|dc.description.abstract||In this study, we deposit buffer layers by sputtering on Si (100) and poly-AlN substrates, providing a cost-effective and compliant surface for epitaxial growth of III-nitride semiconductors. Owing to the huge mismatches in lattice constant and thermal expansion coefficient mismatch between GaN and Si substrate, the strain induced during GaN growth often leads to cracks on epi-layer’s surface, resulting in deteriorated crystal qualities. ZnO, with merely 1.8% lattice mismatch to GaN, was utilized as the buffer material to improve the crystal qualities of GaN-on-Si. By optimizing the buffer layer thickness, the undesired stain can be mitigated, deferring the formation of threading dislocations.
The poly-AlN substrate was produced with compressed AlN powder. To smoothen the surface for epitaxial growth, the poly-AlN substrate was coated with an AlN buffer layer by RF sputtering prior to the growth. According to the results of scanning electron microscopy (SEM) and x-ray diffraction (XRD), the gas mixture of Ar/N2 and sputtered AlN films thickness play important roles in the optimization of AlN epitaxy.
During the epitaxial growth, it is found that the AlN epilayer grown on the poly-AlN substrate exhibited pyramid-like semipolar facets. The semipolar facets have two advantageous properties for solid state lighting: i). Increasing the emission area. ii). Enhancing the radiative recombination efficiencies in the quantum wells. Moreover, pulsed-flow of NH3 precursor was adopted to enhance the lateral growth rate of AlN. The enhanced lateral growth was found effective in improving the smoothness and lattice qualities of the AlN epilayer. This study demonstrates an alternative route for the growth of ultraviolet light emitting diodes.