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)

2. 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

3. Growth techniques Thicknes (µm) Energy resolution References MBE 1 ? VPE 8 4.4% fwhm for 60 keV gamma Hesse et al.(1972) LPE 200 30-120 4.5% fwhm for 60 keV gamma 5% fwhm for 60 keV gamma Alexiev et al. (1992) Gibbons et al.(1972) CVPD (!) 40-325 0.9% fwhm for 60 keV gamma Owens et al. (2002) LPVPE 40 0.2% fwhm for 5 MeV alpha Bates et al. (1999) Chemical Reaction up to 500 ? Aim of the work Epitaxial GaAs detector

4. ohmic contact (Au, Ge, Ni) p+ ion implantation GaAs epilayer n+ substrate (Cz GaAs) 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

5. p+/i/n+ Oscilloscope (1M) Bias (10 V) What has been achieved by Chemical Reaction method: C. Photo current induced by X-ray

6. 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

7. 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.

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

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

10. 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.