【International Papers】Engineering shallow and deep level defects in κ-Ga₂O₃ thin films: comparing metal-organic vapour phase epitaxy to molecular beam epitaxy and the effect of annealing treatments

      Researchers from the University of Parma have published a dissertation titled "Engineering shallow and deep level defects in κ-Ga₂O₃ thin films: comparing metal-organic vapour phase epitaxy to molecular beam epitaxy and the effect of annealing treatments" in Materials Today Physics.

Abstract

      Orthorhombic gallium oxide (κ-Ga₂O₃) is an ultra-wide bandgap semiconductor with great potential in new generation electronics. Its application is hindered at present by the limited physical understanding of the relationship between synthesis and functional properties. This work discusses the effects of growth method (metal-organic vapour phase epitaxy and molecular beam epitaxy) as well as annealing treatments in different atmospheres (O₂, H₂) on point defects in κ-Ga₂O₃ layers epitaxially grown on c-plane sapphire. Comprehensive experimental characterization by X-ray diffraction, photo current-as well as photoluminescence excitation spectroscopy, and X-ray photo electron spectroscopy is combined with first principles calculations of the point defects’ formation and complex-dissociation energies. We demonstrate that for κ-Ga₂O₃ the concentration of shallow and deep level defects can be sensitively controlled through annealing treatments at temperatures (T = 500 °C) well below the thermal stability threshold of this polymorph. In particular, our results suggest that hydrogen-related defects (e.g., H-interstitials, Ga-vacancies—H complexes) play a key role in this process. While we provide direct exemplary implications of our results for the performances of κ-Ga₂O₃ based photodetectors, these findings are predicted to impact further application fields of κ-Ga₂O₃, such as high electron mobility transistors or memory devices.

Fig. 1. Symmetric out-of-plane (a) 2θ-ω (not normalized, logarithmic scale) and (b) ω (normalized, linear scale) XRD scans of the as deposited MOVPE and MBE κ-Ga₂O₃ as-deposited layers (red and black curves, respectively) on c-plane sapphire. In (a) for the MBE layer, “nl” stands for a 20 nm thick epitaxial β-Ga₂O₃ nucleation layer [(-402) reflection]. Measurements performed with monochromatic Cu Kα₁ radiation.

Fig. 2. Photodetector responsivity (i.e., electrical response at different wavelengths normalized by incident power) of (a) MOVPE and (b) MBE deposited κ-Ga₂O₃ layers as-deposited, O₂- and H₂-annealed (black, blue, and red curves, respectively). The respective dark currents measured at 200 V bias are reported in the insets. The yellow region in (a) highlights the significant drop of responsivity in the 300–600 nm range for the O₂-annealed material with respect to the PD fabricated with the MOVPE as-deposited material.

Original link:https://doi.org/10.1016/j.mtphys.2024.101463