Transcript Single crystal diamond detectors

Single crystal diamond detectors
Gianluca Verona Rinati
Dipartimento di Ingegneria Industriale
Università di Roma “Tor Vergata”
[email protected]
Diamond properties
Lattice constant
Nearest neighbours
Band Gap
3.56 Ǻ
1.54 Ǻ
5.5 eV
Diamond properties
Diamond Properties
Diamond applications
 HARDNESS
9000 Kg/mm2
(the higest)
 YOUNG’S MODULES
1012 N/m2
(the strongest)
 FRICTION
0.05
(the lowest)
 THERMAL CONDUCTIVITY
20 W/cm K
(5 times Cu)
 ELECTRICAL RESISTIVITY
1016 cm
 ELECTRICAL BREAKDOWN
107 V/cm
(30 times GaAs)
 ELECTRON, HOLE MOBILITY >2000 cm2/V s
 OPTICAL ABSORPTION
transparent from IR to IV (5.4 eV)
 MELTING POINT
3350 °C
 RADIATION HARDNESS
very high
 CHEMICAL REACTIVITY
extremely low
 Radiation detectors
Particle detectors
E-UV, V-UV sensors
Soft-X sensors
 Transistors
Fast FET
High power FET
 Quantum computing
 Chemical sensors
 Optical windows
 Biological application
 Cold cathodes / field
emitters
 Heat spreaders
Radiation damage
Charge Collection Distance (µm)
 Charge Collection Distance: mean distance traveled by carriers before
being trapped (infinite size material)
 Radiation damage is evidenced when CCD is comparable or smaller
than the thickness of the detector
RD42 Collaboration, Nucl. Instr. Meth. A, 623 (2010) 174
Diamond properties
Natural Diamond
Syngle crystal
Small in size
Low availability - high cost
No reproducibility
High Pressure – High Temperature
Synthetic diamond
Chemical Vapor Deposition (CVD)
Diamond properties
Synthetic HPHT diamond
Single crystal
Small in size
Low cost
Poor electronic quality
Polycrystalline CVD diamond
 Low cost and large area possible
 Polycrystalline (no energy resolution)
 Effect of “priming” or “pumping”
 Polarization and memory effects
Synthetic CVD single crystal diamond
Single crystal
Small in size
High electronic quality
CVD diamond deposition
SUBSTRATE TEMPERATURE
OPTICAL
PYROMETER
Microwave Plasma CVD
Al contact
Output
MICROWAVE POWER
Ag contact
FLOW
CONTROLLERS
CVD slightly B doped
CVD B+ doped
QUARTZ WINDOW
GAS IN
QUARTZ TUBE
HPHT substrate
PLUNGER
MICROWAVE
GENERATOR
2.45 GHZ
PRESSURE CONTROL
SAMPLE
TO PUMP
Oscilloscope
Ionizing particle
Typical growth parameters
Plasma composition 99% H2- 1% CH4,
Temperature
650 – 800 °C
Microwave power
600 - 1300 W
Pressure
100 - 150 mbar
Gas flow rate
100 sccm
Electrical
contacts
h
e
Shaping
Amplifier
Charge
Sensitive
Amplifier
Diamond
Bias
Multichannel
Analyzer
Alpha particle detection
( c h a n n e l)
Triple  source (239Pu, 241Am, 244Cm)
emitting 5.16 MeV, 5.48 MeV and 5.80 MeV -particles
2.5
p o s itio n
1.5
1.0
0.5
0.0
4.8
5.0
5.2
5.4
Energy (MeV)
5.6
5.8
6.0
P e a k
Counts (au)
2.0
2 1 0 0
2 0 0 0
1 9 0 0
1 8 0 0
1 7 0 0
1 6 0 0
0
2
4
6
8
tim e
1 0
1 2
(h )
1 4
1 6
1 8
Neutron detection
Fast Neutrons
n
Thermal Neutrons

n
6LiF
CVD i
CVD p+

9Be
HPHT substrate
neutrons directly interact with C in
the diamond sensing layer:
n + 12C →  + 9Be – 5.7 MeV
(for 14.8 MeV neutrons) with  and Be
having a total energy of 9.1 MeV
CVD i
CVD p+
T
HPHT substrate
neutrons interact with 6Li in the
95% enriched 6LiF layer:
n + 6Li → Tritium +  + 4.8 Mev
T (2.73 MeV) and  (2.06 MeV) are
emitted at 180°, so either one is
detected in the diamond sensing layer
Neutron detection: spectrum
Neutron beam containing both high energy
(14.8 MeV) and thermal neutrons
0.5 mm thick 6LiF layer
20000
Counts
x 100
2.73 MeV
Tritium
18000
200
180
16000
160
14000
140
12000
120
10000
100
2.07 MeV 
12
C(n, n')3
8000
6000
80
12
9
C(n, 0) Be
60
4000
40
2000
20
0
0
0
2
4
6
Energy (MeV)
8
10
2.73 MeV Tritium and the 2.06 MeV
 peaks detected and clearly
resolved
The 2.06 MeV  peak is much
broader than the Tritium peak due
to the higher stopping power (I.e.
energy loss) of  particles in LiF
The 9.1 MeV 12C(n, 0)9Be reaction
peak is also observed and is
produced by the fraction of
neutrons not slowed down by the
PMMA moderator.
The detector thickness is 25 mm, to
be compared with the 38 mm
mean free path of neutrons in
diamond
Thermal neutrons: simulation
25000
0.45 m m LiF
20000
Good agreement between
experimant and simulation
15000
10000
5000
0
1.6 m m LiF
Counts
8000
simulation can be used to
predict the detector behaviour
for any 6LiF layer thickness.
6000
4000
2000
0
3.0 m m LiF
8000
6000
4000
2000
0
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
Energy (MeV)
experimental (red) and simulated
(blue) thermal neutron spectra
4,0
2.73 MeV tritium peak for 0.45
mm 6LiF : equal simulated and
experimental peak area (i.e.
total counts).
real peak wider (and less
intense) because of the
broadening
produced
by
detector inhomogeneities and
by noise (not taken into
account)
Thermal neutrons: resolution
The predicted FWHM vs. 6LiF
layer thickness curves are
calculated from the simulated
spectra.
1000
FWHM (keV)
alpha
Tritium
100
10
Tritium ions peak : good
resolution up to thicknesses in
the range of several microns
0,1
1
10
LiF layer Thickness (mm)
FWHM of the -particles and Tritium ions
peaks as a function of the 6LiF layer
thickness from the simulated thermal
neutron spectra.
-particles peak : sub-micron
thickness required to have a
real peak.
High energy neutrons: resolution
Simulated spectra after convolution with a 0.5 MeV FWHM Gauss function
representing the energy spread of the beam
Standard
Normalized
50000
Normalized counts
3.3 mm
8 mm
20 mm
50 mm
40000
Counts
1,2
30000
20000
1,0
0,8
3.3 mm
0,6
0,4
8 mm
10000
0,2
20 mm
50 mm
0,0
0
0
2
4
6
Energy (MeV)
8
10
12
0
4
8
Energy (MeV)
Peak at 9.1 MeV always 0.5 MeV wide, with “flat” low energy background.
Gradual decrease of the peak height and increase of background with
decreasing film thickness.
Good energy resolution even for very low thickness values (10 mm) : cost
effective solution.
12
High energy neutrons: efficiency
1,0
Peak Efficiency (PE) increases with d
more reactions, more complete collection of the
reaction products). For optimal collection, d >>
penetration lengths of , Be.
Peak efficiency
0,8
90°
0,6
0°
0,4
PE higher at 90° incidence angle
energetic products emitted along the irradiation
direction can easily escape from the detector in the
0° geometry.
0,2
0,0
1
10
100
Thickness (mm)
Peak efficiency (counts below the
9.1 MeV peak / number of 12C(n,α)9Be
reactions) vs. detector thickness d.
Blue : neutron beam  to sample surface
(0°)
Red : neutron beam || to sample surface
(90°)
Circles: measured data at 0° and 90°
Measured data for d =25, 53, 74 and
104 mm agree with simulation
(data are the ratio between the counts in the 12C(n,α)9Be peak
and the number of 12C(n,α)9Be reactions, given by the total
counts number multiplied by cross section of the 12C(n,α)9Be
reaction (72 mb) and divided by total cross section of
14.8 MeV neutrons in C).
simulation allows to predict the
detector behaviour for any d
Sandwich detectors
A low energies background, due to low energy
reactions, is always observed, especially in
presence of high g fluxes.
A higher energy peak would allow a better
discrimination between thermal neutrons and
other ionizing radiations (e.g g and protons).
200
x 100
2.73 MeV
Tritium
18000
Counts
This effect is much more detrimental when a
converter whose reaction products have low
energy is used
20000
180
16000
160
14000
140
12000
120
10000
100
2.07 MeV 
8000
12
C(n, n')3
6000
80
12
9
C(n, 0) Be
4000
2000
n
0
HPHT
60
40
20
0
1
2
3
4
5
6
7
8
9
10
0
11
Energy (MeV)
B-doped CVD

Intrinsic CVD
6LiF
Intrinsic CVD
B-doped CVD
HPHT
T
 The  particle and the tritium ion are simultaneously
detected at 4.8 MeV (ET+E)
 The effective sensitive thickness to fast neutrons is given
by the sum of the two intrinsic CVD layers
“Sandwich” configuration
25000
An intense  + T peak is
observed at 4.8 MeV
500
400
4.8 MeV  + T
Counts
12
20000
Counts
15000
300
12
C(n,n')3
9
C(n,) Be
Residual 2.73 MeV and
2.06 MeV peaks are
observed (peak integral
about a factor 15 lower).
These peaks are due to a
slight misalignment of the
two sandwiched samples.
200
100
0
250
300
350
400
Channel
10000
2.73 MeV T
2.06 MeV 
5000
0
0
50
100
150
200
250
Channel
300
350
400
450
10B
converter
Deposition of B2O3 or BN or B …
About 20% of 10B in natural Boron
Low energy reaction products
Higher stopping power of the reaction products
n
HPHT
B-doped CVD
Intrinsic CVD

10B
B2O3
Intrinsic CVD
B-doped CVD
HPHT
7Li
+ n   (1.47MeV) + 7Li(0.84MeV)
10B
converter
12000
x 100
12
10000
1000
12
counts
8000
C(n,0) Be
600
E
400
2000
0
9
800
6000
4000
Single detector
configuration
C(n,n')3
E+ELi
Sandwich
configuration
1200
200
0
2
4
6
Energy (MeV)
8
0
10
Conclusion
Diamond is a very intersting material for neutron
detection especially in high neutron flux condition, when
high radiation hardness is needed.
Numerical simulations allow accurate prediction of the
behavior of the device under neutron irradiation.
Particular care has to be devoted to the detector design in
order to optimize its performance for the specific
application.
“Sandwich” device allow to increase the discrimination
ratio between neutron spectrum and the background. Incoincidence measurements are possible with such
devices, further improving the background separation.
Collaborations
Università di Roma “Tor Vergata”
Dip. Ing. Industriale
C. Di Venanzio
M. Marinelli
E. Milani
F. Pompili
G. Prestopino
A. Tonnetti
C. Verona
G. Verona Rinati
Enea Frascati
M. Angelone
A. Pietropaolo
M. Pillon
INFN Genova
M. Osipenko
G. Ricco
M. Ripani
Thank you!