High efficient LEDs having columnar structure surface fabricated by block copolymer lithography

Recently, the internal quantum efficiency of LEDs has improved, but the external efficiency remains low due to the high refractive index of semiconductors. To extract more light, a columnar structure with sub-micron period was fabricated on the LED surface by block copolymer lithography. Since the desired pattern is relatively larger than the block copolymer microdomains, a super-high molecular weight block copolymer was used. The polystyrene (PS) - polymethyl methacrylate (PMMA) diblock copolymer was used in this study since the PMMA has a much faster etch rate than the PS by reactive-ion etching (RIE). The PMMA was removed by RIE, and the gallium phosphide (GaP) substrate was etched by chlorine-based inductively coupled plasma RIE using the remaining PS dots as a mask. The optical extraction efficiency of the patterned substrates improved 2.6 times compared to unprocessed flat GaP substrates; the pillars' height was 450 nm, diameter was 100 nm, and pitch was 150 nm. We also prototyped a real LED and increased light emission volume 1.8 times compared with conventional LED at the same energy consumption.