Performances of epitaxial GaAs detectors

1
Performances of epitaxial GaAs detectors

• E. Bréelle, H. Samic, G. C. Sun, J. C.
  Bourgoin
• Laboratoire des Milieux Désordonnés et
  Hétérogènes
• Université Pierre et Marie Curie (Paris 6)

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Introduction

• Material for X-ray imaging
•  
• Bulk
  Epitaxial
•  
• Semi-insulating
  Thick enough
• Large defect concentration,
  Low defect concentration,
• ?Non-uniform electronic
  properties Residual doping (1013-1014
  cm-3)
• ?Short life time
  ?Small depleted depth
•  
• Imaging at room temperature
• Bulk CdTe
  Epitaxial GaAs (InP,
  GaP..)
• Limited area
  Large area
• Bad homogeneity
  Homogenous
• No technology
  Existing technology
• 
  ? Limitation in space
  charge region

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Aim of the work
Epitaxial GaAs detector
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What has been achieved by Chemical Reaction
method
A. Growth of thick epitaxial GaAs layers
100-500 µm thick layers Homogenous
electronic properties Electronic properties
similar to that of standard epilayers
  B. Pixel technology Polishing Ion
implantation annealing Photolithography
Chemical etching Si3N4 deposition
Metallic alloy deposition  
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What has been achieved by Chemical Reaction
method
                   
C. Photo current induced by X-ray
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Results

• 1. Proton detection 
• GaAs detector  2 mm2, 4.3 x 1014 cm-3, bias of
  100 V (depleted depth 18.4 µm)
• Retrodiffusion of 1.2 MeV (a) and 1.3 MeV (b)
  protons

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Results 

• 2. Electron detection
• Si detector 25 mm2, depleted depth 100 µm at 50
  V
• GaAs detector 2 mm2, depleted depth about 13 µm
  at 50 V.

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Results 

•  
• 3. Alpha detection (241Am)-5.49 MeV  
• Bias of 80 V

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Results 

•  
• 4. Gamma detection (241Am)- 59 keV
• Cooled at 50C, at bias of 70V
•  
•  

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 Conclusion

• Good energy resolution
• Width of the space charge region, small !
• Decrease of the residual doping
• Work in photocurrent
• 3. Optimise the technology of the detector.