GaN-based LEDs have been greatly advanced in fabrication and performance, so they have extended their application fields to general illumination and displays. Nevertheless, there remain another opportunities for flexible, foldable, and stretchable applications. GaN-based LEDs are generally fabricated on sapphire substrates due to the quality and cost, so that GaN-based LEDs should be separated from the rigid sapphire substrate for flexible formats. Therefore, we study the fabrication process including LED lift off process and printing process with GaN-based LEDs grown on a sapphire substrate to realize flexible GaN-based LEDs.
1D nanostructures, such as nanowires, nanobelts, and nanowalls provide a good system to investigate the dependence of electrical and thermal transport or mechanical and optical properties. Nanowires are the smallest dimensional structure with high crystallinity that can efficiently transport electrical carriers. Therefore, many researchers can be exploited to make a number of nanoscale devices such as field effect transistors, emitting devices, sensors, photovoltaic devices, memory devices, and logic circuits. Especially, ZnO nanowires have received considerable attention due to their unique properties, such as a wide direct bandgap (~3.37 eV), a large exciton binding energy (~60 meV), and piezoelectricity. Also, the large surface area to volume ratio of ZnO nanowires has a strong influence on electrical transport properties with surrounded elements.
Recently, a few researches have been performed in fabricating p-n heterojunction LEDs by introducing organic semiconductors as p-type materials due to the lack of reliability and reproducibility of p-type ZnO. This is the good method as an alternative approach to the ZnO p-n homojunction LEDs.
Graphene has a large specific surface area, high thermal conductivity (~5000 W/m K), high intrinsic carrier mobility (21000 cm2/V s) at room temperature, high transparency (80%), and good mechanical stability. Its optical transmittance and good electrical conductivity draw attention for applications as transparent conductive electrodes.