Fabrication of nano-patterned sapphire substrates by combining nanoimprint lithography with edge effects

摘要

A volcano-shaped nano-patterned sapphire substrate (VNPSS) was fabricated by nanoimprint lithography and wet etching. The edge effects were used to form a ring mask for wet etching. The widths of the SiO2 rings were obtained as 136 and 91 nm by changing the reactive ion etching time. The crystal planes were determined to be {1 (1) over bar0 (2) over bar} and {1 (1) over bar0 (5) over bar }for the etching facets of the outside and inside of the ring, respectively. X-ray diffraction rocking curves indicate that the dislocation density of the GaN epilayer on the VNPSS is lower than that on the nano-patterned sapphire substrate (NPSS). Temperature-dependent photoluminescence results show that the internal quantum efficiency of the GaN-based light emitting diode (LED) on the VNPSS is 24% larger than that on the NPSS, which is due to the improved crystal quality. 3-D finite difference time domain (FDTD) simulations show that the light extraction efficiency (LEE) of the GaN-based LED on the VNPSS is 21% more than that of the LED on the NPSS, which conforms to the LEE enhancement by PL measurement. The use of edge effects provides ideas for preparing complex NPSS patterns with commonly used imprint stamps to further increase crystal quality and LEE.