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

摘要

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.