• Hf-doped β-Ga 2 O 3 thin films deposited by co-sputtering with tunable properties. • Low Hf doping enables substitutional incorporation with reduced bandgap. • High Hf doping triggers phase separation with a widened bandgap. • Hf doping increases upward band bending and expands depletion width. • High-doping films function as Ga-doped HfO 2 with reduced bandgap and band bending. The impact of hafnium (Hf) incorporation on the structural, chemical, and electronic properties of β-Ga 2 O 3 thin films was investigated. Hf-Ga 2 O 3 thin films were prepared by the co-sputtering technique with Hf concentrations ranging from 0 to 17 atomic percent (at.%). Grazing incidence X-ray diffraction analysis revealed a composition-dependent phase transition. At low Hf concentrations (0–4.5 at.%), substitutional incorporation disrupted the β-Ga 2 O 3 lattice and reduced crystallinity. Whereas high Hf concentrations (9–17 at.%) induced phase separation, yielding crystalline m-HfO 2 –β-Ga 2 O 3 nanocomposites. Optical spectroscopy showed bandgap narrowing from 4.62 to 4.30 eV at low doping levels due to impurity band formation, followed by widening to 5.07 eV at higher Hf content. X-ray photoelectron spectroscopy confirmed Hf incorporation within the oxide structure and revealed upward band bending (1.35–2.89 eV) with a depletion layer width of 38–56 nm. Heavily doped films may alternatively be interpreted as Ga-doped m-HfO 2 , where Ga reduces the bandgap and upward band bending relative to pure m-HfO 2 . This dual perspective underscores the potential of the Hf-Ga 2 O 3 system for tailoring surface electronic properties in advanced device applications.
Ghaithi et al. (Fri,) studied this question.