Deep-level transient spectroscopy has been applied to n-type horizontal gradient freeze grown GaAs that has been subjected to thermal stressing ͑quenching͒ and varying degrees of arsenic outdiffusion during rapid thermal annealing. The concentrations and activation energies of the various deep donor levels have been monitored. As a result of the external excitations in the lattice due to the thermal stress ͑quenching͒, dramatic effects occur in the defect level structure that could be of importance to device technology. It is found that the native EL6 group of defects is nearly absent in rapid thermally annealed material, while the levels EL5 and EL8 appear with EL3 becoming a dominant level that could act as a recombination center. With the lengthening of annealing time and significant As outdiffusion, there is a general reduction of the EL2, EL3, and EL5 defect concentrations together with a complete removal of EL8. Moreover, the EL2 activation energy may be varied from 0.827 to 0.922 eV by controlling the level of As out-diffusion. These observations are discussed in terms of the As Ga-As i model of the EL2 defect and the V As-V Ga divacancy model for the EL6 group of defects. The EL3, EL5, EL8, and EL15 defect levels seen in samples subjected to rapid thermally quenching are attributed to the breakup of V As-As i Frenkel pair defects known to be present in the as-grown material. ͓S0163-1829͑96͒01240-4͔

Deep traps in the boron extended tail region of ion implanted 6H-SiC pn junctions formed during annealing have been studied using deep level transient spectroscopy. Dramatically high concentrations of ϳ10 16 cm Ϫ3 of the D center have been observed through the unusual appearance of minority peaks in the majority carrier spectra. No evidence is found for any shallow boron acceptor in this region, but an induced hole trap I h at E V ϩ0.46 eV is found under cold implantation conditions. These results support the picture of the extended tail, rich in boron-vacancy complexes such as the D center, which forms as a result of vacancy enhanced indiffusion. The dominance of the electrically active D center in the depletion layer of the technologically important SiC pn junction diode suggests the need for further research in this area.

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Effects of strontium doping on electrical properties of gadolinium-doped ceria were investigated. The Ce 0.8−x Gd 0.2 Sr x O 2−δ (0.0 ≤ x ≤ 0.1) compositions were prepared by sol-gel method and sintered at 1300• C for 8 h, the bulk densities were over 93% of theoretical density. These results were consistent with scanning electron microscope. The crystallite size of these materials was determined using the X-ray powder diffractometer and the sizes range from 19.4 nm to 24.4 nm. From the experimental results, it was observed that the composition Ce 0.8−x Gd 0.2 Sr x O 2−δ (x = 0.02) exhibits higher conductivity (23.6 × 10 −3 S cm −1 ) and minimum activation energy (0.83 eV) at 700• C. This composition is thus a potential candidate for use as electrolyte applications in intermediate temperature solid oxide fuel cells.