Hydrogen in Wide Gap Semiconductor

woundcallousSemiconductor

Nov 1, 2013 (3 years and 5 months ago)

53 views

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


~50meV


Hyperfine constant


A

10
-
4
A
0

Unintentional impurity difficult to study(less than
ppm

).

Origin of n type conductivity in wide gap semiconductors.

More then 30 years old problem !


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 !


m
SR

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
m
SR



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
-
MSL

m
SR result on ZnO in KEK
-
MSL

m
SR 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.


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 (TiO
2
)



Widely used as photo catalizer

Strong n type conductivity

Wide Ban Gap 3.3eV

Results in TiO
2

Results in TiO
2


Results in TiO
2


Results in TiO
2



Results in TiO
2

A


0.2 to 1.2MHz

Ionization Energy



meV

Shallow Muonium !

Summary

m
SR is powerful tool for the stiudies of origin of n
type conductivity in GaN, ZnO and TiO
2
, which are
the most promising material for optelectronics and
photo catalysis.

JPARC


m
SR with Ultra Slow muon Beam


(Dilute Magnetic Semiconductor GaMnAs etc.)


m
SR with negative muon Beam


(N in ZnO or TiO
2

etc)

Neutrino

Factor
y or Intense Muon Source (10
10
/s/cm
2
)


Creation of new type of semiconductor



Co
-
doping method H.Yoshida @ Osaka Univ.)