Direct identification of interstitial Mn in Ga 1-x Mn x As and evidence of its high thermal...
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Direct identification of interstitial Mn in Ga 1-x Mn x As and evidence of its high thermal stability Lino Pereira 1, 2, 3 U. Wahl 2 , J. G. Correia 2, , S. Decoster 3 , J. P. Araújo 1 , A. Vantomme 3 1 IN-IFIMUP, DFA, University of Porto, Portugal 2 ITN, Sacavém, Portugal 3 IKS and INPAC, K.U. Leuven, Belgium
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Direct identification of interstitial Mn in Ga 1-x Mn x As and evidence of its high thermal stability Lino Pereira 1, 2, 3 U. Wahl 2 , J. G. Correia 2, , S. Decoster 3 , J. P. Araújo 1 , A. Vantomme 3. 1 IN-IFIMUP, DFA, University of Porto, Portugal 2 ITN, Sacavém, Portugal - PowerPoint PPT Presentation
Transcript of Direct identification of interstitial Mn in Ga 1-x Mn x As and evidence of its high thermal...
Direct identification of interstitial Mn in Ga1-xMnxAsand evidence of its high thermal stability
Lino Pereira1, 2, 3
U. Wahl2, J. G. Correia2,, S. Decoster3, J. P. Araújo1, A. Vantomme3
1 IN-IFIMUP, DFA, University of Porto, Portugal 2 ITN, Sacavém, Portugal 3 IKS and INPAC, K.U. Leuven, Belgium
what? materials that exhibit both semiconducting and magnetic properties
why? Dream material of spintronics: charge and spin electronics in the same system
how? doping conventional non-magnetic semiconductors with magnetic elements
dilute magnetic semiconductorswhat, why and how
Ga As
the archetypal Ga1-xMnxAsoffers all but TC above RT: substitutional vs. interstitial Mn?
MnGa CB
VB
MnGa
h+
h+
H. Ohno et. al, Appl. Phys. Lett. 69, 363 (1996)H. Ohno, Science 281, 951 (1998) T. Dietl, H. Ohno et al., Science 287, 1019 (2000) T. Hayashi et. al, Appl. Phys. Lett. 78, 1691 (2001) K. M. Yu et. al, Phys. Rev. B 65, 201303 (2002).K. W. Edmonds et al., Phys. Rev. Lett. 92, 037201 (2004).
MnI
TC increases with x and p
Ea = 0.7 eV (200 ºC)
MnI
TC increases with annealing
TA 200 ºC
electron emission channelingprinciples
or decay
electron emission channeling@ ISOLDE
sample holder
sample holder
22x22Si pad detector
on-line @ GHM
upgraded with self-triggering readout chips (CR up 3.5 kHz)
suitablefor short-lived
isotopes
implant 56Mn
anneal at temp. T
measure [111]
measure [100]
measure [110]
measure [211]
experimental patterns(n temp. steps x 4 directions)
simulated patterns (134 sites x 4 directions = 536)
lattice locationsensitive
unambiguousquantitative
5 experiments(2008-2010)
GaAs
(bulk)
undoped
p+- doped
n+- doped
Ga1-xMnxAs thin-films
(LT-MBE grown with stable Mn)
x = 0.01 (1% Mn)
x = 0.05 (5% Mn)
lattice location of Mn in GaAs and Ga1-xMnxAs
lattice location of Mn in GaAs and Ga1-xMnxAsidentifying the interstitial site: TAs
[111]
[100]
[110]
[211]
experimental
patternsbest fit
56Mn onGa-substitutional
andTAs interstitial
sites
lattice location of Mn in GaAshigh thermal stability of interstitial Mn
Ga As MnGa
MnI
Arrhenius model for the thermally activated migration:
f(T,Δt) = f0 exp[- ν0 Δt / N exp(-Ea / kBT)] Ea = 1.7 – 2.3 eV
» 0.7 eV(transport measurements)
lattice location of Mn in Ga1-xMnxAshigh thermal stability of interstitial Mn
same high thermal stability as in GaAs
interstitial Mn is not removed by low temperature annealing (< 200 ºC) → it segregates into Mn or MnAs clusters at higher annealing temperatures
conclusions
• unambiguous identification of the interstitial Mn site: TAs
• evidence of its high thermal stability well above 200 ºC activation energy of 1.7-2.3 eV (» 0.7 eV)
• high thermal stability is insensitive to electronic doping
• interstitial Mn in Ga1-xMnxAs is not removed by low temperature annealing it segregates into Mn or MnAs clusters at higher annealing temperatures
outlook
effect of annealing atmosphere (?)
which donnor defect out-diffuses at 200 ºC?
prospects for increasing TC
→ 56Mn emission channeling (2011) (and EXAFS) with air/N2 annealing
As interstitial(?)→ 73As emission channeling (2011)
Mn still in the matrix:→ alternative post-growth treatment for pure substitutional doping (?)
→ RT ferromagnetism (?)
