From dilute to condensed magnetic semiconductors:     a protocol for systematic characterization                          ...
Co-authors   A. Navarro-Quezada, B. Faina, T. Devillers, T. Li, A. rois, T. Winkler,   A. Bonanni   Institute for Semicond...
Outline1   Introduction2   Growth          characterization protocol3   Case studies      Dilute (Ga,Mn)N      Fe segregat...
IntroductionBuilding-blocks for Spintronics devices                                                     [A. Bonanni and T....
DMS → (Ga,Mn)N  With holes → sp-d Zener model       x=5% and 3.5×1020 h/cm3     [T. Dietl et al., Science (2000)] Controve...
DMS → (Ga,Mn)N  With holes → sp-d Zener model                            Without holes → double exchange                  ...
DMS → (Ga,Mn)N  With holes → sp-d Zener model                            Without holes → double exchange                  ...
CMS → (Ga,Fe)NTMs solubility in (most) semiconductors at thermal equilibrium is low  ⇒ chemical/crystallographic phase sep...
CMS → (Ga,Fe)NTMs solubility in (most) semiconductors at thermal equilibrium is low  ⇒ chemical/crystallographic phase sep...
CMS → (Ga,Fe)NTMs solubility in (most) semiconductors at thermal equilibrium is low  ⇒ chemical/crystallographic phase sep...
CMS → (Ga,Fe)NTMs solubility in (most) semiconductors at thermal equilibrium is low  ⇒ chemical/crystallographic phase sep...
CMS → (Ga,Fe)NTMs solubility in (most) semiconductors at thermal equilibrium is low  ⇒ chemical/crystallographic phase sep...
Growth             characterization protocol   M. Rovezzi (HFP/JKU)       DMS & CMS characterization   DEMATEN 2nd worksho...
Metalorganic Vapour Phase Epitaxy(Ga,Mn)N and (Ga,Fe)N[:Si]                               AIXTRON 200RF horizontal reactor...
Limits of conventional high-resolution XRD  No evidence of second phases                        GaN(0002) peak broadening ...
Limits of conventional high-resolution XRD  No evidence of second phases                        GaN(0002) peak broadening ...
European Synchrotron Radiation Facility, Grenoble    M. Rovezzi (HFP/JKU)   DMS & CMS characterization   DEMATEN 2nd works...
Case studies 1   Dilute (Ga,Mn)N                   [W. Stefanowicz et al., arXiv.org 0912.4216 (2010)] 2   Fe segregation ...
TEM                   Wide range of Mn concentration up to ≈ 1 at. %                                                      ...
TEM                   Wide range of Mn concentration up to ≈ 1 at. %                                                      ...
SXRDMeasurements conducted on BM20 at 10 KeV                                                        High crystal quality [...
SXRDMeasurements conducted on BM20 at 10 KeV                                                        High crystal quality [...
EXAFSMeasurements conducted on BM08 at Mn K-edge                                   (a)     kmin                           ...
EXAFSMeasurements conducted on BM08 at Mn K-edge                                   (a)     kmin                           ...
Charge stateRole of TMs charge state in DMS   Exchange interactions   Carriers and their localization   Inter-atomic Coulo...
Charge stateRole of TMs charge state in DMS   Exchange interactions   Carriers and their localization   Inter-atomic Coulo...
XANESMeasurements conducted on BM08 at Mn K-edge                                                                          ...
SQUIDAccurate subtraction of the substrate diamagnetic signal and extra m(H,T)            Magnetization(T)                ...
SQUIDAccurate subtraction of the substrate diamagnetic signal and extra m(H,T)            Magnetization(T)                ...
SummaryDilute (Ga,Mn)N - x ≤ 1%   Mn substitutional in GaN   Mn3+ charge state   ParamagneticOutlook   Increase Mn concent...
SummaryDilute (Ga,Mn)N - x ≤ 1%   Mn substitutional in GaN   Mn3+ charge state   ParamagneticOutlook   Increase Mn concent...
Case studies 1   Dilute (Ga,Mn)N 2   Fe segregation in GaN [A. Navarro-Quezada et al., Phys. Rev. B 81, 205206 (2010)]    ...
(Ga,Fe)N: a high TC magnetic semiconductor?                                                            Ferromagnetism pers...
(Ga,Fe)N: a high TC magnetic semiconductor?                                                            Ferromagnetism pers...
Presence of ε-Fe3 N nano-crystalsBainite structure (hexagonal), ≈ 15 nm average size, TC = 575 K                ⇒ Solubili...
Presence of ε-Fe3 N nano-crystalsBainite structure (hexagonal), ≈ 15 nm average size, TC = 575 K                ⇒ Solubili...
How to control Fe incorporation in GaN?   Growth rate   Co-doping   Growth temperature    M. Rovezzi (HFP/JKU)   DMS & CMS...
Control by growth rate     ⇒ Solubility limit increased by increasing the growth rate (TMGa)    M. Rovezzi (HFP/JKU)      ...
Control by growth rate     ⇒ Solubility limit increased by increasing the growth rate (TMGa)    M. Rovezzi (HFP/JKU)      ...
Fermi-level engineering by co-doping with SiPartial charge state reduction, Fe3+ → Fe2+ , demonstrated by XANES    Fe 3d s...
Fermi-level engineering by co-doping with SiPartial charge state reduction, Fe3+ → Fe2+ , demonstrated by XANES    Fe 3d s...
Fermi-level engineering by co-doping with SiPartial charge state reduction, Fe3+ → Fe2+ , demonstrated by XANES    Fe 3d s...
Control by co-doping                   ⇒ Solubility limit increased by co-doping with Si   M. Rovezzi (HFP/JKU)           ...
Control by co-doping                   ⇒ Solubility limit increased by co-doping with Si   M. Rovezzi (HFP/JKU)           ...
Growth temperatureSXRD and TEM   Additional Fe-rich phases:   γ -Fe4 N, ζ-Fe2 N, α-Fe, γ-Fe   Nano-crystals size: 10-20 nm...
Growth temperatureXANES & EXAFS                                                   S691Norm. Absorption Coefficient − µ(E) ...
Growth temperatureXANES & EXAFS                                                   S691Norm. Absorption Coefficient − µ(E) ...
Growth temperatureSQUID                                                            Paramagnetic part ⇒                    ...
SummarySegregated (Ga,Fe)N   High TC FM → ε-Fe3 N clusters   Solubility limit controlled by      → growth-rate      → co-d...
SummarySegregated (Ga,Fe)N   High TC FM → ε-Fe3 N clusters   Solubility limit controlled by      → growth-rate      → co-d...
CMSSecond generation spintronics devicesSpin batteryElectromotive force and hugemagnetoresistance observed inmagnetic tunn...
ConclusionsGrowth          characterization protocol   Self-consistent loop     1   Growth/optimization     2   Structural...
Thank you for your attention!Contact/further discussion                           mauro.rovezzi@jku.atReferences for this ...
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From DMS to CMS: a characterization protocol

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Transcript of "From DMS to CMS: a characterization protocol"

  1. 1. From dilute to condensed magnetic semiconductors: a protocol for systematic characterization Mauro Rovezzi1 1 Institute for Semiconductors and Solid State Physics, Johannes Kepler University, Linz, Austria [W. Stefanowicz et al., arXiv.org 0912.4216 (2010)] [A. Navarro-Quezada et al., Phys. Rev. B 81, 205206 (2010)] M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 1 / 32
  2. 2. Co-authors A. Navarro-Quezada, B. Faina, T. Devillers, T. Li, A. rois, T. Winkler, A. Bonanni Institute for Semiconductors and Solid State Physics, Johannes Kepler University, Linz, Austria W. Stefanowicz, D. Sztenkiel, R. Jakiela, M. Sawicki, T. Dietl Institute of Physics, Polish Academy of Sciences, Warsaw, Poland R. T. Lechner, G. Bauer Institute for Semiconductors and Solid State Physics, Johannes Kepler University, Linz, Austria F. d’Acapito Italian National Research Council, IOM-OGG, c/o ESRF GILDA, Grenoble, France M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 2 / 32
  3. 3. Outline1 Introduction2 Growth characterization protocol3 Case studies Dilute (Ga,Mn)N Fe segregation in GaN4 Conclusions M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 3 / 32
  4. 4. IntroductionBuilding-blocks for Spintronics devices [A. Bonanni and T. Dietl, Chem. Soc. Rev. (2010)] M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 4 / 32
  5. 5. DMS → (Ga,Mn)N With holes → sp-d Zener model x=5% and 3.5×1020 h/cm3 [T. Dietl et al., Science (2000)] Controversial experimental reports ⇒ accurate nanoscale characterization M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 5 / 32
  6. 6. DMS → (Ga,Mn)N With holes → sp-d Zener model Without holes → double exchange [K. Sato et al., Phys. Rev. B (2004)] x=5% and 3.5×1020 h/cm3 [T. Dietl et al., Science (2000)] [L. Berqvist et al., Phys. Rev. Lett. (2004)] Controversial experimental reports ⇒ accurate nanoscale characterization M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 5 / 32
  7. 7. DMS → (Ga,Mn)N With holes → sp-d Zener model Without holes → double exchange [K. Sato et al., Phys. Rev. B (2004)] x=5% and 3.5×1020 h/cm3 [T. Dietl et al., Science (2000)] [L. Berqvist et al., Phys. Rev. Lett. (2004)] Controversial experimental reports ⇒ accurate nanoscale characterization M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 5 / 32
  8. 8. CMS → (Ga,Fe)NTMs solubility in (most) semiconductors at thermal equilibrium is low ⇒ chemical/crystallographic phase separation ⇒ a priori unknown magnetic properties ⇒ mostly high TC FM Detection and control of phase separation ⇒ nano-characterization tools M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 6 / 32
  9. 9. CMS → (Ga,Fe)NTMs solubility in (most) semiconductors at thermal equilibrium is low ⇒ chemical/crystallographic phase separation ⇒ a priori unknown magnetic properties ⇒ mostly high TC FMExamples of chemical phase separation (spinodal decomposition in DMS literature) (Ga,Mn)As annealing[M. Moreno et al., J. Appl. Phys. (2002)] Detection and control of phase separation ⇒ nano-characterization tools M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 6 / 32
  10. 10. CMS → (Ga,Fe)NTMs solubility in (most) semiconductors at thermal equilibrium is low ⇒ chemical/crystallographic phase separation ⇒ a priori unknown magnetic properties ⇒ mostly high TC FMExamples of chemical phase separation (spinodal decomposition in DMS literature) (Ga,Mn)As annealing (Ga,Mn)N clusters [G. Martinez-Criado et al., Appl. Phys. Lett. (2005)][M. Moreno et al., J. Appl. Phys. (2002)] Detection and control of phase separation ⇒ nano-characterization tools M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 6 / 32
  11. 11. CMS → (Ga,Fe)NTMs solubility in (most) semiconductors at thermal equilibrium is low ⇒ chemical/crystallographic phase separation ⇒ a priori unknown magnetic properties ⇒ mostly high TC FMExamples of chemical phase separation (spinodal decomposition in DMS literature) (Ga,Mn)As annealing (Ga,Mn)N clusters (Ge,Mn) nano-columns [G. Martinez-Criado et al., Appl. Phys. Lett. (2005)][M. Moreno et al., J. Appl. [M. Jamet et al., Nature Mat. Phys. (2002)] (2006)] Detection and control of phase separation ⇒ nano-characterization tools M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 6 / 32
  12. 12. CMS → (Ga,Fe)NTMs solubility in (most) semiconductors at thermal equilibrium is low ⇒ chemical/crystallographic phase separation ⇒ a priori unknown magnetic properties ⇒ mostly high TC FMExamples of chemical phase separation (spinodal decomposition in DMS literature) (Ga,Mn)As annealing (Ga,Mn)N clusters (Ge,Mn) nano-columns [G. Martinez-Criado et al., Appl. Phys. Lett. (2005)][M. Moreno et al., J. Appl. [M. Jamet et al., Nature Mat. Phys. (2002)] (2006)] Detection and control of phase separation ⇒ nano-characterization tools M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 6 / 32
  13. 13. Growth characterization protocol M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 7 / 32
  14. 14. Metalorganic Vapour Phase Epitaxy(Ga,Mn)N and (Ga,Fe)N[:Si] AIXTRON 200RF horizontal reactor c-plane sapphire substrates Precursors: TMGa, NH3 , Cp2 Fe, Cp2 Mn, SiH4 Monitoring: ellipsometryWell established growth procedure 1 Substrate nitridation 2 LT (540 ◦ C) GaN nucl. layer 3 Annealing/recrystallization 4 1 µm HT (1050 ◦ C) GaN 5 0.5 – 1 µm GaN:(Fe/Mn)[:Si] 800 – 950 ◦ C 50 – 490 sccm (→ 0.05 – 1 %) M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 8 / 32
  15. 15. Limits of conventional high-resolution XRD No evidence of second phases GaN(0002) peak broadening ⇒ Synchrotron radiation M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 9 / 32
  16. 16. Limits of conventional high-resolution XRD No evidence of second phases GaN(0002) peak broadening ⇒ Synchrotron radiation M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 9 / 32
  17. 17. European Synchrotron Radiation Facility, Grenoble M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 10 / 32
  18. 18. Case studies 1 Dilute (Ga,Mn)N [W. Stefanowicz et al., arXiv.org 0912.4216 (2010)] 2 Fe segregation in GaN M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 11 / 32
  19. 19. TEM Wide range of Mn concentration up to ≈ 1 at. % Energy dispersive X-ray spectroscopy Low-resolution High-resolution No evidence of crystallographic phase separation No Mn-induced defects Is Mn really dilute? → SXRD M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 12 / 32
  20. 20. TEM Wide range of Mn concentration up to ≈ 1 at. % Energy dispersive X-ray spectroscopy Low-resolution High-resolution No evidence of crystallographic phase separation No Mn-induced defects Is Mn really dilute? → SXRD M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 12 / 32
  21. 21. SXRDMeasurements conducted on BM20 at 10 KeV High crystal quality [from the FWHM of rocking curves around GaN(0002)] No evidence for second phases Increment of the lattice parameters with Mn concentration In situ annealing (under N-rich atmosphere) experiments → samples stable up to 900 ◦ C Where is Mn? → EXAFS M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 13 / 32
  22. 22. SXRDMeasurements conducted on BM20 at 10 KeV High crystal quality [from the FWHM of rocking curves around GaN(0002)] No evidence for second phases Increment of the lattice parameters with Mn concentration In situ annealing (under N-rich atmosphere) experiments → samples stable up to 900 ◦ C Where is Mn? → EXAFS M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 13 / 32
  23. 23. EXAFSMeasurements conducted on BM08 at Mn K-edge (a) kmin kmaxEXAFS signal, k χ(k)2 Mn substitutional in GaN at Ga sites (MnGa ) #490A Fit(MnGa) #100A Low local disorder 2 4 6 8 10 12 Photoelectron wavevector, k [Å−1] Mn-Ga first shell expansion O ∆R=2.5(5)% MnGa MnI T Mn3GaN (b) Mn3GaN MnI Additional contributions can be ruledMagnitude of the FT, |χ(R)| [Å ]−3 MnI Mn O (c) out in the 5% limit I T Mn interstitial defects and Mn3 GaN 1 2 3 4 5 6 Rmin simulated via ab initio codes Rmax [VASP+FEFF8] What Mn charge state? → XANES 1 2 3 4 5 6 7 8 Distance, R [Å] − without phase correction M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 14 / 32
  24. 24. EXAFSMeasurements conducted on BM08 at Mn K-edge (a) kmin kmaxEXAFS signal, k χ(k)2 Mn substitutional in GaN at Ga sites (MnGa ) #490A Fit(MnGa) #100A Low local disorder 2 4 6 8 10 12 Photoelectron wavevector, k [Å−1] Mn-Ga first shell expansion O ∆R=2.5(5)% MnGa MnI T Mn3GaN (b) Mn3GaN MnI Additional contributions can be ruledMagnitude of the FT, |χ(R)| [Å ]−3 MnI Mn O (c) out in the 5% limit I T Mn interstitial defects and Mn3 GaN 1 2 3 4 5 6 Rmin simulated via ab initio codes Rmax [VASP+FEFF8] What Mn charge state? → XANES 1 2 3 4 5 6 7 8 Distance, R [Å] − without phase correction M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 14 / 32
  25. 25. Charge stateRole of TMs charge state in DMS Exchange interactions Carriers and their localization Inter-atomic Coulomb interactionsMn in GaN Mn2+ → 3d 5 Mn3+ → 3d 4 M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 15 / 32
  26. 26. Charge stateRole of TMs charge state in DMS Exchange interactions Carriers and their localization Inter-atomic Coulomb interactionsMn in GaN Mn2+ → 3d 5 Mn3+ → 3d 4 M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 15 / 32
  27. 27. XANESMeasurements conducted on BM08 at Mn K-edge (a) Absorption edge shifts with the #100A #490A charge state ⇒ Mn3+ ⇒ Norm. µ(E) MnO Mn2O3 MnO2 confirmed by pre-edge peaks 6535 6540 6545 6550 6555 6560 6565 6570 (b) #100A #490A Norm. Absorption Coefficient − µ(E) 4 Mn(3d ) 5 Mn(3d ) (c) A4 A3 A1 A2 Bkg Fit 6537 6540 6543 6546 6549 6530 6540 6550 6560 6570 6580 6590 6600 6610 Fine-structure simulated with Energy [eV] FDMNES ⇒ MnGa M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 16 / 32
  28. 28. SQUIDAccurate subtraction of the substrate diamagnetic signal and extra m(H,T) Magnetization(T) Magnetization(H) ⇒ Paramagnetism from non-interacting Mn3+ ions M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 17 / 32
  29. 29. SQUIDAccurate subtraction of the substrate diamagnetic signal and extra m(H,T) Magnetization(T) Magnetization(H) ⇒ Paramagnetism from non-interacting Mn3+ ions M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 17 / 32
  30. 30. SummaryDilute (Ga,Mn)N - x ≤ 1% Mn substitutional in GaN Mn3+ charge state ParamagneticOutlook Increase Mn concentration (in the DMS limit) Co-doping: (Ga,Mn)N:Si → n-type → Mn2+ (Ga,Mn)N:Mg → p-type → itinerant h M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 18 / 32
  31. 31. SummaryDilute (Ga,Mn)N - x ≤ 1% Mn substitutional in GaN Mn3+ charge state ParamagneticOutlook Increase Mn concentration (in the DMS limit) Co-doping: (Ga,Mn)N:Si → n-type → Mn2+ (Ga,Mn)N:Mg → p-type → itinerant h M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 18 / 32
  32. 32. Case studies 1 Dilute (Ga,Mn)N 2 Fe segregation in GaN [A. Navarro-Quezada et al., Phys. Rev. B 81, 205206 (2010)] M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 19 / 32
  33. 33. (Ga,Fe)N: a high TC magnetic semiconductor? Ferromagnetism persisting above Paramagnetism from isolated Fe3+ room temperature What is the origin of the ferromagnetism? M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 20 / 32
  34. 34. (Ga,Fe)N: a high TC magnetic semiconductor? Ferromagnetism persisting above Paramagnetism from isolated Fe3+ room temperature What is the origin of the ferromagnetism? M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 20 / 32
  35. 35. Presence of ε-Fe3 N nano-crystalsBainite structure (hexagonal), ≈ 15 nm average size, TC = 575 K ⇒ Solubility limit at ≈ 0.4 % Fe in our growth conditions M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 21 / 32
  36. 36. Presence of ε-Fe3 N nano-crystalsBainite structure (hexagonal), ≈ 15 nm average size, TC = 575 K ⇒ Solubility limit at ≈ 0.4 % Fe in our growth conditions M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 21 / 32
  37. 37. How to control Fe incorporation in GaN? Growth rate Co-doping Growth temperature M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 22 / 32
  38. 38. Control by growth rate ⇒ Solubility limit increased by increasing the growth rate (TMGa) M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 23 / 32
  39. 39. Control by growth rate ⇒ Solubility limit increased by increasing the growth rate (TMGa) M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 23 / 32
  40. 40. Fermi-level engineering by co-doping with SiPartial charge state reduction, Fe3+ → Fe2+ , demonstrated by XANES Fe 3d states resides in the GaN band gap Co-doping with Si → tuning Fermi level → Fe charge state modification Coulomb repulsion between Fe ions hinders aggregation [T. Dietl, Nature Mat. (2006)] Do this really hinders the aggregation? M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 24 / 32
  41. 41. Fermi-level engineering by co-doping with SiPartial charge state reduction, Fe3+ → Fe2+ , demonstrated by XANES Fe 3d states resides in the GaN band gap Co-doping with Si → tuning Fermi level → Fe charge state modification Coulomb repulsion between Fe ions hinders aggregation [T. Dietl, Nature Mat. (2006)] Do this really hinders the aggregation? M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 24 / 32
  42. 42. Fermi-level engineering by co-doping with SiPartial charge state reduction, Fe3+ → Fe2+ , demonstrated by XANES Fe 3d states resides in the GaN band gap Co-doping with Si → tuning Fermi level → Fe charge state modification Coulomb repulsion between Fe ions hinders aggregation [T. Dietl, Nature Mat. (2006)] Do this really hinders the aggregation? M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 24 / 32
  43. 43. Control by co-doping ⇒ Solubility limit increased by co-doping with Si M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 25 / 32
  44. 44. Control by co-doping ⇒ Solubility limit increased by co-doping with Si M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 25 / 32
  45. 45. Growth temperatureSXRD and TEM Additional Fe-rich phases: γ -Fe4 N, ζ-Fe2 N, α-Fe, γ-Fe Nano-crystals size: 10-20 nm M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 26 / 32
  46. 46. Growth temperatureXANES & EXAFS S691Norm. Absorption Coefficient − µ(E) [arb. shift] S680 S690 950 °C Fit 3 Fit 2 XANES: linear Fit 1 850 °C combination fits of 800 °C theoretical spectra Fe−Ga (FDMNES) ⇒ identification Fe−Fe and concentration of Rmin Fe−N |χ(R)| Rmax different phases EXAFS: refinement of the 1 2 3 4 5 EF Distance, R [Å] − without phase correction local structure 7110 7120 7130 7140 7150 7160 7170 7180 7190 Energy [eV] SXRD, (HR)TEM and XAS ⇒ phase-diagram of Fex Ny in GaN M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 27 / 32
  47. 47. Growth temperatureXANES & EXAFS S691Norm. Absorption Coefficient − µ(E) [arb. shift] S680 S690 950 °C Fit 3 Fit 2 XANES: linear Fit 1 850 °C combination fits of 800 °C theoretical spectra Fe−Ga (FDMNES) ⇒ identification Fe−Fe and concentration of Rmin Fe−N |χ(R)| Rmax different phases EXAFS: refinement of the 1 2 3 4 5 EF Distance, R [Å] − without phase correction local structure 7110 7120 7130 7140 7150 7160 7170 7180 7190 Energy [eV] SXRD, (HR)TEM and XAS ⇒ phase-diagram of Fex Ny in GaN M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 27 / 32
  48. 48. Growth temperatureSQUID Paramagnetic part ⇒ dilute and non-interacting FeGa Superparamagnetic-like part ⇒ ferromagnetic ε-Fe3 N, γ -Fe4 N α-Fe and γ-Fe Antiferromagnetic component ⇒ ζ-Fe2 N and highly-nitrated Fex N (x≤2) phases M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 28 / 32
  49. 49. SummarySegregated (Ga,Fe)N High TC FM → ε-Fe3 N clusters Solubility limit controlled by → growth-rate → co-doping Growth temperature → additional Fex Ny phases → wide range of magnetic behaviorsOutlook Control of single-phase Fex Ny in/on GaN M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 29 / 32
  50. 50. SummarySegregated (Ga,Fe)N High TC FM → ε-Fe3 N clusters Solubility limit controlled by → growth-rate → co-doping Growth temperature → additional Fex Ny phases → wide range of magnetic behaviorsOutlook Control of single-phase Fex Ny in/on GaN M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 29 / 32
  51. 51. CMSSecond generation spintronics devicesSpin batteryElectromotive force and hugemagnetoresistance observed inmagnetic tunnel junctions withzb-MnAs clustersDemonstrated at 30 K [N.H. Pham et al., Nature (2009)] M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 30 / 32
  52. 52. ConclusionsGrowth characterization protocol Self-consistent loop 1 Growth/optimization 2 Structural characterization 3 Magnetic characterization 4 Modeling/simulation Synchrotron radiation as required tool M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 31 / 32
  53. 53. Thank you for your attention!Contact/further discussion mauro.rovezzi@jku.atReferences for this work W. Stefanowicz et al., arXiv.org 0912.4216 (2010) → soon in Phys. Rev. B A. Navarro-Quezada et al., Phys. Rev. B 81, 205206 (2010) M. Rovezzi et al., Phys. Rev. B 79, 195209 (2009) A. Bonanni et al., Phys. Rev. Lett. 101, 135502 (2008) M. Rovezzi (HFP/JKU) DMS & CMS characterization DEMATEN 2nd workshop (June 2010) 32 / 32
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