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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
Hydrogen in Wide Gap Semiconductor
  • Why many types of wide gap semiconductor have n type conductivity ?

K.Shimomura (KEK-MSL)

impurity in semiconductor
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 !

slide3
GaN

1.Direct Wide Band Gap Structure

3.4eV~365nm

Blue LED etc.

2.exhibit strong n type conductivity

production method of gan
Production Method of GaN
  • A lot of hydrogen !
  • Electric structure of hydrogen can be simulated by muonium !
origin of n type conductivity in zno
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)

m sr result on zno in kek msl2
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.

shallow muonium could be found in gan
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)

results in gan
Results in GaN

TRIUMF M15 12H ~600Mev.

results in gan3
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
titanium dioxide tio 2
Titanium dioxide (TiO2)

Widely used as photo catalizer

Strong n type conductivity

Wide Ban Gap 3.3eV

results in tio 24
Results in TiO2
  • A~ 0.2 to 1.2MHz
  • Ionization Energy ~ 3meV
  • Shallow Muonium !
summary
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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