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We investigate the effects of high-rate and high total doses of 60Co gamma rays on the current–voltage (IV) characteristics of GaN p+n diodes grown by metal-organic chemical vapor phase epitaxy on Ga-face (0001) sapphire and hydride vapor phase epitaxy freestanding GaN substrates. We show that diodes grown on sapphire undergo more permanent changes upon irradiation at doses up to 3900 kGy than those grown on freestanding GaN. By combining diode and circular transfer length method measurements, we show that the p-type contact interface and adjacent p++ Mg-doped layer are sensitive to irradiation. In initial experiments, diodes grown on sapphire exhibited p-type contacts with Schottky characteristics, while those on freestanding GaN were Ohmic. Serendipitously, we identified and subsequently irradiated a freestanding sample with a pre-irradiation spatial gradient of p-contact Schottky vs Ohmic behavior across the die. This sample allowed the root cause of induced change to be identified as differences in the p++ contacting layer. We show that the p-type contact's pre-irradiation Schottky behavior is predictive of diodes' IV characteristics changing significantly upon gamma-ray irradiation. Further, we observe that the IV curves of diodes on freestanding GaN recover fully over several weeks at room temperature to be indistinguishable from pre-irradiation. IV curves from diodes on sapphire do not fully recover; we thus hypothesize that interactions between radiation-induced point defects and threading dislocations affect the evolution of radiation damage. [ABSTRACT FROM AUTHOR]

PurposeTo compare the potential retinal toxicity of two commercially Brilliant blue G dyes (Brilliant Peel and Ocublue Plus) and Indocyanine green (ICG) at usual clinical concentration.MethodsBrilliant Peel 0.025% (n=9), Ocublue Plus 0.025% (n=9), and ICG 0.05% (n=9) were injected intravitreally into Sprague-Dawley rat left eyes with balanced salt solution injected in the contralateral eyes as control. Evaluation of the effect of the dyes on retinal architecture was done by histological analysis of neurosensory retinal thickness and retinal ganglion cell (RGC) counts 7 days after intravitreal injection. Paired t-test was done to detect the presence of biologically significant thinning in neurosensory retina and five retinal layers for each dye (paired t-tests). One-way ANOVA and Tukey's Honestly Significant Difference test were used to assess whether different dyes caused significant thinning in mean neurosensory retinal thickness and reduction of mean RGC density.ResultsEyes treated with ICG had significantly thinner mean total neurosensory retinal thickness compared with the control eyes (P-value=0.01), followed by those treated with Ocublue Plus (P-value=0.03). Brilliant Peel did not cause significant thinning in any of the five retinal layers (all P-values>0.05). No significant difference in mean thinning of the total retinal thickness was detected between dyes (P-value=0.11). The mean thickness of the photoreceptor outer segment and outer plexiform layers were significantly reduced in ICG-injected eyes when compared with the control eyes (P-value=0.02). No significant difference in mean thinning between the three dyes was detected at all five retinal layers using one-way ANOVA (all P-values>0.35). RGC density was significantly reduced for ICG (P-value=0.01) but only marginally for Ocublue Plus (P-value=0.05). No significant reduction in RGC density was observed for Brilliant Peel (P-value=0.2).ConclusionIntravitreal Brilliant Peel is safe to rats retina. The retinal thinning and reduction in RGC density induced by Ocublue Plus requires further studies to determine the safety profile of this product. Potential retinal toxicity is seen with ICG 0.05%. [ABSTRACT FROM AUTHOR]