Dislocation mechanisms in the GaN lateral overgrowth by hydride vapor phase epitaxy

We have carried out a series of lateral epitaxial overgrowths (LEO) of GaN through thin oxide windows by the hydride vapor phase epitaxy (HVPE) techni que at different growth temperatures. High lateral growth rate at 1100 degr eesC allows coalescing of neighboring islands into a continuous and flat fi lm, while the lower lateral growth rate at 1050 degreesC produces triangula r-shaped ridges over the growth windows, in either case, threading dislocat ions bend into laterally grown regions to relax the shear stress developed in the film during growth. In regions close to the mask edge, where the she er stress is highest, dislocations interact and multiply into arrays of edg e dislocations lying parallel to the growth window. This multiplication and pileup of dislocations cause a large-angle tilting of the laterally grown regions. The tilt angle is high (similar to8 degrees) when the growth is at 1050 degreesC and becomes smaller (3-5 degrees) at 1100 degreesC. At the c oalescence of growth facets, a tilt-type grain boundary is formed. During t he high-temperature lateral growth, the tensile stress in the GaN seed laye r and the thermal stress from the mask layer both contribute to a high shea r stress at the growth facets. Finite element stress simulations suggest th at this shear stress may be sufficient to cause the observed excessive disl ocation activities and tilting of LEO regions at high growth temperatures.