Reduction mechanisms for defect densities in GaN using one- or two-step epitaxial lateral overgrowth methods

A transmission electron microscopy study of the reduction mechanisms for de fect densities in epitaxial lateral overgrown (ELO) GaN films is presented. In the standard one step ELO, the propagation of defects under the mask is blocked, whereas the defects in the window regions thread up to the surfac e. We propose an alternative two step ELO method. In a first step, dislocat ions close to the edge of the (0001) top facet bend at 90 degrees, thereby producing a drastic reduction in the density of defects above the window. A fter the coalescence, induced by lateral growth in a second step, dislocati ons are mainly observed in the coalescence boundaries. The density of defec ts is decreased to 2x10(-7) cm(-2) over the entire surface and areas nearly 5 mu m wide with 5x10(6) cm(-2) dislocations between the center of the win dows and the coalescence boundaries are obtained. (C) 2000 American Institu te of Physics. [S0021-8979(00)06409-4].