Effect of a SiO₂ anti-reflection layer on the optoelectronic properties of Germanium metal-semiconductor-metal photodetectors

The interdigitated germanium (Ge) metalsemiconductor-metal (MSM) photodetectors (PDs) with and without an SiO₂ anti-reflection (AR) layer was fabricated, and the effect of SiO₂ AR layer on their optoelectronic response properties were investigated in detail. The lowest reflectance of 15.6% at the wavelength of 1550 nm was obtained with a SiO₂ AR layer with a thickness of 260 nm, which was in a good agreement with theoretically calculated film thickness for minimizing the reflection of Ge surface. The Ge MSM PD with 260 nm-thick SiO2 AR layer exhibited enhanced device performance with the maximum values of responsivity of 0.65 A/W, the quantum efficiency of 52.2%, and the detectivity of 2.49 × 10⁹cm Hz^0.5W^-1under the light illumination with a wavelength of 1550 nm. Moreover, time-dependent switching analysis of Ge MSM PD with 260 nm-thick SiO₂ AR layer showed highest on/off ratio with excellent stability and reproducibility. All this investigation implies that 260 nm-thick SiO₂ AR layer, which is effective in the reduction in the reflection of Ge surface, has a great potential for Ge based optoelectronic devices.