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Hydrogen in Wide Gap Semiconductor

Hydrogen in Wide Gap Semiconductor. Why many types of wide gap semiconductor have n type conductivity ? K.Shimomura (KEK-MSL). Impurity in Semiconductor. Shallow donor acceptor Bohr radious a= e ×(m e /m*)×a 0 ~20×a 0 Ionization Energy (13.6eV) × (m*/m e )/ e 2

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Hydrogen in Wide Gap Semiconductor

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  1. Hydrogen in Wide Gap Semiconductor • Why many types of wide gap semiconductor have n type conductivity ? K.Shimomura (KEK-MSL)

  2. Impurity in Semiconductor Shallow donor acceptor Bohr radious a=e×(me/m*)×a0 ~20×a0 Ionization Energy (13.6eV) × (m*/me)/ e2 ~50meV Hyperfine constant A～10-4A0 Unintentional impurity difficult to study(less than ｐｐｍ). Origin of n type conductivity in wide gap semiconductors. More then 30 years old problem !

  3. GaN 1.Direct Wide Band Gap Structure 3.4eV~365nm Blue LED etc. 2.exhibit strong n type conductivity

  4. Production Method of GaN • A lot of hydrogen ! • Electric structure of hydrogen can be simulated by muonium !

  5. mSR

  6. Discovery of Shallow Muonium (CdS,1999 Gil et. al)

  7. Origin of n type conductivity in ZnO • Theoretical Study C.G.Van de Walle Hydrogen behaves as a shallow donor/ Phys.Rev.Lett.85,1012(2000) • Experimental Study by mSR Discovery of Weakly Bounded Muonium S.F.Cox et. al Phys.Rev.Lett.86,1012(2001) K.Shimomura et. al Phys.Rev.Lett.89,25505(2002)

  8. mSR result on ZnO in KEK-MSL

  9. mSR result on ZnO in KEK-MSL

  10. mSR result on ZnO in KEK-MSL 1.Two kinds of Muonium have been clearly observed. 2.Both Muonium has axial symmetry along to [0001] axis. 3.Hyperfine constants of the observed muoniums are 10-4 times smaller than the muonium in va cuuum. These value is well correspond to the simple model calculation for shallow donor. 4.Ionization energy of these muoniums are also similar to the ionization energy of the un-intentional donor observed by Hall effect measurements. These results indicate hydrogen could behave as a shallow donor and might be an origin of n type conductivity in ZnO.

  11. ZnO ENDOR

  12. Shallow Muonium could be found in GaN ? Theory Hydrogen negative U Deep center J.Neugebaner, C.G.Van de Walle Phys.Rev.Lett,75, 4452(1995) C.G.Van de Walle, J.Neugebaner Nature 423, 626(2003) Experiment K.Shimomura et al PRL92,135505 (2003)

  13. Theoretical studies in GaN、ZnO

  14. Results in GaN TRIUMF M15 12H ~600Mev.

  15. Results in GaN

  16. Results in GaN

  17. Results in GaN • External field dependence of the ratio of satellite peaks are explained by muonium’s electron polarization in high magnetic field ( ~Tesla). Muonium have [0001] axis symmetry. • Hyperfine parameter A//=+337(10) kHz, A⊥=-243(30)kHz • Ionization Energy ~5meV

  18. Hydrogen level in semiconductors(Theoretical Study by C.G.Van de Walle et al.)

  19. Hydrogen level in oxides(Theoretical study )

  20. Titanium dioxide (TiO2) Widely used as photo catalizer Strong n type conductivity Wide Ban Gap 3.3eV

  21. Results in TiO2

  22. Results in TiO2

  23. Results in TiO2

  24. Results in TiO2

  25. Results in TiO2 • A～ 0.2 to 1.2MHz • Ionization Energy ～ ３meV • Shallow Muonium !

  26. Summary • mSR is powerful tool for the stiudies of origin of n type conductivity in GaN, ZnO and TiO2, which are the most promising material for optelectronics and photo catalysis. • ＪＰＡＲＣ • mSR with Ultra Slow muon Beam • (Dilute Magnetic Semiconductor GaMnAs etc.) • mSR with negative muon Beam • (N in ZnO or TiO2 etc) • Ｎｅｕｔｒｉｎｏ　Ｆａｃｔｏｒy or Intense Muon Source (1010/s/cm2) • Creation of new type of semiconductor • 　（Co-doping method H.Yoshida @ Osaka Univ.)

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