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I n s t i t u t e of H i g h E n e r g y P h y s i c s

I n s t i t u t e of H i g h E n e r g y P h y s i c s. Influence of cooling on the working parameters of GaAs detectors. S. Golovnia a* , S. Gorokhov a , Y. Tsiupa a , A. Vorobiev a O. Koretskaja b , L. Okaevich b , O. Tolbanov b

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I n s t i t u t e of H i g h E n e r g y P h y s i c s

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  1. I n s t i t u t e of H i g h E n e r g y P h y s i c s Influence of cooling on the working parameters of GaAs detectors. S. Golovnia a*, S. Gorokhov a, Y. Tsiupa a, A. Vorobiev a O. Koretskaja b, L. Okaevich b, O. Tolbanov b a Institute of High Energy Physics, Protvino, Russia b Tomsk State University, Tomsk, Russia И н с т и т у т Ф и з и к и В ы с о к и х Э н е р г и й

  2. The following semiconductor detector parameters is testing to find the influence of cooling on it. • Detector’s Dark Current vs. Bias Voltage • Detector’s Capacitance vs. Bias Voltage • Detector’s Noise vs. Bias Voltage • Detector’s Response on β-particles and γ-rays • Detector’s Charge Collection Efficiency • Detector’s γ -Ray Detection Efficiency & Thickness

  3. Detectors geometry and types • Resistive, doped Cr. Sample dimensions 3,3x3,4 mm, thickness 780 mkm. initial indot of GaAs is ~ 0,8 – 1,2 * 10 ^17 [1/cm^3], bulk resistivity 0,5 – 0,8 *10^9 • Epitaxial grown and Cr compensated. Sample dimensions 1,1 x 6,6 mm, thickness 500 mkm initial indot is 1*10^17 [1/cm^3] Concentrations ratio is Cr/Sn = 6.8

  4. The Dark Current temperature dependence vs. High Voltage The typical I-V characteristic of resistive type detector sample. The characteristic is independent from the voltage polarity and forward and reverse branches is equal. The dark current decreases in ten times if the detector temperature is decreasing on 20 °C

  5. The detector capacitance dependence from the detector temperature at different modulation frequencies The typical C-V characteristic of resistive type GaAs detector samples. The temperature changes is not affected on the detector capacitance if the modulation frequency higher then 10 kHz

  6. The detector noise can be predicted in case of 2 stage integration Shot noise Current & Thermal noise Flicker noise Where: λ = Tdif/Tint ~1 k = 1.380*10-23 J/K T =~300 temperature (0K) g = ~20 C = ~ 10 -12 total capacitance I = ~ 10 -9total current Vf = flicker noise voltage • The contribution from different noise sources can be easy separated • Shot noise is proportional ~ C2/Tint • I and Thermal noise ~Tint • Flicker noise does not depend on Tint

  7. The detector system noise can be predicted in case of 2 stage integrating Shot noise Current & Thermal noise Flicker noise Where: λ = Tdif/Tint ~1 k = 1.380*10-23 J/K T =~300 temperature (0K) g = ~20 C = ~ 10 -12 total capacitance I = ~ 10 -9total current Vf = flicker noise voltage • The contribution from different noise sources can be easy separated • Shot noise is proportional ~ C2/Tint • I and Thermal noise ~Tint • Flicker noise does not depend on Tint

  8. The LED system setup for Noise vs. Current measurements The schematic view of the test system setup. Both the detector and the LED put into shielded box filled with dry gas mixture to prevent condensate. The temperatures from -40 to +50 °C can be reached. By changing the voltage in the LED chain the photocurrent in the test sample can be easily changed.

  9. The dependence of Sigma noise (in ADC channels) vs. detector current at different shaping times is given for resistive type detector sample.

  10. The dependence of Sigma noise (in ADC channels) vs. detector current is given for resistive type detector sample. dSigma/dI for both 50 and 100 high voltages is equal. It is mean, that noise is put together additive, without influence on each other and noise linked with high voltage only.

  11. The dSigma/dI [e2/nA] vs. Shaping time is given for resistive type detector samples. The dSigma/dI = 5768,9 [e2/nA] that much more that predicted value of 1171,8 [e2/nA] calculated before.

  12. The epitaxial detector response on γ-rays from 241Am source This spectrum from the radioactive source 241Am on the epitaxial type detector show us that Charge Collection Efficiency is ~ 86-90%.

  13. The epitaxial detector response on beta particles from 90Sr radioactive source

  14. Charge collection efficiency vs. high voltage at different temperatures measured on Diffusion Samples

  15. Charge collection efficiency vs. temperature at different high voltage measured on Epitaxial Samples

  16. Detection Efficiency vs. GaAs Detector thickness for γ-Ram Energy Region from 20 to 60 keV

  17. The epitaxial detector active area thickness vs. detector temperature for high voltages 50 & 100 V

  18. The resistive detector active area thickness vs. high voltage at temperature +20 oC

  19. Conclusion • The presented experimental results show, that cooling both GaAs resistive & epitaxial detectors can increase their working parameters • The high charge collection efficiency of epitaxial detectors together with their active area thickness up to 100 mkm make us possible to us them as a detector for X-Ray imaging application • The resistive type detectors have the ability to operate with both polarity of high voltage have been presented

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