고려대학교

초록/요약

The growth of high-quality GaN films on silicon substrates is very attractive for low cost optoelectronic and electronic devices, such as light emitting diodes, laser-diodes, and high electron mobility transistors and so on. However, the large lattice and thermal mismatch between GaN and Si generates a high dislocation density and cracks in the epitaxial layer. Therefore, many studies have focused on stress and defect management techniques to reduce the density of cracks and dislocations. Epitaxial lateral overgrowth (ELOG) based on selective area growth (SAG) is promising technique whose value has been demonstrated in fabrication of those devices. The structural quality and optical efficiency of GaN-based materials can be improved using both techniques taking advantage of the strain relaxation and reduced piezoelectric field at the sidewalls of selectively grown ridges. Both techniques were studied in many different ways and especially based on regions of a wafer covered by a dielectric material, such as silicon dioxide or silicon nitride. By dielectric coating and patterning the underlying epitaxial substrate, the growth proceeds selectively only on the exposed regions. Ion implantation technique is a useful way to engineer the surface of the substrate. The dependence of implantation induced crystal damage on dose rate has been known for a long time, and it is well established that the amount of damage increase with dose rate. Then, the structural properties of the patterned ion implanted Si substrates were investigated on different implantation conditions and the characteristics of epitaxially grown GaN on patterned ion implanted Si substrates were characterized. The epitaxial GaN growth on the implantation induced crystal damaged regions on the substrate was disturbed due to the surface crystallinity changes, then the epitaxial GaN was only grown on the non-implanted regions of the substrate. According to the direction of the stripes, SAG and ELOG GaN were separately obtained using MOCVD. Complete coalescence was achieved with a flat surface for ELOG GaN and high optical and crystalline quality GaN was achieved.