GaN基LED图形衬底的性能研究

蓝宝石图形衬底可以降低外延位错密度并增强背散射光, 已经成为制备高亮LED有效技术手段。本研究运用时域有限差分(FDTD)法模拟和比较了GaN基微纳米图形衬底LED几种衬底图形结构对光的提取效率的影响。模拟结果显示纳米图形衬底(NPSS)对光效的提高明显优于微米图形衬底(MPSS)。在对圆柱、圆孔、圆台、圆锥和曲面锥等纳米结构的研究中, 圆台柱结构的纳米图形衬底对光提取效果最好。通过进一步模拟优化, 得到圆台结构的最佳参数, 此时相对于普通衬底LED光的提取效率提高了96.6%。试验中, 采用软模压印技术在蓝宝石基片上大面积制备出纳米圆台图形衬底, 并测得外延生长GaN层后的外延片的PL强度增加了8倍, 可见纳米图形衬底对提高LED的出光效率有显著效果。

Research for Patterned Sapphire Substrates of GaN-based LEDs

Patterned Sapphire Substrate (PSS) which can reduce the density of threading dislocation and enhance the effect of scattering is widely used to fabricate high-power Light-Emitting-Diode (LED) chip. In this paper, the finite- difference time-domain (FDTD) method was used to simulate and analyze the light extraction efficiency (LEE) of GaN-based micro-scale and nano-scale patterned sapphire substrates LED. The results show that the nano-patterned sapphire substrate (NPSS) has a significantly better LEE than that of micro-patterned sapphire substrate (MPSS). And in NPSS, the LEE of the pillar structure improveed 96.6% comparing to other nano-patterned structures. Large areas of table-like nano-sapphire patterned substrates are successfully prepared through soft embossing technology. The photoluminescence (PL) of the LED grown on table-like nano-sapphire patterned substrates is 8 times stronger than that of the LED grown on the unpatterned sapphire wafers.