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Effects of metallization on TlBr single crystals for detector applications. V. Kozlov a , M. Leskelä a , M. Vehkamäki a and H. Sipilä b. a Department of Chemistry, University of Helsinki, Finland b Oxford Instruments Analytical Oy, Espoo, Finland. TlBr properties. - PowerPoint PPT Presentation
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PSD-7, Liverpool, GB, 2005
Effects of metallization on TlBr single crystals for detector applications
V. Kozlova, M. Leskeläa, M. Vehkamäkia and H. Sipiläb
a Department of Chemistry, University of Helsinki, Finlandb Oxford Instruments Analytical Oy, Espoo, Finland
PSD-7, Liverpool, GB, 2005
TlBr properties
• high atomic numbers Z: 81+35 => stopping power
• density (7.56 g/cm3) => compact device
• bandgap (2.68 eV) => room temperature
• inter-pixel resistance ~500 GΩ (gap 100μm, 50V)
=> 2D-array detector*
• optical transparency: 440nm – 50µm => scintillator?
*Owens et al., Nucl. Instr. and Meth. A 531, 18 (2004)
PSD-7, Liverpool, GB, 2005
Material problems
• Purity
• Crystal quality
• Manufacturing process
• TlBr – toxic compound
(Knoop hardness of 12 kg/mm2)
Na Pb Nb Sb Al Co S Ca V Si P Pd Pt Cr Cu Fe Mg Zn Sum:0.1
1
10
100
Improving during re-crystallistaion and annealing
S/SR D/DR D/DA
Co
nce
ntr
atio
n, p
pb
Elements
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
0
200
400
600
800
1000
SourceSet67
13(1) 2(1)2=39.134
Hydrothermal Annealing, 150oC
An04Set55
Inte
nsity
, cn
ts
scan angle
PSD-7, Liverpool, GB, 2005
Metallization methods
Chemical: photographic process, Pd-dielectrics => possible water inclusion => X
Glue: Ag- and graphite-paste=> crater formation, if poor crystal quality properly treated samples: 2.5 kV/cm
Physical: vapour (PVD), electron beam and sputtering deposition methods =>
Melt: metal melting on TlBr surface =>
PSD-7, Liverpool, GB, 2005
Interaction at the interface
“Adhesion”:physical deposition
“Diffusion” physical or melt methods
“Compound” melt deposition orphysical + annealing
-20 -15 -10 -5 0
0
2
4
6
8
10
Depth across interface, A.U.
Me
con
cen
trat
ion
, A.U
.
ADHESION DIFFUSION COMPOUND
PSD-7, Liverpool, GB, 2005
Metal – Tl halide interface parameters
“Adhesion”
“Diffusion”
“Compound”
Metal mp, oC Tensile strength*
Stability* Electro-negativity
Cu 1083 24 Atm 1.9
Ag 962 27 Atm 1.9
Au 1064 27 Atm 2.4
Zn 419 13 1.6
Cd 321 36 1.7
Al 660 Split. Bad 1.5
In 157 18 Good 1.7
Tl 304 1.8
Sn 232 6 1.8
Ti 1660 18 Good 1.5
Cr 1857 14 Good 1.6
Fe 1535 23 Good Atm 1.8
Co 1495 22 Good 1.8
Ni 1453 22 Atm 1.8
Mn 1244 X Bad 1.5
Mg 649 X Bad 1.2
Abr.: Atm. - unstable in atmosphere,
Split. – SplittingX – Chemical reaction
*Me-thickness – 0.5 μm units - MN/m2 [6, 8]
TlBr (mp = 460oC)
PSD-7, Liverpool, GB, 2005
Results: Vacuum deposition
Electron beam evaporation: thickness 25 and 40 nm Ti, Cr and Al
Ti and Cr: good electrical contacts, stable for ~year in a laboratory environment
Al: stable during all measurements for several days
Fe and Ni – direct contact with TlBr molten => No reaction, if pure metals and complete degassing of system=> Ni-boat was used for the melting of TlBr powder
Output: - Ti, Cr, Fe and Ni elements were inert to TlBr - Ti and Cr could be used as reliable electrodes- Al ?
PSD-7, Liverpool, GB, 2005
Results: Al/TlBr interface
TlBr was deposed on a clean Al surface:(surface temperature control)
• t < 100oC => fine films, R% spectra=> stable for ~year, XRD
• t > ~150oC => Tl-drops on Al=> amorph. phase + Tl
peaks
Al(solid) + 3TlBr(gas) => 3Tl(drop) + AlBr3(gas)
Output: no heating, low current
100 200 300 400 500 600 700 800 900 1000 1100
0
3
6
9
12
15
Al4v1cNor Al3v1cNor Al2v1cNor Al1v1cm90
R,
%
, nm
15 20 25 30 35 40 45 50 55 60 65 70 75 80 85
0
50
100
150
200
250
310210
200
111220
211
110
100 (311)
220
200
111
TlBr Al
Inte
nsity
, cnt
s
2
PSD-7, Liverpool, GB, 2005
Results: Tl/, In/,Sn/TlBr interfaces
Tl, In and Sn were shortly melted at ~310 oC: ( N2 atmosphere)
• Sn: no reaction, no underlayer
• In: Yellow underlayer compound”pressed drop” on surface
• Tl: Brown underlayer compoundeasily peeled off from TlBr
+ New process + annealing 20h=> active reaction
Output: Tl - aggressive with TlBr
TlBr
metal drop
underlayerIn
PSD-7, Liverpool, GB, 2005
Results: In/,Sn/TlBr interfaces
In and Sn were shortly melted at ~250 oC: (opposite side)
• Sn, In: no reaction, no underlayer (In-case)
• Sn: I-V characteristics of Sn-TlBr-Sn were asymmetrical for both electrodes
=> higher temperature for the intermediate compound
Output: Sn electrode was reliable at our conditions.
TlBr
In
In
PSD-7, Liverpool, GB, 2005
Results: In/TlBr interface
• In: I-V curves of In-TlBr-Layer-In => rectifier effect was observed
Output: low crystal quality, inner boundaries still limit the use of TlBr detector
-120 -100 -80 -60 -40 -20 0 20 40 60-6.0n
-3.0n
0.0
3.0n
6.0n
9.0n
12.0n
15.0n
18.0n
SL04: Signal to OldDrop of In.
iPPM iMMP
Cur
rent
, nA
Bias Voltage, V
(+)
(-)• High currentconnections:
Breakdown during further I-V & CVat ~200 V/cm
Compare: working field 500 V/cm,Owens et al., Nucl. Instr. and Meth. A 531, 18
(2004)
PSD-7, Liverpool, GB, 2005
Conclusions
• Ti, Cr, Fe and Ni elements were inert to TlBr and Ti and Cr could be used as reliable electrodes.
• Al contact can be used for tests at low current without heating.
• Tl is reacting aggressively with TlBr.
• Sn electrode was reliable at our conditions.
• In was shown to form intermediate layer compound.
• In/TlBr interface possesses rectifier properties; however, the crystal quality currently limits the use of this interface.
PSD-7, Liverpool, GB, 2005
Acknowledgements
• Crystal growth: I.S. Lisitsky and M. Kuznetsov (GIREDMET, Russia)
• Finnish Technology Agency TEKES
PSD-7, Liverpool, GB, 2005
END
• Thank You!
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