- Email: [email protected]
57Fe Mössbauer studies on 57Mn∗ implanted InP and InAs
Nuclear Instruments and Methods in Physics Research B 272 (2012) 414–417
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
57
Fe Mössbauer studies on
57
Mn⁄ implanted InP and InAs
K. Bharuth-Ram a,⇑, W.B. Dlamini a, H. Masenda b, D. Naidoo b, H.P. Gunnlaugsson c, G. Weyer c, R. Mantovan d, T.E. Mølholt e, R. Sielemann f, S. Ólafsson e, G. Langouche g, K. Johnston h, the ISOLDE Collaboration h a
School of Physics, University of KwaZulu-Natal, Durban 4001, South Africa School of Physics, University of The Witwatersrand, Johannesburg 2050, South Africa Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Århus C, Denmark d Laboratorio MDM CNR-IMM, 20041 Agrate Brianza (MB), Italy e Science Institute, University of Iceland, 107 Reykjavik, Iceland f Helmholtz-Zentrum für Materialien und Energie, D-14109 Berlin, Germany g Instituut voor Kern en Stralingsfysika, University of Leuven, 3001 Leuven, Belgium h PH Department, ISOLDE/CERN, CH-1211 Geneva 23, Switzerland b c
a r t i c l e
i n f o
Article history: Available online 2 February 2011 Keywords: InAs InP 57 Mn implantation Mössbauer spectroscopy Fe sites
a b s t r a c t 57 Fe Mössbauer spectroscopy studies, following implantation of radioactive 57 Mn , have been conducted on InP and n- and p-type InAs at temperatures above 300 K. The 57 Mn ions are produced at the ISOLDE facility at CERN, ionized and accelerated to 60 keV energy and implanted with fluences of 6 2 1012 ion=cm2 into single crystal samples. Mössbauer spectra were collected with a parallel plate avalanche counter. Analysis of the Mössbauer spectra required three components: an asymmetric doublet attributed to Fe atoms in implantation induced damaged environments, a single line assigned to Fe on substitutional In sites and a weak symmetric doublet assigned to impurity–vacancy complexes. In InP the substitutional Fe component ðFeS Þ becomes significant above 400 K; while in InAs the FeS fraction is already appreciable (>30%) after implantation at room temperature. The asymmetric doublet dominates the spectra of all samples but shows significant reduction in intensity with increasing temperatures. The radiation damage shows strong annealing above 400 K in the InAs samples and above 450 K in InP; the Fe-defect complex dissociates at 500 K, and the FeS component dominates the spectra at higher temperatures. There was no evidence of any magnetic components in the spectra, indicating that at the low concentrations used in our measurements, the Fe ions were predominantly in the Fe2þ state. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Some of the electronic properties of III–V compound semiconductors such as their direct band gaps (making them efficient light emitters) and higher electron mobilities make them superior to silicon in certain applications. These properties make the III–V’s suited materials for particular applications, for example, in mobile telephones, satellite communications and optoelectronics [1,2]. Ion implantation methods are increasingly being applied in both the modification of semiconducting substrates and their characterization. In the case of InP, there exist several studies following both low pressure metallorganic chemical vapor deposition (LPMOCVD)
⇑ Corresponding author. Tel.: +27 (0) 12 818 8602; fax: +27 (0)86 681 0144. E-mail addresses: [email protected] (K. Bharuth-Ram), [email protected] (W.B. Dlamini), [email protected] (H. Masenda), [email protected] (D. Naidoo), [email protected] (H.P. Gunnlaugsson), [email protected] (G. Weyer). 0168-583X/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2011.01.112
and high temperature ion implantation of substitutional Fe in ntype InP to produce semi-insulating layers as well as study the thermal evolution of deep levels in the Fermi gap [3–8]. The high temperature implantation studies have tracked the evolution of the substrate from n-type to semi-insulating InP, which appears to be related to the introduction of Fe2+/3+ midgap levels in the material. High fractions of Fe at substitutional In sites were achieved on implantation, but defect diffusion with increasing annealing temperatures led to a progressive reduction in FeIn . In the case of InAs, very few ion implantation studies have been reported. Early studies were the use of implantation of Zn and S ions to achieve of p–n junctions [9], and characterization of implantation induced damage [10,11]. In the present study, we apply 57Fe–Mössbauer measurements on InP and n- and p-type InAs, implanted with radioactive 57 Mn ions (which b decays to populate the 57Fe 14.4 keV Mössbauer state), to investigate the lattice sites of the Fe ions, the complexes they form and the annealing characteristic of implantation induce damage.
415
K. Bharuth-Ram et al. / Nuclear Instruments and Methods in Physics Research B 272 (2012) 414–417
2. Experimental details
Data Fit Fe D
2.0 1.5
303 K
1.0 2.5
Fe X
2.0
Fe S Fe i
1.5 348 K 1.0 2.5 2.0 1.5 426 K 1.0 2.5 2.0
Normalized Yield
The method of populating the 57Fe Mössbauer state via the radioactive parent isotope 57 Mn has several unique features that make it particularly useful for ion implantation studies in crystalline material. In this approach radioactive 57 Mn ðT 1=2 ¼ 1:5 minÞ are produced using 1.4 GeV proton induced fission in a UC2 target. The fission products are irradiated with tunable multi-stage lasers to produce 57 Mnþ ions (i.e. ions with charge +1e), which are accelerated to 60 keV energy, and beams with intensities of ð1—3Þ 108 ions=s are obtained [12]. The accelerated 57 Mnþ ions are implanted into the host sample, which may be held at 80–1100 K in an implantation chamber. Annealing of the radiation damage during the 57 Mn lifetime leads to the Mn atoms being incorporated on substitutional lattice sites. In the 57 Mn ! 57 Fe b-decay, which leads to the population of the isomeric Mössbauer state in 57 Feð57m FeÞ, an average recoil energy of 40 eV is imparted to the 57m Fe atom, leading to a relocation of a fraction of the Fe atoms into interstitial sites and the remainder on substitutional sites or at defect complexes. In general, spectra of good statistics are generally obtained in <10 min. with the beam intensity available at ISOLDE/CERN. This assures that implantation fluences are kept below 2 1012 ions=cm2 and that single ion implantation is achieved. In the present measurements the three samples were mounted on a multiple sample holder in a ladder arrangement, and for each sample species the set of temperature dependent spectra was collected from a single sample without changing the implantation spot. An 57 Mnþ beam flux of 2 108 =s gave peak implanted ion concentrations ranging from 2:5 104 at:% for the first measurement to a total of 2 103 at:% when the last implantation on a sample was made. The extremely low concentrations assured single ion implantation and no overlap of implantation damage cascades. Mössbauer emission spectra were collected (at the implantation temperatures) with a parallel-plate resonance detector, equipped with 57Fe enriched stainless steel electrode and mounted on a velocity drive unit outside the implantation chamber. Velocities and isomer shifts were calibrated relative to the center of the a-Fe spectrum at room temperature.
InP 2.5
1.5
495 K
1.0 2.5 2.0 1.5
537 K
1.0 2.5 2.0 1.5
592 K
1.0 2.5 2.0 1.5
633 K
1.0
-2 3. Results and discussion Mössbauer spectra for the InP and InAs samples obtained at the temperatures indicated are displayed in Figs. 1 and 2. The spectra show no evidence of any magnetic sextet. For InP, the spectra up to 426 K are dominated by an asymmetrically broadened quadrupole split doublet ðFeD Þ, similar to that observed in group IV semiconductors, which is assigned to Fe in damaged lattice sites (amorphous pockets) due to the implantation process. At 495 K a strong single line (S1) is evident, dominating the spectra above 590 K. The spectra were analyzed in simultaneous fits to the data set for a given sample over the entire temperature range of our measurements. Gaussian broadened Lorentzian line-shapes (Voigt profiles) were used and the isomer shifts of the lines and the quadrupole splittings of the doublets were constrained to follow the expected second order Doppler shift and T 3=2 temperature dependence, respectively. To obtain satisfactory fits throughout the whole temperature range it was necessary to introduce a small contribution from a quadrupole split component FeX and, at temperatures below 350 K, a weak single line (S2) which had an isomer shift d 1 mm=s. The line widths of the doublets did not show any systematic trends and were set as temperature independent constants. The hyperfine parameters extracted from the analysis are listed in Table 1.
-1
0
1
2
Velocity (mm/s) Fig. 1. Mössbauer spectra obtained after implantation of temperatures indicated.
57
Mnþ into InP, at the
The bonding in the cubic III–V’s are predominantly covalent, with a small but not insignificant ionic contribution due to a reduction in the electron density around the IIIþ ion (and a corresponding increase around the V ion) [13]. The positive isomer shift of S1 therefore leads us to attribute this component to Fe at substitutional In sites. This assignment is consistent with the high temperature implantation studies of Fe in InP of Cesca et al. [6–8] whose results show that within the temperature range of our measurements the majority of Fe ions were located at susbstitutional In sites. Emission channeling studies in 167Er implanted into InP also show that 75% of the implanted ions, after annealing at 425 K, are located on substitutional In sites [14]. The electron density at an interstitial Fe ion is much less than at a substitutional site, supporting our assignment of S2 ðd ¼ 0:96 mm=sÞ to interstitial FeðFei Þ. The weak doublet FeX vanishes at the higher temperatures and the corresponding increase in the substitutional fraction suggests that this is associated with substitutional FeIn in complex either with a vacancy, as been identified in positron annihilation in GaAs
416
K. Bharuth-Ram et al. / Nuclear Instruments and Methods in Physics Research B 272 (2012) 414–417
1.2
p-InAs
n-InAs
n_InAs:
FeS
Data Fit FeD FeS FeX
303K
1.5 1.0 2.0
359K
359 K
p-InAs:
Fei
FeD FeS FeX FeD FeS FeX
0.6 0.4 0.2
1.0
Normalized Yield
FeX
0.8
1.5
2.0
FeD
1.0
303 K
Areal Fraction
2.0
416K
416 K
0.0 300
400
500
Temperature (K)
1.5
600
300
400
500
600
Temperature (K)
Fig. 3. Areal fractions of components FeS ; Fei ; FeD and FeX required to fit the InP and InAs spectra, as discussed in the text.
1.0 2.0 448 K
448K
1.5 1.0 2.0
495K
495 K
592K
592 K
1.5 1.0 2.0
The relative areas of the spectral components are presented in Fig. 3, as a function of sample temperature. Prominent annealing of implantation induced damage is evident in the temperature range from 300 to 500 K, with the FeS fraction in InP increasing from zero at RT to above 65% at 600 K; the corresponding increase in FeS in InAs is from 30% to 70%. The FeX component, attributed to FeIn -defect complexes, is stronger in InP than in InAs, and dissociates at 500 K. In GaAs, positron life time studies [15] show that the Ga vacancies ðVGa Þ are mobile above 300 K, which suggests that vacancy mobility could also be the likely mechanism leading to the dissociation of these complexes in InAs and InP.
1.5
4. Conclusions 1.0
-2
-1
0
1
2
Velocity (mm/s)
-2
-1
0
1
2
Velocity (mm/s)
Fig. 2. Mössbauer spectra obtained after implantation of 57 Mnþ into n- and p-type InAs, at the temperatures indicated.
Table 1 Isomer shifts (d) and quadrupole splittings ðDEQ Þ at RT and gaussian broadening (r) of the components used to fit the spectra in Figs. 1 and 2.
DEQ (mm/s)
r (mm/s)
0.33(4) 0.57(4) 0.09(4) 0.95(5)
– 1.27(5) 1.42(8) –
0.21–0.10 0.30(3) 0.16(5) –
FeS FeD FeX
0.61(4) 0.62(4) 0.29(5)
– 1.22(5) 0.65(4)
0.25–0.11 0.25(3) 0.15(4)
FeS FeD FeX
0.61(4) 0.62(4) -0.30(5)
– 1.17(5) 0.49(4)
0.22–0.14 0.23(3) 0.15(4)
Sample
Component
InP
FeS FeD FeX Fei
n-InAs
p-InAs
d (mm/s)
We have performed Mössbauer measurements on single crystal InP, and n- and p-type InAs implanted with low fluence 57 Mn ions, over a temperature range 300–630 K. The spectra show no evidence of any magnetic features, and have been analyzed in terms of three components, a single line assigned to Fe at substitutional In sites, a doublet to Fe in regions of extensive defect in the lattice, and a weaker doublet to contributions from FeIn - defect complexes. In addition, for InP a small fraction of interstitial Fe is evident below 350 K. The lattice damage anneals quickly in the temperature range 300–600 K. At the highest temperatures Fe ions located at essentially defect-free substitutional sites of 60–70% have been achieved. Acknowledgements This work has been supported by the Danish Natural Science Research Council within the ICE Center, the EU under contract no. HPRICT-1999-00018, and the South African National Research Foundation under Grant GUN2064730. T.E. Mølholt acknowledges support from the Icelandic Research Fund. References
[15] and Mössbauer studies on Sn implanted InAs and GaAs [16,17], or a neighboring P ion [6–8]. The spectra of the p- and n-type InAs samples are very similar, but different from that observed for InP. There is no evidence of interstitial Fe, but already at room temperature (RT) implantation a significant FeS component is evident, which again dominates the resonance area at the higher temperatures.
[1] S. Adachi, Physical Properties of III–V Semiconductor Compounds, Wiley Interscience, 1999. [2] S. Mokkapati, C. Jagdish, Materials Today 12 (2009) 22. [3] H. Cheng, C.B. Su, K.D. Buehring, C.P. Chien, J.W. Ure, D. Perrachione, D. Renner, K.L. Hess, S.W. Zehr, Appl. Phys. Lett. 49 (1986) 1415. [4] A. Gasparatto, A. Canera, C. Frigeri, F. Priolo, B. Fraboni, A. Comporese, G. Rosetto, J. Appl. Phys. 85 (1999) 753. [5] B. Fraboni, A. Gasparotto, F. Priolo, G. Scamarcio, Appl. Phys. A 73 (2001) 35.
K. Bharuth-Ram et al. / Nuclear Instruments and Methods in Physics Research B 272 (2012) 414–417 [6] T. Cesca, A. Verna, G. Mattei, A. Gasparotto, B. Fraboni, G. Impellizzeri, F. Priolo, J. Appl. Phys. 100 (2006) 023539. [7] A. Amore Bonapastaa, F. Filippone, A. Gasparotto, T. Cesca, Appl. Phys. Lett. 88 (2006) 251912. [8] T. Cesca, A. Gasparotto, E. Piana, B. Fraboni, J. Appl. Phys. 102 (2007) 093711. [9] P.J. McNally, Radiat. Eff. Defect Semiconductors 6 (1970) 149. [10] S.J. Pearton, A.R. Von Neida, J.M. Brown, K.T. Short, L.J. Oster, R. Chakrabarti, J. Appl. Phys. 64 (1988) 629. [11] H. Ulrich, A. Knecht, D. Bimberg, H. Krautle, W. Schlaak, J. Appl. Phys. 72 (1992) 3514.
417
[12] V.N. Fedoseyev et al., Nucl. Instr. Meth. B 126 (1997) 88. [13] N.W. Ashcroft, N.D. Mermin, Solid State Physics, W.B. Saunders Publications, 1976. pp. 387–389. [14] U. Wahl, A. Vantomme, G. Langouche, Nucl. Instr. Meth. B 148 (1999) 492. [15] K. Saarinen, P. Hautojärvi, C. Corbel, Nucl. Instr. Meth. A 388 (1997) 434. [16] G. Weyer, S. Damgaard, J.W. Petersen, J. Heinemeier, J. Phys. C: Solid State Phys. 113 (1980) L181–L183. [17] O.H. Nielsen, F.K. Larsen, S. Damgaard, J.W. Petersen, G. Weyer, Z. Phys. B – Condensed Matter 52 (1983) 99.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
57
Fe Mössbauer studies on
57
Mn⁄ implanted InP and InAs
K. Bharuth-Ram a,⇑, W.B. Dlamini a, H. Masenda b, D. Naidoo b, H.P. Gunnlaugsson c, G. Weyer c, R. Mantovan d, T.E. Mølholt e, R. Sielemann f, S. Ólafsson e, G. Langouche g, K. Johnston h, the ISOLDE Collaboration h a
School of Physics, University of KwaZulu-Natal, Durban 4001, South Africa School of Physics, University of The Witwatersrand, Johannesburg 2050, South Africa Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Århus C, Denmark d Laboratorio MDM CNR-IMM, 20041 Agrate Brianza (MB), Italy e Science Institute, University of Iceland, 107 Reykjavik, Iceland f Helmholtz-Zentrum für Materialien und Energie, D-14109 Berlin, Germany g Instituut voor Kern en Stralingsfysika, University of Leuven, 3001 Leuven, Belgium h PH Department, ISOLDE/CERN, CH-1211 Geneva 23, Switzerland b c
a r t i c l e
i n f o
Article history: Available online 2 February 2011 Keywords: InAs InP 57 Mn implantation Mössbauer spectroscopy Fe sites
a b s t r a c t 57 Fe Mössbauer spectroscopy studies, following implantation of radioactive 57 Mn , have been conducted on InP and n- and p-type InAs at temperatures above 300 K. The 57 Mn ions are produced at the ISOLDE facility at CERN, ionized and accelerated to 60 keV energy and implanted with fluences of 6 2 1012 ion=cm2 into single crystal samples. Mössbauer spectra were collected with a parallel plate avalanche counter. Analysis of the Mössbauer spectra required three components: an asymmetric doublet attributed to Fe atoms in implantation induced damaged environments, a single line assigned to Fe on substitutional In sites and a weak symmetric doublet assigned to impurity–vacancy complexes. In InP the substitutional Fe component ðFeS Þ becomes significant above 400 K; while in InAs the FeS fraction is already appreciable (>30%) after implantation at room temperature. The asymmetric doublet dominates the spectra of all samples but shows significant reduction in intensity with increasing temperatures. The radiation damage shows strong annealing above 400 K in the InAs samples and above 450 K in InP; the Fe-defect complex dissociates at 500 K, and the FeS component dominates the spectra at higher temperatures. There was no evidence of any magnetic components in the spectra, indicating that at the low concentrations used in our measurements, the Fe ions were predominantly in the Fe2þ state. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Some of the electronic properties of III–V compound semiconductors such as their direct band gaps (making them efficient light emitters) and higher electron mobilities make them superior to silicon in certain applications. These properties make the III–V’s suited materials for particular applications, for example, in mobile telephones, satellite communications and optoelectronics [1,2]. Ion implantation methods are increasingly being applied in both the modification of semiconducting substrates and their characterization. In the case of InP, there exist several studies following both low pressure metallorganic chemical vapor deposition (LPMOCVD)
⇑ Corresponding author. Tel.: +27 (0) 12 818 8602; fax: +27 (0)86 681 0144. E-mail addresses: [email protected] (K. Bharuth-Ram), [email protected] (W.B. Dlamini), [email protected] (H. Masenda), [email protected] (D. Naidoo), [email protected] (H.P. Gunnlaugsson), [email protected] (G. Weyer). 0168-583X/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2011.01.112
and high temperature ion implantation of substitutional Fe in ntype InP to produce semi-insulating layers as well as study the thermal evolution of deep levels in the Fermi gap [3–8]. The high temperature implantation studies have tracked the evolution of the substrate from n-type to semi-insulating InP, which appears to be related to the introduction of Fe2+/3+ midgap levels in the material. High fractions of Fe at substitutional In sites were achieved on implantation, but defect diffusion with increasing annealing temperatures led to a progressive reduction in FeIn . In the case of InAs, very few ion implantation studies have been reported. Early studies were the use of implantation of Zn and S ions to achieve of p–n junctions [9], and characterization of implantation induced damage [10,11]. In the present study, we apply 57Fe–Mössbauer measurements on InP and n- and p-type InAs, implanted with radioactive 57 Mn ions (which b decays to populate the 57Fe 14.4 keV Mössbauer state), to investigate the lattice sites of the Fe ions, the complexes they form and the annealing characteristic of implantation induce damage.
415
K. Bharuth-Ram et al. / Nuclear Instruments and Methods in Physics Research B 272 (2012) 414–417
2. Experimental details
Data Fit Fe D
2.0 1.5
303 K
1.0 2.5
Fe X
2.0
Fe S Fe i
1.5 348 K 1.0 2.5 2.0 1.5 426 K 1.0 2.5 2.0
Normalized Yield
The method of populating the 57Fe Mössbauer state via the radioactive parent isotope 57 Mn has several unique features that make it particularly useful for ion implantation studies in crystalline material. In this approach radioactive 57 Mn ðT 1=2 ¼ 1:5 minÞ are produced using 1.4 GeV proton induced fission in a UC2 target. The fission products are irradiated with tunable multi-stage lasers to produce 57 Mnþ ions (i.e. ions with charge +1e), which are accelerated to 60 keV energy, and beams with intensities of ð1—3Þ 108 ions=s are obtained [12]. The accelerated 57 Mnþ ions are implanted into the host sample, which may be held at 80–1100 K in an implantation chamber. Annealing of the radiation damage during the 57 Mn lifetime leads to the Mn atoms being incorporated on substitutional lattice sites. In the 57 Mn ! 57 Fe b-decay, which leads to the population of the isomeric Mössbauer state in 57 Feð57m FeÞ, an average recoil energy of 40 eV is imparted to the 57m Fe atom, leading to a relocation of a fraction of the Fe atoms into interstitial sites and the remainder on substitutional sites or at defect complexes. In general, spectra of good statistics are generally obtained in <10 min. with the beam intensity available at ISOLDE/CERN. This assures that implantation fluences are kept below 2 1012 ions=cm2 and that single ion implantation is achieved. In the present measurements the three samples were mounted on a multiple sample holder in a ladder arrangement, and for each sample species the set of temperature dependent spectra was collected from a single sample without changing the implantation spot. An 57 Mnþ beam flux of 2 108 =s gave peak implanted ion concentrations ranging from 2:5 104 at:% for the first measurement to a total of 2 103 at:% when the last implantation on a sample was made. The extremely low concentrations assured single ion implantation and no overlap of implantation damage cascades. Mössbauer emission spectra were collected (at the implantation temperatures) with a parallel-plate resonance detector, equipped with 57Fe enriched stainless steel electrode and mounted on a velocity drive unit outside the implantation chamber. Velocities and isomer shifts were calibrated relative to the center of the a-Fe spectrum at room temperature.
InP 2.5
1.5
495 K
1.0 2.5 2.0 1.5
537 K
1.0 2.5 2.0 1.5
592 K
1.0 2.5 2.0 1.5
633 K
1.0
-2 3. Results and discussion Mössbauer spectra for the InP and InAs samples obtained at the temperatures indicated are displayed in Figs. 1 and 2. The spectra show no evidence of any magnetic sextet. For InP, the spectra up to 426 K are dominated by an asymmetrically broadened quadrupole split doublet ðFeD Þ, similar to that observed in group IV semiconductors, which is assigned to Fe in damaged lattice sites (amorphous pockets) due to the implantation process. At 495 K a strong single line (S1) is evident, dominating the spectra above 590 K. The spectra were analyzed in simultaneous fits to the data set for a given sample over the entire temperature range of our measurements. Gaussian broadened Lorentzian line-shapes (Voigt profiles) were used and the isomer shifts of the lines and the quadrupole splittings of the doublets were constrained to follow the expected second order Doppler shift and T 3=2 temperature dependence, respectively. To obtain satisfactory fits throughout the whole temperature range it was necessary to introduce a small contribution from a quadrupole split component FeX and, at temperatures below 350 K, a weak single line (S2) which had an isomer shift d 1 mm=s. The line widths of the doublets did not show any systematic trends and were set as temperature independent constants. The hyperfine parameters extracted from the analysis are listed in Table 1.
-1
0
1
2
Velocity (mm/s) Fig. 1. Mössbauer spectra obtained after implantation of temperatures indicated.
57
Mnþ into InP, at the
The bonding in the cubic III–V’s are predominantly covalent, with a small but not insignificant ionic contribution due to a reduction in the electron density around the IIIþ ion (and a corresponding increase around the V ion) [13]. The positive isomer shift of S1 therefore leads us to attribute this component to Fe at substitutional In sites. This assignment is consistent with the high temperature implantation studies of Fe in InP of Cesca et al. [6–8] whose results show that within the temperature range of our measurements the majority of Fe ions were located at susbstitutional In sites. Emission channeling studies in 167Er implanted into InP also show that 75% of the implanted ions, after annealing at 425 K, are located on substitutional In sites [14]. The electron density at an interstitial Fe ion is much less than at a substitutional site, supporting our assignment of S2 ðd ¼ 0:96 mm=sÞ to interstitial FeðFei Þ. The weak doublet FeX vanishes at the higher temperatures and the corresponding increase in the substitutional fraction suggests that this is associated with substitutional FeIn in complex either with a vacancy, as been identified in positron annihilation in GaAs
416
K. Bharuth-Ram et al. / Nuclear Instruments and Methods in Physics Research B 272 (2012) 414–417
1.2
p-InAs
n-InAs
n_InAs:
FeS
Data Fit FeD FeS FeX
303K
1.5 1.0 2.0
359K
359 K
p-InAs:
Fei
FeD FeS FeX FeD FeS FeX
0.6 0.4 0.2
1.0
Normalized Yield
FeX
0.8
1.5
2.0
FeD
1.0
303 K
Areal Fraction
2.0
416K
416 K
0.0 300
400
500
Temperature (K)
1.5
600
300
400
500
600
Temperature (K)
Fig. 3. Areal fractions of components FeS ; Fei ; FeD and FeX required to fit the InP and InAs spectra, as discussed in the text.
1.0 2.0 448 K
448K
1.5 1.0 2.0
495K
495 K
592K
592 K
1.5 1.0 2.0
The relative areas of the spectral components are presented in Fig. 3, as a function of sample temperature. Prominent annealing of implantation induced damage is evident in the temperature range from 300 to 500 K, with the FeS fraction in InP increasing from zero at RT to above 65% at 600 K; the corresponding increase in FeS in InAs is from 30% to 70%. The FeX component, attributed to FeIn -defect complexes, is stronger in InP than in InAs, and dissociates at 500 K. In GaAs, positron life time studies [15] show that the Ga vacancies ðVGa Þ are mobile above 300 K, which suggests that vacancy mobility could also be the likely mechanism leading to the dissociation of these complexes in InAs and InP.
1.5
4. Conclusions 1.0
-2
-1
0
1
2
Velocity (mm/s)
-2
-1
0
1
2
Velocity (mm/s)
Fig. 2. Mössbauer spectra obtained after implantation of 57 Mnþ into n- and p-type InAs, at the temperatures indicated.
Table 1 Isomer shifts (d) and quadrupole splittings ðDEQ Þ at RT and gaussian broadening (r) of the components used to fit the spectra in Figs. 1 and 2.
DEQ (mm/s)
r (mm/s)
0.33(4) 0.57(4) 0.09(4) 0.95(5)
– 1.27(5) 1.42(8) –
0.21–0.10 0.30(3) 0.16(5) –
FeS FeD FeX
0.61(4) 0.62(4) 0.29(5)
– 1.22(5) 0.65(4)
0.25–0.11 0.25(3) 0.15(4)
FeS FeD FeX
0.61(4) 0.62(4) -0.30(5)
– 1.17(5) 0.49(4)
0.22–0.14 0.23(3) 0.15(4)
Sample
Component
InP
FeS FeD FeX Fei
n-InAs
p-InAs
d (mm/s)
We have performed Mössbauer measurements on single crystal InP, and n- and p-type InAs implanted with low fluence 57 Mn ions, over a temperature range 300–630 K. The spectra show no evidence of any magnetic features, and have been analyzed in terms of three components, a single line assigned to Fe at substitutional In sites, a doublet to Fe in regions of extensive defect in the lattice, and a weaker doublet to contributions from FeIn - defect complexes. In addition, for InP a small fraction of interstitial Fe is evident below 350 K. The lattice damage anneals quickly in the temperature range 300–600 K. At the highest temperatures Fe ions located at essentially defect-free substitutional sites of 60–70% have been achieved. Acknowledgements This work has been supported by the Danish Natural Science Research Council within the ICE Center, the EU under contract no. HPRICT-1999-00018, and the South African National Research Foundation under Grant GUN2064730. T.E. Mølholt acknowledges support from the Icelandic Research Fund. References
[15] and Mössbauer studies on Sn implanted InAs and GaAs [16,17], or a neighboring P ion [6–8]. The spectra of the p- and n-type InAs samples are very similar, but different from that observed for InP. There is no evidence of interstitial Fe, but already at room temperature (RT) implantation a significant FeS component is evident, which again dominates the resonance area at the higher temperatures.
[1] S. Adachi, Physical Properties of III–V Semiconductor Compounds, Wiley Interscience, 1999. [2] S. Mokkapati, C. Jagdish, Materials Today 12 (2009) 22. [3] H. Cheng, C.B. Su, K.D. Buehring, C.P. Chien, J.W. Ure, D. Perrachione, D. Renner, K.L. Hess, S.W. Zehr, Appl. Phys. Lett. 49 (1986) 1415. [4] A. Gasparatto, A. Canera, C. Frigeri, F. Priolo, B. Fraboni, A. Comporese, G. Rosetto, J. Appl. Phys. 85 (1999) 753. [5] B. Fraboni, A. Gasparotto, F. Priolo, G. Scamarcio, Appl. Phys. A 73 (2001) 35.
K. Bharuth-Ram et al. / Nuclear Instruments and Methods in Physics Research B 272 (2012) 414–417 [6] T. Cesca, A. Verna, G. Mattei, A. Gasparotto, B. Fraboni, G. Impellizzeri, F. Priolo, J. Appl. Phys. 100 (2006) 023539. [7] A. Amore Bonapastaa, F. Filippone, A. Gasparotto, T. Cesca, Appl. Phys. Lett. 88 (2006) 251912. [8] T. Cesca, A. Gasparotto, E. Piana, B. Fraboni, J. Appl. Phys. 102 (2007) 093711. [9] P.J. McNally, Radiat. Eff. Defect Semiconductors 6 (1970) 149. [10] S.J. Pearton, A.R. Von Neida, J.M. Brown, K.T. Short, L.J. Oster, R. Chakrabarti, J. Appl. Phys. 64 (1988) 629. [11] H. Ulrich, A. Knecht, D. Bimberg, H. Krautle, W. Schlaak, J. Appl. Phys. 72 (1992) 3514.
417
[12] V.N. Fedoseyev et al., Nucl. Instr. Meth. B 126 (1997) 88. [13] N.W. Ashcroft, N.D. Mermin, Solid State Physics, W.B. Saunders Publications, 1976. pp. 387–389. [14] U. Wahl, A. Vantomme, G. Langouche, Nucl. Instr. Meth. B 148 (1999) 492. [15] K. Saarinen, P. Hautojärvi, C. Corbel, Nucl. Instr. Meth. A 388 (1997) 434. [16] G. Weyer, S. Damgaard, J.W. Petersen, J. Heinemeier, J. Phys. C: Solid State Phys. 113 (1980) L181–L183. [17] O.H. Nielsen, F.K. Larsen, S. Damgaard, J.W. Petersen, G. Weyer, Z. Phys. B – Condensed Matter 52 (1983) 99.