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Prezentace aplikace PowerPoint

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Magnetick polovodi (Ga,Mn)As: technologie, mo nosti aplikace Fyzik ln stav AV R, v.v.i. theory (Jugwirth, Sinova, ...) MBE (Nov k, Cukr, Olejn k, ...) – PowerPoint PPT presentation

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Title: Prezentace aplikace PowerPoint


1
Magnetický polovodic (Ga,Mn)Astechnologie,
možnosti aplikace
  • Fyzikální ústav AV CR, v.v.i.
  • theory (Jugwirth, Sinova, ...)
  • MBE (Novák, Cukr, Olejník, ...)
  • SQUID, transport (Olejník, Novák, ...)
  • University,of Nottingham, UK
  • MBE (Foxon, Campion)

Tato prezentace je spolufinancována Evropským
sociálním fondem a státním rozpoctem Ceské
republiky.
  • Hitachi Lab Cambridge, UK
  • lithography (Irvine, ...)
  • transport (Wunderlich, Owen, ...)

2
Outline
  • magnetic semiconductors
  • (Ga,Mn)As
  • technology issues
  • optimized xMn-series
  • gating GaMnAs

3
Modern electronics
  • semiconductors
  • magnetism

(ferro)magnetic semiconductors
electrically tunable magnetic properties
spintronics !
spin degree of freedom
Eu-chalcogenides (EuO, EuGdS, ...)
problems technology, TC , ...
diluted magnetic semiconductors (GaMnAs, GaMnP,
...)
4
Ga1-xMnxAs - semiconductor
Mn Ar 4s2 3d5
xMn lt 0.1 EA 100 meV
E
xMn gt 1
DOS
EF
Jungwirth et al., PRB 76, 125206 (2007)
5
Ga1-xMnxAs - ferromagnet
1 hole per Mn
carrier mediated FM
4.5 mB per Mn
TC M.p1/3
6
Ga1-xMnxAs - technology
Problem solubility limit of Mn in GaAs ( 0.1)
hex. MnAs in cub. GaAs
Solution Molecular Beam Epitaxy
low-temperature MBE
GaAs at TS gt 150C, but defects , t
, s
growth parameters critical
7
Molecular Beam Epitaxy
UHV growth chamber
growth kinetics
substrate
beams
sources
  • high crystallographic quality
  • low growth rate
  • atomically smooth interfaces
  • heterostructures, superlattices

8
MBE in FZU AV CR
  • 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
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10
Ga1-xMnxAs - technology
Problem solubility limit of Mn in GaAs ( 0.1)
hex. MnAs in cub. GaAs
Solution Molecular Beam Epitaxy
low-temperature MBE
GaAs at TS gt 150C, but defects , t
, s
growth parameters critical
11
LT-MBE of GaMnAs
  • crystal quality / surface morphology ?

amorphous / poly / 2D / 3D ?
RHEED images (non-rotating)
7 Mn
gt
lt
growth T
240C ? 3D
220C ? 2D
260C ? poly
12
LT-MBE of GaMnAs
  • crystal quality / surface morphology
  • temperature stability ?

7 Mn
band-gap thermometry doping-induced overheating
5 Mn
3 Mn
J. Appl. Phys. 102, 083536 (2007)
13
LT-MBE of GaMnAs
  • surface morphology 2D/3D best!
  • temperature stability

3D
2D
also Campion et al., J. Mater. Sci. 15, 727
(2004)
14
LT-MBE of GaMnAs
  • surface morphology 2D/3D
  • temperature stability
  • As(GaMn) stoichiometry

3D
AsGa31
AsGa11
2D
15
LT-MBE of GaMnAs
  • surface morphology 2D/3D
  • temperature stability
  • As(GaMn) stoichiometry
  • annealing

Mn in interstitial position (double donor, AF
coupling)
Mni out-diffusion
increase in p, s, M, TC
8 h / 160C
16
LT-MBE of GaMnAs
  • surface morphology 2D/3D
  • temperature stability
  • As-flux stoichiometric
  • optimal annealing

optimum time
17
LT-MBE of GaMnAs
  • surface morphology 2D/3D
  • temperature stability
  • As-flux stoichiometric
  • optimal annealing

optimum time
optimum temperature
... for given thickness
18
LT-MBE of GaMnAs
  • surface morphology 2D/3D
  • temperature stability
  • As-flux stoichiometric
  • optimal annealing
  • optimal sample thickness

12.0 Mn, 20 nm
e.g. PRB 78, 054403 (2008) APL 93, 132103
(2008), ...
room temperature in Antarctica ! (-89.2C,
Vostok, 21 July 1983)
19
GaMnAs, xMn series
  • optimally grown/annealed samples (Ga1-xMnxAs,
    xMn0.05 14 , 20nm)

Curie temperature
magnetization
  • characterization

- transport - magnetometry - IR absorption
- MO - ...
20
GaMnAs, gating
  • Conventional MOS FET structure
  • 10-100 Volts (Ohno et al. Nature 00, APL 06,
    ...)
  • high-k dielectrics (Chiba et al., Nature 08,
    Sawicky et al., Nature 09, ...)
  • alternatively ...

21
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 (k 10)
  • low gate voltage
  • Problems !

22
GaMnAs, low voltage gating
  • Built-in gate problems
  • breakdown field 1MV/cm _at_ 300 K
  • technology issues
  • p-type substrates in MBE ?
  • unintentional Mn-doping at high TS
  • backward Mn diffusion
  • AsGa at low TS

23
GaMnAs, low voltage gating
gate I-V
Corbino geometry (gate leak reduction)
xMn 2.0
barrier 20 nm
VG3 V -1 V
n 2x1019 cm-3
Olejník et al, PRB 78, 054403 (2008) Owen et al,
NJP 11, 023008 (2009)
depletion possible
24
GaMnAs, low voltage gating
DR 100
Corbino geometry (gate leak reduction)
DTC 2 K
Olejník et al, PRB 78, 054403 (2008) Owen et al,
NJP 11, 023008 (2009)
25
GaMnAs, low voltage gating
tunable coercivity
switching by gate pulses
bistability
26
GaMnAs, low voltage gating
VG dependent competition of uniaxial and cubic
anisotropies
30 AMR tuneable
27
Summary
  • technology optimization, high TC
  • TC keeps increasing (although hardly)
  • GaMnAs close to metals (but still semiconducting)
  • gating control of AMR
  • Thank you !

28
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