1. 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

2. 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 semiconductors what, why and how

3. GaAs the archetypal Ga 1-x Mn x As offers all but T C above RT: substitutional vs. interstitial Mn? Mn Ga CB VB Mn Ga h+h+ 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). Mn I T C increases with x and p E a = 0.7 eV (200 º C) Mn I T C increases with annealing T A  200 º C

4. electron emission channeling principles  or  decay

5. electron emission channeling @ ISOLDE sample holder 22x22 Si pad detector on-line @ GHM upgraded with self-triggering readout chips (CR up 3.5 kHz) suitable for short-lived isotopes

6. implant 56 Mn 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 location sensitive unambiguous quantitative 5 experiments (2008-2010) GaAs (bulk) undopedp + - dopedn + - doped Ga1- x MnxAs 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 Ga 1-x Mn x As

7. identifying the interstitial site: T As [111] [100] [110] [211] experimental patterns best fit 56 Mn on Ga-substitutional and T As interstitial sites

8. lattice location of Mn in GaAs high thermal stability of interstitial Mn GaAs Mn Ga Mn I Arrhenius model for the thermally activated migration: f(T,Δt) = f 0 exp[- ν 0 Δt / N exp(-E a / k B T)]  E a = 1.7 – 2.3 eV » 0.7 eV (transport measurements)

9. lattice location of Mn in Ga 1-x Mn x As high thermal stability of interstitial Mn same high thermal stability as in GaAs interstitial Mn is not removed by low temperature annealing (< 200 º C) → it segregates into Mn or MnAs clusters at higher annealing temperatures

10. conclusions unambiguous identification of the interstitial Mn site: T As evidence of its high thermal stability well above 200 º C activation energy of 1.7-2.3 eV (» 0.7 eV) high thermal stability is insensitive to electronic doping interstitial Mn in Ga 1-x Mn x As is not removed by low temperature annealing it segregates into Mn or MnAs clusters at higher annealing temperatures

11. outlook effect of annealing atmosphere (?) which donnor defect out- diffuses at 200 º C? prospects for increasing T C → 56 Mn emission channeling (2011) (and EXAFS) with air/N 2 annealing As interstitial(?) → 73 As emission channeling (2011) Mn still in the matrix: → alternative post-growth treatment for pure substitutional doping (?) → RT ferromagnetism (?)