## 1 Introduction  
Atomic layer deposition (ALD) is a technique based on sequential, self-limiting surface reactions, in which gas-phase precursors are alternately introduced into the ALD reaction chamber to form a single layer. Each cycle includes adsorption and reaction steps [1]. The thickness of the film can be controlled by varying the number of deposition cycles. ALD enables the deposition of very high-quality films at the atomic scale. Films prepared using this method are extremely smooth and uniform, without pinholes, even on complex substrates. Both the thickness and composition of the films can be precisely controlled at the atomic level [2]. ALD plays a key role in a wide range of high-quality thin-film coating industries, such as semiconductors, microelectronics, electroluminescent displays, photovoltaics, and medical devices [3, 4, 5, 6, 7, 8, 9]. In particular, the semiconductor industry today relies heavily on ALD technology due to ongoing miniaturization, as the size of modern semiconductor chips continues to decrease. Films must be uniformly deposited over increasingly larger wafer sizes while also conforming to the complex three-dimensional (3D) structures of integrated circuit (IC) devices. The uniformity, conformality, and composition of thin films have been successfully achieved using ALD. Currently, no other technology can match ALD in this regard, and it holds great potential for applications in the coating industry [10]. Gallium nitride (GaN) belongs to the group of III-V semiconductors and has a direct band gap, high breakdown field, excellent electron mobility, and good thermal stability [11]. GaN plays a crucial role in a wide range of applications, including light-emitting diodes (LEDs) [12; 13], heterojunction field-effect transistors (FETs) [14], p-i-n rectifiers [15; 16], and photodiodes [17]. Although GaN offers many advantages over silicon (Si), its high production cost limits large-scale commercialization. Producing GaN in large quantities is expensive, making mass production challenging [11]. To reduce production costs, silicon is commonly used as a substrate in the GaN deposition process [18], as it also offers better thermal conductivity and good electrical conductivity [19; 20]. Despite these advantages, the mismatch in thermal expansion coefficients between GaN and silicon substrates can lead to film cracking and structural failure, particularly when the growth temperature exceeds 1000 \({}^{\circ}\)C [21; 22]. Several conventional methods have been developed for GaN deposition, such as molecular beam epitaxy (MBE) [23], sputtering [24], supersonic gas jet-assisted vapor deposition [25; 26], metalorganic chemical vapor deposition (MOCVD) [27; 28], and hydride vapor phase epitaxy (HVPE) [29]. Although these techniques can deposit GaN films at temperatures below 1000 \({}^{\circ}\)C, the resulting film quality is often relatively low. Additionally, most of these methods still require high deposition temperatures (typically above 700 \({}^{\circ}\)C), which are unsuitable for heat-sensitive substrates, such as flexible substrates used in light-emitting applications [30; 31]. ALD is a method that was developed for depositing conformal metal thin films at low temperature. The ALD technique can grow a high quality GaN film. At the temperatures of 800-1100 \({}^{\circ}\)C, GaN film was grown based on MOCVD using trimethylgallium (TMG) and NH3 [27; 28]. A thermal ALD process has been reported at a processing temperature of 375-425 \({}^{\circ}\)C using TMG and NH\({}_{3}\) sources [11]. Additionally, the plasma and electron-enhanced ALD processes make it possible to reduce the process temperature to near room temperature (RT) [30; 32]. This allows for the GaN films to be grown on heat-sensitive materials and expands their applications as well as reducing the thermal budget in mass production. Amorphous GaN films grown at low temperatures can be crystallized through temperature-programmed rapid annealing at minimal cost [32]. [PERSON] et al.