Growth Mechanism of Nonpolar and Semipolar GaN Layers from Sapphire Sidewalls on Various Maskless Patterned Sapphire Substrates

Nonpolar and semipolar GaN layers can be selectively grown from sapphire sidewalls of maskless patterned sapphire substrates (PSSs) by selective-area growth using a low-temperature (LT) GaN buffer layer. Various PSSs, such as a-PSS for m-GaN, r-PSS for (1122) GaN, c-PSS for m-GaN, and m-PSS for a-GaN, were prepared to investigate the growth mechanisms. It was revealed that the growth windows of various PSSs to achieve nonpolar or semipolar GaN grown from only the sapphire sidewall by changing the growth conditions are different. To determine the cause of selective-area growth in each PSS, GaN nucleation after annealing of the LT-GaN buffer layer was investigated by scanning electron microscopy, atomic force microscopy and X-ray diffraction analysis. Consequently, GaN was predominantly grown on a region with higher quality and better crystallo-ordered c-oriented GaN nucleation. When such nucleation of GaN occurs on the sapphire sidewall, it proceeds to grow selectively from the sapphire sidewall, and nonpolar or semipolar GaN can be obtained using maskless PSS.