Surface Leakage Reduction in MSM InGaAs Photodetector on III–V CMOS Photonics Platform

By evaluating the leakage current components of Ni/InGaAs Schottky junctions, we have revealed that the surface leakage current was dominant in the dark current of the waveguide metal-semiconductor-metal (MSM) InGaAs photodetector (PD) fabricated on the III-V CMOS photonics platform. To suppress the surface leakage, we have investigated the impact of the InAlAs Schottky barrier enhancement (SBE) layer on the surface leakage. It is found that the surface leakage can be significantly reduced by the surface passivation effect of the InAlAs SBE layer in addition to the reduction in the junction bulk leakage. We have also found that the surface passivation by an improper oxide such as Al₂O₃ on the SBE layer increased the dark current probably due to the fixed charges in the oxide layer. By introducing the InP/InAlAs SBE layer without any oxide passivation, we have successfully demonstrated the low-darkcurrent MSM InGaAs PD which was monolithically integrated with an InP photonic-wire waveguide fabricated on a III-V-on-insulator wafer. When a bias voltage of 1 V was applied, the dark current of 7 nA was obtained with 0.15 A/W responsivity for a 1550-nm wavelength.