (1998) 1426. [12] S. Libertino, S. Coa, G. Franzo, F. Priolo, J. Appl. Phys. 78 (1995) 3867. [13] R. People, J.C. Bean, Appl. Phys. Lett. 47 (1985) 322. [14] D.V. Lang, J. Appl. Phys. 45 (1974) 3014. [15] F.D. Auret, P.N.K. Deenapanray, S.G. Goodman, W.E. Meyer, G. Myburg, J. Appl. Phys. 83 (1998) 5576. [16] Y. Zohta, M.O. Watanabe, J. Appl. Phys. 53 (1982) 1809.