Probing The Transient Response To Improve The Stability Of Diamond Devices Under Pulsed Periodic Excitation

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1039-P06-01

Probing The Transient Response To Improve The Stability Of Diamond Devices Under Pulsed Periodic Excitation Philippe Bergonzo, Hassen Hamrita, Dominique Tromson, Caroline Descamps, Christine Mer, and Milos Nesladek CEA, LIST, Laboratoire Capteurs Diamant, Centre d'Etudes de Saclay, Gif-sur-Yvette, 91191, France ABSTRACT CVD diamond combines attractive properties for the fabrication of detection devices operating in specific environments. One problem that remains critical for device stability is the presence of defect levels that alter the detection performances, and the detection characteristics often appear as they are very depending on time, temperature, and history of the preceding irradiations. One issue we have proposed is to adapt one technique that is commonly used for time of flight spectroscopy in order to maintain a uniform electric field in the probed device, and based on the synchronisation of the device bias with the period of the excitation source. This can be applied to several types of detection applications, as long as we can rely on periodical triggering in order to synchronise the device polarisation. We apply it here to a LINAC electron accelerator used for photon pulse generation at the frequency of 25Hz. The result is a remarkable improvement of the performance of a polycrystalline diamond detector that exhibits a particularly defective response when used in the steady state excitation, to reach that of a perfectly stable and reproducible device response in the pulsed mode. We claim this method to be applicable to several types of excitations and particularly to present a high interest for monitoring accelerator sources, e.g. for medical dosimetry applications.

INTRODUCTION The attractive properties of diamond for detection device fabrication have been well documented [1]. Diamond combines specific advantages that are of high benefit for its operation as a detector in specific environments. One problem however and also well documented is the presence of defect levels that are altering the detection characteristics [2, e.g. 3]. These are present in most synthetic materials just like they were observed in natural diamonds. They result in unstable responses and carrier losses. This motivated the challenge to grow materials with the least defect concentrations: synthetic single crystals (SC) are now forseen as good candidates for most detection applications [4, 5, 6,7]. However, SC diamond are remaining difficult to grow, especially on large areas, and only small size substrates can be used, typically in the 5x5 mm range at reasonable costs, that imposes to selectively grow each SC diamond detector. Further, it is now evidenced that the detection performances of the SC diamond strongly depend on the surface treatment made on the crystal used for growth, since dislocations and defects propagates during synthesis from the bulk of the substrate to the grown layer [ 8 , 9 ]. For such aspects the possibility to grow polycristalline diamonds over large areas remains a choice since it enable