Transcript Strip detectors based on vapor phase grown (Cd,Zn)Te

Investigations of CdTe and (Cd,Zn)Te crystals
grown by the Bridgman method
M. Fiederle, A. Fauler, V. Babentsov, J. Franc, J. Ludwig, K.W. Benz
Freiburger Materialforschungszentrum FMF
Albert-Ludwigs-Universität
Stefan-Meier-Straße 21, D-79104 Freiburg
www.2-6.uni-freiburg.de;
Email: [email protected]
• growth of 25 and 75 mm CdTe
• defects and compensation
• material properties and detector performance
Freiburger Materialforschungszentrum FMF
M. Fiederle
Why is doping of CdTe/(Cd,Zn)Te necessary?
• there are three posibilities to obtain high resistivity:
– intrinsic material (problem of shallow impurities)
– shallow compensation (problem of stability)
• Cl, In, ...
– three level compensation
• deep intrinsic defect (TeCd, VCd, ??)
• deep donor – V, Ge, Fe, ... (problem of deep traps)
• doping is mandatory to obtain high resistivity!
Freiburger Materialforschungszentrum FMF
M. Fiederle
configuration
of growth
•
ampoule
– inner diameter 24 and 75 mm
– semiconductor quality
HSQ300 / HSQ800 Heraeus
– graphitized ampoule
•
furnace
– ceramic tube (safety)
– 4 PtRh-Pt thermocouples
– online monitoring
(4 values / 10 sec.)
•
material
– 7N Cd, Te, Zn (6N)
– dopants: Ge, Sn, Al, In, Cl
– C[dopants]: 1018 - 1019
Freiburger Materialforschungszentrum FMF
M. Fiederle
temperature timeline 75 mm CdTe
1200
melting point CdTe
800
o
temperature / C
1000
600
exothermic reaction
(400 K in 10 sec)
400
200
melting Cd and Te
0
0
20000
40000
60000
time
80000
Freiburger Materialforschungszentrum FMF
100000
120000
M. Fiederle
(Cd,Zn)Te undoped crystal 24 mm
Freiburger Materialforschungszentrum FMF
M. Fiederle
grains and twins – problems of melt growth
CdTe:Ge wafer
grown with
modifications
Freiburger Materialforschungszentrum FMF
M. Fiederle
resistivity of 75 mm CdTe:Ge wafer (TDCM)
resistivity 
in cm
70
6,6E9
6,6E9
6,3E9
6E9
5,7E9
5,4E9
5,1E9
4,9E9
4,6E9
4,3E9
4E9
3,7E9
3,4E9
3,2E9
2,9E9
2,6E9
2,3E9
2E9
1,7E9
1,4E9
1,2E9
8,8E8
60
length / mm
50
40
30
20
10
0
0
10
20
30
40
50
60
70
length / mm
Freiburger Materialforschungszentrum FMF
axial distribution:
2.0 – 8.0 x109 cm
M. Fiederle
chemical analysis GDSM and LIMS
cooperation with
Li
B
Na
Mg
Al
Si
P
S
Cl
K
Ca
Fe
Co
Ni
Cu
Zn
As
Se
Ag
In
S1
< 0.001
0.0004
0.01
0.014
0.015
0.013
0.0003
0.003
< 0.001
0.002
0.006
0.034
< 0.0001
0.004
0.002
0.003
0.003
< 0.01
< 0.05
0.01
R. James, Brookhaven National Lab. and
E. Cross, Sandia National Labs.
S2
< 0.023
0.0004
0.02
0.004
0.021
0.016
0.002
0.002
0.002
0.006
0.004
0.047
0.0001
0.0005
0.39
0.010
0.010
< 0.01
< 0.05
0.01
S3
0.013
0.0007
0.027
0.004
0.007
0.001
0.003
0.005
0.006
0.001
0.005
0.13
< 0.0001
0.009
2.9
0.005
0.003
< 0.01
< 0.05
0.01
•
•
•
•
•
concentration of impurties in ppm
GDMS data of three different locations of
CdTe:Ge crystal
concentration of Ge (AAS):
– 2 – 3 x 1016 cm-3
total concentration of shallow impurities
less than 3 ppm (~ 4 x 1016 cm-3)
concentration of possible deep level:
– Fe 47 ppb (~ 7 x 1014 cm-3)
Freiburger Materialforschungszentrum FMF
M. Fiederle
deep levels in CdTe:Ge
Level
Energy (eV)
Capture cross
section (cm2)
Beginning
End
P1
P2
P4
0.11
0.21
1.10-18
1.10-15
P5
P7
P8
0.35
0.75
0.95-1.05
5.10-13
1.10-11
6.10-8
0.16
0.34
0.42eV
0.74
0.95-1.05
1.10-7
8.10-13
3.10-16
1.10-11
6.5.10-8
transition
transition
transition
transition
Fe or Cu related
VCd-2 - V band
Ge related defect-
Fe related
Tentative
transition
identification
A center- V band
unknown
defect-V band
defect-C band
C band
Freiburger Materialforschungszentrum FMF
M. Fiederle
CdTe:Ge
PL maps at 80K
A-centre
FE
0.8 eV
1.0 eV
70
50
12
40
9
30
5
20
PL Intensity in colors
Crystal length (mm)
60
2
10
0
0
10
20
Crystal diameter (mm)
0
10
20
0
Crystal diameter (mm)
10
20
Crystal diameter (mm)
0
10
20
Crystal diameter (mm)
Freiburger Materialforschungszentrum FMF
M. Fiederle
Resistivity and PL signal of undoped (Cd,Zn)Te
PL map at 80K
Resistivity map at RT
( h nmax = 1.636 eV )
1E10
3,000
7E9
25
5,5E9
20
4E9
15
2,5E9
10
25
Resistivity (  cm)
30
Crystal length (mm)
30
8,5E9
2,449
20
1,760
15
10
1,209
5
1E9
5
0,6578
0
5
10
15
20
25
Crystal diameter (mm)
30
0
0
5
10
15
20
Crystal diameter (mm)
Freiburger Materialforschungszentrum FMF
M. Fiederle
PL Intensity in pseudo-colors
35
Detektor properties
• Setup:
– Amptek A250 Preamplifier
– module with bonded detector
– detector with guarding
properties
(alpha particles)
detector
mete
t. b. measured
(10-4 cm2/V)
mhth
6 x 10-5 cm2/V
resolution
bias
Freiburger Materialforschungszentrum FMF
10 %
30 – 200 V
M. Fiederle
technolgy
•
detector processing
– lithography
– metalization
– wire bonding
– passivation (BCB)
•
fabrication of strip detectors
– 127 µm pitch
– 24 x 14 mm detector array
500 µm
14 x 24 mm detection area
crystal
board
Freiburger Materialforschungszentrum FMF
M. Fiederle
X-ray analysis of a copper-cable ( 500 µm diameter)
1
Dunkelwert- und Verstä rkungsnormiert
Photocurrent a.u.
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2.2
2.4
2.6
2.8
3
3.2
3.4
Weg in mm
X [mm]
3.6
3.8
4
©Sikora Industrieelektronik GmbH
Freiburger Materialforschungszentrum FMF
M. Fiederle
Technology: Flip Chip Bonding CdTe
• cooperation with
Prof. G. Anton,
H. Braml
Friedrich-Alexander-Universität
Erlangen-Nürnberg
• in-house processing of CdTe
and (Cd,Zn)Te
Quelle: Pac Tech
Freiburger Materialforschungszentrum FMF
M. Fiederle
Technology: Flip Chip Bonding CdTe
• technology:
Solder bumps
• material:
PbSn and In
• processing:
Electroplating (Cu+PbSn)
Deposition (Indium)
• backend:
manual Flip-Chip-Bonding
Freiburger Materialforschungszentrum FMF
M. Fiederle
Summary
•
successful growth of 75 mm and 24 mm CdTe and (Cd,Zn)Te
– large single crystalline areas
•
high resistivity material (>5 x 109 cm)
– successful compensation by
• deep donor Ge, Sn and undoped (Cd,Zn)Te
– homogeneous distribution of material properties
– deep levels correlated with Ge, Fe and Cu were detected
•
detector performance suffient
– reduction of impurities / dopants necessary
•
successful detector technology
– pixel detectors under developing
Freiburger Materialforschungszentrum FMF
Acknowledgement:
• European Space Agency
– MAP programm
• Humboldt Stiftung
M. Fiederle
compensation in CdTe:Ge
• 3 level compensation
– shallow acceptor NA(Cu, ...)
– shallow donor ND(Cl, In, ..)
– deep donor NDD
• germanium

N DD

N DD
 E  EDD
1  exp F
 kT




p  N D  N DD
 n  N A
Freiburger Materialforschungszentrum FMF
M. Fiederle
compensation in CdTe:Ge
• 3 level compensation
– shallow acceptor NA(Cu, ...)
– shallow donor ND(Cl, In, ..)
– deep donor NDD
• germanium

N DD

N DD
 E  EDD
1  exp F
 kT




p  N D  N DD
 n  N A
Freiburger Materialforschungszentrum FMF
M. Fiederle
photoluminescence of
CdTe:Ge
• mapping of 45 mm wafer
• selection of different energy
levels corresponding to:
– A-center
– exciton
– deep level at 1.0 eV
• comparison with resitivity mapping
Freiburger Materialforschungszentrum FMF
M. Fiederle
Comparison resistivity and photosensitivity
Freiburger Materialforschungszentrum FMF
M. Fiederle
photoluminescence spectra
(77K) of CdTe:Ge
• found emissions:
– near band gap emmision
(FE)
– A-center
– 1.1 eV emission
– 0.82 eV
• slightly reduction of crystal
quality from beginning of
growth to the end
Freiburger Materialforschungszentrum FMF
M. Fiederle
growth of 25 mm (Cd,Zn)Te
•
•
•
ampoule
– inner diameter 24 mm
– semiconductor quality
HSQ800 Heraeus
– graphitized ampoule
furnace
– ceramic tube (safety)
– 4 PtRh-Pt thermocouples
– online monitoring
(4 values / 10 sec.)
material
– 7 N Cd, Te
– 6 N Zn
– 5 percent Zn
Freiburger Materialforschungszentrum FMF
M. Fiederle
P L I n t e n s i ty ( a r b . u n .)
P L s p e c tru m o f C Z T c ry s ta l
DX
6
1. 22 eV
5
4 .2 K
1. 115 eV
4
3
x20
1
P L In te n s i t y ( a r b . u n . )
FE
AX
2
0
0 .8
0 .9
1 .0
1 .1
1 .2
1 .3
1 .4
1 .5
1 .6 0
1 .6 5
1 .7 0
1 .5
80K
D -h
1. 09 eV
G a u s s ia n f it
1 .0
FE
0 .5
x40
0 .0
0 .8
0 .9
1 .0
1 .1
1 .2
1 .3
1 .4
1 .5
1 .6 0
1 .6 5
1 .7 0
hn, eV
Freiburger Materialforschungszentrum FMF
M. Fiederle
Resistivity and Zn concentration
• strong correlation between zinc
concentration and resistivity
5,2
Zn (at.%)
4,8
• resistivity and zinc show the
same behaviour
4,4
a
4,0
3,6
3,2
10
2,0x10
 ( cm)
• experimental data close to the
theoretical ones
1
10
1,6x10
theoretical
10
1,2x10
9
8,0x10
2
9
4,0x10
0,0
0
5
10
15
20
X (mm)
Freiburger Materialforschungszentrum FMF
M. Fiederle
25
35
zinc concentration in the lower part
30
25
1E10
Crystal length (mm)
20
7E9
15
5,5E9
10
4E9
2,5E9
Resistivity (  cm)
8,5E9
5
1E9
10
15
20
25
0
30
Crystal diameter (mm)
10
4,800
zn1
y (mm)
4,444
8
4,089
6
4
3,733
Zn (at. %)
5
2
2
4
6
8
10
12
14
16
18
20
22
24
3,378
x (mm)
Freiburger Materialforschungszentrum FMF
M. Fiederle
deep levels in CdTe:Ge
Conduction band
Shallow
donors
0.9eV
0.6eV
Thermal transitions
1 eV
Eg = 1.59eV
1.21eV
Optical transitions
Ge2+/Ge3+
(R-center)
1.47eV
0.69eV
Fe2+/Fe3+
(R-center)
Phonons
0.12eV
0.38eV
A center
Freiburger Materialforschungszentrum FMF
Valence band
M. Fiederle