Growth and Characterization of Ga₂O₃ for Power Nanodevices Using Metal Nanoparticle Catalysts

Abstract

A simple and inexpensive thermal oxidation process is used to grow β-Ga₂O₃ oxide (β-Ga₂O₃) thin films/nanorods on a c-plane (0001) sapphire substrate using Ag/Au catalysts. The effect of these catalysts on the growth mechanism of Ga₂O₃ was studied by different characterization techniques, including X-ray diffraction analysis (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray analysis (EDX). The XRD results of the grown Ga₂O₃ on a sapphire substrate show three sharp diffraction peaks located at 19.31°, 38.70° and 59.38° corresponding to the $\left(\overline{2}01\right), \left(\overline{4}02\right)$ and $\left(\overline{6}03\right)$ planes of β-Ga₂O₃. Field Emission Scanning Electron Microscope (FESEM) analysis showed the formation of longer and denser Ga₂O₃ nanowires at higher temperatures, especially in the presence of silver nanoparticles as catalysts.

1. Introduction

Gallium oxide (Ga₂O₃), a semiconductor with a broad bandgap of about 4.9 eV, has drawn a lot of interest because of its potential applications in ultraviolet, photodetection, high-power electronics and optoelectronics [1,2]. Its exceptional properties, such as excellent electron mobility, high breakdown voltage and outstanding thermal stability, make it an ideal candidate for high-temperature and high-voltage applications [3]. However, the performance of Ga₂O₃-based devices depends on the material’s crystal size, morphology and defect density. Therefore, understanding and controlling the growth mechanism of Ga₂O₃ is crucial for optimizing its properties and scaling up production for industrial purposes.

Several studies have been reported in the literature to investigate the growth mechanism and produce high-quality Ga₂O₃ nanostructures using various methods. Shi et al. [4] created Ga₂O₃ thin films using vacuum thermal evaporation and post-annealing in air at different temperatures. They observed an increase in the bandgap from 4.70 eV to 5.13 eV as the annealing temperature increased from 400 °C to 1100 °C. While this post-annealing procedure improves the quality of the material, it requires high temperatures, leading to higher energy costs and longer processing times. This may be expensive, especially for large-scale production. Recent research has explored the use of metal nanoparticles, such as gold and silver, as catalysts to enhance the formation of Ga₂O₃ nanostructures, with the aim of solving these drawbacks [5,6].

Catalysts such as Ag and Au significantly enhance the wettability of liquid gallium on substrates, leading to more oxidation and high-density formation of Ga₂O₃ nanostructures. Alhalaili et al. [7] demonstrated that using an Ag catalyst with photoelectrochemical etching on silicon surfaces significantly improved Ga wettability, resulting in homogeneous and dense development of Ga₂O₃, even in deep pores. Without the Ag catalyst, Ga formed irregular droplets causing non-uniform Ga₂O₃ production and partial oxidation. These catalysts are crucial for regulating the shape and quality of Ga₂O₃ nanostructures. In addition to increased Ga wettability, Ag and Au catalysts help promote oxygen molecule dissociation by lowering the activation energy for oxygen adsorption and dissociation on their surfaces, facilitating the reaction with gallium to form Ga₂O₃. This process involves the metal nanoparticles acting as oxygen reservoirs, where oxygen molecules adsorb onto the catalyst surface, dissociate into atomic oxygen and subsequently react with liquid gallium to nucleate Ga₂O₃ nanostructures [8,9].

Keerthana et al. [10] found that Ag-decorated β-Ga₂O₃ heterostructures have better photocatalytic activity for hydrogen evolution due to improved electron-hole pair separation. Woo et al. [11] developed an Ag/GaO₃ bilayer electrode for near-ultraviolet light-emitting diodes (LEDs), which showed enhanced conductivity, stability and transparency, improving LED performance. Zhou et al. [12] studied the interstitial oxygen position in both Ag and Au, finding that while Au had a higher oxygen diffusivity, Ag had a higher oxygen concentration. These findings further support the role of Ag and Au as catalysts. The growth rate and quality of Ga₂O₃ can be influenced by this variation in oxygen dynamics, where Ag promotes the synthesis of Ga₂O₃ and Au facilitates faster oxidation.

This study investigates the growth of Ga₂O₃ nanostructures on sapphire substrates using Ag and Au nanoparticles as catalysts at 800 °C and 900 °C. Unlike previous research work that generally discussed catalyst effects, our work focuses on how temperature, catalyst type and catalyst concentration affect Ga₂O₃ morphology, crystallinity and composition. These variables were analysed with X-ray diffraction (XRD) and Field Emission Scanning Electron Microscope Energy Dispersive Spectroscopy (FESEM-EDS). The FESEM analysis reveals how different temperatures and catalyst conditions affect the formation of denser nanowires or nanosheets, aiding in optimizing properties for optoelectronics, sensors and high-power electronics.

The synthesis of Ga₂O₃ nanowires in the presence metal nanoparticles such as Ag [8,9] or Au [13] significantly influences developments in electronics and optoelectronics. These Ga₂O₃ nanowires have potential applications in FinFETs [14], UV detectors [9] and field-emitters [15]. Previous studies, such as those by Chunyang et al. [13], Xu et al. [14] and Tang et al. [15], have utilized Au nanoparticles as catalysts for β-Ga₂O₃ nanowire growth via metal-organic chemical vapor deposition (MOCVD) and demonstrated applications in FinFETs and field-emitters. In contrast, this work employs a cost-effective thermal evaporation method, which is simpler and more scalable than MOCVD, reducing energy costs and equipment complexity. Furthermore, we compare the efficacy of Ag and Au catalysts, revealing that Ag nanoparticles enhance the formation of denser and longer β-Ga₂O₃ nanowires due to higher oxygen solubility and diffusion, a novel aspect not extensively explored in prior studies. This systematic investigation of catalyst type, concentration, gallium amount and temperature provides critical insights for optimizing β-Ga₂O₃ nanostructures for applications in optoelectronics, sensors and high-power electronics.

2. Materials and Methods

2.1. β-Ga₂O₃ Thin Films/Nanorod Growth

The thermal evaporation method was used to grow β-Ga₂O₃ thin films/nanorods on an Al₂O₃ substrate (100 × 0.9 mm, single-polished) with two different catalysts. This method is inexpensive and compatible with the preparation of a wide variety of nanomaterials. Silver and gold nanopowders (99.99%, 50–100 nm) obtained from US Research Nanomaterials, Inc. Corporation (Houston, TX, USA) were used as catalysts. The sapphire substrates were cleaned using acetone and ethyl alcohol, rinsed with deionised water and dried with a nitrogen gun. A total of 0.2 grams of gallium (Ga), with a purity of 99.99% obtained from Sigma Aldrich, St. Louis, MO, USA, was carefully dripped onto the polished surface of the sapphire substrate. After that, the catalyst nanopowder was added in varying amounts: 0, 5, 10 and 15 milligrams. For comparison, samples were grown under identical conditions on bare substrates. The samples were placed into a quartz crucible and then loaded into a Protherm laboratory tube furnace (model PTF 12/105/750) made in Turkey. This horizontal alumina tube furnace has a temperature range of up to 1200 °C, with a power of 3300 W and a current of 15 A. It operates at a frequency of 50–60 Hz and heating occurs in a 20 sccm nitrogen atmosphere. The oxygen required for Ga₂O₃ formation was sourced from residual oxygen present in the nitrogen atmosphere (20 sccm) within the tube furnace and from oxygen dissolved in the Ag and Au nanoparticles, which serve as oxygen reservoirs due to their high oxygen solubility [16,17]. An oxygen analyser (EO-W/1000, MTI Corporation, Richmond, CA, USA) was used to monitor the background oxygen concentration during the experiment. Figure 1 illustrates the sample set-up inside the furnace, which was used to grow gallium oxide on the alumina surface.

2.2. Characterisation Method

The surface morphological properties and elemental characterisation of the as-grown Ga₂O₃ thin films and nanorods were analysed by a Field Electron Scanning Electron microscope equipped with Energy-Dispersive X-ray spectroscopy (FESEM-EDX). X-ray diffraction (XRD) analysis was conducted to identify the crystal nature of the material formed using a Rigaku MiniFlex-600 diffractometer with Cu Kα (λ = 0.15406 nm; 20–40 kV, 2–15 mA) from 10° to 70° two-theta (2θ) at the temperature of 21° in step-scan mode with a scanning rate of 1°/min.

3. Results and Discussions

3.1. X-Ray Diffraction Analysis

X-ray diffraction analysis was used to study the effect of different catalyst loadings during the preparation of Ga₂O₃ and the crystal quality of the thin films/nanorods grown on the sapphire substrate. The X-ray diffraction pattern (Figure 2) of gallium oxide crystals grown on sapphire surfaces at 800 °C with varying amounts of silver catalyst. The X-ray diffraction pattern clearly shows that the gallium oxide crystals grown on the surface of sapphire using Ag/Au as a catalyst are pure β-Ga₂O₃ without any other gallium oxide phases [18]. A preferential crystal growth in the $\left(\overline{2}01\right)$ direction can be observed with the increase in the amount of catalyst due to the preferred arrangement of oxygen atoms in the β-Ga₂O₃ $\left(\overline{2}01\right)$ plane that is equivalent to sapphire (0001) [19]. No other peaks corresponding to different gallium oxide phase configurations were seen in the XRD spectrum.

Figure 3 shows the variation of the full width at half maximum (FWHM) of the $\left(\overline{2}01\right)$ diffraction peak of β-Ga₂O₃ with different catalyst loading. For the Ag catalyst, as the amount of Ag increased from 5 mg to 15 mg, an increase in the intensity of the $\left(\overline{2}01\right)$ diffraction peak and a decrease in the FWHM were observed. However, no clear trend was observed in the case of the Au catalyst.

3.2. Effect of Temperature on the Growth of Ga₂O₃ by FE-SEM Analysis

The temperature of the reaction medium significantly influences the kinetics mechanism of Ga₂O₃ nanoparticle growth. The physical properties, such as the solubility and diffusivity of oxygen molecules on metal nanoparticles, change with temperature. Specifically, the oxygen diffusion coefficients of Ag and Au nanoparticles are crucial in determining the growth density and length of Ga₂O₃ nanostructures. As the temperature increases, the diffusivity of oxygen molecules on these metal nanoparticles also increases, thereby promoting the growth of Ga₂O₃ nanostructures [8,20]. Similarly, the solubility of oxygen molecules in metal nanoparticles increases with temperature. At higher temperatures, the surface energy of nanoparticles increases, causing increased diffusion of gas molecules at the nanoparticle surfaces. Thus, increasing the surface area of nanoparticle droplets will lead to increased oxygen adsorption and diffusivity. In addition, it increases the mobility, agglomeration and distribution of NPs [18], leading to an increase in oxygen absorption.

The effect of temperature on the growth mechanism of Ga₂O₃ was studied by conducting the thermal oxidation process at 800 °C and 900 °C in the presence of Ag and Au nanoparticles (50–100 nm) deposited on the surface of liquid gallium. For the first time, an enhancement in the growth of Ga₂O₃ nanowires was observed during the thermal oxidation process. These results are consistent with the previous studies [12,21], highlighting the impact of catalytic effects at elevated temperatures. Figure 4 shows the SEM images of Ga₂O₃ nanostructures grown in the presence of metal nanoparticles at 800 °C and 900 °C for a duration of 45 min. The SEM image shows the growth of nanocrystalline grains coated with short nanostructures at 800 °C, whereas longer, denser and thinner nanowires were formed at 900 °C. This is due to the increased oxygen solubility of metal catalysts (i.e., Au or Ag) above its melting point. Even though the solubility of oxygen gases usually decreases in liquids with increasing temperature, for a few gases in some solvents and temperature ranges, solubility increases with an increase in temperature [22,23,24]. Silver exhibits high oxygen solubility at elevated temperatures, as reported by Ramanarayanan et al. [16], which enhances the availability of oxygen for Ga₂O₃ nucleation, contributing to the formation of denser and longer nanowires.

The variability in size and direction of β-Ga₂O₃ nanostructures observed in Figure 4 can be attributed to the self-diffusion of metal nanoparticles, leading to non-uniform catalyst distribution. To improve growth uniformity, techniques such as substrate pre-patterning via lithography or template-assisted deposition can be employed to control nanoparticle placement, as demonstrated in prior work with Ag-patterned quartz [8]. Additionally, optimizing substrate surface roughness and implementing precise control of oxygen flow during thermal evaporation could enhance directional growth and uniformity. These strategies will be investigated in future studies to achieve more consistent nanowire morphology.

3.3. Effect of Gallium Concentration on the Growth of Ga₂O₃ by FE-SEM

Gallium concentration is one of the critical factors controlling the growth of Ga₂O₃ nanostructures. Figure 5 and Figure 6 represent FESEM images of Ga₂O₃ nanostructure grown using Au NPs and Ag NPs, respectively. A common observation is that as the concentration of gallium increases, the density of Ga₂O₃ nanostructures increases. This is attributed to the higher tendency of gallium to react with oxygen. In addition, the presence of Ag or Au nanoparticles enhances the absorption capacity, leading to high-density nanostructures [16].

As the diffusion length of Ga increases with temperature, more Ga atoms diffuse to metal nanoparticles [25]. Consequently, liquid Ga extracts oxygen from the metal nanoparticles, which act as a reservoir of more oxygen at the interface, allowing it to react with Ga. This leads to the nucleation of Ga₂O₃ with high density at 800 °C. However, at 900 °C, Ga₂O₃ nanowires or nanosheets continue to grow as the diffusivity and solubility of oxygen molecules increase with temperature. This results in denser and longer nanowire (Figure 5 and Figure 6d) due to the supersaturation of various species. Annealing at 800 °C causes the metal catalysts to react with more residual oxygen molecules in the chamber, increasing the concentration of O₂ in the metal [25]. At all temperatures, the oxidation enthalpy of Ga is much higher than that of Ag. Nucleation of Ga₂O₃ is expected to initiate on the metal nanoparticle surface, as observed in Figure 5a and Figure 6a for Au and Ag catalysts, respectively, at lower gallium concentrations and temperatures.

The presence of Ag or Au on the bare quartz and Ga enhances nucleation of Ga₂O₃. The kinetics and growth mechanism have been explained earlier in details [9]. Due to the self-diffusion of metal nanoparticles, more oxygen molecules will enhance the dissolution of gallium suboxide (Ga₂O) in the liquid metal nanoparticles and deposit Gallium (III) oxide (Ga₂O₃) through crystal nucleation on the bare quartz by a vapor–liquid–solid (VLS) growth mechanism to increase the synthesis of Ga₂O₃ nanostructures [26].

The incorporation of Ag or Au catalysts enhances the growth process to a denser and longer β-Ga₂O₃ nanowires or nanostructures due to several factors that increase oxygen molecules in the system. For example, the solubility of O₂ in Ag and Au [27] is much higher than the solubility of oxygen in liquid Ga molecules [28]. Furthermore, the oxygen molecules solubility in Ag nanoparticles are significantly increased by increasing the temperature at fixed pressure, leading to more oxygen molecules attraction to increase the growth of Ga₂O₃ nanostructures. Interestingly, the Ga atoms enthalpy is much more negative than that of the oxidation of Ag or Au, at all temperatures. This causes a constant nucleation of Ga₂O₃ nanostructures to occur on Ag-Ga-O liquid mixture, where Ga strips the dissolved O₂ away from Ag nanoparticles liquid islands at the higher temperature.

At 800 °C, oxygen’s solubility in Ag nanoparticles is highly increased, leading to Ga₂O₃ nucleation as shown in Figure 7. However, at a higher temperature (1000 °C), the growth mechanism saturates when reaching equilibrium phase of AgGaO_x (Ag-Ga-O phase diagram No. 209084) [29]. Consequently, a constant amount of Ga₂O and O₂ in the presence of Ag nanoparticles would raise the growth of Ga₂O₃.

Figure 8 shows the effect of various gallium concentrations at 800 °C in the presence of 10 mg of silver (Ag) nanoparticles. As the gallium concentration increases, the Ga₂O₃ nanowires becomes denser and thicker. This suggests that while the oxidation of metal nanoparticles enhances their attraction to oxygen molecules, a low concentration of gallium results in a lower density of Ga₂O₃ nanowires or nanosheets as previously observed by Yuan et al. [30].

Different diffusion mechanisms, influenced by metal nanoparticles such as Ag and Au NPs, facilitate Ga₂O₃ nanostructures growth. Self-diffusion affects nanoparticle distribution, with Ag NP surface diffusion exhibiting the lowest activation energy (0.39 eV) compared to grain boundary (0.99 eV) and volume diffusion (1.98 eV) [31], allowing rapid, unconstrained movement and surface distribution. As temperature rises, surface diffusion increases, spreading more nanoparticles and enhancing Ga₂O₃ nanostructure growth [32,33]. Figure 9 summarizes how metal nanoparticle catalysts yield denser and longer Ga₂O₃ nanostructures.

3.4. Effect of Catalyst Selection and Concentration on the Growth of Ga₂O₃ by FE-SEM Analysis

The ideal catalyst metal nanoparticles play a crucial role in enhancing the growth of Ga₂O₃ nanostructures. Figure 10 shows the growth of Ga₂O₃ at 800 °C with two different catalysts, Ag and Au nanoparticles, under identical conditions. A sheet-like continuous morphology was observed for the Ga₂O₃ sample grown with Au nanoparticles, whereas much denser and thicker crystalline structures were observed for samples grown with Ag nanoparticles. Silver’s higher oxygen solubility than gold makes it an effective catalyst for the growth of Ga₂O₃ nanostructures. In addition, silver has the lowest activation energy for surface diffusion (0.39 eV) compared to the activation energy of grain boundary diffusion (0.99 eV) and volume diffusion (1.98 eV) [12]. Hence, silver nanoparticles can interchange easily with no restriction when distributing at the surface. At low activation energy and high diffusion rate, the flux of atoms increases as the concentration gradient and temperature increase. As the temperature increases, the density of metal nanoparticles also increases [34]. However, grain boundary and surface diffusion are both expected in the oxidation process. Surface diffusion can be further increased as the duration of thermal annealing increases at a fixed temperature [32,33]. The final morphology of the Ga₂O₃ nanoparticles is determined by the shape and size of the initial Ga₂O₃ crystal nucleation sites [17,35].

To better understand the kinetics and mechanism of interaction between metal nanoparticles (Ag and Au) and oxygen molecules, FESEM images of Ga₂O₃ nanostructures grown at 900 °C and 1.5 g of gallium with different amounts of catalysts (5, 10 and 15 mg) were analysed (Figure 11). Ga₂O₃ samples grown in the presence of Au exhibited more nanosheet-like textures, whereas Ag nanoparticles change the morphology of Ga₂O₃ nanostructures and form longer and denser nanowires. Our research team was able to achieve enhanced nanowire growth while using Ag as a catalyst due to its superior oxygen diffusion capability compared to other catalysts at higher temperatures. The oxygen diffusion coefficient of silver nanoparticles is much higher than Au [12], making Ag the best catalyst for enhancing the growth density and length of Ga₂O₃ nanowires. Although the diffusivity of oxygen molecules in Au nanoparticles is higher than in Ag nanoparticles, the oxygen molecule concentration in silver nanoparticles is higher than in gold nanoparticles [12]. This is due to the transformation of interstitial sites of oxygen molecules into O-Ag oxide, reducing the possibility of oxygen diffusion in silver nanoparticles, reducing the diffusion of oxygen, whereas gold nanoparticles are not easily transformed into O-Au oxide, allowing for higher oxygen diffusion in Au. Additionally, as the metal nanoparticle concentration increased, higher-density and longer Ga₂O₃ nanowires were formed (Figure 11). This can be primarily attributed to the increased availability of oxygen due to the presence of more metal nanoparticles.

The growth of β-Ga₂O₃ nanostructures using Ag and Au catalysts exhibits distinct differences. Ag nanoparticles promote the formation of denser and longer nanowires, while Au nanoparticles favor nanosheet-like structures (Figure 10 and Figure 11). This is attributed to Ag’s higher oxygen solubility and diffusion coefficient compared to Au [12], leading to enhanced nucleation and growth of β-Ga₂O₃ nanowires. XRD analysis (Figure 2) confirms that Ag-catalyzed samples exhibit sharper diffraction peaks, indicating superior crystal quality. Additionally, Ag’s lower activation energy for surface diffusion (0.39 eV compared to 0.99 eV for Au [31]) facilitates more uniform nanoparticle distribution, improving growth uniformity and ease of control. Therefore, Ag is the preferred catalyst for achieving high-quality, uniform β-Ga₂O₃ nanowires.

3.5. Elemental Composition of Ga₂O₃ by EDS Analysis

Energy Dispersive Spectroscopy (EDS) was used to perform elemental and chemical microanalysis on the samples. Figure 12 presents the FESEM-EDX spectra of Ga₂O₃ nanostructures grown on sapphire substrates at 800 °C and 900 °C, with and without Au or Ag catalysts, corresponding to the elemental compositions listed in

Table 1. The elemental composition of Ga₂O₃ nanostructures grown on sapphire substrates at 800 °C or 900 °C. (a) without a catalyst; (b) with Au or Ag catalyst.

Temperatures	800 °C					900 °C
(a)
Elemental compositions (at. %)	Ga		O		Ga			O
No catalyst	32.9		67.1		36.6			63.4
(b)
Elemental Composition (at. %)	Ga	O	Ag/Au		Ga		O	Ag/Au
1.03 g Ga and 10 mg Au	74.2	25.4	0.4		56.3		43.7	0.0
1.5 g Ga and 10 mg Ag u	77.3	22.7	0.0		55.0		44.8	0.2
1.03 g Ga and 10 mg Au	73.2	24.9	1.9		54.4		44.3	1.3
1.5 g Ga and 10 mg Ag	78.1	21.7	0.2		65.8		33.0	1.1

. The spectra confirm higher oxygen concentrations at elevated temperatures and in the presence of catalysts, consistent with increased oxygen solubility in liquid gallium and metal nanoparticles [16,24,25].

Compared to previous studies [36,37,38], we were able to create longer and denser Ga₂O₃ nanowires (

Table 2. The average diameter, length and morphology of the nanowires were measured for 10 samples and the results were compared with those reported in the literature based on the different catalysts, techniques and substrates used.

Catalyst		Technique	Substrate	Average Nanostructures
				Diameter	Length
Experimental Results (this work)
Au		Oxidation	Sapphire	2–4 µm	15–25 µm
Ag				0.5–1.0 µm	>20 µm
NPs	Ref.	Reported Results
Free-Catalyst	[38]	CVD	Ga/Ga2O3 mixture and O2	40–70 nm	10–20 µm
	[37]		Si/SiO2 & Al2O3	50-75 nm	>10 µm
Ag NPs	[26]	Sol-gel and VLS	GaAs	18 to 30 nm	several 10s of nm to a few 100 µm
Au NPs	[39]	Thermal-VLS	Au pre-treated on Si	34 nm	20 to 60 nm

). A careful analysis of the length and morphology of Ga₂O₃ nanowires grown using Au and Ag catalysts revealed that only Ag nanoparticles formed longer nanowires.

Interestingly, the percentage of oxygen absorption is much higher in both catalysts. However, the morphology of Ga₂O₃ has exposed major differences in the growth shape and direction of Ga₂O₃. Ag NP catalysts form denser and longer distribution of Ga₂O₃ nanowires only. However, Au NP catalysts forms denser nanowires and nanoflakes as well. Consequently, the presence of Ag NPs shows a better growth process rather than the Au NP catalyst in terms of growth uniformity and ease of control.

More investigation is required to evaluate the unintentional residual impurities of Ga₂O₃ nanowires with catalyst Au and Ag during their growth process. The influence of these impurities on device performance also requires further study. Some procedural challenges for the growth of Ga₂O₃ nanostructures also need to be explained. For instance, more directional Ga₂O₃ nanowire growth is highly desirable and the nanowires should also be more uniform in size and length. Finally, techniques to pattern and etch the Ga₂O₃ nanowires would be highly valuable.

A STEM image of a bright field (BF) and high-angle annular dark-field (HAADF) of a Ga₂O₃ nanowire grown at 1000 °C on uncoated quartz and on coated with 5 nm Ag thin film [9]. The bright field showed dark crystalline NPs due to diffraction contrast. Meanwhile, HAADF showed much brighter nanoparticles due to the z-contrast, suggesting that the presence of significant larger atomic mass and density than the adjacent β-Ga₂O₃, which points to Ag NPs. These Ag nanoparticles assist to synthesize β-Ga₂O₃ nanowires during the growth process and will be remain within the crystal lattice, exposing their size in the range of 1–5 nm [9] and it will be difficult to remove them.

Residual Ag and Au nanoparticles, ranging from 1–5 nm, are incorporated into the β-Ga₂O₃ nanowire lattice, as observed in STEM images. These impurities can enhance morphological, electrical and optical properties, such as bandgap and photoconductance, due to their catalytic role [9]. However, they may also introduce defects that could impact device performance, necessitating further investigation to quantify their concentration and effects. Techniques such as selective chemical etching or post-annealing in an inert atmosphere could be explored to minimize residual catalysts and improve nanowire purity.

4. Conclusions

Ga₂O₃ nanostructures grown on sapphire substrates using different catalysts (Au or Ag nanoparticles) were studied using X-ray diffraction analysis and FESEM-EDS to understand the growth mechanism, kinetics, and morphology of the nanostructures. The influence of different factors such as temperature, nature of the catalyst and concentration of the catalyst and Ga on the growth of Ga₂O₃ nanostructures were also studied using FESEM. The FESEM analysis showed the formation of more nucleation of Ga₂O₃ nanostructures at 800 °C, whereas much denser and longer nanowires and nanosheets were formed at 900 °C. The XRD results of the grown Ga₂O₃ on sapphire substrate show three sharp diffraction peaks located at 19.31°, 38.70° and 59.38° corresponding to $\left(\overline{2}01\right), \left(\overline{4}02\right)$ and $\left(\overline{6}03\right)$ planes of β-Ga₂O₃ (JCPDS No. 43-1012). A high atomic percentage of oxygen in Ga₂O₃ nanostructures grown on sapphire surfaces was detected by EDS in samples exposed to high temperatures. This is due to the increased oxygen solubility in liquid gallium and metal nanoparticles, as well as the effects of self-diffusion. Using silver and gold as catalysts, we obtained β-Ga₂O₃ nanowires thinner than those grown with other catalysts, such as Ni [37], Pt [40] or Fe [41], demonstrating the superior control over nanowire morphology offered by Ag and Au nanoparticles. Ag nanoparticles, as a catalyst for Ga₂O₃ nanowire growth, lead to denser nanowires, while Au nanoparticles result in more nanosheet-like structures of Ga₂O₃. With these morphology and structural characteristics, the proposed technique shows great potential for applications in optoelectronic devices, sensors and high-power electronics.