Progress in low energy X-rayX spectroscopy using semi-insulating insulating GaAs detectors F. Dubecký 1, B. Zaťko 1, P. Boháček 1, L. Ryć 2, E. Gombia 2, and V. Nečas 3 1 IEE SAS, Bratislava, Slovakia 2 IPP&LM, Warsaw, Poland 3 IMEM-CNR, Parma, Italy 4 FEE&IT SUT, Bratislava, Slovakia
Outline Introduction, motivation Readout electronics, Peltier cooling Input J-FETsJ and PA evaluation SI GaAs detector for low energy X-raysX Current-voltage measurement Detection of X and γ-rays Summary, conclusion
Introduction Semi-insulating GaAs as a material of radiation detector Wide bandgap energy E g = 1.42 ev Relative high atomic number 31 & 33: efficient detection of X- and gamma rays Fast reaction rate: high drift mobility High resistance to damage by irradiation Drawback: high leakage current at RT for application in soft X-ray spectroscopy
Motivation Energy gained from a fusion reaction could solve problem of energy Fusion has many attractive features in terms of safety, fuel reserves, and minimal damage to the environment The primary disadvantage being associated with difficult scientific and engineering challenges that are inherent in the fusion process Problem that must be solved: On-line hot plasma diagnostics Application in detection of Extreme UV photons
10 8 Attenuation coefficent µ, cm -1 10000 2.5x 23x 1000 100 10 1 1 10 Photon energy, kev GaAs Si InP CdTe V D (cms -1 ) 10 7 10 6 Electrons in GaAs Holes in GaAs Detector operation 10 5 region 10 2 10 3 10 4 10 5 10 6 E (Vcm -1 )
Measuring spectrometric system Battery voltage source U 0 COOLING NECCESSARY Required performance: Noise: < 100 e - rms SDD: < 140 ev FWHM 13 e - rms R b γ-photon SI GaAs Detector Charge sensitive preamplifier Eurorad PR-307 Shaping amplifier CREMAT CR-200 Analog-to-digital converter ORTEC 800 ADC e - h + J-FET ohmic contact pasive region depletion layer Schottky contact M2D multichannel analyzer MCA + PC
J-FETs evaluation 2000 2S K 152 G 8 1.48 k ev 2N 4416 1.54 kev B F 826 1.77 kev Counts per channel 1500 1000 5 0 0 0 0 2 0 4 0 60 8 0 1 0 0 1 2 0 140 1 6 0 1 8 0 C h a nnel Transistor Yfw, ms Ciss, pf Noise, nvhz-1/2 Package Notice 2SK152 25 7,2 1,20 TO92 obsolete, SMD unavailable BF862 45 9 0,8 TO236, SOT23 Noise at 100 khz, SMD 2N4416 6 2,20 6 TO72, TO236 SMD package available MX-16 28 4 1 TO72 Chip available, Ciss at -4 V MX-120 16 1,7 1,2 TO72 Chip available, Ciss at -4 V NJ14AL 5,5 2,3 4 Chip Chip U310 17 5 10 SMD package available SMPJ309 10 7,5 6 SMD package available SMPJ310 8 7,5? SMD package available
Preamplifiers testing and evaluation Counts per channel 2200 2000 1800 1600 1400 1200 1000 800 600 400 200 0 2400 55 Fe: 5.9 kev Si3-8 V, E = 1.50 kev, ST = 1 µs, CR 102B Si3-8 V, E = 1.68 kev, ST = 1 µs, CR 110 (1) Si3-8 V, E = 1.65 kev, ST = 1 µs, CR 110 (2) 2200 2000 55 Fe: 5.9 kev Si3-8 V, E = 1.78 kev, ST = 1 µs, Eurorad PR 307 (1) 1800 Si3-8 V, E = 1.62 kev, ST = 1 µs, Eurorad PR 307 (2) Si3-18 V, E = 1.67 kev, ST = 1 µs, battery source 1600 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Energy, kev 241 Am: 59.5 kev Counts per channel 1400 1200 1000 800 600 400 200 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Energy, kev 241 Am: 59.5 kev Hybride Preamp, separated FET CR-110 CREMAT 1.5 kev CR-102B CREMAT, obsolete 1.2 kev PR307 EURORAD 0.85 kev A-250 AMPTEC 1 kev ASICS various < 300 ev * e.g. Bertuccio, G., Caccia, S., NIM A 579 (2007) 243 Noise FET dependent, @RT
Blocking scheme of developed charge sensitive preamplifier Part cooled by the Peltier cooler Charge sensitive preamplifier with cooled first stage and SI GaAs detector
Cooled stage detailed layout Temperature Sensor (AD590 chip) Testing capacitor SMD J-FET Substrate < 200 µm: Al 2 O 3 AlN Be-based ceramic SI GaAs detector Working resistor Feedback resistor Feedback capacitor 6x6 mm 2
Developed low noise preamplifiers Input J-FET Charge sensitive preamplifier based on CR-102B hybrid circuit and external input J-FET 2SK152 Noise: 135 e - rms at RT Detector SI GaAs detector is directly coupled to the input of the charge sensitive preamplifer
Charge sensitive preamplifier with Peltier cooler PR307 SI GaAs detector Cooled J-FET stage with detector SMD BF862 J-FET
New solution: 3 stage Peltier cooler Additional tasks neccessary to solve: input thin window with a low absorption collimator micro-temperature sensor efficient cooling of the heat sink compact bias source improvement of detector radiation and neutron damage resistance PR-307 CERAMIC SUPPORT with detector and J-FET
Compact DC biasb source Rechargable batteries (AA) 1k2 V 1 + C L 12 2 8 6 TMR dc-dc 1 7 +12 V 0 +V in V in 1 2 6 MHV Series 180, 300, 350 V out V ref 4 3 V adj 5 HV out C2 4700 pf V out Com 6-12 AA V 2 V 3 + C + C L L 2 6 TMR 1 2 6 TMR 1 7 8 7 8 0 0 1k2 1k2 +12 V Output 12 V +12 V Output 12 V R1 R2 VR = 5kΩ +/- 12 V bias for charge sensitive preamplifier and shaping amplifier High voltage output for detector
Simple SI GaAs detector for low energy X-raysX square 0.4 mm Ti/Pt/Au (10/40/70 nm) Schottky contact SI GaAs wafer (130 µm) AuGeNi/Au (50/70 nm) contact bulk VGF SI GaAs wafer (100) - detector grade producer: CMK Ltd. Žarovica, Slovakia RT resistivity: 1.8 10 7 Ωcm RT Hall mobility: 7060 cm 2 V -1 s -1
Current-voltage characteristic of SI GaAs detector @ RT 100n DC current decrease: 10 with each 20 deg. of temperature lowering: e.g. @ 260 K I sat 10 pa Current, A 10n 1n 100p Optimal operation area SI GaAs detector T = 300 K φ (Schottky) = 0.5 mm 0 200 400 600 Bias, V
Detection of X-X and γ-rays: @ RT 160 µm Counts per channel 2000 1500 1000 500 Np X Lα, Lβ, Lγ 13.9 17.8 kev 14.4 20.3 kev escape Ag K α 33.2 kev FWHM 7.7 kev γ 59.5 kev Pb K α and K β LEC SI GaAs 160 µm, φ = 0.5 mm 241 Am, 57 Co, RT Bias = - 250 V escape γ 122.1 kev 0 K α Ga & As *7 γ 136.5 kev 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Channel
RT pulse-height spectrum of 241 Am Counts 5000 4000 3000 2000 1000 Np X 241 Lα, Lβ, Lγ Am 17.8 kev 20.8 kev 13.9 kev 26.3 kev escape FWHM 5.11 kev U bias = - 130 V τ = 0.5 µs T = 295 K γ 59.5 kev 130 µm 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 Energy, kev
LT: Pulse-height spectrum of 241 Am 5000 4000 Np X Lα, Lβ, Lγ 17.8 kev 241 Am U bias = - 130 V τ = 3 µs T = 255 K 130 µm Counts 3000 2000 1000 13.9 kev 20.8 kev 26.3 kev escape FWHM 4.64 kev γ 59.5 kev 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 Energy, kev
RT< LT: Pulse-height spectrum of 241 Am using optimized electronics 4000 Np X Lα, Lβ, Lγ 17.8 kev 241 Am Spectra: RT and LT OPERATION 130 µm Counts 3000 2000 1000 13.9 kev 20.8 kev 26.3 kev escape U bias = - 110 V τ = 0.5 µs T = 295 K τ = 3 µs T = 255 K FWHM 4.3 kev 4.0 kev γ 59.5 kev 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 Energy, kev
Energy resolution Temperature, K Energy resolution, % FWHM (kev) 295 295 improved 265 265 improved 17.8 kev peak < 25 (< 4.5) < 23 (< 4.2) < 22 (3.9) < 19 (< 3.6) < 16 (< 3.0) < 14 (< 2.8) 59.5 kev peak 8.6 (5.0) 12.9 (7.7) 7.2 (4.3) 7.8 (4.6) 7.2 (4.3) 6.8 (4.0)
Two-line SI GaAs detector module One detection mini-module with 2 64 pixel detectors Zaťko, B., Dubecký, F., Přibil, J., Boháček, P., Frollo, I., Ščepko, P., Mudroň, J., Grybos, P., and Nečas, V.: On the development of portable X-ray CT mini-system using semi-insulating GaAs radiation imaging detectors, Nuclear Instr. and Methods in Phys. Res. A 607 (2009) 67-70. IF: 1.019 COST MP601 Meeting
Block diagram of single channel Grybos et al.: IEEE Nucl. Sci. Sym. Conf. Record (2006) 693. Photograph of SI GaAs radiation detectors coupled to ASIC DX64 readout chip. Current (A) 1µ 100n 10n 1n 100p Forward Reverse T = 300 K 10p 0 50 100 150 200 250 300 350 400 Diameter 0.75 mm 0.5 mm 0.3 mm 0.2 mm Detector R Detector L Voltage (V) I-V characteristics of SI GaAs detectors measured at RT. Total counts 100k 10k 1k 100 Diameter, Bias = 220 V 0.75 mm 10 0.5 mm 0.3 mm 0.2 mm 1 0 50 100 150 200 250 Threshold Integral spectra of SI GaAs detectors measured using ASIC DX-64 readout chip. Total counts 1 400 1 200 1 000 800 600 400 200 0 RT 3.8 kev 0 10 20 30 40 50 60 70 80 Energy (kev) Calculated differential spectra of 241 Am measured using ASIC DX-64 with SI GaAs detector 0.3 mm in diameter
New choice: electrodes technology 1µ Forward 35,0n 300 V Noise rms 0-3 10-11 A Noise rms 0.1-2 10-11 A Current (A) 100n 10n 1n Reverse AuGeNi In Mg Gd Current (A) 30,0n 25,0n 20,0n 200 V Noise rms 1-3 10-12 A Noise rms 0.1-4.0 10-11 A AuGeNi In Mg Gd 0 100 200 300 400 Voltage (V) 0 5 10 15 20 25 30 35 40 Time (min) 20000 Counts per channel 10000 1000 100 noise SI GaAs: Schottky Ti/Pt/Au φ = 0.5 mm AuGeNi In Mg Gd Counts per channel 15000 10000 5000 SI GaAs: Schottky Ti/Pt/Au φ = 0.5 mm AuGeNi In Mg Gd 10 1 0 50 100 150 200 250 Channel 0 0 20 40 60 80 100 120 Channel
Conclusions We developed and tested charge sensitive preamplifiers with external J-FET operated at RT and lowered temperature. SI GaAs detector dc coupled to the developed front-end electronics gives detectable energy threshold of 4.5 kev at 295 K and < 3 kev at 265 K. Fabricated and evaluated surface SI GaAs Schottky barrier detector has an active base width of 130 µm and gives energy resolution of about 2.8 kev FWHM for 17.8 kev peak from 241 Am source at 265 K. The results show that first of all the noise of the front-end electronics chain must be reduced to <100 e - rms. Future plan toward spectrometric detector technology: electrodes, topology, material aspects, neutron damage
Acknowledgements This work was done within the Center of Excellence CENAMOST (Contract No. VVCE-0049-07) With parial support from grants: No. APVV 0655-07 (Slovak Research and Development Agency), No. 2/0163/09, 1/0689/09, 2/0192/10 (Grant Agency for Science), EURATOM/CU (Project P3) and COST MP0601
THANK YOU FOR YOUR ATTENTION