Radiation hard radiation detectors based on wide band gap semiconductors

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1 Radiation hard radiation detectors based on wide band gap semiconductors Surrey University: P.J. Sellin S. Gkoumas A.W. Davies P. Veeramani M. Hodgson P. Bryant F. Schirru Annika Lohstroh Department of Physics, University of Surrey, SEPnet, UK I. Gomez Morilla G. Grime C. Jeynes A. Cansell M. Browton A.Simon Acknowledgements CEA (P. Bergonzo, N. Tranchant, C. Deschamps) ESRF (J. Morse) P. Edwards (Strathclyde) Element Six Ltd, Diamond Detectors Limited EPSRC/STFC/PPARC British Council IAEA (CRP: F11016-CR-2) Page 1

electronic engineering Centre for nuclear and radiation physics (CNRP) Experimental & Theoretical Nuclear Physics Medical and

2 Department of Physics - 30 academic staff Part of he Faculty of Engineering and Physical Sciences (FEPS) Soft condensed matter (SCM) Astrophysics Photonics & Semiconductor devices - Advanced Technology institute (ATI) - in collaboration with electronic engineering Centre for nuclear and radiation physics (CNRP) Experimental & Theoretical Nuclear Physics Medical and Radiation Physics Medical Physics & Imaging Radiation Detector development 2 academics and approx. 12 research students & staff Page 2

Wide band gap semiconductor materials for room

on natural diamonds Page 3 Application areas

detection & monitoring in nuclear industry High

security applications Photon science/synchrotron

3 Wide band gap semiconductor materials for room temperature radiation detector application Commercially available PTW chambers based on natural diamonds Page 3 Application areas High energy and nuclear physics Neutron detection & monitoring in nuclear industry High energy X- and γ-ray detection for medical and security applications Photon science/synchrotron instrumentation Medical dosimetry High fluence backgrounds and harsh environments...

4 Talk outline Basic semiconductor detector operation Advantages of wide band gap semiconductors Low Z Radiation hard materials SiC/D (General) Effects of Radiation damage on semiconductor detector operation Quantifying radiation hardness Identifying created defects Conclusion Future work Page 4

Signal formation E V d bias V Bias R B Induced current + + + _ charge sensitive preamplifier Time Signal duration The current signal is induced by the movement of the

5 Signal formation E V d bias V Bias R B Induced current _ charge sensitive preamplifier Time Signal duration The current signal is induced by the movement of the created charge carriers: the current is proportional to the number of carriers lifetime τ > transit time T R the charge carrier velocity mobility μ, electric field strength Page 5

6 Signal formation E V d bias V Bias R B Induced current _ charge sensitive preamplifier Time Signal duration Induced charge Time Signal amplitude Page 6

blind) Fast charge transport * Tissue equivalence* UV sensor Neutron

7 Diamond & SiC for sensor applications (Radiation) hardness Large heat conductance Low Z (low absorption) Tissue equivalence* Wide band gap (solar blind) Fast charge transport * Tissue equivalence* UV sensor Neutron detection Dosimetry (s)lhc Beam monitor * stronger advantage in diamond compared to SiC Page 7

Two main groups of materials studied High Z material

Tissue equivalent Neutron detection, TOF Cd x Zn 1-x

http://www.contech.com/mer curic_iodide_detectors.

8 Two main groups of materials studied High Z material for X/ spectroscopy and imaging Radiation hardness/ Tissue equivalent Neutron detection, TOF Cd x Zn 1-x Te 3 mm Birefringence pattern diamond HgI 2 & TlBr curic_iodide_detectors.htm CdTe CdZnTe HgI 2 TlBr 3 mm Diamond SiC polymers Page 8

9 Challenges in the material synthesis Diamond is meta-stable: High Temperature/High Pressure (HP/HT) limited volume, purity Several polytypes of SiC exist Physical Vapour Transport (bulk single crystal) Chemical vapour deposition (CVD) Heteroepitaxy (typically polycrystalline large area possible) Diamond on Iridium might be able to provide sufficiently thick, homogenous large areas in the future Homoepitaxy (typically < 1 cm 2 area) Columnar growth increasing grain size towards the top 1 to 10 μm h -1 Chemical vapour deposition (CVD) Common defects Impurities, Vacancies, Interstitials Dislocations Grain boundaries Stacking faults Polytype inclusions Substrate Page 9

10 Signal Amplitude CCE [%] Contact edge Non-uniform response in polycrystallline material Polycrystalline Columnar growth increasing grain size towards the top (a) 100 Single crystalline Silver paint A B D Substrate 270 μm K μm C Page 10 abstract

11 Electronic grade single crystal detector performance Energy resolution similar to Silicon Time resolution, time of flight: 28 ps See Figure 8 and 9 in M. Pomorski et al. phys. stat. sol. (a) 203 (12), pp (2006) See Figure 22 in M.Ciobanu, IEEE TNS 58 (4), pp (2011) hhlljlk Page 11

12 SiC excellent Schottky diodes for Spectroscopy have been demonstrated See Figure 2 in Ruddy et al, Nucl. Instr. Meth. B 263 (2007) Page 12

13 SiC thick (350 m) bulk material Bryant et al, IEEE TNS 60(2), pp , 2013 Page 13

p1x 1998, D. Saada, J. Adler, and R. Kalish Dissociation and diffusion then can lead to many more defect Complexes K.

14 Creation of defects due to irradiation E K =60 kev 4 fold 3 fold Energy transfer to the lattice atoms moves them from a substitutional to an interstitial site: Creation of [ V C i ] (Frenkel pair) International Journal of Modern Physics C 9, p1x 1998, D. Saada, J. Adler, and R. Kalish Dissociation and diffusion then can lead to many more defect Complexes K. Schmetzer, The Journal of Gemmology / 2010 / Volume 32 / No. 1 4 Annealing can change the defect types and concentrations further Page 14

15 Effect of damage on electrical properties changes the type/concentration of defects present in the material and hence introduces/removes energy levels in the band gap - - E C - Close to E C / E V : Dopants Near mid gap : Recombination centres E V Page 15

16 Effect of damage on electrical properties changes the type/concentration of defects present in the material and hence introduces/removes energy levels in the band gap Leakage current:: In an ideal intrinsic semiconductor, free charge carrier density is given by - - E C n N C exp E 2k G B T N c, density of states in the conduction band ~ cm -3 - Large E G gives lower dark currents, but experimentally intrinsic leakage current dominated by free carriers from defect states in the band gap E V Page 16

17 Effect of damage on electrical properties phys. stat. sol. (a) 204, No. 9, (2007) / DOI /pssa increase leakage increase in effective doping reduce leakage Compensation (reduction in doping) Reduction in carrier life time (recombination) Signal acquisition: Reduction in free carrier lifetime possibly reduced signal Trapping/De-trapping slower signal Reduction in active thickness (depletion thickness depends on doping in diodes) Page 17

lifetime (priming) (a) 0 to 20 % of the data file (b) 80 to 100 % of the data file (c) +110 V, hole sensitive CCE [%] 25 53 77 110 +110 V 0 to 10

18 Polarisation a contact problem? Surface and temporary effects: - temporary changes in space charge distribution (polarisation) - increase in number of occupied traps increase in lifetime (priming) (a) 0 to 20 % of the data file (b) 80 to 100 % of the data file (c) +110 V, hole sensitive CCE [%] V 0 to 10 % 10 to 20 % 20 to 30 % 30 to 40 % 40 to 50 % 50 to 60 % 60 to 70 % 70 to 80 % 80 to 90 % 90 to 100 % CCE [%] Counts Inconsistencies as a function of contacting method also observed by W. DeFerme, Hasselt Diamond Workshop 2009 Page 18

19 The challenge of quantifying radiation hardness for detector applications The NIEL concept assumes s displacement damage cross- section D (MeV mb) assumes that lifetime scales with # displacements Seems to work for protons/neutrons > 0.1 GeV See Figure 4 De Boer, phys. stat. sol. (a) 204, No. 9, (2007) Damaging radiation and probing radiation penetrate through the device thickness. (26 MeV H + / 20 MeV n/ MIPs) Signal halves after p: 4.5 (1.5)x10 14 cm -2 n: 1.3 (3)x10 15 cm -2 Page 19

20 CCE [%] Contact edge CCE [%] The challenge of quantifying radiation hardness for detector applications What if the damaging/probing radiation does not penetrate the whole device? (a) Silver paint 500 μm Vacancy concentration [cm -3 ] A B C D E (b) 26 MeV SRIM calculation [11,12] kev protons x cm MeV protons cm cm cm -2 5x10 14 cm cm cm cm Depth [ m] F A. Lohstroh et al, phys. stat. sol. (a) 2008, 205(9); p Damaged area not visible in Raman SRIM calculation spectra tration [cm -3 ] Page

CCE [%] Contact edge CCE [%] CCE [%] The challenge of quantifying radiation hardness for detector applications What if the damaging/probing radiation does not penetrate the whole device?

21 CCE [%] Contact edge CCE [%] CCE [%] The challenge of quantifying radiation hardness for detector applications What if the damaging/probing radiation does not penetrate the whole device? (a) A Silver paint B C 500 μm D E Silver paint 500 μm (b) Label A 100 B D C E 25 F +150 V (holes) -100 V (electrons) D A. Lohstroh et al, phys. stat. sol. (a) 2008, 205(9); p A C F Area [10-3 cm 2 ] CCE [%] Dose [cm -2 ] (b) Counts [x10 3 ] (1.1 01)x10 12 (1.1 01)x10 13 (1.0 01)x10 14 ( 5 1)x F ( )x10 E 15 0 (5 4)x10 15 Damaged area not visible in Raman spectra Page 21

22 Introducing a corrected Damage factor Z. Pastuovic et al, Proc. of SPIE Vol A-1 Assume that trapping probability increases linearly with radiation fluence Take into account damage profile (e.g. SRIM or other code) Ionisation profile of probing radiation (e.g. SRIM or other code) See Figure 4, Z. Pastuovic et al, Proc. of SPIE Vol A-1 Works well for low level damage Page 22

TOF measurements Can confirm whether the mobility is affected by damage 1 10 12 cm -2 2 10 13 cm -2 0 cm -2 S.

23 TOF measurements Can confirm whether the mobility is affected by damage cm cm -2 0 cm -2 S. Gkoumas, PhD thesis, University of Surrey = ( ) cm 2 V -1 s -1 v sat = ( ) V cm -1 Page 23

24 Identifying defect levels DLTS not useful for high resistivity PICTS light source/limited time scale Luminescence not quantitative/ cannot see non-radiative defects Optical absorption detection limits/sample size EPR sample size, only sensitive to paramagnetic PAS sample size Page 24

TL after annealing 20 Gy pre-irradiation 313 K to 650 K, 10 K/s 1 10 12 n cm -2 : 0.5 ev 0.6 ev 1.7 ev 0.

8 to 1.9 ev observed by S. Gkoumas, PhD thesis, University of Surrey 2012 Gonon et al.

25 TL after annealing 20 Gy pre-irradiation 313 K to 650 K, 10 K/s n cm -2 : 0.5 ev 0.6 ev 1.7 ev 0.7 ev n cm -2 : 0.6 ev 0.6 ev 1.8 ev 0.6 ev n cm -2 : 0.6 ev 0.6 ev 0.8 ev 0.9 ev B: n cm -2 (A has similar shape) In pc: 1.8 to 1.9 ev observed by S. Gkoumas, PhD thesis, University of Surrey 2012 Gonon et al. (APL 70 (1997) ) and Benabdesselam et al. (DRM 10 (2001) ) (substitutional Nitrogen?) Page 25

26 CL before annealing 0 cm cm cm cm -2 S. Gkoumas, PhD thesis, University of Surrey H and ev centre also seen in neutron irradiation study Almaviva et al JAPP 106 (2009) Reference for defect levels: A. M. Zaitsev, Optical Properties of Diamond: A Data Handbook, Springer-Verlag, Berlin Heidelberg, 2001 Page 26

27 Signal (CPS per incident Fluence) I/ϕ (x CPS/s) Bulk - SiC of Surrey 3000 E (kev) (kev) MeV Page 27 M. Hodgson et al, University

28 Conclusion Future work Estimating the operational lifetime of detectors needs more understanding of the effects of radiation induced damage on their characteristics In wide band gap semiconductors, separating priming/polarisation and structural damage is challenging Radiation hardness as a material property independent of radiation and probe is not trivial Improving our understanding of hardness and defect characteristic with the help of IAEA coordinated research programme Page 28

29 Thank you! Questions? Page 29

SiC and diamond as radiation hard semiconductor detectors

SiC and diamond as radiation hard semiconductor detectors Annika Lohstroh Department of Physics, University of Surrey, SEPnet, UK Email: A.Lohstroh@surrey.ac.uk Acknowledgements Surrey University: P.J.