Radiation tolerance of epitaxial silicon carbide detectors for electrons and gamma-rays

Particles detectors were made using semiconductor epitaxial 4H-SiC as the detection medium. The investigated detectors are formed by Schottky contact (Au) on the epitaxial layer and an ohmic contact on the backside of 4H-SiC substrates with different micropipe densities from CREE. For radiation hardness studies, the detectors have been irradiated with electrons (8.2 MeV) and gamma-rays (Co-60 source) at fluences and doses ranging from 0 to 9.48 x 10(14) e/cm(2) and 40 Mrad, respectively. We present experimental data on the charge collection properties by using 4.14 MeV alpha-particles impinging on the Schottky contact. Hundred percent Charge Collection Efficiency, CCE, is demonstrated for reverse voltages higher than the one needed to have a depletion region equal to the a-particle projected range, even after the irradiation at the highest dose. By comparing measured CCE values with the outcomes of drift-diffusion simulations, values are inferred for the hole lifetime, tau(p), within the neutral region of the charge carrier generation layer. tau(p) was found to decrease with increasing radiation levels, ranging from 300 ns in non-irradiated detectors to 3 ns in the most irradiated ones. The diffusion contribution of the minority charge carriers to CCE is pointed out

Pulse radiolysis and theoretical investigation on the initial mechanism of e-beam polymerization of epoxy resins. The results obtained on (phenoxymethyl)oxirane

The radical cation of (phenoxymethyl)oxirane (PGE .+) is generated by pulse radiolysis in dichloromethane solution and by direct action of radiation on the title compound. In the pure system its UV–vis spectrum is characterized by two bands at 340 and 430 nm, such that the electronic structure corresponds to a dipole bearing the positive charge on the phenoxy side. At the same time, the phenoxyoxirane bridge is weakened. Then, the radical cation fragments into a phenoxonium ion and an oxyranylmethyl radical (kPGEfragm = 1,16 x 10^7 s^-1). The latter immediately rearranges to an allyloxyl radical by ring opening. It is then conceived that the action of onium salts, as radiation curing initiators of phenoxy-oxirane derivatives, occurs after epoxy ring opening

Pulse radiolysis and theoretical investigation on the initial mechanism of the e-beam polymerization of epoxy resins. The results obtained on (phenoxymethyl)oxirane

The radical cation of (phenoxymethyl)oxirane (PGE .+) is generated by pulse radiolysis in dichloromethane solution and by direct action of radiation on the title compound. In the pure system its UV–vis spectrum is characterized by two bands at 340 and 430 nm, such that the electronic structure corresponds to a dipole bearing the positive charge on the phenoxy side. At the same time, the phenoxyoxirane bridge is weakened. Then, the radical cation fragments into a phenoxonium ion and an oxyranylmethyl radical (kPGEfragm = 1,16 x 10^7 s^-1). The latter immediately rearranges to an allyloxyl radical by ring opening. It is then conceived that the action of onium salts, as radiation curing initiators of phenoxy-oxirane derivatives, occurs after epoxy ring opening

Radiation tolerance of epitaxial silicon carbide detectors for electrons, protons and gamma-rays

Particle detectors were made using semiconductor epitaxial 4H-SiC as the detection medium. The investigated detectors are formed by Schottky contact (Au) on the epitaxial layer and an ohmic contact on the back side of 4H-SiC substrates with different micropipe densities from CREE. For radiation hardness studies, the detectors have been irradiated with protons (24 GeV/c) at a fluence of about 10e14 cm^(-2) and with electrons (8.2 MeV) and gamma-rays (Co-60 source) at doses ranging from 0 to 40 Mrad. We present experimental data on the charge collection properties by using 5.48, 4.14 and 2.00 MeV alpha-particles impinging on the Schottky contact. Hundred percent charge collection efficiency (CCE) is demonstrated for reverse voltages higher than the one needed to have a depletion region equal to the alpha-particle projected range, even after the irradiation at the highest dose. By comparing measured CCE values with the outcomes of drift-diffusion simulations, values are inferred for the hole lifetime, within the neutral region of the charge carrier generation layer. The hole lifetime was found to decrease with increasing radiation levels, ranging from 300 ns in non-irradiated detectors to 3 ns in the most irradiated ones. The diffusion contribution of the minority charge carriers to CCE is pointed out

RADIATION TOLERANCE OF THE FOXFET BIASING SCHEME FOR AC-COUPLED SI MICROSTRIP DETECTORS

The radiation response of FOXFETs has been studied for proton, gamma and neutron exposures. The punch-through behaviour, which represents the normal FET operating conditions in Si microstrip detectors, has been found to be much less sensitive to radiation damage than threshold voltage. The device performance has been elucidated by means of two-dimensional simulations. The main radiation effects have been also taken into account in the numerical analysis and separately examined

Study of breakdown effects in silicon multiguard structures

The purpose of this work is to study layout solutions aimed at increasing the breakdown voltage in silicon micro-strip detectors. Several structures with multiple floating guards in different configurations have been designed and produced on high- resistivity silicon wafers. The main electrical characteristics of these devices have been measured before and after irradiation. Both radiation-induced surface and bulk damage effects were considered as well. The highest breakdown voltage was found on devices featuring p(+) guards without field plates. A simulation study has been carried out on simplified structures to evaluate the distribution of the breakdown field as a function of the guard layout, The aim was the design optimization