Pulsed epitaxial lateral overgrowth of GaN by metalorganic vapour phase epitaxy

A mixed pulsed and normal GaN epitaxial lateral overgrowth (ELO-GaN) by epitaxy metalorganic vapour phase epitaxy (MOVPE) is reported in this study. Monitoring by using an in situ spectroscopic reflectometer has shown that a varying vertical growth rate during the pulsed growth was observed as in the normal ELO-GaN growth process, however, the growth rate was dramatically reduced in pulsed growth. Cross-section scanning electron microscope (SEM) images have shown that a lateral to vertical growth ratio (LTVGR) of 7 was obtained under a set of growth conditions on a template with a GaN trench and SiO2SiO2 mask width of 5 and 15μm, respectively, and with the stripes aligned in the GaN 〈1¯100〉 crystallographic direction. Two types of growth instability associated with pulsed growth were observed under some growth conditions. One is the formation of large steps on the ELO-GaN stripes before coalescence; the other is the formation of hexagonal pyramids on the coalesced surface. The origin of pyramidal formation was found exactly on the coalescence boundaries. A mixed pulsed and normal ELO-GaN growth technique has been established to eliminate the large steps, and formation of pyramids can be avoided by switching to normal growth conditions before ELO-GaN stripes coalesce. The thickness of ELO-GaN has been successfully controlled below 1μm before coalescence, and below 3μm for a fully coalesced ELO-GaN film by this technique. Atomic force microscope (AFM) has confirmed that ELO-GaN films grown by this technique are of high structural quality.