Performance of Monocrystalline Diamond Radiation Detectors Fabricated Using TiW, Cr/Au and a Novel Ohmic DLC/Pt/Au Electrical Contact

Abstract

We investigated the performance of synthetic high purity monocrystalline diamond radiation detectors fabricated with TiW, Cr/Au and a novel metallization technique utilising diamond-like carbon tunnelling junction and Pt/Au as electrical contacts. The investigation was carried out under irradiation with 60Co gamma-rays, 90Sr electrons and 241Am alpha-particles. The experimental results with respect to I-V dark current levels, irradiation photocurrent, signal-to-noise ratio and time response have been compared and discussed. Results show an ohmic behaviour of the DLC/Pt/Au contact, a charge collection efficiency of 100% at an applied electric field of 0.377 V/ mum for all electrical contacts (under 90Sr electrons irradiation) at a correspondent dark current value of less than a picoAmpere. The single crystal CVD DLC/Pt/Au diamond radiation detector reported here shows spectroscopic energy resolution of 1.1% at an applied voltage of +450 volts (0.9 V/mum) under 5.5 MeV alpha particle irradiation. No dasiamemorypsila or dasiapumpingpsila effect was observed for the DLC/Pt/Au contact at positive bias; the signal was also stable (fluctuations below 0.5%) and reproducible under 60Co irradiation, with a signal-to-noise ratio > 10000:1 and a linearity in the dose rate response

High- quality polycrystalline CVD diamond for conformal radiotherapy applications

“…Chromium deposition on oxygen terminated diamond, used in order to achieve a good mechanical adhesion, brings to the formation of chromium carbide on the oxygen terminated surface. Since the work function of chromium is 4.5 eV, at the metal-diamond interface a junction with a potential difference of the order of 1 volt is created [10]. Considering the sandwich configuration of our samples, the diamond dosimeter will result in a metal-semiconductor-metal (MSM) device in transverse configuration with two back-to-back Schottky barrier contacts.…”

Zero-bias operation of polycrystalline chemically vapour deposited diamond films for Intensity Modulated Radiation Therapy

“…Before metallization diamond surfaces were cleaned in a highly acidic and corrosive environment leaving the diamond surface partially oxygen terminated. Chromium deposition on oxygen terminated diamond surface was used in order to achieve a good mechanical adhesion and, as discussed in [27], to create a built-in potential barrier at the metalsemiconductor interfaces. A complete dosimetric characterisation of the devices when an external voltage is applied has been reported in [9].…”

“…Recently a novel metallization technique using diamond-like carbon tunnelling junction and Pt/Au as electrical contacts has been developed in view to get ohmic contacts at metal semiconductor interfaces [27]. The manufacturing and test of pCVD diamond dosimeters made with such electrode structure will be the subject of our studies in forthcoming works.…”

“…Recently, it was pointed out that, in spite of the ohmic behaviour observed in the typical operational range of applied voltages, the electrode inner structure of a diamond-based on-line dosimeter is in fact characterised by a back-to-back Schottky barrier configuration [26,27]. The work function of diamond is very high and it depends on its surface treatment, with an oxygen terminated surface its value is as high as 5.8 eV.…”

“…The work function of diamond is very high and it depends on its surface treatment, with an oxygen terminated surface its value is as high as 5.8 eV. As the work function of titanium and chromium are respectively 4.3 eV and 4.5 eV, the metallization process creates at the metal-diamond interface a junction with a potential difference of the order of 1 V and an in-built electric field of around 1 V/nm, with the diamond surface negatively biased and the titanium/chromium surface positively biased [27]. This experimental evidence suggests that null-bias operation during exposure to radiation is viable.…”