Plzeň, 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)

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

Plzeň, 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 !

Plzeň, 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, (2007) x=0.05% 1% 2% 7% ~100 meV E G /2 E DOS EFEF

Plzeň, 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

Plzeň, 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

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

Plzeň, 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

Plzeň,

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

Plzeň, 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: > <

Plzeň, J. Appl. Phys. 102, (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

Plzeň, D 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

Plzeň, D 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

Plzeň, 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

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

Plzeň, 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

Plzeň, K 12.0% Mn, 20 nm 188K188K e.g. PRB 78, (2008); APL 93, (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)

Plzeň, 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:

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

Plzeň, 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 !

Plzeň, GaMnAs, low voltage gating Built-in gate problems breakdown field ~ 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

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

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

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

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

Plzeň, 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 !

Plzeň,