## 2 Materials and Methods  
The spray pyrolysis method is a widely recognized and versatile technique, valued for its ability to deposit thin films and synthesize nanoparticles with high precision [57; 58]. The process offers numerous advantages that make it suitable for a broad range of applications, from laboratory research to large-scale industrial production [59; 57]. One of the key benefits of spray pyrolysis is its simplicity and cost-effectiveness [57; 58; 59]. The equipment used for spray pyrolysis is relatively simple and inexpensive, especially when compared to other deposition techniques, like chemical vapor deposition or atomic layer deposition. This makes it an accessible option for many research labs and industries. The versatility of spray pyrolysis is another major advantage. It can be employed to deposit a wide variety of materials, such as metals, metal oxides, sulfides, nitrides, and complex compounds [60,61]. This makes the technique suitable for producing not only thin films and coatings but also nanoparticles [58]. Spray pyrolysis is also applicable on different substrates, including glass, ceramics, polymers, and metals, providing flexibility for various applications [59,62]. In terms of control over film properties, spray pyrolysis is distinguished by allowing precise adjustments to parameters like the spray rate, solution concentration, substrate temperature, and spray distance. These parameters allow for accurate control over the thickness of the deposited films [60]. Another significant advantage is the uniformity of the coatings, which provides highly uniform and homogeneous coatings [62,63]. This makes it suitable for applications such as solar cells, sensors, and optoelectronic devices [59,60,62]. Additionally, the produced films typically exhibit good adhesion to the substrate, which is important for ensuring the durability and reliability of the final product. Spray pyrolysis is also known for its low temperature process, which is particularly beneficial when working with temperature-sensitive substrates, such as plastics or flexible materials [61]. The high deposition rate of spray pyrolysis is another advantage, making it an attractive choice for applications where high throughput is essential [60]. In terms of environmental impact, spray pyrolysis stands out due to its minimal material waste. Since the precursor solution is directly converted into the thin film or nanoparticles, there is little waste produced. The Zn\({}_{1-x}\)Mg\({}_{x}\)O, (In\({}_{2}\)O\({}_{3}\))\({}_{1-x}\)(MgO)\({}_{x}\), (In\({}_{1-x}\)Ga\({}_{x}\))\({}_{2}\)O\({}_{3}\), ITO\({}_{1-x}\)Ga\({}_{x}\), undoped Ga\({}_{2}\)O\({}_{3}\) as well as _Sn_- and _Al_-doped Ga\({}_{2}\)O\({}_{3}\) films were prepared on Si substrates with (100) crystallographic orientation using the spray pyrolysis technique schematically presented in Figure 1. Prior to deposition, the Si substrates were chemically degreased in a chemical solution with a volume fraction of H\({}_{2}\)O:NH\({}_{3}\):H\({}_{2}\)O\({}_{2}\) equal to 8:1:1, at a temperature of 80 \({}^{\circ}\)C for 10 min. Further, the Si substrates were dipped in hydrofluoric acid (HF) for 2 min, followed by washing in distilled water and immediately starting the deposition process. All solutions were prepared at a molar concentration of 0.25 M, mixed in an ultrasonic bath at 50 \({}^{\circ}\)C for 30 min and left for 24 h before characterization. The deposition process was conducted under an O\({}_{2}\) gas flow with an injection rate of 1.2 cc/min. The substrate temperature was maintained at 480 \({}^{\circ}\)C, resulting in a deposited layer thickness of approximately 200 nm after 3 min and a maximum surface area of 2 cm\({}^{2}\). Figure 1: Schematic representation of spray pyrolysis process. All the key details of the precursor materials, such as solvents, deposition conditions, and other experimental parameters are presented in Table 1 for each type of oxide film.