Aplicaciones: Defectos en semiconductores

Presentación del tema: "Aplicaciones: Defectos en semiconductores"— Transcripción de la presentación:

1 Aplicaciones: Defectos en semiconductores
Sustitución catiónica en polvos nanocristalinos

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4 t(ns)

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7 Aplicaciones: Volúmenes libres en polímeros
Polivinilsiloxanos (PVS) POSITRONFIT CONTIN Alessandrini, SLAP 2004, Spain

8 Aplicaciones: Volúmenes libres en polímeros
Polímeros de Poli(Acrilato de Etilo) Se determinó el tamaño de los huecos: R~2.5 Å M.A.Hernández-Fenollosa, APHYS 2003, Spain

9 Aplicaciones: Volúmenes libres en polímeros
Estructuras CB[n] to-Ps en función del tamaño del hueco en las CB[n] Variación de tave con el llenado de las cavidades para CB[7]

10 Application of positron annihilation techniques
for semiconductor studies Techniques: - Doppler broadening (depth profile) - lifetime (in bulk) - coincidence (in bulk) Samples: - He-implanted silicon - Czochralski-grown silicon low-k materials - SiO2 and GeO2 conducting glasses

11 Positron identity e+ is antiparticle of e- : Ps is light H :
mass keV/c2 spin ½ opposite Q opposite μ stable in vacuum (>2x1021y) Ps is light H : Energy E= ½ Ry p-Ps: τ=125 ns, 2γ o-Ps: τ=142 ns, 3γ

12 Positron history History of “slow” positrons
1930 – e+ postulated by Dirac 1932 – discovered in cosmic rays by Anderson “out of 1300 photographs of cosmic tracks, 15 were od positive particles which could not have a mass greater as that of the proton” 1950 – Madanski-Rasetti try to moderate 1951 – evidence of Ps atom (Deutsch) 1958 – moderated e+ , ε=3x10-8 (Cherry) 1979 – single crystal moderator (Mills) 1980 – brightness enhancement (Mills)

13 Positron slowing down

14 Positron sources Moderators Radioactive nuclides W (100): ε= 4x10-4
Solid Ne: ε=1% ?

15 Positrons in Solid State Physics

16 Trento Positron Annihilation Set-up

17 Trento-München Positron Microscope
E=500 eV – 25 keV spot = 2 μm

18 Positron walking

19  Positron in a crystal

20 Espectroscopía de aniquilación de positrones

21 Positron lifetime technique
τdefect > τbulk

22 Doppler broadening technique
ptot=pe+pp ΔE = cpz / 2 S=(E0±0.85keV)/(E0±4.25keV)

23 Doppler-broadening: normalization

24 He bubbles in Si He – implantation n=0.5x1016cm2 NO! n=2x1016cm2 YES!

25 He bubbles in Si

26 He bubbles in Si

27 He bubbles in Si quantization of S - values

28 Doppler-coincidence technique

29 Doppler-coincidence spectra

30 D-C - chemical sensitivity

31 D-C - chemical sensitivity

32 Si – Czochralski grown cO≈ 1018 cm-3 cB≈ 1016 cm-3

33 Oxygen in Cz-grown silicon
thermal donors precipitates new donors “as grown”: annealed at 450°C

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35 Oxygen in Cz-grown silicon

36 Oxygen in Cz-grown silicon

37 Oxygen in Cz-grown silicon

38 Conducting glasses (SiO2+Bi2O3)
AFM picture of Si-Pb glass; a) freshly broken; b) Annealed at 580ºC for 21h

39 Conducting glasses (SiO2+Bi2O3)

40 Conducting glasses (SiO2+Bi2O3)

41 Conducting glasses (SiO2+PbO2)

42 Conducting glasses (GeO2+Bi2O3)

43 Conducting glasses (SiO2+Bi2O3)

44 Silica based, low ε materials - structure
From K.Maex et al. J. Appl. Phys. 11, 93, 8793

45 low ε materials - annealing

46 low ε materials - annealing

47 low ε materials - ageing

48 Positron Spectroscopy in Solid State Physics
Intense beams ! Future ? Auger Spectroscopy Low-energy Positron Diffraction

49 Positron Spectroscopy in Solid State Physics
Intense beams ! Future ? Auger Spectroscopy Low-energy Positron Diffraction