Transferred Graphene Monolayer to β-Ga₂O₃ as a Diffusion Barrier for Based Power Device Applications

The quality of the metal contact of devices can be significantly improved through high-temperature annealing, which enhances the crystal structure and reduces contamination. However, high-temperature annealing can adversely deteriorate the metal/semiconductor interface, resulting in the oxidation of the metal by the interdiffusion of oxygen atoms. Here, we explored the oxidation of the tungsten (W) contact interface on the β-Ga₂O₃ epitaxial layer after high-temperature annealing, causing the electrical instability of W/β-Ga₂O₃ Schottky barrier diodes (SBDs). To address the challenge posed by the trade-off between the improvement of the tungsten's crystalline structure and the oxidation of the tungsten surface after annealing, we proposed to exfoliate and transfer graphene to β-Ga₂O₃ utilizing a layer-resolved graphene transfer (LRGT) technique as an oxygen diffusion barrier for the surface of β-Ga₂O₃. The insertion of a graphene monolayer has exhibited a clean and abrupt W/β-Ga₂O₃ interface without oxygen intermixing. This resulted in a stable leakage current for β-Ga₂O₃ SBD, approximately 4.34 × 10^-5 A/cm², 2.97 × 10^-5 A/cm², and 2.55 × 10^-5 A/cm² for as-deposited, 400 °C-annealed, and 600 °C-annealed devices, respectively. Additionally, a consistent Schottky barrier height of approximately 0.80 eV and an ideality factor of 2 were maintained across all devices. Notably, the breakdown voltage remained stable at approximately -200 V, which is relatively low compared to other reported β-Ga₂O₃ devices. However, the key achievement of our work is the minimal dependence of the device's performance on annealing temperature, a result directly attributed to the incorporation of the graphene monolayer. This highlights the primary objective of using graphene: to enhance the thermal stability of β-Ga₂O₃-based devices, facilitating more reliable performance in high-temperature environments. Furthermore, the insertion of a graphene monolayer resulted in heightened thermal stability, allowing devices to operate reliably up to a temperature of 150 °C, with stable Schottky barrier height and ideality factor in stark contrast to their counterparts without the graphene Schottky barrier diode. Utilizing SILVACO TCAD simulations, we observed a crucial role played by the graphene monolayer in significantly improving heat dissipation in β-Ga₂O₃ Schottky barrier diodes. These unchanging device parameters, subsequent to the insertion of a graphene monolayer, provide a compelling explanation for the role of the graphene monolayer as an effective diffusion barrier material for β-Ga₂O₃ for improving its application in high-power devices.