Structure, surface/interface chemistry and optical properties of W-incorporated β-Ga2O3 films made by pulsed laser deposition

Abstract

Gallium oxide (Ga₂O₃), which is one among the ultra-wide band gap materials, is promising for the next generation of electronic and optoelectronic devices due to its fascinating material properties for utilization in extreme environments. In this work, Ga₂O₃ films containing refractory tungsten (W) (GWO or Ga–W–O) were fabricated via pulsed laser deposition (PLD) by varying the oxygen partial pressure (pO₂), which is the most important thermodynamic parameter that governs the growth, structure and properties of the resulting multi-component oxide films. The effect of variable pO₂ on the structure, surface chemistry, chemical bonding, optical properties and photodetector device performance of the resulting Ga–W–O films was studied using X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, UV-vis spectroscopy, and photoluminescence spectroscopy measurements. The films containing Ga₂O₃ combined with W exhibited no secondary phase development. The impact of W on the chemical and optical characteristics of Ga₂O₃ films was found to be substantial. W⁵⁺ formation is prevalent when the adatom mobility is high at lower working pressure, whereas lower migration energy favors W⁶⁺ at higher working pressure. In contrast, the valance band maxima (VBM) of the films have a minor shift to higher energies with increasing pO₂, confirming the dominance of O 2p states on VBM in PLD GWO films. Additionally, there is not much change in the optical band gap, but it shows a slight blue shift of the luminescence peak, directing a selective W incorporation into the Ga₂O₃ matrix. The processing conditions were optimized to demonstrate the excellent performance UV-photodetectors based on PLD GWO films. The structure–property correlation established will be useful in the production of W-alloyed β-Ga₂O₃ films with superior structural and optical properties for integration into optoelectronic and photonic device applications.