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Scintillating films are usually used to improve the sensitivity of CCD-based X-ray imaging detectors. For an optimal spatial resolution and detection efficiency, a tradeoff has to be made on the film thickness. However, these scintillating layers can also be structured to provide a pixellated screen. In this paper, the study of CsI(TI)-filled pore arrays is reported. The pores are first etched in silicon, then oxidized and finally filled with CsI(TI) to form scintillating waveguides. The dependence of the detector sensitivity on pore depth, varied from 40 to 400 [micro]m here, follows rather well theoretical predictions. Most of the detectors produced in this work have a detective quantum efficiency of the incoming X-ray photons of about 25%. However, one detector shows that higher efficiency can be achieved approaching almost the theoretical limit set by Poisson statistics of the incoming X-rays. Thus, we conclude that it is possible to fabricate scintillating waveguides with almost ideal performance. Imaging capabilities of the detectors are demonstrated. Index Terms--Pixellated detectors, scintillating waveguides, X-ray imaging.

The propagation of light emitted from silicon nanocrystals forming planar waveguides buried in SiO(sub 2) is studied both experimentally and theoretically. A theoretical model developed in the framework of wave optics identifies these modes as substrate modes propagating along the waveguide boundary.

Silicon charge-coupled devices (CCDs) covered with a scintillating film are now available on the market for use in digital medical imaging. However, these devices could still be improved in terms of sensitivity and especially spatial resolution by coating the CCD with an array of scintillating waveguides. In this paper, such waveguides were fabricated by first etching pores in silicon, then performing metallization or oxidation of the pore walls and finally filling the pores with CsI(TI). The resulting structures were observed using scanning electron microscopy and tested under X-ray exposure. Theoretical efficiencies of macropore arrays filled with CsI(TI) were also calculated, indicating that the optimal pore depth for metallized macropore arrays is about 80 [micro]m while it is around 350[micro]m for oxidized ones. This result, together with the roughness of the metal coating, explains why lower SNR values were measured with the metallized macropores. Indeed, the macropore arrays had depths in the range of 210-390 [micro]m, which is favorable to oxidized structures. Index Terms--CsI(TI), pixenated detectors, scintillating waveguides, X-ray imaging.

The properties of the ferroelectric films, lead zirconate titanate (PZT) and lead titanate (PTO), deposited on bare SiC substrates via pulsed laser ablation are studied. It is shown that PTO films crystallized into pure perovskite phase in situ at temperatures ranging from 600 to 650 degrees Centigrade. PZT films deposited at the temperature range of 570-650 degrees Centigrade were dominated by the pyrochlore phase.

In this paper, an alternative method to characterize the interface between 4H polytype of Silicon Carbide (4H-SiC) and passivating dielectric layers is established. The studies are made on dielectric-semiconductor test structures using Al2O3 as dielectric on 4H-SiC n-type epitaxial layers. Samples with different pre- and post-dielectric deposition preparations have been fabricated on epilayers of varying thicknesses. Effective lifetimes (τeff) of all the samples were measured by an optical pump-probe method utilizing free carrier absorption (FCA) to analyse the influence of the 4H-SiC/dielectric interface on charge carrier recombination. The relative contribution to τeff) from the surfaces increases with decreasing epilayer thickness, and by analysing the data in combination with numerical modelling, it is possible to extract values of the surface recombination velocities (SRVs) for interfaces prepared in different ways. For instance, it is found that SRV for a standard cleaning procedure is 2×106 cm/s compared to a more elaborate RCA process, yielding a more than 50 times lower value of 3.5×104 cm/s. Furthermore, the density of interface traps (Dit) is extracted from capacitance-voltage (CV) measurements using the Terman method and a comparison is made between the SRV extracted from FCA measurements and Dits extracted from CV measurements on the same structures fabricated with metal contacts. It is observed that the SRV increase scales linearly with the increase in Dit. The strong qualitative correlation between FCA and CV data shows that FCA is a useful characterization technique, which can also yield more quantitative information about the charge carrier dynamics at the interface. [ABSTRACT FROM AUTHOR]

[Bi.sub.4][Ge.sub.3][O.sub.12] films were deposited by pulsed laser ablation on glass and Si[O.sub.2]/Si substrates. The crystal structures of the films depend on the deposition temperature. XRD patterns indicate that the films deposited at substrate temperature less than 400 [degrees] C are amorphous. The as deposited amorphous films can be crystallized by post rapid thermal annealing (RTA) in the temperature window from 750 [degrees] C to 800 [degrees] C for 2 minutes in a oxygen ambient environment. RBS measurements confirm that the films have the same chemical composition as that of the target. The surface morphology of the films were characterized by atomic force microscopy(AFM).

There are defects with concentration approaching 10(super14) cm-13 in a region near the front surface of n-type 6H-SiC epitaxial layers grown by vapor phase epitaxy. A Ti concentration of 1 x 10(super16) cm-13 in this region indicates a link between the near-surface defects and metallic impurities. The rest of the epitaxial layer contains a much lower concentration of defects. The presence of the defects substantially reduces the carrier lifetime.

Fundamental band edge absorption is investigated in nominally undoped (n<1014 cm-3) and heavily doped (n∼8×1018 cm-3) 4H-SiC by a spectroscopy technique based on spatially and time-resolved free-carrier absorption. The spectra are extracted over a wide absorption range (0.02–500 cm-1) at temperatures from 75 to 450 K. The experimental results are supported by an indirect transition theory with a unique set of dominating momentum-conserving phonons, showing good correlation with earlier findings of differential absorption measurements at 2 K. Exciton binding energy of 30±10 meV is derived from fitting the data at 75 K. The detected polarization anisotropy of absorption with respect to c axis is shown to be consistent with the selection rules for the corresponding phonon branches. An analytical model related to constant degree of involved phonons describes well the obtained energy gap variation with temperature. Finally, doping induced band gap narrowing is characterized above the impurity-Mott transition and compared with theoretical calculations in the random phase approximation. The shape of the fundamental absorption edge at high carrier concentrations is discussed in terms of excitonic enhancement above the Mott transition, as recently detected in Si. [ABSTRACT FROM AUTHOR]

Si nanocrystals were formed in synthetic opals by Si-ion implantation and their optical properties studied using microphotoluminescence and reflection techniques. The properties of areas with high crystalline quality are compared with those of disordered regions of samples. The photoluminescence spectrum from Si nanocrystals embedded in silica spheres is narrowed by the inhibition of emission at wavelengths corresponding to the opal photonic pseudoband gap (∼690 nm). Measurements of photoluminescence spectra from individual implanted silica spheres is also demonstrated and the number of emitting Si nanocrystals in single brightly emitting spheres is estimated to be of the order of one thousand. [ABSTRACT FROM AUTHOR]

An optical emission microscopy technique with spatial and spectral resolution capabilities is applied for stability studies of 4H–SiC material properties. From the example of a 4H–SiC p[sup +]/n[sup -]/n[sup +] diode imaged at different stages of electrical overstress the mechanism of degrading performance is directly unveiled. We correlate this phenomenon with irreversible structural changes within the active region created by a nonuniform heating related stress. The stress-generated features are interpreted as multiple stacking faults spreading throughout the whole base region and nucleated in the vicinity of built-in defects and process-induced structural deficiencies. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the influence of dose rate on the ion-beam-induced crystallization of amorphous layers in silicon. Dose rate dependence; Intermittent beam experiment; role of the displacement density at the interface; Reversible movement of the interface.

Presents a study which examined the regrowth of the amorphous layers in silicon with the Rutherford backscattering channeling technique. Experimental procedure; Results; Conclusion.

Deals with a study which investigated the isotope effect of boron implantation in silicon using secondary ion mass spectrometry. Methods; Results; Discussion.

Presents information on a study which fabricated palladium (Pd) features by high-energy ion irradiation of thin Pd acetate films. Information on spin coating a Pd acetate; Structure of Pd acetate; Illustration of the fluence dependence of the infrared spectrum; Monitoring of gas evolution.

Presents a study that investigated the electrical properties of ion beam recrystallized and laser beam annealed arsenic-implanted silicon on sapphire. Methodology; Determination of the structural properties of the recrystallized layers; Analysis of the electrical resistivity of the samples.

We have developed and preliminary tested a new digital X-ray imaging sensor based on a scintillating guide screen. The scintillating guides are used to channel the emitted visible light to the pixel detector. This enables us to avoid the well-known tradeoff between detection efficiency and spatial resolution which is encountered when a non-patterned scintillating layer is used on top of a CCD. A prototype has been fabricated using microtechnologies. The scintillator is CsI:T1 and the low-index cladding material used to channel the light is silicon dioxide. The performance of this prototype has been compared to that of a thick CsI single crystal. The results concerning the spatial resolution are quite promising and demonstrate a proof-of-principle. However, the performance in terms of signal to noise ratio and sensitivity have to be improved. These problems are currently addressed.