Noboru Fukuoka

F-Type Centers in Neutron-Irradiated AIN

The production of point defects by neutron irradiation and thermal decay in sintered AIN polycrystal are investigated. The absorption band at 370 nm is observed after reactor neutron irradiation to a dose of 1016 n/cm2 (E>0.1 MeV). The defect corresponding to the band is tentatively assigned as an F-type center from the optical absorption and electron spin resonance.

Electron Paramagnetic Center in Neutron-Irradiated AlN

Neutron-Irradiated AlN was investigated using electron paramagnetic resonance. The broad spectrum arising from the electrons trapped in N3- vacancies can be explained by the hyperfine interaction with the surrounding 27Al nuclei. The obtained parameters, the g-value and the hyperfine constant are g=2.007±0.001 and A=(10.9±0.5)×10-4 cm-1, respectively.

Defect States in n-Type Germanium Irradiated with 1.5 MeV Electrons

The defect levels produced in antimony- or arsenic-doped germanium by irradiation with 1.5 MeV electrons and the annealing behaviour of these materials were studied by the DLTS technique. The position of the levels formed by radiation-induced defects was determined and the dependence of the level position on the species and concentration of the impurity atoms are reported. The defects associated with the Ec–0.40 eV level and the Ec–0.23 eV level are thought to be formed by the association of antimony atoms with unidentified defects. From the results of annealing under injection, the defects associated with the Ec–0.23 eV level are considered to be annealed by a recombination-enhanced mechanism.

New Donor Formation in n-Type Czochralski-Grown Silicon

The effects of preannealing in the temperature range from 350°C to 550°C on new donor formation were studied in n-type Czochralski-grown silicon, and it was found that the new donor formation rate is controlled by the density of electrically inactive embryos of new donors. The energy of formation of new donors was found to be 1.7 eV. The effect of new donors on the thermal donor formation was studied through 650°C annealing and subsequent 450°C annealing. The thermal donor formation is suppressed in the sample containing new donors. The results indicate that carbon atoms have a complex effect on the formation of oxygen donors.

Oxygen-Related Defects in Irradiated Germanium

Oxygen-related defects produced in oxygen-doped germanium by 1.5 MeV electron irradiation were studied by DLTS technique. Three electron trapping levels attributable to this type of defect were found. The Ec-0.25 eV level is deduced to be introduced by two kinds of defects, namely, the germanium A-center (oxygen-vacancy complex) and the defect associated with the 715 cm-1 infrared absorption band reported by Whan. The Ec-0.29 eV level and the Ec- 0.13 eV level are attributable to the defects associated with the 819 cm-1 and the 731 cm-1 infrared absorption bands in her paper.

The Defects Produced by Electron Irradiation and Annealed at About 360K in n-Type Germanium

Annealing of the radiation induced defect associated with the Ec-0.2eV level was studied through electrical measurements in the range 280–380 K. It was found that the level annealed in two stages, for the convenience they are nomenclatured as first and second stages. The first stage was observed only for samples containing group V impurities, and its step height as expressed in fraction unannealed increased with an increasing impurity concentration, and the activation energy was found to be dependent on the impurities. A model for the defect which is annealed in the first stage is proposed to be an association of group V impurity and a vacancy. The second stage of annealing was observed in all n-type samples regardless of the impurity. The step hight of this stage increased with increasing fluence. The activation energy was obtained to be 0.93 eV for all samples. By assuming that the defect is divacancy, the experimental results can be explained.

Nature of oxygen donor in Czochralski-grown silicon

Changes in the substitutional carbon and interstitial oxygen concentrations due to the formation of oxygen donors were studied on carbon-rich Czochralski-grown silicon (7-9×1017 carbon atoms/cm3). The result suggests that the new donor formation is controlled not by the substitutional carbon concentration directly, but by a density of some unknown embryo. A donor formation was observed in a 450°C annealing which was preceded by a 650°C annealing without new donor formation. This donor does not exhibit a 0.767 eV line in a measurement of the photoluminescence spectrum. However,it exhibits an infrared absorption band which is characteristic to the thermal donor.

Point Defects in Cubic Boron Nitride after Neutron Irradiation

The production of point defects induced by reactor neutrons and the thermal behavior of defects in sintered cubic boron nitride are investigated using the optical absorption and electron spin resonance (ESR) methods. A strong structureless absorption over the visible region was observed after fast neutron irradiation to a dose of 5.3×1016 n/cm2 (E>0.1 MeV) at 25 K. This specimen also shows an ESR signal with g-value 2.006±0.001, which can be tentatively identified as an electron trapped in a nitrogen vacancy. On examination of the thermal decay of the signal, the activation energy for recovery of the defects was determined to be about 1.79 eV.

Defects in Neutron-Transmutation-Doped Germanium

The nature of the defects produced in arsenic- or antimony-doped germanium by the recoil energy associated with capture gamma-ray emission after thermal neutron absorption was studied by measuring the Hall coefficient and the DLTS spectrum. It was concluded that the defects produced by thermal neutron irradiation are removed by annealing for 20 min at 600 K. Electron trapping levels located at Ec-0.20 eV, Ec-0.22 eV, Ec-0.27 eV and Ec-0.40 eV are formed after irradiation with thermal neutrons. The defect associated with the Ec-0.22 eV level is considered to contain an interstitial arsenic atom.

Radiation Defects in n-Type Germanium Studied by Deep Level Transient Spectroscopy

Defect levels produced in n-type germanium by 1.5 MeV electron irradiation and their annealing behaviour were studied by DLTS. Two electron traps located at Ec-0.20 eV and Ec-0.40 eV and a hole trap at Ev+0.24 eV were found to be formed by the irradiation with introduction rates of 0.05/cm, 0.54/cm and 0.22/cm respectively. When the specimen was annealed at 370 K for 10 minutes, a considerable part of the Ec-0.20 eV level was observed to be transformed into a new electron trap at Ec-0.23 eV.