Transcript 光照射mSR法によるZnO中の反磁性ミュオンの電子構造の研究 ワイド

Hydrogen in Wide Gap
Semiconductor
Why many types of
wide gap
semiconductor have n
type conductivity ?
K.Shimomura (KEK-
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 ｐｐ
ｍ ).
Origin of n type conductivity in wide gap
GaN
1.Direct Wide Band Gap Structure
3.4eV~365nm
Blue LED etc.
2.exhibit strong n type conductivity
Production Method of GaN
A lot of hydrogen !
Electric structure of hydrogen can be
simulated by muonium !
mSR
Discovery of Shallow
Muonium (CdS,1999 Gil et. al)
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)
mSR result on ZnO in KEKMSL
mSR result on ZnO in KEKMSL
mSR result on ZnO in KEKMSL
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.
ZnO ENDOR
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)
Theoretical studies in GaN、
ZnO
Results in GaN
TRIUMF M15 12H ~600Mev.
Results in GaN
Results in GaN
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
Hydrogen level in semiconductors
(Theoretical Study by C.G.Van de Walle et al.)
Hydrogen level in oxides
(Theoretical study )
Titanium dioxide (TiO2)
Widely used as photo catalizer
Strong n type conductivity
Wide Ban Gap 3.3eV
Results in TiO2
Results in TiO2
Results in TiO2
Results in TiO2
Angular Dependence
1.60
1.40
Fre q u e n c y Sp littin g
1.20
1.00
satelite1
0.80
satelite2
0.60
0.40
0.20
0.00
0
10
20
30
40
50
Angle (100) vs. External Field
60
70
80
90
Results in TiO2
A～ 0.2 to 1.2MHz
Ionization Energy ～ ３meV
Shallow Muonium !
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.)