Enhanced light output from vertical light-emitting diodes with an imprinted highly refractive polymer layer

Abstract

Hexagonal arrays of submicron polymer patterns with a high refractive index were fabricated on a vertical light-emitting diode (LED) device by means of nanoimprint lithography (NIL) to improve the light extraction efficiency. An organic-inorganic hybrid resin containing a polymeric titanium dioxide precursor was spin-coated on the n-GaN top layer of a vertical LED wafer. The coated layer was then imprinted for 10 min with an elastomeric polydimethylsiloxane stamp at 200 degrees C and 5 atm. The NIL process formed pillar patterns on the n-GaN layer of the vertical LED wafer. The pillar patterns have a high refractive index (n approximate to 2.0) in the visible wavelength range; they also have a diameter of 200 nm and a pitch of 700 nm. The light output power of the patterned vertical LED device is 28% greater than that of a non-patterned vertical LED device with a driving current of 350 mA. The I-V characteristics of the vertical LED device confirm that the patterning process induces no electric degradation. (C) 2011 Elsevier B. V. All rights reserved.