Abstract

In this study, we proposed germanium (Ge) metal–interlayer–semiconductor–metal (MISM) photodiodes (PD), with an anode of a metal–interlayer–semiconductor (MIS) contact and a cathode of a metal–semiconductor (MS) contact, to efficiently suppress the dark current of Ge PD. We selected titanium dioxide (${\mathrm{TiO}}_2$) as an interlayer material for the MIS contact, due to its large valence band offset and negative conduction band offset to Ge. We significantly suppress the dark current of Ge PD by introducing the MISM structure with a ${\mathrm{TiO}}_2$ interlayer, as this enhances the hole Schottky barrier height, and thus acts as a large barrier for holes. In addition, it collects photo-generated carriers without degradation, due to its negative conduction band offset to Ge. This reduces the dark current of Ge MISM PDs by $\times 8000$ for 7-nm-thick ${\mathrm{TiO}}_2$ interlayer, while its photo current is still comparable to that of Ge metal–semiconductor–metal (MSM) PDs. Furthermore, the proposed Ge PD shows $\times 6,600$ improvement of the normalized photo-to-dark-current ratio (NPDR) at a wavelength of 1.55 μm. The proposed Ge MISM PD shows considerable promise for low power and high sensitivity Ge-based optoelectronic applications.

© 2016 Optical Society of America

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