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A photoluminescence study of Cd, In and Sn in ZnO using radioisotopes

A photoluminescence study of Cd, In and Sn in ZnO using radioisotopes. Joseph Cullen, Martin Henry , Enda McGlynn Dublin City University Karl Johnston Universitat des Saarlandes and CERN/ISOLDE. The nature of ZnO. ZnO - semiconductor at room temperature, energy gap ~ 3.4 eV

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A photoluminescence study of Cd, In and Sn in ZnO using radioisotopes

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  1. A photoluminescence study of Cd, In and Sn in ZnO using radioisotopes Joseph Cullen, Martin Henry, Enda McGlynn Dublin City University Karl Johnston Universitat des Saarlandes and CERN/ISOLDE

  2. The nature of ZnO ZnO - semiconductor at room temperature, energy gap ~ 3.4 eV - universally n-type as-grown - p-type conduction can be obtained, but not readily Difficult to purify for growth of large single crystal boules Questions: Origin(s) of dominant n-type conduction Understanding impurities / defects

  3. The neighbourhood of ZnO • Group III impurity on Zn site should: • provide one excess electron • act as donor: n-type conductivity • provide binding centre for e-h pairs under optical excitation • Group V impurity on O site should: • create a free hole • act as acceptor: p-type conductivity • BUT these prefer to occupy Zn sites and/or form complex defects

  4. Our research programme: • Proof of common donor impurity identifications • Wider study of Zn-site and O-site impurities • Principal experimental technique: • Photoluminescence at low temperatures • - in conjunction with other techniques/partners in ISOLDE collaboration

  5. Multiplicity of lines • Various impurities • Various transition types I-lines PL intensity D0X – neutral donor-bound excitons D+X – ionised donor bound excitons Also - DAP, eA, A0X 3.34 3.36 3.38 Photon energy (eV)

  6. Proof of identity of common donor impurities

  7. ZnO:Ga I-line identification b- 46.5 hr 72Zn 14.1 hr b- 72Ga 4.86 hr b- 72Ge 73Ga 73Ge

  8. ZnO:73As → 73Ge decay Half-life: 80.3 days

  9. Decay of Ga-related I8 (and I1) Growth of Ge-related DD2

  10. New results from Ga → Ge decay • Ge-related luminescence observed for the first time • Large spectral binding energy compared to III impurities • Low thermal binding energy • Similar to I-lines under stress

  11. Nature of Ge-related luminescence? Theory: Ge and Si should act as shallow double-donors Lyons et al (2009) • Ge on Zn site: • two extra electrons per Ge atom • several electron-hole recombination paths are possible • we are pursuing this using Zeeman/stress

  12. ZnO:In I-line identification Is I-9 the DoX for In ? Any evidence for D+X line ? Also: does Sn behave like Ge? 111In → 111Cd Muller at al – APL (2007) I-9 identified with In D0X No evidence for D+X line Possible Cd-related weak band

  13. We examined the reverse decay path 117Ag 72 s 117Cd 3 h 117In 43 m

  14. ZnO:117Cd/In/Sn I-2 line I-9 line • Confirm Muller et al result for I-9 • New results: • I-2 is D+X for In • No Cd or Sn signals observed

  15. Fits to experimental data

  16. Summary For Zn-site impurities in ZnO Lines I-1 and I-8 due to Ga Lines I-2 and I-9 due to In New PL line due to Ge Not observed: Sn counterpart of Ge line Cd counterpart of Hg line (Agne et al 2003)

  17. Thank you! ENSAR

  18. Zn-site impurities

  19. Pb in ZnO…. R. J. Mendelsberg et al. J. Vac. Sci. Technol. B 27(3) (2009)

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