Radiation hardness of polycrystalline diamond

Abstract

Undoped and B-doped polycrystalline diamond films have been irradiated with 2-MeV alpha particles and 3-MeV protons at doses ranging from D =10 12 to D =10 17 cm −2 . The radiation damage has been studied using conductivity measurements and Raman/photoluminescence spectroscopy. For undoped diamond films, the H3 luminescent center (NVN) is detected around 2.45 eV for D ≥10 14 He + cm −2 . The diamond peak broadens and shifts to lower wavenumbers for D ≥10 16 He + cm −2 , indicative of the appearance of crystalline defects and tensile stress. No graphite is detected. On the contrary we observe an annealing of the as-grown sp 2 defects as evidenced by a decrease in the intensity of the Raman band at 1500 cm −1 after irradiation. At D =3 × 10 16 He + cm −2 we observe two new defect peaks at 1496 and 1635 cm −1 . The I(V,T) characteristics of the undoped samples remain unaffected up to D =10 16 He + cm −2 . For D =3 × 10 16 He + cm −2 the conductivity increases drastically and the I(T) characteristics show the presence of irradiation defects at 0.3-0.4 eV. Similar phenomena are observed after H + irradiation, but for doses 100 times higher. Less damage is detected by Raman spectroscopy in the B-doped films. The conductivity of these films decreases as a result of He + and H + irradiation. The activation energy decreases after He + irradiation, and increases after H + irradiation. The latter case corresponds to the compensation of the boron acceptor level by irradiation defects.