Germanium on double-SOI photodetectors for 1550 nm operation

Abstract

We have fabricated and characterized the first resonant cavity enhanced (RCE) germanium photodetectors on double silicon-on-insulator substrates (Ge/DSOI) for operation around the 1550 nm communication wavelength. The Ge layer is grown through a novel two-step UHV/CVD process, while the underlying double-SOI substrate is formed through an ion-cut process. Absorption measurements of an undoped Ge-on-Si (Ge/Si) structure reveal a red-shift of the Ge absorption edge in the NIR, due primarily to a strain-induced bandgap narrowing within the Ge film. By using the strained-Ge absorption coefficients extracted from the absorption measurements, in conjunction with the known properties of the DSOI substrate, we were able to design strained-Ge/DSOI photodetectors optimized for 1550 nm operation. We predict a quantum efficiency of 76% at 1550 nm for a Ge layer thickness of only 860 nm as a result of both strain-induced and resonant cavity enhancement, compared to 2.3% for the same unstrained Ge thickness in a single-pass configuration. We also estimate a transit-time limited bandwidth of 28 GHz. Although the fabricated Ge/DSOI photodetectors were not optimized for 1550 nm operation, we were able to demonstrate an over four-fold improvement in the quantum efficiency, compared to its single-pass counterpart.

Metal semiconductor metal photodiodes based on all-epitaxial Ge-on-insulator-on- Si(111), grown by molecular beam epitaxy

“…At the same laser power, bulk-Gebased MSM PDs show a much larger photocurrent (2.386 mA), with a dark current of only 428 µA. The absorption coefficient of Ge is 460 cm -1 at 1550 nm wavelength [14] and the above results indicate that epi-Ge layer thickness plays an important role for a good photo-response. The obtained responsivity of GOI MSM devices is ~ 2 mA/W (at -5V) with a noise equivalent power (NEP) of 15.32 nW(Hz) -1/2 [15] (at 1550 nm).…”

Design and Fabrication of High Performance InGaAs near Infrared Photodetector

“…The optical absorption data, which were used for the numerical calculations, was obtained from Ref. [24], and no anti-reflective coating was utilized. It is evident that variations in the absorber doping concentrations resulted in some differences in the quantum efficiency of the detectors.…”

Germanium on Silicon Avalanche Photodiode for High-Speed Fiber Communication

“…Considering photodiode's top surface is typically made by antireflection (AR) coating with low reflectivity <5%, a high reflectivity surface at bottom is critical for enhancing responsivity. Several papers reported Ge/Si RCE devices by using different bottom reflectors [24][25][26][27]. One common solution is using SOI substrate: a reflection happens at the interface between Si and buried oxide (BOX) layers because of large refractive index gap.…”

“…One common solution is using SOI substrate: a reflection happens at the interface between Si and buried oxide (BOX) layers because of large refractive index gap. Especially for double SOI substrate, the bottom reflectivity can reach >90% with optimized silicon and oxide thicknesses [24]. Alternative method is to use CMOS-compatible metals such as aluminum with >95% reflectivity at optical communication wavelengths (Figure 2) [28].…”