1. " Sampling the Universe above 10 keV"
The Extreme Sky
" Sampling the Universe above 10 keV"
  October 2009 Otranto
Recent Trends in the Development of CdTe and CdZnTe Semiconductor Detectors for Astrophysical Applications
S. Del Sordo1, L. Abbene1,2, N. Auricchio 1 ,E. Caroli1, M. Quadrini1, J.B. Stephen1 , A. Zappettini3, R.M. Curado Da Silva4, O. Limousin5, A. Meuris5 and P. Ubertini1
1IASF-INAF, Italy
2DiFTeR Università di Palermo, Palermo, Italy
3IMEM-CNR, Parma, Italy
4Departmento de Física, Universidade de Coimbra, Coimbra, Portugal
5CEA – DSM - Irfu - Service d’Astrophysique, Saclay, France

2. Outline Scenario (projects and collaborations)
CdTe / CdZnTe X-ray and gamma ray detectors
Detector prototypes
Work in progress and future developments
Conclusions

3. The Italian collaboration
Projects and Collaborations
Progetto ASI Alte Energie (Study for the Gamma Ray Imager mission)
Progetto PRIN INAF SGRIP (funded by INAF)
Development of an high efficiency wide band 3D CZT detector prototype for Laue telescope focal plane
Progetto PRIN (funded by MIUR)
Growth technologies and spectroscopic optimization for X and Gamma ray detectors based on CdTe/CdZnTe.
International collaborations
The Italian collaboration
ESRF Grenoble
Leicester University
DTU Space Copenaghen
Coimbra University
CEA Saclay Paris
ICE-CSIC Barcelona
IASF-INAF (Milano Bologna Roma Palermo)
IMEM-CNR di Parma (crystal growth)
Università di Lecce (crystal growth and bonding)
IMM-CNR di Lecce (bonding and electrical characterization)
DIFTER Università di Palermo (medical applications) 3

4. CdTe and CdZnTe I High Z semiconductors (Zmax = 52)
Wide band gap semiconductors
Del Sordo S. et al., Sensors, Vol. 9, , 2009.

5. CdTe and CdZnTe II Critical Issues
Poor transport properties of the charge carriers:
hh ~ cm2/ V
ee ~ cm2/V)
Small electrical signals at the electrodes
Small crystal size: typically < 2 cm3
Development of single charge carrier sensing detectors (pixel, strip, Frisch grid, multiple electrodes) to overcome the poor transport properties of the holes is mandatory.
1 mm
L. Abbene et al., NIM A 583 (2007)

6. A. Zappettini et al., IEEE Nucl. Sci. Symp. Conf. Rec. 2008, 118-121.
CdTe and CdZnTe III
Suppliers of Spectrometer grade crystals
Italian group at IMEM-CNR (A. Zappettini): CdZnTe crystals grown by the boron oxide encapsulated vertical Bridgman technique
1.1 mm
A. Zappettini et al., IEEE Nucl. Sci. Symp. Conf. Rec. 2008,
2-inch CdZnTe crystal

7. DETECTORS CHARACTERISTICS
CdZnTe detector prototypes
CZT pixel detectors
DETECTORS CHARACTERISTICS
Pixel detectors
CZT (eV Products)
Geometric surface
10×10 mm2
Active area
8×8 mm2
Thickness
1 mm and 2 mm
Number of pixels
256
Pitch
0.5 mm
(0.45 mm anodes, 0.05 mm gap)
focal plane detector prototypes for Hard X-ray multilayer telescopes ( keV)

8. CZT pixel detectors performance
CdZnTe detector prototypes
CZT pixel detectors performance
Energy (keV)
Energy resolution (%)
Peak to valley ratio (2 x FWHM)
59.5
5.80 ± 0.16
28.1 ± 1.1
88,1
3.9 ± 0.2
19.5 ± 1.1
L. Abbene et al., JAP, Vol. 105, 2009.

9. CdZnTe detector prototypes
CZT pixel detectors performance
2 mm thick detector vs 1 mm
thickness
1 mm
2 mm
energy resolution (%) (59.5 keV)
5.80 ± 0.16
5.50 ± 0.10
energy resolution (%) (88.1 keV)
3.9 ± 0.2
3.50 ± 0.13
deviation of the FW.1M/FWHM ratio from the Gaussian ratio (1.82) (59.5 keV)
8 %
5 %
deviation of the FW.1M/FWHM ratio from the Gaussian ratio (1.82) (88.1 keV)
16 %
10 %
“Small pixel effect”
H. Barrett, J. Eskin, H. Barber, Phys. Rev. Lett. 75 (1995) 156

10. CdZnTe detector prototypes
CZT pixel detector for the POLCA II Experiment (POLarimetry with CdZnTe Arrays)
Detector
CZT Imarad
4x4 cm2, 5 mm thick
HV = -600 V
16x16 pix with 2.5 mm pitch
11x pix used
Readout Electronics
8 eV products ASIC
16 channels/chip
33/50/100/200 sel. Gain
0.6/1.2/2.4/4 μs shaping time
The POLCA quick look S/W user interface (LABVIEW)

11. Counts maps (scattered events)
CdZnTe detector prototypes
Polca experiment: Set-up at ESRF beam line ID15B and Results
Counts maps (scattered events)
pixel 186, Energy 200 keV, Angle 0, 45 degree

12. CdZnTe detector prototypes
Small 3D CZT position sensitive spectrometer (SmallGRIPrototype)
3D detector prototype packaging scheme:
The detector assembly is built with 8 identical modules packed together (64 anodes and 32 cathodes).
I/O pads
Alumina support
Basic sensitive CZT unit
▶External Dimensions: 10×10×2.5 mm3
Anode side: 8 anodes strips 0.15 mm wide
(pitch=2.5 mm)
correcting field strips 0.15 mm wide
gap between strips=0.15 mm
Cathode side: 4 cathodes strips 2.4 mm wide
gap between strips=0.10 mm
Front end electronics board
Redout Electronics NOVARAD Rena3
data handling and logic board
See Poster E. Caroli et al. SGRIP …

13. CdTe Schottky detector
Future Developments The POLCaliste experiment
CdTe Schottky detector
Caliste Module
Low noise readout electronics r.m.s. 80 e-

14. Energy resolution 1.5 % (FWHM) @ 59.5 keV
Future Developments The POLCaliste experiment
POLCaliste Experiment (POLarimetry with Caliste)
Caliste module performance
Energy resolution 1.5 % 59.5 keV
T = -15 °C
Polarimetric measurements at ESRF with the PolCaliste prototype are foreseen in We foresee to use in a first run the 64 ch device and in a next step the new 256 ch device. The device thickness will be 0.5, 1, 2 mm

15. Conclusions (I)
Italian CZT detector development (crystal growth and detectors assembly) activities are in progress with quite good expectations.
Experimental activities devoted to characterize imaging spectrometer operative in the keV energy band are in progress.
The SGRIP experiment (considered as a pathfinder for GRI) is in an advanced realization phase. The study of the prototype performances, foreseen in the 2010, will allow the optimization of the main operative parameters for a detector operative up to 800 keV in stack configuration.
The polarimetric performances of the POLCAII experiment are under evaluation. Measurements with the improved POLCaliste experiment are foreseen in the 2010 at ESRF.

16. Conclusions (II)
Very recently ASI funded a technological project named :
“LAUE - A Gamma Ray Lens”. In this project our collaboration has the responsibility of the focal plane detector (4 x 4 cm2 , 0.5 mm spatial resolution, good energy resolution) for the test of the lens prototypes. In this framework one of the most appealing possibilities will be the use of an array of Calliste detectors in the new 256 channel version.