1. Imaging and Spectroscopy With Cd(Zn)Te Detectors H. Lambropoulos (lambrop@teiste.gr)lambrop@teiste.gr Technological Educational Institute of Sterea Ellada

2. Outline of the presentation  Properties of C(Z)T and how they are connected to imaging and spectroscopy figures of merit  Methods to take into account the properties of C(Z)T for the imaging and spectroscopic systems  Some comments on interconnection technologies  A brief presentation of the work done in Greece for the development of hybrid pixel detectors.  Some Final Remarks

3. CdTe binary compound Z ave =50 (48,52), ρ=5.85 g/cm 3 Eg= 1.572 eV Zn, K shell absorption edge total photoelectric Compton pair production L shell absorption edge K shell absorption edge Cd, Te Rayleigh CdZnTe ternary compound Z ave =48.2, (48,30,52), ρ=5.78 g/cm 3 Eg= 1.572 eV

4. Figure of merit for imaging: Detective quantum efficiency gain = light conversion × gain Direct Conversion: Indirect Conversion: (for monoenergetic X-rays) Where (for indirect conversion) (spatial frequency)

5. Conclusion: Cd(Zn)Te means sharp line spread function + high absorption efficiency => high detective quantum efficiency

6. Examples not a complete reference …

7. A good detector for spectroscopy + Holes ++ Cathode Electrons Holes + Anode - - HV bias X=0 X=X 0 (t=0) X=L Electric Field (Homogeneous) d1 d2 Where mean free path λ e/h : Should have: for CCE=1 and low leakage current (either bulk or surface)

8. Resistivity due to the band gap @ room temperature(RT) CdTe bandgap 1.5eV@RT Cd 0.9 Zn 0.1 Te Bandgap 1.572eV@RT high purity single crystals resistivity: Is an upper limit Electrical compensation is needed

9. τ : carrier lifetime v thermal : thermal velocity N + D : electrically active defect concentration σ : capture cross section Δμ : Fermi level E d : Defect energy level mobility – lifetime product electrons (M. Amman et al., IEEE Trans. Nucl. Sci. 56(2009) 795) : Holes (T. Takahashi and S. Watanabe, IEEE Trans. Nucl. Sci. 48(2001) 950) : Am-241 spectrum low energy tail 3-D map of tellurium inclusions in a cut CdTe wafer: A. Zapettini, (IMEM Parma)

10. CdTe In doped 75 mm diameter ingot grown at Freiburg M. Fiederle (FMF-Freiburg) CdZnTe growth furnace at Madrid E. Dieguez (UAM-Madrid) Polizon facility for growth in Space (FOTON- Russia) But we all know that the winners in Cd(Zn)Te material are not in this Continent

11. How to deal with insufficient charge collection COPLANAR GRID FRISCH GRID

12. Hemispherical detectors Bi-parametric spectra Montemont G. et al.,

13. The small pixel effect and some complications R. Ballabriga et al., 2016 JINST 11 P01007 Barrett H.H., Eskin J.D., Barber H.B., Phys. Rev. Lett. 1995, 75, 156-159

14. Bumping and interconnect technologies The present Cd(Zn)Te detector Readout circuit Sensor hybrid

15. Bumping and interconnect technologies the (very near) future

16. WORK IN GREECE ON C(Z)T HYBRID PIXEL DETECTORS Acknowledgments to: D. Loukas, J. Kazas (NCSR D) K. Potiriadis, I. Kaissas (GAEC) C. Papadimitropoulos (TEISTE), D. Hatzistratis, G. Theodoratos, M. Zervakis, V. Zografos (formerly TEISTE)

17. P4DI=Photon 4-dimensional Digital Information= hybrid of the COCAE Compton Camera concept real life

18. Number of channels P4DI_v2F:50 rows x25 col=1250 pixels P4DI_v1 and v28 rows x 8 col =64 pixels Pixel pitch400μm Charge measurement capability P4DI_v1 Up to 225000 electrons (36fCb) Up to 43750 electrons (7Cb) Time measurement capability0 to 4.5 ms Power consumption200μW/channel @1.8V Detector leakage current P4DI_v1: +100pA P4DI_v2, v2_F: + 900pA ENC @Detector capacitance300 electrons @ 600fF

19. Images

20. Gain measurements with pulser and external ADC Gain measurement with pulser and in-pixel ADC Time tag linearity measurement with pulser and external ADC

21. Am 241 spectra

22. A high dynamic range x/γ ray hybrid pixel detector But power consumption : XPAD3: 40μW/pixel Medipix 3: 10μW/pixel Photon counting Impressive results Charge integration power consumption < 1μW/pixel Cmos image sensor 60db dynamic range Cmos image sensor 154db dynamic range Medipix 3

23. Folded multiple captures

24. Specification Threshold value Target value Number of pixels(128 x 8 )(128 x 256 ) Pixel pitch 100 x 100um frames/sec100 Integration time10ms Readout modesnapshot Num. of captures in 1frame 4 Min. time between captures 1.5ms column clock10MHz row clock10MHz/(8xN) 10MHz/(128x N) Video data rate10MHz Analog output voltage range 0.5V-1.5V Integrating capacitance1pF Dynamic range enhancement method folded multiple captures Dynamic range>100db Power Supply1.8V Power consumption 1.7uW/pixel +34.2uW/col HV bias-500V for Al/CdTe/Pt +500V for In/CdTe/Pt The HDRAPS CMOS ASIC

25. some thoughts… C(Z)T material needs to be improved further New detector concepts will help but for the moment the winner in molecular imaging and security seems to be the the Scintillator + SiPm For hybridization and CMOS electronics the next step is 3-d integration