【Member Papers】Laser-assisted in situ fabrication of atomically thin Ga₂O₃ films for dielectric applications

      Researchers from the Nanjing Tech University and Southern University of Science and Technology have published a dissertation titled " Laser-assisted in situ fabrication of atomically thin Ga₂O₃ films for dielectric applications" in FlexMat.

Background

      Two‐dimensional (2D) gallium oxide (Ga₂O₃) has emerged as a high‐κ dielectric material for optoelectronic applications due to its ultra‐wide bandgap and large‐scale productivity. However, the usage of thermal treatment during the liquid‐metal‐assisted fabrication process could degrade the quality of channel materials. Conventional fabrication methods for 2D Ga₂O₃, such as solution‐based synthesis, chemical vapor deposition (CVD), and physical vapor deposition (PVD), face significant challenges. Solution‐based approaches require high‐temperature annealing, vapor deposition techniques rely on hazardous chemical precursors or vacuum processing, and liquid metal‐based techniques still necessitate a thermal annealing process, introducing imperfections in oxygen‐sensitive materials.

Abstract

      Two‐dimensional (2D) gallium oxide (Ga₂O₃) has emerged as a high‐κ dielectric material for optoelectronic applications due to its ultra‐wide bandgap and large‐scale productivity. However, the usage of thermal treatment during the liquid‐metal‐assisted fabrication process could degrade the quality of channel materials. Here, we report a laser‐assisted in situ oxidation method combined with a confinement template‐assisted squeeze technique to fabricate centimeter‐scale 2D atomically thin Ga₂O₃ films from liquid gallium metal surfaces at room temperature. This approach avoids thermal damage to vulnerable materials. The laser‐accelerated oxidation mechanism is elucidated as photocatalytic oxidation of initial Ga/Ga₂O₃₋ₓ surface through the integration of multi‐wavelength laser radiation experiments and density functional theory calculations. We further demonstrate top‐gated field‐effect transistors (FETs) using black phosphorus (BP) and MoS₂ as channel materials, with thin‐film Ga₂O₃ as the gate dielectrics. BP‐based FETs show gate‐ tunable mid‐infrared photoresponse with responsivity at the order of 0.1 A·W⁻¹ level. MoS₂‐based FETs exhibit a photo‐detectivity of 6.8 ×10¹² Jones in the visible‐light spectrum, an on/off ratio over 10⁸, a subthreshold swing of 73.6 mV decade⁻¹, and gate leakage currents below 4 ×10⁻⁶ A cm⁻² at 8 MV cm⁻¹. This room‐temperature laser‐oxidation approach enables scalable integration of ultrathin oxide dielectrics with sensitive 2D materials for next‐generation nanoelectronics.

Highlights

      A laser-assisted in situ oxidation method combined with a confinement template-assisted squeeze technique is developed to fabricate centimeter-scale atomically thin Ga₂O₃ films at room temperature, avoiding thermal damage to thermally vulnerable 2D materials.

      The laser-accelerated oxidation mechanism is elucidated as the photocatalytic oxidation of the non-stoichiometric Ga/Ga₂O₃₋ₓ surface, with shorter-wavelength laser irradiation showing higher oxidation efficiency.

      The as-prepared Ga₂O₃ films serve as high-performance gate dielectrics and encapsulation layers for air-sensitive 2D materials like black phosphorus (BP).

      Top-gated MoS₂ FETs with the Ga₂O₃ dielectric exhibit an on/off ratio over 10⁸, a subthreshold swing of 73.6 mV decade⁻¹, a detectivity up to 6.8 ×10¹² Jones, and ultralow gate leakage currents below 4 ×10⁻⁶ A cm⁻² at 8 MV cm⁻¹.

Conclusion

      This study presents a laser‐assisted in situ oxidation method, combined with a confinement template‐assisted squeeze technique, to fabricate atomically thin Ga₂O₃ films for dielectric applications. This approach addresses the limitations of conventional thermal annealing, which can cause thermal damage to sensitive materials, enabling the production of centimeter‐scale and high‐quality Ga₂O₃ films. The changes in optical contrast and electrical resistance upon laser irradiation demonstrate that laser irradiation significantly accelerates the oxidation process. The first‐principles calculations reveal the critical role of laser‐induced non‐equilibrium free carriers in enhancing oxidation kinetics. The resulting Ga₂O₃ films were successfully employed as dielectric layers in phototransistors with BP and MoS₂ as channel materials. BP‐based phototransistors exhibit gate‐tunable photoresponse in the mid‐infrared range with a room‐temperature responsivity at order of 0.1 A·W⁻¹ level. MoS₂‐based FETs demonstrate a detectivity of 6.8 ×10¹² Jones in the visible spectrum, an on/off ratio of 10⁸, a SS of 73.6 mV decade⁻¹, and gate leakage currents below 4 ×10⁻⁶ A cm⁻² at 8 MV cm⁻¹. These results indicate good compatibility of the laser‐assisted in situ oxidation method with thermally sensitive materials and highlight the potential of this method to advance electronic and optoelectronic device applications.

Project Support

      National Natural Science Foundation of China, Grant/Award Numbers: 62275117, 62374079, 62304097, 92477123, 52373290, 62288102, U25A20484; Shenzhen Excellent Youth Program, Grant/Award Number: RCYX20221008092900001; The Pearl River Talent Recruitment Program, Grant/Award Number: 2019QN01C177; Guangdong Basic and Applied Basic Research Foundation, Grant/Award Number: 2024A1515030224; Shenzhen Fundamental Research Program, Grant/Award Number: JCYJ20240813094508011