1. Plzeň, 5.1.101 Tato prezentace je spolufinancována Evropským sociálním fondem a státním rozpočtem České republiky. Magnetický polovodič (Ga,Mn)As: technologie, možnosti aplikace Fyzikální ústav AV ČR, v.v.i. theory (Jugwirth, Sinova,...) MBE (Novák, Cukr, Olejník,...) SQUID, transport (Olejník, Novák,...) Hitachi Lab Cambridge, UK lithography (Irvine,...) transport (Wunderlich, Owen,...) University,of Nottingham, UK MBE (Foxon, Campion)

2. Plzeň, 5.1.102 magnetic semiconductors (Ga,Mn)As technology issues optimized x Mn -series gating GaMnAs Outline

3. Plzeň, 5.1.103 semiconductors magnetism (ferro)magnetic semiconductors Eu-chalcogenides (EuO, EuGdS,...) problems: technology, T C,... diluted magnetic semiconductors (GaMnAs, GaMnP,...) Modern electronics electrically tunable magnetic properties spin degree of freedom spintronics !

4. Plzeň, 5.1.10 Ga 1-x Mn x As - semiconductor Mn : [Ar] 4s 2 3d 5 x Mn < 0.1 % : E A ~ 100 meV x Mn > 1 % : Jungwirth et al., PRB 76, 125206 (2007) x=0.05% 1% 2% 7% ~100 meV E G /2 E DOS EFEF

5. Plzeň, 5.1.105 Ga 1-x Mn x As - ferromagnet x Mn > 1 % : ~ carrier mediated FM 1 hole per Mn ~ 4.5  B per Mn T C ~ M.p 1/3

6. Plzeň, 5.1.106 Ga 1-x Mn x As - technology hex. MnAs in cub. GaAs Problem: solubility limit of Mn in GaAs (~ 0.1%) Solution: Molecular Beam Epitaxy low-temperature MBE GaAs at T S > 150°C, but: defects, ,  growth parameters critical

7. Plzeň, 5.1.107 Molecular Beam Epitaxy UHV growth chamber growth kinetics substrate beams sources high crystallographic quality low growth rate atomically smooth interfaces heterostructures, superlattices

8. Plzeň, 5.1.108 MBE in FZU AV ČR III-V semiconductors Kryovak Veeco Gen II - 2” substrates - 3 chambers (load-lock, preparation, growth) - elements:group V – As group III – Ga, Al, In dopants – Si, C, Mn - in situ diagnostics: RHEED band-edge thermometry

9. Plzeň, 5.1.109

10. 10 Ga 1-x Mn x As - technology hex. MnAs in cub. GaAs Problem: solubility limit of Mn in GaAs (~ 0.1%) Solution: Molecular Beam Epitaxy low-temperature MBE GaAs at T S > 150°C, but: defects, ,  growth parameters critical

11. Plzeň, 5.1.1011 crystal quality / surface morphology ?crystal quality / surface morphology ? amorphous / poly / 2D / 3D ? ~ 240°C  3D RHEED images (non-rotating) LT-MBE of GaMnAs ~ 220°C  2D ~ 7% Mn ~ 260°C  poly growth T: > <

12. Plzeň, 5.1.1012 J. Appl. Phys. 102, 083536 (2007) LT-MBE of GaMnAs crystal quality / surface morphologycrystal quality / surface morphology temperature stability ?temperature stability ? band-gap thermometry doping-induced overheating 3 % Mn 5 % Mn 7 % Mn

13. Plzeň, 5.1.1013 3D 2D also: Campion et al., J. Mater. Sci. 15, 727 (2004) LT-MBE of GaMnAs surface morphology: 2D/3D best!surface morphology: 2D/3D best! temperature stabilitytemperature stability

14. Plzeň, 5.1.1014 3D 2D As:Ga=3:1 As:Ga=1:1 LT-MBE of GaMnAs surface morphology : 2D/3Dsurface morphology : 2D/3D temperature stabilitytemperature stability As:(Ga+Mn) stoichiometryAs:(Ga+Mn) stoichiometry

15. Plzeň, 5.1.1015 LT-MBE of GaMnAs surface morphology : 2D/3Dsurface morphology : 2D/3D temperature stabilitytemperature stability As:(Ga+Mn) stoichiometryAs:(Ga+Mn) stoichiometry annealingannealing Mn in interstitial position (double donor, AF coupling) 8 h / 160°C Mn i out-diffusion increase in p, , M, T C

16. Plzeň, 5.1.1016 optimum time LT-MBE of GaMnAs surface morphology : 2D/3Dsurface morphology : 2D/3D temperature stabilitytemperature stability As-flux stoichiometricAs-flux stoichiometric optimal annealingoptimal annealing

17. Plzeň, 5.1.1017 optimum temperature LT-MBE of GaMnAs surface morphology : 2D/3Dsurface morphology : 2D/3D temperature stabilitytemperature stability As-flux stoichiometricAs-flux stoichiometric optimal annealingoptimal annealing optimum time... for given thickness

18. Plzeň, 5.1.1018 176K 12.0% Mn, 20 nm 188K188K e.g. PRB 78, 054403 (2008); APL 93, 132103 (2008),... LT-MBE of GaMnAs surface morphology: 2D/3Dsurface morphology: 2D/3D temperature stabilitytemperature stability As-flux stoichiometricAs-flux stoichiometric optimal annealingoptimal annealing optimal sample thicknessoptimal sample thickness room temperature in Antarctica ! (-89.2°C, Vostok, 21 July 1983)

19. Plzeň, 5.1.1019 GaMnAs, x Mn series optimally grown/annealed samples (Ga 1-x Mn x As, x Mn =0.05 – 14 %, 20nm) Curie temperature magnetization - transport - magnetometry - IR absorption - MO -... characterization:

20. Plzeň, 5.1.1020 Conventional MOS FET structure ~10-100 Volts ( Ohno et al. Nature ’00, APL ’06,...) high-  dielectrics ( Chiba et al., Nature ’08, Sawicky et al., Nature ’09,...) GaMnAs, gating alternatively...

21. Plzeň, 5.1.1021 GaMnAs, low voltage gating Built-in gate AlGaAs barrier LT-GaAs barrier p-i-p, p-i-n, p-n structures Benefits single technology no surface states high quality barrier (  ~ 10) low gate voltage Problems !

22. Plzeň, 5.1.1022 GaMnAs, low voltage gating Built-in gate problems breakdown field ~ 1MV/cm @ 300 K technology issues p-type substrates in MBE  unintentional Mn-doping at high T S backward Mn diffusion As Ga at low T S

23. Plzeň, 5.1.1023 GaMnAs, low voltage gating Corbino geometry (gate leak reduction) Olejník et al, PRB 78, 054403 (2008) Owen et al, NJP 11, 023008 (2009) gate I-V n ~ 2x10 19 cm -3 barrier 20 nm x Mn = 2.0 % depletion possible V G =+3 V -1 V

24. Plzeň, 5.1.1024 GaMnAs, low voltage gating  R ~ 100%  T C ~ 2 K Olejník et al, PRB 78, 054403 (2008) Owen et al, NJP 11, 023008 (2009) Corbino geometry (gate leak reduction)

25. Plzeň, 5.1.1025 GaMnAs, low voltage gating tunable coercivity switching by gate pulses bistability :

26. Plzeň, 5.1.1026 GaMnAs, low voltage gating 30% AMR tuneable V G dependent competition of uniaxial and cubic anisotropies

27. Plzeň, 5.1.1027 Summary technology optimization, “high” T C T C keeps increasing (although hardly) GaMnAs close to metals (but still semiconducting) gating control of AMR Thank you !

28. Plzeň, 5.1.1028