| dc.description.abstract | Currently, the most common process method for GaN-on-Si epi layer gallium nitride (GaN) is a single-layered or multilayered thick aluminum nitride (AlN) buffer layer grown on Si substrate by using Metal-organic chemical vapor deposition (MOCVD). In this study, we employed high-power impulse magnetron sputtering (HiPIMS) to deposit 100-nm GaN buffer layer on silicon substrates under high energy and high density of plasma. Then, MOCVD has been used to deposit a GaN epitaxial layer. This approach aims to improve lattice mismatch problem.
In this research, the MOCVD epitaxial layer was maintained at a process temperature of 1095 °C and a pressure of 200 mbar. The primary focus was adjusting the buffer layer parameters, including process temperature, buffer-layer thickness, and discharge time of HiPIMS, to explore their effects on the epitaxial layer. Additionally, we investigated the improvement of substrate back-etching through nitrogen plasma pretreatment, as well as adjusting the Nitrogen-Argon ratio during the buffer layer process and the V/III ratio during the epitaxial layer process. For measurements, we utilized X-ray diffractometer (XRD) to analyze the Full Width at Half Maximum (FWHM) and intensity of the crystal diffraction, assessing the consistency of lattice alignment and the crystalline quality of the buffer and epitaxial layers. Atomic Force Microscopy (AFM) was employed to determine the surface roughness. Scanning Electron Microscopy (SEM) was used to examine the surface and cross-sectional structures of the films. Finally, Alpha-Step was used to determine polarity assessment after KOH etching.
The results revealed that incorporating the GaN buffer layer significantly improved the MOCVD-grown epitaxial layer, transforming it from approximately 10 μm GaN discontinuous film grains to a continuous film of about 2 μm. Before the GaN buffer layer process, a nitrogen plasma pretreatment on the silicon substrate was performed. It shows that the process with the nitrogen plasma pretreatment transformed the epitaxial layer from numerous triangular crystal columns to hexagonal crystal columns, enhancing the lateral growth of the GaN epitaxial layer. XRD results showed an improvement in the FWHM of the optimized GaN epitaxial layer from 0.24 degree to 0.18 degree. SEM analysis also confirmed the improved surface morphology. After KOH etching, SEM examination revealed a nitrogen polarity phenomenon. Consequently, the surface smoothness of the film has to be improved to further enhance the quality of direct GaN epitaxy on silicon substrates. | en_US |