Characterization and optimization of AlN nucleation layer for nonpolar a-plane GaN grown on r-plane sapphire substrate.

Nonpolar (11–20) a-plane GaN films with AlN nucleation layer were grown on (10–12) r-plane sapphire substrate by metal organic chemical vapor deposition (MOCVD). The crystalline and surface qualities of a-plane GaN were found to closely depend on the growth conditions of AlN nucleation layer. With decreasing AlN growth temperature, the AlN grains became larger and sparser, which significantly reduced the defects density of a-plane GaN films. The growth time of the low temperature AlN layer was further optimized, and a-plane GaN films with reduced anisotropy in the crystalline quality, surface morphology and in-plane strains were achieved. It was found that the lateral growth lengths along different directions of GaN could be modulated by the growth time of AlN nucleation layer, thus changing the anisotropy of a-plane GaN films. • The crystalline and surface qualities of a-plane GaN were found to closely depend on the growth conditions of AlN layer. • Better crystal quality could be obtained when low temperature AlN nucleation layer was used. • The optimum growth time of low temperature AlN buffer effectively reduced the anisotropy of a-plane GaN films. • The lateral growth lengths along different directions of GaN could be modulated by the growth time of AlN nucleation layer. [ABSTRACT FROM AUTHOR]