Two-step epitaxial lateral overgrowth of GaN

A two-step epitaxial lateral overgrowth (ELO) method was proposed to improve the quality of GaN-based epitaxial layers. In the first step, we grew a three-dimensional GaN low temperature buffer layer at 520 °C for different amount of time, and the second step is similar to conventional ELO. For two-step ELO GaN samples on SiO₂ stripes along 〈112̄0〉 direction, it was found that an 8min first step growth time could provide us the highest lateral to vertical growth rate ratio and the largest angle between sidewalls and basal plane. Under such growth conditions, we could achieve a surface root-mean-square (rms) roughness of 0.480nm and an etch pits density (EPD) of 1.6×10⁷cm^-2 in the stripe regions. The surface morphology of the two-step ELO GaN sample is also much better than that of the one-step ELO GaN sample.