Hydride vapor phase epitaxy of GaN on the vicinal c-sapphire with a CrN interlayer

Recently, an innovative method of fabricating vertical light-emitting diode (LED) was introduced by the chemically lift-off (CLO) process. Such fabrication of the vertical LED could be realized by inserting the CrN interlayer between sapphire substrate and gallium nitride (GaN) layer. In this paper, by using off-cut sapphires, we tried to find out the influence of off-angles on the overgrown GaN films with respect to crystal quality and surface roughness. The CrN is formed by nitridizing the deposited Cr layer on the sapphire substrate at 1080 °C, and then GaN was grown on the nitrided Cr. By X-ray diffraction system (XRD) measurements, the crystal quality tendency of the GaN film on the variation of the off-angles was similar with that of the CrN interlayer. Through high-resolution transmission electron microscopy (HRTEM) measurement, it was found out that AlN layer with a thickness of a few nanometers also formed between sapphire and CrN during the nitridation treatment of Cr layer. Compared with the previous reports, such tendency of the crystal quality for the vicinal sapphires with CrN interlayer was well matched with the tendency of the previous results in the vicinal sapphire without the CrN interlayer. Therefore, it can be surmised that the AlN layer between sapphire and CrN was precedently influenced by the vicinal substrate and then, the AlN layer had an influence on the upper layers of GaN as well as CrN. In addition, it was found that the vicinal sapphires with the off-angles of 0.2-0.3° had the minimum full-width at half-maximum (FWHM) values by XRD measurements, which were lower by 20% than the others.