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Infrared, Self Assembled InAs/ GaAs Quantum Dot, Photodetectors. Michiel C. Donker. June 23, 2005. R u G. VLWIR > 12 μ m < 0.10 eV. SWIR = 0.7 - 3 μ m 1.77 - 0.41eV. LWIR = 7 - 12 μ m 0.18 - 0.10 eV. MWIR = 3 - 7 μ m 0.41 - 0.18 eV. Infrared Light. - PowerPoint PPT Presentation
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Infrared, Self Assembled InAs/ GaAs Quantum Dot, Photodetectors
Michiel C. Donker
June 23, 2005
RuG
Infrared Light
SWIR = 0.7 - 3 μm 1.77 - 0.41eV
MWIR = 3 - 7 μm 0.41 - 0.18 eV
LWIR = 7 - 12 μm 0.18 - 0.10 eV
VLWIR > 12 μm < 0.10 eV
Infr
are
d
IR Detector Applications
• Medicine
8.5 μm 0.15 eV LWIR
• Astronomy
• Defense
• Environment
• Medicine
• Astronomy
• Defense
• Environment
Content
• Introduction
• Quantum Dots
• Device Fabrication
• Electronic Structure
• Characterisation and Performance
• Conclusion
HgCdTe Detectors
• Hg1-xCdxTe
• Wavelength 0.7- 25 μm
• High detectivity
• Difficult to process
0.0495 - 1.77 eV
IR
HgCdTeIR
Vbias =1.0 V
• Dark Current
• Photo CurrentHole
Electron
Quantum Confinement
InAs
Quantum Wire 1D
cross section
InAs
Quantum Dot 0D
cross section
GaAs
Bulk 3D
InAs
GaAsInAs
Quantum Well 2D
cross sectionz
E
z
GaAs GaAs
Conduction band
Valence band
InAs
50 nm
InAs: Eg =0.36 eV
GaAs: Eg= 1.52 eV
InAs
GaAs
Density of States
Bulk Quantum Well Quantum Wire Quantum Dot
g(E)= density of states
Quantum Dot: Particle in a Box
• Infinite potential barrier
• Ψ~ sin(nπx/ Lx) sin(mπy/ Ly) sin(lπz/ Lz)
• Selection rules: < Ψi I r I Ψj > = 0 111 211
x=0 x=L 1-D
Self Assembled Quantum Dots
• Host: GaAs 5.653 Å
• Quantum Dot: InAs 5.867 Å
• Stranski- Krastanov growth
GaAs
InAs
InAs GaAs
Heavely n- doped GaAs
Heavely n- doped GaAs
Electronic Structure
• Lens shaped QD’s
• Pyrimidal QD’s
GaAs conduction band
GaAs 3D valence bandWetting Layer
Wetting Layer
0 meV
56 meV63 meV
121 meV128 meV
115 meV
h 000
p 100 010
d
0 meV
31 meV
55 meV57 meV61 meV
h 100 010
h 110h 200h 020
s 000
930 meV
S.Sauvage et al. C.R. Physique 4, p1133 (2003)
IRIR
IR
Characterisation
In plane as well as normal incidence absorption
Conductionband
S P transition
ConductionBand edge
S wetting layer, conduction bandS P transition
• Intersubband: absorption e e Δn=odd non zeroΔn=even zero
S.Sauvage et al. C.R. Physique 4, p1133 (2003)
Dark and Photo Current-Thermionic emission
-Tunneling
-Thermally assisted tunneling
Energy
z direction
GaAs conduction band
InAs wetting layer
IR
-Wetting layer
-Conduction band
-Bound state
-Thermal generation e/ h pair
Vbias
Capture Probability
• phonon (lattice vibration)• e-e scattering• e-h scattering
IR
Carrier relaxation processes:
E
z
InAs
GaAs
• recombination
GaAs
S P D
phonon
phonon
The more electrons in a QD, the more charge.
ΔE= h c/ λcut off
Dark and Photo Current• Thermal generation• Tunneling• Number of electrons per QD• QD density• Number of QD layers• Capture probability
H.C. Liu, Opto Electronic Review 11, p.1-5 (2003)
77 K
Vbias (V)
x
zy ·
z
xy
S.Sauvage et al. C.R. Physique 4, p1133 (2003)
• Angle of incidence • Shape and size• Absorption cross section
• Vbias
D.Pang et el. Appl. Phys. Lett. 75, p. 2719 (1999)
20 K
Da
rk
Responsivity and Detectivity
• Responsivity (mA/ W) = =
- η = quantum efficiency = # generated electrons by photons# incident photons
Poptical power
Iphotocurrent
h v
e η g
- g = gain = =# carriers through device # generated carriers by photons τ carrier transit time
τ carrier lifetime
• Detectivity (cm Hz1/2/ W) = signal to noise ratio
- Background photon noise
- Photo electron noise; detectable carrier η, not detectable (1- η)
- Receiver circuit noise
Responsivity and Detectivity
• Responsivity (mA/ W) =Poptical power
Iphotocurrent
Res
po
nsi
vity
(A
/ W
)
Wavelength (μm)
165 eV
L. Jiang et al. Appl. Phys. Lett. 82, p.1986 (2003)
• Detectivity (cm Hz1/2/ W) = signal to noise ratio
77 K Vbias= -2.0 V QD density = 1.2 x 1010 Size 26 nm 6 nm
D = 3.6 x 1010 cm Hz1/2/ W
Conclusion
• QD: D = 3.6 x 1010 cm Hz1/2/ W
• HdCdTe: D = 2.2 x 1012 cm Hz1/2/ W
• # electrons per dot
• dot density
• dot size and shape
• spacing thicknessVbias
• transport directionz
xy
J.Philips et al. Encyclopedia of Nanoscience and Nanotechnology, 9 p. 131 (2004)
Acknowledgements
Quantum Well Camera
Paul van Loosdrecht
Questions
• Infinite potential barrier
• Ψ~ sin(nπx/ L) sin(mπy/ L) sin(lπz/ L)
• Selection rules:
• Fermi golden rule:
< Ψi I r I Ψj > = 0
x=0 x=L
Δn=odd, on the same axis
000 100 100 010100 200 000 200
XX
<1 | z | 2>= (16/9π2)/L<1 | z | 4>= (4/45π2)/L
Questions
• Interband: Photo Luminescense
• Intersubband: AbsorptionIntersubband selection rules:
e e Δn=odd strongΔn=even zero
S.Sauvage et al. C.R. Physique 4, p1133 (2003)
Interband selection rules:
h e Δn=0 strongΔn=0 odd weakΔn=0 even zero
H 000 E 000
Questions
• D= R AΔf / Inoise
• H= Hk·p + Hstrain + Vconfining potential
• En (k) = En (0) + h2k2/2m +
h2/m2 Σ’ n= band index
| <n0| k·p |j0> |2
En(0) – Ej (0)
Questions
InAs
GaAs GaAs
AlGaAs AlGaAs
Vbias
E
z
Questions
L. Jiang et al. APL 82, p.1986 (2003)
Questions
S.F. Tang et al. APL 78, p. 2428 (2001)
Questions