High-quality germanium photodiodes integrated on silicon substrates using optimized relaxed graded buffers

Abstract

The integration of Ge photodetectors on silicon substrates is advantageous for various Si-based optoelectronics applications. We have fabricated integrated Ge photodiodes on a graded optimized relaxed SiGe buffer on Si. The dark current in the Ge mesa diodes, Js=0.15 mA/cm2, is close to the theoretical reverse saturation current and is a record low for Ge diodes integrated on Si substrates. Capacitance measurements indicate that the detectors are capable of operating at high frequencies (2.35 GHz). The photodiodes exhibit an external quantum efficiency of η=12.6% at λ=1.3 μm laser excitation in the photodiodes. The improvement in Ge materials quality and photodiode performance is derived from an optimized relaxed buffer process that includes a chemical mechanical polishing step within the dislocated epitaxial structure.

Ge-on-Si photonic devices for photonic-electronic integration on a Si platform

“…Due to the reduction of threading dislocation density by the post-growth annealing, the dark leakage current is reduced to ∼20 mA/cm 2 at the reverse bias of 1 V. As summarized in Fig. 8(c), the dark leakage current tends to decrease with decreasing the threading dislocation density in Ge [23,30,31,32,33]. However, the high-temperature annealing to reduce the dislocation density could be eliminated from the viewpoint of compatibility with the CMOS process for electronic circuits, otherwise Ge layers need to be formed at the beginning of front-end process, causing a drastic change in the existing CMOS process.…”

Direct gap Ge1-ySny alloys: Fabrication and design of mid-IR photodiodes

“…This suggests that even higher Sn concentrations may be attainable by this method by growing successive layers of ever increasing Sn concentrations, following a process similar to the early efforts to grow Ge on Si by using intermediate Ge 1-x Si x layers of graded composition. 31 The ultimate limit of this approach may be given by the ever decreasing growth temperature needed to incorporate an increasing amount of Sn.…”

Silicon-Germanium multi-quantum well photodetectors in the near infrared

“…Epitaxial germanium on silicon for photodetection by graded buffer layers [6,7], molecular beam epitaxy [8], a two-step growth by ultra-high vacuum chemical vapor deposition (UHVCVD) [9,10], and cyclic thermal annealing to reduce dislocation density in grown films were reported [11][12][13]. Metal-semiconductor-metal (MSM) and p-i-n type optical detectors were previously fabricated on blanket [3], and selective area grown germanium on silicon by MHAH technique are also reported earlier [5].…”