【Domestic Papers】Research from the South China University of Technology about Ohmic Contact Formation to β-Ga₂O₃ Nanosheet Transistors with Ar-Containing Plasma Treatment

      Researchers from the  South China University of Technology have published a dissertation titled "Ohmic Contact Formation to β-Ga₂O₃ Nanosheet Transistors with Ar-Containing Plasma Treatment" in Electronics.

Abstract

      Effective Ohmic contact between metals and their conductive channels is a crucial step in developing high-performance Ga₂O₃-based transistors. Distinct from bulk materials, excess thermal energy of the annealing process can destroy the low-dimensional material itself. Given the thermal budget concern, a feasible and moderate solution (i.e., Ar-containing plasma treatment) is proposed to achieve effective Ohmic junctions with (100) β-Ga₂O₃ nanosheets. The impact of four kinds of plasma treatments (i.e., gas mixtures SF₆/Ar, SF₆/O₂/Ar, SF₆/O₂, and Ar) on (100) β-Ga₂O₃ crystals is comparatively studied by X-ray photoemission spectroscopy for the first time. With the optimal plasma pre-treatment (i.e., Ar plasma, 100 W, 60 s), the resulting β-Ga₂O₃ nanosheet field-effect transistors (FETs) show effective Ohmic contact (i.e., contact resistance R_C of 104 Ω·mm) without any post-annealing, which leads to competitive device performance such as a high current on/off ratio (>10⁷), a low subthreshold swing (SS, 249 mV/dec), and acceptable field-effect mobility (μ_eff, ~21.73 cm² V⁻¹ s⁻¹). By using heavily doped β-Ga₂O₃ crystals (N_e， ~10²⁰ cm⁻³) for Ar plasma treatments, the contact resistance R_C can be further decreased to 5.2 Ω·mm. This work opens up new opportunities to enhance the Ohmic contact performance of low-dimensional Ga₂O₃-based transistors and can further benefit other oxide-based nanodevices.

Figure 1. XPS results for the (100)-oriented β-Ga₂O₃ bulk samples. (a) Ga 2p_3/2, (b) Ga 3d, and (c) O 1s core-level spectra from the pristine β-Ga₂O₃ without any plasma treatments. (d) Ga 2p_3/2, (e) Ga 3d, and (f) O 1s core-level spectra from the β-Ga₂O₃ treated with SF₆/Ar plasmas.

Figure 2. (a) Schematic view of the bottom-gated β-Ga₂O₃ nanosheet transistor with a 110 nm thick SiO₂ gate insulator. (b) Optical microscopy image of a prepared β-Ga₂O₃ nanosheet-based FET. (c) Thickness profile and optical micrograph from the peeled β-Ga₂O₃ nanosheet as acquired by AFM. (d) I–V characteristics at a low V_ds regime for this β-Ga₂O₃ nanosheet FET. (e) Output curves (I_ds-V_ds) from the β-Ga₂O₃ nanosheet FET. (f) Transfer characteristics (I_ds-V_bg) obtained from the β-Ga₂O₃ nanosheet transistor.

DOI：

doi.org/10.3390/electronics13163181