Heavy ion induced damage in crystalline silicon and diodes

Abstract

N-type crystalline silicon samples (preferred 〈1 1 1〉 oriented), after irradiation using different fluences (from 1 × 10 10 to 5 × 10 14 ions/cm 2) of 45 and 65 MeV boron ions and 60 and 80 MeV oxygen ions, were studied by the grazing angle X-ray diffraction (XRD), and the optical radiation reflectivity techniques. In these samples the lifetime of the minority carriers was also measured with a pulsed electron beam and damage coefficients were estimated. The XRD peak intensity at 28.4° (2 θ), the reflectivity of 200–700 nm radiation and the lifetime of minority carriers were found to decrease continuously with increasing ion fluence. These results reveal that a fraction of the near surface silicon atoms were displaced from their lattice positions. Moreover, the degree of the damage induced by 65 MeV boron ions was higher than that of 45 MeV boron ions, even though the energy deposited by 45 MeV boron ions was greater than that deposited by 65 MeV boron ions. Similar results were also obtained with 60 and 80 MeV oxygen ions. The feasibility of reducing the turn-off time of silicon diodes with heavy ions was examined by irradiating a large number of diodes with different fluences (from 10 10 to 10 12 ions/cm 2) of 35 MeV lithium, 50 MeV boron and 104 MeV silicon ions. Among the ions used, only 35 MeV lithium ions could reduce the turn-off time from 1000 to 50 ns, with marginal increase in the forward voltage drop. In each diode the lifetime of minority carriers was estimated by measuring the turn-off time. The variations of the damage coefficient in the n-type silicon and the lifetime of minority carriers in the diodes, with the ion fluence indicate that a fraction of the induced damage in silicon was annealed out with the energy deposited through the electronic energy loss process by heavy ions.