High-Performance Lateral Metal-Germanium-Metal SWIR Photodetectors Using a-Si:H Interlayer for Dark Current Reduction

In this work, we propose the lateral metal-germanium-metal photodetectors (PDs) structure on the silicon-on-insulator platform for short-wave infrared (SWIR) applications. The proposed device utilizes the highly n-doped amorphous silicon (a-Si:H) interlayer between metallic contact and low n-doped germanium active region to achieve a low dark current. Additionally, the tuning of Schottky barrier height (SBH) by the selection of various metallic contacts (Cr/W/Mo) has been investigated in order to achieve a large reduction in dark current. With a-Si:H interlayer and Mo metallic contacts at both anode and cathode terminals, the simulated energy band diagram shows that an effective increase in SBH of 0.17 eV and 0.766 eV for electrons and holes, respectively, and thus acts as barriers for electron and hole dark currents. The result shows that the Mo metallic contact device manifests the least dark current (dark current density) of 0.27 pA (0.027 mA/cm²) at V_bias of 0.25 V and compared to Cr contact, it has been significantly decreased by two orders of magnitude. In addition, with Mo contact, the proposed device achieves the photogenerated-to-dark current $( {{I}_{ph}/{I}_{dark}} )$ ratio and the responsivity of $\sim 1.7 \times {10}^6$ and 0.96 A/W, respectively at λ = 1.55 μm with V_bias of 0.25 V. Furthermore, the proposed Mo-Ge-Mo PD shows high detectivity (NEP) of $9 \times {10}^{11}$ cmHz^1/2W⁻¹ ($\sim 3 \times {10}^{ - 16}$WHz^−0.5), which is nearly 15 (one order lower) times higher than those of Cr-Ge-Cr PD. The results hold great potential for optoelectronic applications requiring low-power Ge-based PD.