Infrared, Self Assembled InAs GaAs Quantum Dot, Photodetectors

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Infrared, Self Assembled InAs/ GaAs Quantum Dot,
Photodetectors
June 23, 2005

• Michiel C. Donker

RuG
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Infrared Light
Infrared
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IR Detector Applications

• Medicine

• Medicine

• Astronomy

• Astronomy

• Defense

• Defense

• Environment

• Environment

8.5 µm 0.15 eV
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Content

• Introduction
• Quantum Dots
• Device Fabrication
• Electronic Structure
• Characterisation and Performance
• Conclusion

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HgCdTe Detectors

• Hg1-xCdxTe
• Wavelength 0.7- 25 µm
• High detectivity
• Difficult to process

0.0495 - 1.77 eV
Hole
Vbias 1.0 V

• Photo Current

HgCdTe

• Dark Current

Electron
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Quantum Confinement
InAs
Bulk 3D
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Density of States
Bulk
Quantum Well
Quantum Wire
Quantum Dot
g(E) density of states
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Quantum Dot Particle in a Box

• Infinite potential barrier
• ? sin(npx/ Lx) sin(mpy/ Ly) sin(lpz/ Lz)
• Selection rules

1-D
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Self Assembled Quantum Dots

• Host GaAs 5.653 Å
• Quantum Dot InAs 5.867 Å
• Stranski- Krastanov growth

GaAs
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Electronic Structure

• Lens shaped QDs
• Pyrimidal QDs

S.Sauvage et al. C.R. Physique 4, p1133 (2003)
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Characterisation

• Intersubband absorption

e ? e ?nodd non zero ?neven zero
In plane as well as normal incidence absorption
S.Sauvage et al. C.R. Physique 4, p1133 (2003)
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Dark and Photo Current

• Thermionic emission

• Tunneling

• Thermally assisted tunneling

• Thermal generation e/ h pair

GaAs conduction band
Energy
InAs wetting layer

• Wetting layer
• Conduction band
• Bound state

z direction
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Capture Probability
Carrier relaxation processes

• phonon (lattice vibration)
• e-e scattering
• e-h scattering

GaAs

• recombination

D
?E h c/ ?cut off
P
S
The more electrons in a QD, the more charge.
E
GaAs
InAs
z
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Dark and Photo Current

• Thermal generation
• Tunneling
• Number of electrons per QD
• QD density
• Number of QD layers
• Capture probability

Dark
20 K

• Angle of incidence
• Shape and size
• Absorption cross section
• Vbias

D.Pang et el. Appl. Phys. Lett. 75, p. 2719 (1999)
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Responsivity and Detectivity

• Responsivity (mA/ W)

• Detectivity (cm Hz1/2/ W) signal to noise ratio

• Background photon noise
• Photo electron noise detectable carrier ?,
  not detectable (1- ?)
• Receiver circuit noise

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Responsivity and Detectivity
Iphotocurrent

• Responsivity (mA/ W)

Poptical power
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
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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 thickness

• transport direction

J.Philips et al. Encyclopedia of Nanoscience and
Nanotechnology, 9 p. 131 (2004)
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Acknowledgements
Paul van Loosdrecht
Quantum Well Camera
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Questions

• Infinite potential barrier
• ? sin(npx/ L) sin(mpy/ L) sin(lpz/ L)
• Selection rules
• Fermi golden rule

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Questions

• Interband Photo Luminescense
• Intersubband Absorption

S.Sauvage et al. C.R. Physique 4, p1133 (2003)
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Questions

• D R A?f / Inoise
• H Hkp Hstrain Vconfining potential
• En (k) En (0) h2k2/2m
• h2/m2 S n band
  index

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Questions
GaAs
GaAs
AlGaAs
AlGaAs
InAs
E
z
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Questions

• L. Jiang et al. APL 82, p.1986 (2003)

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Questions

• S.F. Tang et al. APL 78, p. 2428 (2001)

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Questions