Microstructure of GaN grown by lateral confined epitaxy 2. GaN on patterned sapphire

Transmission electron microscopy (TEM), atomic force microscopy (AFM), and photoluminescence (PL) spectroscopy were used in order to study the microstructure and optical properties of GaN films grown by metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire by lateral confined epitaxy (LCE). In this method, the substrate is etched prior to growth to form uniform mesas separated by trenches for laterally restricting growth area. As previously observed for LCE GaN on Si(111), the density of threading dislocations was significantly reduced in the areas close to the edge of mesas due to the lateral propagation of the dislocations. Hence, the overall material quality improves with decreasing mesa size, which is consistent with the observed increase in photoluminescence band-edge peak intensity. Electron diffraction indicated ∼1° rotation about the [11̄00] axis between the mesa and trench material, which was also observed in the image contrast of these two regions with g = 112̄0. Additionally, LCE samples prepared in [11̄00] and [112̄0] cross sections were used for comparing the growth rates in these two perpendicular directions. As theoretically expected, growth in the [112̄0] direction appears to proceed considerably faster than that in the [11̄00] direction.