G. Mazzeo

Radiation-induced modification of trap occupancy in polycrystalline diamond detectors

AbstractMetal–semiconductor–metal (MSM ) diamond structures are investigated for radiation detection in the UV and X-ray spectralrange. Several priming procedures by UV or X-ray irradiation are carried out in order to overcome device performance limitationsrelated to the film polycrystalline structure. Sub-bandgap spectral responses monitored after different priming steps by UV laserpulses or X-ray beams exhibit a modification of trap occupancy, particularly in the 1–3 eV energy range. These variations appearresponsible for both an increase of the minority carrier lifetime product and a radiation-induced barrier lowering, as deduced byphotoelectric characteristics modeling. 2002 Elsevier Science B.V. All rights reserved. Keywords: Diamond properties and applications; Priming; Detectors; Carrier trapping 1. IntroductionDiamond films deposited by chemical vapor deposi-tion (CVD ) techniques are ideal candidates for photondetection in a wide energy range, covering from UV toX-ray w1–3 x. Owing to the extremely high radiationhardness of diamond, a further extension of detectioncapability towards high energy beams appears veryattractive and is currently widely investigated w3,4x.However, due to the polycrystalline structure of thesefilms, the real performances of diamond based detectorsare still far from ideal, both in terms of sensitivity andresponse times. In order to circumvent these problems,device exposure to a high intensity ionizing radiationprior to the device operation is usually performed w4–6 x. The effect of this curing procedure (called primingor pumping ) is generally attributed to saturation ofelectrically active defects w4x. Many authors havealready demonstrated the effectiveness of priming forthe improvement of collection efficiency values w3,7x.However, the priming process itself, the nature oftrapping states involved, their density and energy distri-bution need to be further investigated. Indeed, rather

Diamond deep-UV position sensitive detectors

The feasibility of diamond position sensitive detectors for deep UV light monitoring is reported. Based on voltage-division principle, a very simple one-dimensional photosensitive structures have been developed exploiting the strong variation of polycrystalline diamond conductivity under UV-light irradiation and dark conditions. Lumped and finite elements analysis have been used to compare the theoretical expectations with the experimental results obtained under excimer laser illumination. A complete characterization of such a 1D position sensitive device has been performed in terms of: the beam intensity insensitivity (over three orders of magnitude); the output signal dependence on the beam width; and the contact structure and its resistance influence on the device performances.

X ray diamond 2D array

X-ray 2D array detectors based on polycrystalline diamond have been fabricated and tested in the dark and under low energy X-ray beams, as well as under UV laser pulses. Depending on the metallic contacts distance or crossover-area, each pixel exhibit low dark current values down to 2 pA and light to dark current ratio as large as 20 when biased at 50 V. The intensity dependence of X-ray photocurrent, as measured for different thickness of Al absorbers, changes according the square root of the beam intensity, thereby suggesting a good crystalline quality of the used diamond slab. A similar behaviour is found when UV laser pulses of high energy are used for device irradiation. At lower energies, a larger photocurrent change with the beam intensity is found, eventually becoming a linear dependence. Such a result confirms the expected good diamond sample quality and suggests a device use for X-ray beam profiler with a large dynamics. The diamond sample and detector uniformity has been also tested under UV laser pulses. The observed pixel response uniformity further support the possible device application as image sensor