Epitaxial Growth of AlGaN/AlN Strained-Layer Superlattices by Metalorganic Vapor Phase Epitaxy for Far-UV Second Harmonic Generation

Ultrathin AlN (<100 nm) layers fabricated via sputtering and subsequent face-to-face annealing (SP-FFA) over sapphire substrates can be applied as templates for the growth of AlGaN/AlN-based second harmonic generation (SHG) devices due to the high crystalline quality and smooth surface. This paper provides a concise overview of the crystalline characteristics of SP-FFA and metalorganic vapor phase epitaxy. An atomic force microscopy obtained a root-mean-square (RMS) roughness of 0.13 nm after the ultrathin growth of SP-FFA AlN. Subsequently, the impact of the SP-FFA AlN template on the regrowth of AlN and AlGaN by metalorganic vapor phase epitaxy has been examined. The phenomenon of the strong composition-pulling effect for the growth of AlGaN on the SP-FFA AlN template has been discussed. Finally, the paper discusses the successful growth of Al_0.88Ga_0.12N/AlN strained-layer superlattices, while ensuring a smooth surface morphology with an RMS roughness value of 0.15 nm, which effectively reduces the scattering loss in a waveguide. The growth of the strained-layer superlattice augments the nonlinear coupling coefficient kappa by utilizing the piezoelectric field in the transverse quasi-phase matching SHG device.