IonoLuminescence (IL) and ThermoLuminescence (TL) techniques have been used in order to characterize the defects induced by doping due to different precursors in cubic boron nitride (c-BN) growth. Crystallites of dimensions of the order of 10–40 µm obtained by HPHT (High Pressure and High Temperature) method were used. Protons microbeams of 2 MeV – corresponding to a penetration depth of 26 µm in c-BN – with a spot diameter of few µm, in connection with an ellipsoidal mirror characterized by a large light collection efficiency and a 0.25 m monochromator, allowed to acquire wide area luminescence spectra. We observed that IL spectra for samples characterized by a large Mg content, as obtained by PIXE (Particle Induced X-ray Emission) analysis, displayed three peaks at 1.95 eV, 3.2 eV and 3.9 eV respectively, while in samples with a large Ca content a fourth peak appeared around 1.7 eV. Even if the number of available samples was relatively low, a fair correlation was observed between the total area under the peaks at 1.7 and 1.95 eV and the total Ca content (up to 25 ppm) on one side and between the total area under the peak at 3.9 eV and the total Mg content (up to 100 ppm), even if this peak appeared with a much smaller intensity also in all the other samples. Moreover, TL measurements were carried out from RT up to 400 °C with a standard Harshaw TL reader after the exposure of samples to some Gy doses from a collimated α-particle 241Am source. Specimens obtained by a Mg-based precursor did not show any thermoluminescence, while samples obtained by a Ca-based precursor showed a large and very reproducible TL spectrum. From the initial rise TL method, coupled to a preheating in order to separate the contributions from different traps, three series of centres were found out at 0.21, 0.35 and 0.6 eV. Samples obtained without a Ca-based precursor probably have a level at 0.45 eV instead of at 0.35 eV and, likely, there is also another level at 0.52 eV in Ca-doped platelets.
Characterization of impurities in cubic boron nitride crystallites with thermoluminescence and ionoluminescence
MANFREDOTTI, Claudio;LO GIUDICE, Alessandro;VITTONE, Ettore;COSSIO, Roberto
2004-01-01
Abstract
IonoLuminescence (IL) and ThermoLuminescence (TL) techniques have been used in order to characterize the defects induced by doping due to different precursors in cubic boron nitride (c-BN) growth. Crystallites of dimensions of the order of 10–40 µm obtained by HPHT (High Pressure and High Temperature) method were used. Protons microbeams of 2 MeV – corresponding to a penetration depth of 26 µm in c-BN – with a spot diameter of few µm, in connection with an ellipsoidal mirror characterized by a large light collection efficiency and a 0.25 m monochromator, allowed to acquire wide area luminescence spectra. We observed that IL spectra for samples characterized by a large Mg content, as obtained by PIXE (Particle Induced X-ray Emission) analysis, displayed three peaks at 1.95 eV, 3.2 eV and 3.9 eV respectively, while in samples with a large Ca content a fourth peak appeared around 1.7 eV. Even if the number of available samples was relatively low, a fair correlation was observed between the total area under the peaks at 1.7 and 1.95 eV and the total Ca content (up to 25 ppm) on one side and between the total area under the peak at 3.9 eV and the total Mg content (up to 100 ppm), even if this peak appeared with a much smaller intensity also in all the other samples. Moreover, TL measurements were carried out from RT up to 400 °C with a standard Harshaw TL reader after the exposure of samples to some Gy doses from a collimated α-particle 241Am source. Specimens obtained by a Mg-based precursor did not show any thermoluminescence, while samples obtained by a Ca-based precursor showed a large and very reproducible TL spectrum. From the initial rise TL method, coupled to a preheating in order to separate the contributions from different traps, three series of centres were found out at 0.21, 0.35 and 0.6 eV. Samples obtained without a Ca-based precursor probably have a level at 0.45 eV instead of at 0.35 eV and, likely, there is also another level at 0.52 eV in Ca-doped platelets.
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