一类二元二次函数取值范围之新解法

很多作者研究过“实数x,y满足Ax^2＋Bxy＋Cy^2=D（D≠0），求S=ux^2＋vxy＋wy^2的取值范围”这类问题的求解方法，本文应用“实数的平方是非负数”这一性质，给出这类问题一种非常简捷的统一解法，供参考．     

Simulation of the light extraction efficiency of nanostructure light-emitting diodes

The light extraction efficiencies have been calculated for various InGaN/GaN multiple quantum well nanostructure light-emitting diodes including nanopillar,nanorough of P-GaN surface,coreshell and nano-interlayer structure.From the calculated results we can see that the light extraction efficiency is remarkably improved in the nanostructures,especially those with an InGaN or AlGaN nano-interlayer.With a 420-nm luminescence wavelength,the light extraction efficiency can reach as high as 65% for the InGaN or AlGaN nano-interlayer structure with appropriate In or Al content while only 26% for the planar structure.     

Effect of surface treatment of GaN based light emitting diode wafers on the leakage current of light emitting diode devices

To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au (5~nm/5~nm) film deposition. The surface morphology of wafers and the current--voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.