Graphene/Al₂O₃/Si Schottky diode with integrated waveguide on a silicon-on-insulator wafer

Waveguide-integrated graphene photodiodes are on-chip optoelectronic devices with promising applications in telecommunications. Here, we present the electrical properties of a heterostructure consisting of multilayer graphene (MLGr) over a Si waveguide covered by an ultrathin Al₂O₃ layer. The waveguide is fabricated by etching a silicon-on-insulator (SOI) substrate with 220 nm Si and 1.5 μm buried oxide. The 5 nm-thick Al₂O₃ film is deposited by atomic layer deposition (ALD), while graphene, synthesized on copper by chemical vapor deposition (CVD), is transferred onto the Al₂O₃/Si rib by a wet transfer method. The MLGr/Al₂O₃/Si rib forms a Schottky structure with rectifying current–voltage characteristics, which are examined using the thermionic emission theory and Norde’s method. A Schottky barrier height \({\Phi }_{{\text{B}}} = 0.79\mathrm{ eV}\) ${\mathrm{\Phi }}_{\text{B}}=0.79\mathrm{eV}$ , an ideality factor n = 26, and a series resistance \({{\text{R}}}_{{\text{S}}} = 11.6\mathrm{ M\Omega }\) ${\text{R}}_{\text{S}}=11.6\mathrm{M}\mathrm{\Omega }$ are obtained. The device is promising for operation at the optical fiber communication wavelength of 1550 nm.