Semiconductor Scintillator and 3D I ntegration Serge Luryi ECE - - PowerPoint PPT Presentation

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Semiconductor Scintillator and 3D I ntegration Serge Luryi ECE Department and Sensor CAT Radiation Detection for Homeland Security: Isotope identification spectroscopic energy resolution Direction to source angular resolution Apr

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SLIDE 1

Apr 24, 2007 Physics Colloquium 1

Semiconductor Scintillator and 3D I ntegration

Serge Luryi ECE Department and Sensor CAT

  • Isotope identification

spectroscopic energy resolution

  • Direction to source

angular resolution

Radiation Detection for Homeland Security:

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SLIDE 2

Apr 24, 2007 Physics Colloquium 2

X-ray (γ-ray) attenuation

1 mm 1 cm 1 dm absorption length

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SLIDE 3

Apr 24, 2007 Physics Colloquium 3

Compton Scattering

θ3 θ1

L3 L1 L2

θ2

E0

0.0 0.5 1.0 1.5 2.0 30 60 90 120 150 180 210 240 270 300 330 0.0 0.5 1.0 1.5 2.0

σ(θ)

θ

γ ′ γ

e

γ γ

θ

′

− + = E c m E c m

e e 2 2

1 cos

kinematics (Compton):

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − + ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ =

′ ′ ′

) ( sin ) (

2 2

θ σ θ σ

γ γ γ γ γ γ

E E E E E E

dynamics (Klein-Nishina):

γ γ ′

− = E E L ) (Cs KeV 662 KeV 511

137 2

= =

γ

E c me

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SLIDE 4

Apr 24, 2007 Physics Colloquium 4

Diodes and scintillators

Si or Ge pin diode

Thallium levels

EC EV hν = 3 eV EG = 7 eV NaI scintillator

cm > 100 nS 77K > 10 kV up to 300,000 e-h/MeV > 200 nS 38,000 ph/MeV

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SLIDE 5

Apr 24, 2007 Physics Colloquium 5

Gamma spectroscopy

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SLIDE 6

Apr 24, 2007 Physics Colloquium 6

Main I dea*

  • Radiative decay time ≈ 1 ns
  • Photon re-absorption suppressed

due to high Fermi level (Burstein shift)

  • Expected light yield ≈ 100%
  • Absolute yield ≈ 240,000 ph/MeV

material transparent to its own fundamental light emission photons are delivered to the surface from deep inside the semiconductor

EC EV EF

hν InP or GaAs

*A. Kastalsky, S. Luryi, B. Spivak, Nucl. Instr. and Methods in Phys. Research A 565, pp. 650-656 (2006)

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SLIDE 7

Apr 24, 2007 Physics Colloquium 7

Burstein shift

1.3 1.4 1.5 1.6 1.7 1.8 0.0 0.1 0.3 0.4 0.5 0.6 0.8 0.9 1.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

n =3.7 ·1018 cm-3 undoped Energy (eV) Emission (a. u.) Absorption (104 cm-1)

InP, 300K

kT EF

e

/

λ λ ≈

absorption mean free path λ is exponentially enhanced compared to λ0 ≈ 1 µm

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SLIDE 8

Apr 24, 2007 Physics Colloquium 8

Comparison of I nP scintillator with activated crystalline NaI

Thallium levels

EC EV hν = 3 eV EG = 7 eV

γ γ

ν E h E E

G

× 3

33% 12% EV EC hν = 1.3 eV EG = 1.3 eV InP NaI

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SLIDE 9

Apr 24, 2007 Physics Colloquium 9

Response time

Radiative recombination

rad

τ p Bnp R = =

Radiative efficiency 99% with response time: τrad

nr 2 nonrad

τ p p Cn R ≡ =

Nonradiative recombination

EC EV EF

τnr ≈ 100 ns (Auger) τrad ≈ 1 ns

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SLIDE 10

Apr 24, 2007 Physics Colloquium 10

Free-carrier absorption

EF EG

∆E 10

18

10

19

1 10 Free-carrier 150 K 200 250 300 K Absorption length (mm) Concentration (cm

  • 3)

InP (at 0.92 µm)

  • Room temperature optimum ≈ 1mm

with re-emission several mm (explained on next viewgraph)

  • Standard GaAs or InP

wafer thickness 0.5 mm

  • Stack up layered systems
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SLIDE 11

Apr 24, 2007 Physics Colloquium 11

Diffusive propagation of light

λ λ λ λ λ λ

2 2 2 2 1

N h N h h h

j i i j j j N j j

= = ⋅ + = =

∑ ∑ ∑

≠ =

after every interband absorption event the photon is regenerated (in a random direction) with probability 99%

1

λ j λ

N

λ h

each re-emission introduces delay τrad ≈ 1 nS

We can take 1 cm thick slab and still collect over 80%

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SLIDE 12

Apr 24, 2007 Physics Colloquium 12

Heterostructures ….

EC2 EC1 EV1 EV2 EF Emitted light

  • virtually unlimited absorption length
  • free-carrier absorption also suppressed
  • tough to make, however !

100 ~ ≈ × = D D λ λ

(Duty cycle)

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SLIDE 13

Apr 24, 2007 Physics Colloquium 13

Epitaxial detector enables 3D integration

0.5 mm 2 µm

n+ InP scintillator pin InGaAsP photodiode

EG = 1.35 eV EG = 1.25 eV

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SLIDE 14

Apr 24, 2007 Physics Colloquium 14

back to DHS applications

  • Scintillator with a “semiconductor” resolution: excellent isotope discrimination

high spectroscopic resolution results from 240,000 photons per MeV and nearly 100% photoelectric conversion at epitaxial photodetector expected Fano factor F=0.1

  • Exceptional sensitivity results from virtually unlimited

detector thickness by 3D integration: increased stand-off distance

  • Room temperature operation: moderate cost
  • Ultrafast response (1 ns): rapidly moving targets
  • Pixellated and layered photodetector system: directional capability

the technique provides both angular resolution and isotope identification

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SLIDE 15

Apr 24, 2007 Physics Colloquium 15

3D Pixellation

Flip Chip Silicon Circuitry Data & Power Buses Photosensitive Layer γ - Detection Semiconductor Slab Stack of Detector Slabs 2D pixel

  • where ionization occurred
  • time of the event
  • amplitude of the event

Upon analog-to-digital conversion each unit reports not a 1 ns pulse but an information-carrying signal:

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SLIDE 16

Apr 24, 2007 Physics Colloquium 16

Photodetection Matrix

m m

2-D CPU

Data Converter Photo Detector

IPD

“X” Bus “Y” B u s Position + Intensity +VBIAS

n m×

n m +

detector array # of data lines and converters

n

A A

GND VDD

m

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SLIDE 17

Apr 24, 2007 Physics Colloquium 17

Partition between I nP and Si

Address

VCC IB IC = β IB A R C n+ scintillator pin photodiode flip-chip

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SLIDE 18

Apr 24, 2007 Physics Colloquium 18

Compton “telescope”

i i i i i i

E E L E E − = − + =

− − − − 1 1 1 1

1 cosθ

θ3 θ1

L3 L1 L2

θ2

E0 ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − + + + =

2 2 2 2 2 1

cos 1 4 2 1 2 θ L L L L E

keV) 511

2 =

c me (in units of

1

ˆ n ˆ n

1 0 ˆ

ˆ n n

Having identified first three interactions (in the correct order) we find the energy

  • f the incident photon:

Also the directional cosine

⋅

about the measured direction n1 i.e., the object is placed on a cone kinematics:

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SLIDE 19

Apr 24, 2007 Physics Colloquium 19

Direction to source

( )

n n N j j n n

N np N

n

δ ρ ρ ρ r v r r + − = ≡

∑

=

1 1

1 ) ( 1 1

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − + ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ =

− − −

) ( sin ) (

2 1 1 2 1 i i i i i i i i

E E E E E E θ σ θ σ

anisotropic scattering cross-section 662 keV: dynamics (Klein-Nishina formula):

1

ρ r

Center

  • f mass

cluster of n interactions

0.0 0.5 1.0 1.5 2.0 30 60 90 120 150 180 210 240 270 300 330 0.0 0.5 1.0 1.5 2.0

σ(θ)

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SLIDE 20

Apr 24, 2007 Physics Colloquium 20

GaAs versus I nP

  • GaAs pros
  • Higher radiative recombination coefficient, while nonradiative similar
  • Higher bandgap (good for low-noise photodetection at room temperature)
  • Lower cost, mature electronics
  • GaAs cons
  • Lighter weight elements
  • Epitaxial detector questionable

InP GaAs

7B B ≈

InP GaAs

C C ≈

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SLIDE 21

Apr 24, 2007 Physics Colloquium 21

1E-3 0.01 0.1 1 10 0.1 1 10 100 1000 10000 100000

Si Ge CdTe InP

Attenuation Coefficients (cm

  • 1)

hν (MeV)

Element Z Si 14×2 Ga/As 31/33 Ge 32×2 In/P 49/15 Cd/Te 48/52

X-ray (γ-ray) attenuation

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SLIDE 22

Apr 24, 2007 Physics Colloquium 22

GaAs versus I nP

epitaxial photodetector issues

0.5 mm 2 µm

n+ scintillator pin photodiode

EG = 1.45 eV EG = 1.35 eV EG = 1.35 eV EG = 1.25 eV GaAs InP (In)GaAs-N InGaAsP

  • U. Michigan (Rachel Goldman)

collaboration: dilute nitride epitaxial photodiodes on GaAs

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SLIDE 23

Apr 24, 2007 Physics Colloquium 23

Dilute Nitride

GaN GaAs

Due to their high electronegativity and small size, atoms of nitrogen, when added in small amount (atomic %) to III-V compounds, dramatically reduce the material bandgap. see, e.g. “Dilute Nitride Semiconductors”, ed. by M. Henini, Elsevier (2005)

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SLIDE 24

Apr 24, 2007 Physics Colloquium 24

Summary

The basic issue for any semiconductor scintillator

semiconductor is not transparent to the radiation it produces

We have resolved this issue

Moss-Burstein shift in a direct-gap, low-effective-mass semiconductor, such as InP or GaAs, makes it transparent to its own radiation, permits extracting photons from as deep as several millimeters from the detector surface

New type of scintillator is proposed, advantageous for:

multiple applications, including 3D pixellation for: radiation spectrometry and SNM identification rapid determination of direction to source

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SLIDE 25

Apr 24, 2007 Physics Colloquium 25

“Semiconductor high-energy radiation detector with excellent isotope identification and directional capability”

Cooperative Agreement 2007-DN-077-ER0005 (started March 1, 2007)

SB Team: PI’s Serge Luryi Alex Kastalsky Nadia Lifshitz Milutin Stanacevic Other SB participants Michael Gouzman Oleg Semenov Peter Shkolnikov

  • U. Michigan (Ann Arbor)

Rachel Goldman Brookhaven National Lab Aleksey Bolotnikov