Results of photoconductivity measurements in undoped n-type and Se-doped GaN epitaxial thin films are presented. Similar to the photoluminescence spectra, the photoconductivity also shows a broad yellow band centered around 2.2 eV. It is found that persistent photoconductivity (PPC) does exist in all the studied thin films. In addition, the PPC effects can be observed for the pumping photon energy down to the yellow band. The results reveal that the origin of the PPC effect and yellow luminescence may arise from the same intrinsic defect. It is shown that the most probable candidate of the intrinsic defect is nitrogen antisite.

Photoluminescence, resonant Raman scattering, and photoconductivity measurements have been employed to study the yellow emission in undoped n-type and a set of Se-doped GaN epitaxial films. It is best described by a transition from the conduction-band edge to a deep acceptor. Unlike the donors and acceptors used in most previous studies that substitute Ga sites, Se atoms can replace N sites. With this unique fact, we identify that the origin of the yellow emission involves the nitrogen antisite. In addition, it is found that persistent photoconductivity can be observed after the yellow band excitation. We further suggest that the nitrogen antisite exhibits a metastable behavior similar to the arsenic antisite in GaAs. ͓S0163-1829͑97͒07735-7͔ YELLOW LUMINESCENCE IN n-TYPE GaN EPITAXIAL FILMS

Supplementations with vitamin BC capsules plus corresponding deficient hematinics or with vitamin BC capsules only can reduce the high serum homocysteine levels to significantly lower levels in AG patients.

No abstract