Cho et al. Nanoscale Research Letters 2011, 6:578 http://www.nanoscalereslett.com/content/6/1/578 Page 5 of 6 Figure 5 The optical power of the electroluminescence emission of a light emitting diode that was grown on the patterned sapphire substrate with or without micro- and nanoscale complex structures: (a) with respect to wavelength at 20 mA, (b) with respect to current, and (c) with a 60° tilt. microscale surface protrusion pattern on the PSS wafer already compensated the light direction to make it fit inside the escape cone, thus significant light extraction efficiency enhancement of the device was reported. Micro- and nanoscale complex polymer structures allow the photons to be extracted out of the LED structure via the photon scattering effect. In addition, the EL was Figure 6 I-V characteristics of the patterned and non-patterned section of the LED device. measured in the other direction (angle) at a 60° tilt as shown in Figure 5c. In this case, similar EL emission intensity enhancement was observed compared with normal EL measurement. In order to confirm the effect of the nanoimprint pat- terning process on the electrical performance of the LED devices, I-V measurements were performed for the LED devices, including those with the micro- and nanoscale complex structures. In all cases, identical I-V characteristics were observed and the turn-on voltage and leakage current levels of the LED devices remained unchanged as shown in Figure 6. This finding implies that no electrical degradation was induced by the pat- terning process. Conclusions The micro- and nanoscale complex structures were formed on the LED devices using the nanoimprint process. A high refractive index resin containing the TiO2 nanoparticles was used as the imprint resin. The I-V characteristics showed that the electrical perfor- mance of the LED devices was not degraded by the process used to fabricate the micro- and nanoscale structures. The EL intensity of the LED devices was increased by up to 13% for the LED structures grown on the PSS. Acknowledgements This work was supported by the Nano Research and Development program through the Korea Science and Engineering Foundation funded by the Ministry of Education, Science and Technology (2010-0019152). Author details 1Department of Materials Science and Engineering, Korea University, Anam- dong 5-ga, Seongbuk-gu, Seoul 136-713, South Korea 2Department of Electrical and Electronics Engineering, Chung-Ang University, Seoul 156-756, South Korea