Recently gallium nitride (GaN)-based solid-state devices have demonstrated extraordinary effectiveness for high-power, high-frequency, and high-temperature technology. The basic properties of the AlGaN/GaN material combination make it an excellent choice for microwave devices. Silicon is the most cost-effective adopted substrate for large-scale fabrication of GaN devices [1]. However, interfacial stress, dislocation density and meltback etching caused by Silicon outdiffusion remain significant disadvantages. GaN on SiC offers superior thermal performance and fewer defects due to better lattice and thermal matching but comes at a higher cost and with manufacturing difficulties. A further challenge is represented by the common use of SiC off-axis substrates. In the off-axis orientation the two orthogonal directions in the vicinal c-plane, along [1120] and [1100] (with and without periodic surface steps, respectively) can stimulate anisotropic epitaxy and amplify the effects of the different thermal expansion rates during the cooling process post-growth, potentially causing additional strain and cracking in the GaN layer [2]. In this work Trimethylgallium (TMGa), Trimethylaluminum (TMAl) and ammonia (NH3) were used as the precursors for Gallium (Ga), Aluminium (Al) and Nitrogen (N) sources respectively. HEMT layer was carried out on 3 processes where the deposition of a 2 m GaN buffer layer at 1020 °C was followed by the growth of 16 nm thick AlGaN layer. The epitaxial growth of GaN was conducted employing three distinct methodologies: the Standard Process (SP) method adhered to the established protocol for GaN epitaxy on Si substrates. Subsequently, a specialized procedure was formulated for SiC substrates, which was further bifurcated into two stages, designated as P1 and P2. Each stage differing on AlN growth parameters. Within the specialized SiC procedure, one of the stages was subjected to trials on SiC substrates measuring 500 µm, both on-axis and 4° off-axis, as well as on a 350 µm SiC substrate. Additionally, a control epitaxial growth on a Silicon substrate was performed to serve as a reference point. Upon wafer flatness evaluation, distinct behaviors were observed. Adopting the conventional SP process, wafer exhibited a curvature with a bow range of 187.2 µm, whereas the Silicon wafer demonstrated a bow range of 46.2 µm. As depicted in Figure 1a, in the case of on axis SiC substrates, the process variations resulted in flatness values susceptible to thinner SiC substrate thicknesses due to augmented thermal stress during cooling rate, ranging from 78.3 µm to 178.2 µm when transitioning from a 500 µm to a 350 µm SiC substrate in P1 and from 37.22 µm to 136.1 µm in P2. Among all processes, it is worth noting that off-axis oriented GaN on SiC growths resulted in the lowest bow range as high as 29.65 µm in the P1 and 19.75 µm in the revised process P2. Full Automated Optical microscopy inspection of the wafers revealed a high percentage of Total Usable Area (TUA). Particularly in Figure 1b, the inspections indicated that the highest 1mm2 TUA was 99.57% in P2 with 0.46 cm-2 defects density. It is noted that the surface remains smooth in the case of GaN on SiC (Figure1c), while, in the case of GaN on Silicon, onset of microcracking is disclosed due to stress (Figure1d). Full wafer Photoluminescence (PL) analysis, performed with a =266 nm excitation laser, revealed that the off-axis GaN on SiC underwent P2 growth exhibited a standard deviation in the GaN signal intensity of 9.9% in band edge spectral region. As depicted in Figure 1e, the spatial map of the emission wavelength indicates a localized emission peak at (364.1±0.1) nm. As attested for GaN grown under P2, the emission intensities exhibit variations that rely on crystallographic orientation. Peak intensities are demonstrably higher for the on-axis GaN on SiC sample compared to the off-axis sample, suggesting that the misorientation in the off-axis sample may intensify lattice mismatch and consequently increase the concentration of dislocations. As a result, the off-axis sample manifested a reduced PL intensity. Conversely it was attested the rising in PL signal in the intrabandgap region in Figure 1e. The emission map delineates a specific area indicative of intrabandgap recombination from 500 to 650 nm. This spectral region corresponds to the commonly observed yellow luminescence (YL) band associated with defects in GaN. Potential origins of the YL band in GaN include dislocations as well as various point defects such as Ga vacancies (VGa) or VGa complexes, such as VGaON or VGaSiN and C related point defects [3]. The uniformity of this signal across the wafer is quantified by a standard deviation of 6.5%, with a marginal intensification noted towards the periphery of the wafer. Concurrently, the presence of Fabry-Perot oscillations indicates that uniformity in the arrangement of the grown layers is preserved. This is further corroborated by Vertical Scanning Interferometry (VSI) profilometry measurements, which reveal that the Root Mean Square roughness (Sq) on a 250×100 mm2 area is (3.98±0.16 nm) nm for the off-axis sample in P2 as displayed in Figure (1g). This result is notably comparable to the Sq of (3.35±0.09) nm observed for the GaN on Si grown underwent SP. Comparative evaluations of the data suggest that Sq is elevated for the on-axis samples processed through P2, exhibiting a range from (8.96±0.96) nm to (7.36±0.66) nm. In contrast, for P1, the Sq values are recorded between (7.04±1.78) nm and (5.02±0.40) nm. The compositional analysis depicted in Figure 1h illustrates that the off-axis sample from process P2 contains an Al fraction of (30.4± 0.71)%. This data suggests that the P2 facilitates a higher Al incorporation rate, and exhibit an upward trend in the Al fraction from process P1 to process P2. In light of the results, the research presented herein provides valuable insights into the optimization of 150 mm GaN on SiC MOCVD growth, establishing the 4° off-axis SiC substrate as a promising contender for the improvement of GaN on SiC High Electron Mobility Transistors (HEMTs).