Influence of Thermal and Fast Neutron Irradiation on dc Electrical Performances of AlGaN/GaN Transistors
The influence of thermal neutron irradiation and fast neutron irradiation on the electrical properties of AlGaN/GaN HEMTs is investigated. An increase in the drain current and a decrease in the access resistances are observed when devices are irradiated with a thermalized neutrons fluence of 4.3 × 1010 neutrons.cm-2 while no evolution is observed with the same fluence of fast neutrons. However, the same phenomenon is observed when the fast neutron fluence is higher (1.8 × 1012 neutrons.cm-2). AlGaN/GaN heterojunctions are analyzed by gamma spectroscopy after thermalized or fast neutron irradiations to understand the physical mechanisms induced by irradiations. In fact, we have shown that the improvement of electrical properties of devices after thermal neutrons irradiation is linked to a Ga-Ge transmutation effect. Moreover, the evolution of the drain current and access resistance when the AlGaN/GaN heterojunctions are irradiated by fast neutrons can be induced by N vacancies creation and/or a change of the strain state of the layers and/or Ga-Ge transmutation effect.
Depth uniformity of electrical properties and doping limitation in neutron-transmutation-doped semi-insulating GaAs
Depth uniformity of electrical properties has been evaluated for neutron‐transmutation‐doped (NTD), semi‐insulating GaAs irradiated with thermal neutrons of 1.5×1018 cm−2 by the van der Pauw method combined with iterative etching of the surface. In NTD‐GaAs wafers (thickness ∼410 μm) annealed for 30 min at 700 °C, the depth profiles of the resistivity, the carrier concentration, and the Hall mobility show constant values of 1×10−2 Ω cm, 2.0×1017 cm−3, and 3100 cm2/V s, respectively, within an experimental error of 5%. In an annealing process, the redistribution and/or the segregation of NTD impurities is not observed. We also discuss the limitations of low‐level NTD in semi‐insulating GaAs. It is suggested that the activation of the NTD‐impurities below ∼1×1016 cm−3 is mainly restricted by the presence of the midgap electron trap (EL2).
Use of laser scanning confocal microscopy for morphological taxonomy and the potential for digital type specimens (e-types)
The use of laser scanning confocal microscopy (LSCM) for creating taxonomic descriptions of copepods is investigated. A new technique is described, which employs a contour filter to process digital LSCM images, allowing taxonomic information to be quickly and accu- rately distilled into a simple illustration. LSCM allows the imaging of whole specimens, which can be rotated and viewed from any angle—a major benefit over light microscopy. Using this tech- nique, it is suggested that taxonomic descriptions can be rapidly produced in a fraction of the time required to produce similar descriptions using traditional light microscopy and hand drawing techniques. Good staining of specimens is, however, essential to produce accurate descriptions and more research is required in this area. The use of LSCM for morphological taxonomy shows great potential, not only for producing taxonomic descriptions, but also providing a comple - mentary adjunct to traditional type specimens in the form of 3D digital 'e-types' deposited in recognised international databases.