Determination of the Thickness of Nanometer-Thick β‑Ga₂O₃ Membranes from Optical Interference and Colorimetric...

β-phase gallium oxide is emerging as a next-generation semiconductor material due to its ultrawide bandgap, high breakdown voltage, capabilities as a solar-blind ultraviolet photodetector, and resistance to extreme conditions. β-Ga₂O₃ membranes are available in various thicknesses and can be characterized by using standard techniques, e.g., atomic force microscopy (AFM). In this work, the use of optical interference patterns is demonstrated as an alternative characterization technique, highlighting its noncontact, user-friendly, and high-throughput thickness assessment for submicron-thick β-Ga₂O₃ membranes. Thicknesses of (100) β-Ga₂O₃ membranes on 290 nm SiO₂/Si substrates are determined by applying Fresnel's law to fit the contrast profile via optical interference patterns, while accuracy is assessed by atomic force microscopy. Moreover, the color map, calculated to assign the observed color of the membranes to their thickness, shows excellent agreement with the experimental results. The color-to-thickness correspondence is not always univocal and shows repeating color trends over thickness. Membranes of lesser thickness display colors of red, green, and pink, whereas membranes exceeding 600 nm predominantly exhibit orange and yellow tones. Finally, total color differences (TCD) analysis illustrates that (100) β-Ga₂O₃ membranes on 129, 221, 310, 392, and 467 nm SiO₂/Si substrates have the best contrast; thus, membranes are more distinguishable.