Search

Neutron irradiation effects on the I-V characteristics of AlGaAs-GaAs high electron mobility transistors and AlGaAs-InGaAs heterostructure insulated gate field-effect transistors are studied. Physical mechanisms responsible for the observed degradation of the device parameters are discussed. Index Terms--High electron mobility transistors (HEMT), heterostructure insulated gate field-effect transistor (HIGFET), MODFET, neutron irradiation.

An elliptic focusing neutron guide is combined with a cold neutron imaging instrument to produce a cone-beam, whose parameters are then analyzed both at the focal point and at the detector position. The studies have shown superior spectral and geometric homogeneity of the cone-beam setup when compared to the conventional pinhole geometry.

Specular polarized neutron reflectometry has shown a difference in nuclear and magnetic roughness in Fe/Ge thin film and also asymmetric magnetic scattering length density distributions at Fe on Ge and Ge on Fe interfaces. The interface magnetic moments are dependent on the crystalline state of Fe and Ge as well as the deposition sequence and the difference between nuclear and magnetic roughness at magnetic-semiconductor interfaces have played a key role in spintronics.

The high temperature edge of the broad deep level transient spectroscopy (DLTS) feature has cut off at the same temperature in both n- and p-GaAs indicating that the cut of is due to the DLTS behavior for the continuous density of defect states that spans midgap. Band gap narrowing is consistent with measurements of lattice expansion in neutron irradiated GaAs, leading to a model of defect cascades that are regions of narrowed band gap with defect levels that are inhomogeneously broadened.

Dark-field neutron tomography was applied to obtain three-dimensional volumetric data representing the distribution of micrometer and submicrometer sized structures in bulk samples. The study results for different samples demonstrated the application of the method to study structural materials.

The damaging effects induced in chemical vapor deposition (CVD) diamond based detectors by neutron fluence are studied and significant changes in spectroscopic, electrical and optical properties are observed. The nature and the distribution of the radiation induced damage are examined by cathodoluminescence spectroscopy.

The correlation of neutron emission with pinch energy for a Mather-type plasma focus energized by a single capacitor 12.5 [micro]F, 21 kV (2.7 kJ) is examined by using time resolved and time integrated detectors for two different anode shapes. The studies have shown that the neutron yield and optimum gas filling pressures are strongly dependent on the anode shape.

A study was conducted to examine the effect of neutron irradiation on optical and electrical properties of self-assembled InAs/GaAs quantum dots (QDs) which are embedded in n-type GaAs Schottky diodes grown by molecular beam epitaxy on GaAs(001). Electrical characterization of the Schottky diodes via capacitance-voltage spectroscopy revealed that the changes observed in the doping condition of the diodes is attributed to the introduction of defects.

Neutron resonance capture analysis (NRCA) method is used for determining the bulk composition of various kinds of objects and materials and it is based on analyzing direct capture resonance peaks. The new Delft elemental analysis program (DEAP) is described that has analyzed multiple NRCA spectra in a simple way, producing the elemental bulk composition of an object that is independent of its shape and size.

A compact pyroelectric accelerator with intense pulsed D-D neutron emission with rates of >[10.sup.10] n/s during the pulse, pulse widths of approximately hundreds of nanoseconds and neutron yields of greater than 10000 per pulse is described. The accelerator consisting of a small pyroelectric LiTa[O.sub.3] crystal that provides the accelerating voltage and an independent compact spark plasma ion source could find potential applications of pyroelectric based neutron generators.

The development of a new two-dimensional microanode image porous dielectric detectors (PDD) (MAIPDD) that could expand the methods of image registration of charged particles, neutrons, and x rays to a great extent is reported. The preliminary results showed that the MAIPDD for 5.9 keV x rays and two types of microstrip PDDs operate stably in dc mode.

The skin effect in the bulk of an electrical conductor is examined with spatial resolution by using spin-polarized neutron imaging. The results have proved the suitability of spin-polarized neutron imaging as a unique tool for examinations of current density distributions in bulk materials.

The clustering of the primal defects in recoil cascades were considered to model the transient reactions among irradiation defects, dopants, impurities, and carriers in pulse-neutron-irradiated Si. The results obtained offer insight into the influence of defect clustering during neutron bombardment.