Sub-mA/cm2 Dark Current Density, Buffer-Less Germanium (Ge) Photodiodes on a 200-mm Ge-on-Insulator Substrate

In recent years, Germanium (Ge) photodiodes have established a widespread utilization in photonic-integrated circuits (PICs). However, the devices commonly exhibit a prominent dark current due to the substantial defects at the Ge/Si heteroepitaxial interface. Herein, we demonstrate normal-incidence, buffer-less Ge vertical p-i-n photodiodes with remarkably low dark current density (J(dark), 0.78mA/cm(2) at -1 V), on a high-quality 200-mm Ge-on-insulator (GOI) substrate. The high- quality GOI was achieved by the removal of the highly dislocated Ge/Si interfacial region, sequentially via wafer bonding, layer transfer, and oxygen (O-2) furnace annealing. Compared to un-annealed GOI, the threading dislocation density (TDD) in Ge was reduced by more than two orders of magnitude to 1.2 x 10(6) cm(-2). Correspondingly, the device Jdark and bulk leakage (J(bulk)) were reduced by similar to 70x and similar to 145x. On the other hand, the photodiodes present a reasonable responsivityof 0.29A/W at 1,550nm and a nearly 100% internal quantum efficiency without external bias. The specific detectivity (D*, 2.17 x 10(10) cm center dot Hz(1/2) center dot W-1 at 1,550 nm and -0.1 V) is comparable with that of commercial bulk Ge photodiodes. In addition, the low temperature bonding and layer transfer can enable a compact integration at the backend-of-line for PIC applications. This work paves the way for GOI photodiodes toward advanced high-resolution imaging and sensing applications on PICs at the near-infrared and short-wave infrared wavelength.

Automated summary

This study demonstrates a vertical p-i-n Ge photodiode with remarkably low dark current on a high-quality GOI substrate. By reducing threading dislocation density in Ge and improving device fabrication, the photodiodes show high responsivity and specific detectivity at specific wavelengths and voltages. These findings pave the way for advanced imaging and sensing applications in PICs at near-infrared and short-wave infrared wavelengths.