Design and analysis of Si–Ag–graphene–HfO₂ heterojunction based ultraviolet photodetector

This study reports on Si–Ag–Graphene ultraviolet (UV) photodetector (PD) design under zero bias while analyzing the role of varying thicknesses of antireflection HfO₂ layers. The performance of the proposed PD is analyzed using the FDTD (finite difference time domain) solver, while considering the condition of normal incidence of radiation. The simulation findings reveal that for Si–Ag–Graphene PD design, a coating of 10 nm-thick HfO₂ layer is beneficial to attain higher magnitudes of quantum efficiency (ƞ) and responsivity (ρ). The Si–Ag–Graphene–HfO₂ (10 nm) PD design exhibits a maximum magnitude of ƞ = 0.63 and ρ = 0.15 A/W at an operating wavelength (λ₀) of 294.7 nm. Additionally, at λ₀ = 294.7, the device shows an impressive UV-to-visible rejection ratio (ρ₂₉₄/ρ₅₅₀) of 36.58.Also, this PD design, around λ₀ ~ 232 nm, shows a maximum photocurrent (I_p) of 3.5 mA. Further, the electrical performance of the Si–Ag–Graphene–HfO₂ (10 nm) PD design is analyzed to evaluate the dark current (I_d), detectivity (D*), and minimum detectable power (P_d) for the possible practical implementation of the proposed PD structure. With an applied bias of -1.5 V to 1.5 V, the Si–Ag–Graphene–HfO₂ (10 nm) PD design exhibits an I_d of 7.09 × 10⁻²¹A, D* of 0.94 × 10¹² Jones, and P_d value of 4.73 × 10^–20 W at 0V. This Si-Ag–Graphene–HfO₂ (10 nm) PD design possesses exceptionally large magnitudes of absorbance with superior ρ and D* compared to the current state-of-the-art. The proposed DUV PD can find applications in various high-end fields such as microelectronics and solar missions etc.