Performance of a diamond x-ray sensor fabricated with metal-less graphitic contacts

Abstract

We report the x-ray photocurrent response of a coplanar chemical vapor deposition diamond detector fabricated using a metal-less graphitic ohmic contact. Ion implantation of 70 keV boron ions to a dose of 2 ϫ 10 16 cm −2 was performed through a patterned photoresist to produce a coplanar graphitic contact structure. The device photocurrent showed a fast response to pulsed x-ray irradiation, and showed no evidence of photocurrent persistence that is observed in devices fabricated using metal Schottky contacts. The graphite-contact device also showed no extrinsic photoconductivity when illuminated with white light. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2035885͔Chemical vapor deposition ͑CVD͒ diamond has considerable potential for use as a radiation sensor, particularly for deep ultraviolet ͑UV͒ and x-ray detection. Various authors have reported investigations of coplanar CVD diamond detectors as a tissue equivalent radiation dosimeter, and have demonstrated an x-ray photocurrent sensitivity similar to that of silicon photodiodes. The unique properties of diamond are well suited for this application, including extreme radiation hardness, high resistivity, and good charge transport. However the development of practicable diamond x-ray detectors has been restricted by a combination of priming effects and slow time response, or photocurrent persistence. These effects are due to a complex interplay between bulk trapping centers inherent in CVD material and the nature of the metaldiamond ohmic contacts used to fabricate the devices. In this work, we describe the performance of a coplanar x-ray sensor fabricated using a metal-less graphitized contact which was produced using a high dose implantation of boron ions. The interdigitated electrode structure was produced using only graphitized diamond, patterned by ion implantation through a photoresist.Two coplanar diamond devices were fabricated, using free-standing 70 m thick undoped polycrystalline CVD diamond film grown by Element Six Ltd. Device 1 consisted of a single coplanar electrode structure, with an electrode width and interelectrode gap of 100 m. The contacts were fabricated by a conventional photolithographic lift-off process, using thermally evaporated chromium ͑50 nm͒ followed by gold ͑200 nm͒. After lift off, the sample was annealed for 10 min at 400°C in a nitrogen atmosphere to form a metal-carbide contact. Device 2 was fabricated using ion implantation with no metal contact. Prior to implantation, a 2.5 m thickness photoresist was spun onto the diamond and patterned using a conventional optical mask. The mask design was divided into four quadrants, containing four coplanar devices with a central common electrode and with electrode widths and interelectrode gaps of 5 m, 10 m, 20 m, and 50 m ͑Fig. 1͒. A broad beam ion implantation was applied to the device at room temperature using 70 keV boron ions and a dose of 2 ϫ 10 16 cm −2 . After removal of the photoresist in acetone, the device was annealed for 4 min at 700°C in a nitrogen atmosphere ...

The effect of annealing on the X‐ray induced photocurrent characteristics of CVD diamond radiation detectors with different electrical contacts

“…The variation in the time response has been reported previously in CVD diamond samples as a function of the incident X‐ray energy 9, 19–22. The fastest results reported are at low energy 9, 19 (10 keV and below) around 100 ms 1, 9, 23, 24. Similar measurements were performed at high energies (used for radiotherapy) 20, 21, above 250 keV, where the rise time is in the order of several seconds.…”

“…Similar measurements were performed at high energies (used for radiotherapy) 20, 21, above 250 keV, where the rise time is in the order of several seconds. A study by Sellin and Galbiati 23 reported a correlation between the rise time and the type of contact. The graphitised contact showed both a fast rise time and a fast turn‐off time of the signal current.…”

Fabrication and electrical characterization of three-dimensional graphitic microchannels in single crystal diamond

“…The definition of graphitic conductive regions in diamond has found several interesting applications, such as ohmic contacts [27][28][29][30], infrared radiation emitters [31], field emitters [32], bolometers in both single-crystal [33] and polycrystalline [34] samples, metallo-dielectric photonic crystals [35] and ionizing radiation detectors for x-ray [36] and MeV ion [37] beams.…”

Temperature sensors based on synthetic diamond films

“…These characteristics make the diamond films ideal systems for different technologic applications (see, for instance, Refs. [2,3]). Artificially synthesized diamond thin films are usually grown by chemical vapor deposition using hot-filament or microwave-plasma techniques [4].…”