Surface, Structural and Optical Studies of GaN Grown on Si by MOCVD

In the last two decades, there has been considerable research focused on investigating GaN films grown on silicon as a wide bandgap semiconductor material. Optical techniques, such as ellipsometry, have been widely employed for characterizing thin films and bulk materials, enabling the determination of layer thicknesses and surface roughness. X-ray diffraction (XRD) has proven to be an essential tool for analyzing semiconductor crystal structures, while Raman spectroscopy provides insights into the composition and homogeneity of epitaxial semiconductor samples. This study examines four GaN thin films grown on silicon substrates using metalorganic chemical vapor deposition (MOCVD). Variable angle spectroscopic ellipsometry (VASE) measurements were conducted to determine film thickness and surface roughness as well as the dependence of n & k versus wavelength in 250-1000 nm for these GaN on Si samples. The obtained results indicate specific values for each sample: the first sample has a film thickness of 180 nm and a surface roughness of 47 nm, the second sample has a thickness of 106 nm and a surface roughness of 8 nm, the third sample has a thickness of 1004 nm and a surface roughness of 3 nm, and the fourth sample has a thickness of 1510 nm and a surface roughness of 2 nm, as derived from Spectroscopic ellipsometry (SE) fits. The highest recorded refractive index among the four samples is 2.76, XRD measurements were performed on the first two samples, while Raman scattering measurements were conducted on the remaining two samples. The XRD experiments involved wide scans and fine scans with step sizes of 0.1° and 0.005°, respectively. The XRD analysis revealed distinct peaks corresponding to silicon (002) and (004) orientations at approximately 28° and 90°, respectively, in the first sample. Additionally, a weak peak at around 35° indicated the presence of the GaN (0002) peak. In the second sample, the XRD analysis demonstrated clear peaks for the Si substrate (002) and (004) orientations at 28° and 90°, respectively, along with distinct peaks corresponding to GaN at (0002), (0004), and (0006) orientations. Notably, the first-order GaN peak was observed at approximately 34.6°, the second-order peak at around 73°, and the third-order peak at approximately 127°, providing valuable information about the crystallographic properties of the GaN films. Raman scattering measurements were conducted on two samples under a microscope at room temperature, employing different excitation laser powers (5%, 1%, and 0.5%). The first Raman experiment revealed characteristic peaks at 520 cm^-1 for Si, confirming its crystalline nature, while peaks at 565 cm^-1 corresponded to the GaN crystallinity characteristics of the E₂ (High) and A₁ (LO) vibrational modes. In the second Raman experiment, distinctive peaks at 520 cm^-1, 567 cm^-1, and 734 cm^-1 were identified for Si, GaN E₂ (High), and GaN A₁ (LO), respectively, further supporting the exceptional crystalline purity of the GaN films grown on silicon substrates. Through these comprehensive surface, structural, and optical characterizations, our study provides compelling evidence of the exceptional crystalline purity of the investigated GaN films on silicon substrates. These findings, achieved through Ellipsometry, XRD, and Raman spectroscopy techniques, enhance our understanding of the surface, structural, and optical properties of GaN films and open up exciting possibilities for their utilization for high-power and spintronic applications.<br/>&lt;quillbot-extension-portal&gt;&lt;/quillbot-extension-portal&gt;