Impact of the Incorporation of In and Cu Dopants into β-Ga₂O₃ Nanostructures for Resistive Switching Applications

The ultra-wide bandgap semiconductor beta gallium oxide (β-Ga₂O₃) has become a potential candidate for power electronics, ultraviolet optoelectronics, high-temperature gas sensors, and memristors. β-Ga₂O₃ exhibits outstanding properties, including a bandgap of 4.5–4.9 eV, a high critical electric field of around 8 MV/cm, a high Baliga's figure of merit (BFoM), and good stability at elevated temperatures. Doping and transitioning from bulk single crystal to micro- and nano-crystallite promotes the unique features of β-Ga₂O₃, resulting from larger surface-to-volume ratios, fewer defects, and reduced strain. This study investigates the impact of the incorporation of indium (In) and copper (Cu) with the precursor material during the synthesis process on the structural, morphological, and optical properties of the β-Ga₂O₃ nanostructures (NS) obtained by the conventional CVD method. The β-Ga₂O₃ NS were grown on a (100) p-type silicon substrate inside a quartz tube furnace at 900 °C for 2 h with an argon flow of 30 SCCM. Ga was used as a precursor material mixed with different ratios of In or Cu (1:0, 3:1, 2:1). Various characterization techniques were used in this investigation, including grazing-incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and UV-visible- NIR spectrophotometry. GIXRD scans showed that all NS exhibit the β-Ga₂O₃ phase with the monoclinic crystal structure (space group C2/m) and dominant orientation along the (111) plane. No additional peaks of other Ga₂O₃ polymorphs were detected, and the strong diffraction peaks indicate the high crystalline quality of the β-Ga₂O₃ NS. SEM images demonstrated that pure Ga formed short β-Ga₂O₃ nanorods of diameter varies from 400 nm up to 800 nm and length between 600 nm and 1 µm. Although the diameter remained the same, the nanorods became considerably longer, reaching a length of about 1 µm – 5 µm, when Ga was combined with In or Cu with a small amount. β-Ga₂O₃nanorods transitioned into nanoplates and nanosheets at a further increase in the In and Cu concentrations. EDS analysis revealed the presence of Ga and O and a small amount of In and Cu traces. All β-Ga₂O₃ NS has exceptional transparency in the visible and ultraviolet wavelength ranges, with an optical bandgap of 4.56 eV, which was slightly reduced to 4.50 eV as the concentration of In and Cu increased. The current-voltage characteristics of the NS demonstrated promising resistive switching characteristics, which included bipolar resistive switching, a low operation voltage, and strong repeatability and retention.