Nuclear Instruments and Methods in Physics Research A 487 (2002) 102–106 Performances of epitaxial GaAs p/i/n structures for X-ray imaging G.C. Sun a , H. Samic a , V. Haguet b , J.C. Pesant b , J.P. Montagne c , M. Lenoir c , J.C. Bourgoin a, * a Laboratoire des Milieux D ! esordonn ! es et H! et ! erog " enes, Universit ! e Pierre et Marie Curie (Paris VI), CNRS (UMR 7603), Tour 22, Case 86, 4 Place Jussieu, F-75252 Paris Cedex 05, France b Institut d’Electronique et de Microelectronique du Nord, CNRS (UMR 8520), Avenue Poincar ! e, Cit ! e Scientifique, BP 69, 59652 Villenevve d’Asq, France c Hospital Armand Trousseau, 26 Avenue du Docteur Arnold Netter, 75571 Paris Cedex 12, France Abstract We have realized 150 mm  150 mm pixels using ion implantation followed by photolithography, metallic contact evaporation and chemical etching on about 200 mm thick GaAs epitaxial layers. These layers were grown on n + and p + substrates by an already described Chemical Reaction technique, which is economical, non-polluting and can attain growth rates of several microns per minute. The mesa p + /i/n + pixel were characterized using current–voltage and capacitance–voltage measurements. The charge collection efficiency was evaluated by photoconductivity measurements under typical conditions of standard radiological examinations. r 2002 Elsevier Science B.V. All rights reserved. PACS: 81.10 Bk; 85.30 Fg; 85.60 Gz Keywords: GaAs; Pin structure; X-ray; Detector; Imaging 1. Introduction Since July 1960 [1], when it was first suggested that p/n GaAs junctions could be good g detectors, many attempts have been made to realize them. Up to now these attempts were not as successful as expected because the materials available in large enough thickness are from bulk Czochralski (Cz) non-intentionally doped (semi-insulating) grown ingots, materials which do not exhibit a good homogeneity of the electrical properties, a long enough lifetime, and contain too many defects to allow the realization of detectors, especially for imaging (for a review of the electrical properties of these materials see Ref. [2]). However, it has been demonstrated that epitaxial layers have the re- quired properties to make outstanding X-ray detectors but the development of detectors with such materials [3,4] is strongly limited because of the difficulty to grow thick enough epitaxial layers to absorb efficiently X-ray photons. It is only recently [5] that a new, low cost, non-polluting *Corresponding author. Tel.: +33-1-4427-7998; fax: +33-1- 4427-7998. E-mail address: bourgoin@ccr.jussieu.fr (J.C. Bourgoin). 0168-9002/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0168-9002(02)00952-X