【International Papers】Electrical and thermal characterisation of liquid metal thin-film Ga₂O₃–SiO₂ heterostructures

      Researchers from the HH Wills Physics Laboratory at University of Bristol have published a dissertation titled " Electrical and thermal characterisation of liquid metal thin-film Ga₂O₃–SiO₂ heterostructures " in IEEE Transactions on Electron Devices.

Abstract

      Heterostructures of Ga₂O₃ with other materials such as Si, SiC or diamond, are a possible way of addressing the low thermal conductivity and lack of p-type doping of Ga₂O₃ for device applications, as well as of improving device reliability. In this work we study the electrical and thermal properties of Ga₂O₃–SiO₂ heterostructures. Here, thin-film gallium oxide with thickness ranging between 8 and 30 nm was deposited onto a silicon substrate with a thermal oxide by means of oxidised liquid gallium layer delamination. The resulting heterostructure is then characterised by means of X-ray photoelectron spectroscopy and transient thermoreflectance. The thin-film gallium oxide valence band offset with respect to the SiO₂ is measured as 0.1 eV and predicted as -2.3 eV with respect to diamond. The thin-film’s out-of-plane thermal conductivity is determined to be 3 ±0.5 Wm^-1K^-1, which is higher than what has been previously measured for other polycrystalline Ga₂O₃ films of comparable thickness.

FIG. (a) Schematic of the exfoliation method - a liquid gallium droplet is isolated and its passivation oxide is directly transferred onto a substrate. (b) Microscope image of the Ga\(_2\)O\(_3\) film deposited on thermally oxidised Si substrate after annealing at 250\(^{\circ }\)C for 1 hour. (c) Atomic Force Microscopy linescans taken across thin-film oxide to substrate edges in two different areas.

FIG. XPS energy spectra recorded from the (a) SiO₂ and Ga₂O₃ film on SiO₂; a zoom into the valence band region for the SiO₂ is shown separately in (b), where the intersect of dashed lines is used to identify the valence band maximum (VBM); (c) shows a diagram of the band alignment of the Ga₂O₃ film to the SiO₂ and extended to other materials. A band gap of 4.9 eV is assumed for our Ga₂O₃ film to determine conduction band offsets.

Paper Link：https://www.nature.com/articles/s41598-023-30638-4/figures/2