Abstract
Si/Ge uni-traveling carrier photodiodes exhibit higher output current when space-charge effect is overcome and the thermal effects is suppressed. High current is beneficial for increasing the dynamic range of various microwave photonic systems and simplifying high-bit-rate digital receivers in many applications. From the point of view of packaging, detectors with vertical-illumination configuration can be easily handled by pick-and-place tools and are a popular choice for making photo-receiver modules. However, vertical-illumination Si/Ge uni-traveling carrier (UTC) devices suffer from inter-constraint between high speed and high responsivity. Here, we report a high responsivity vertical-illumination Si/Ge UTC photodiode based on a silicon-on-insulator substrate. When the transmission of the monolayer anti-reflection coating was maximum, the maximum absorption efficiency of the devices was 1.45 times greater than the silicon substrate owing to constructive interference. The Si/Ge UTC photodiode had a dominant responsivity at 1550 nm of 0.18 A/W, a 50% improvement even with a 25% thinner Ge absorption layer.
Highlights
1High-current photodiodes, which receive communication signals in the near-infrared range, are highly beneficial in various photonic systems for increasing their dynamic range[ 1][ 2] and simplifying high-bit-rate digital receivers[ 3 ]
A simulated band-gap diagram and electric field distribution at 0 V of such a device are illustrated in Fig. 1(b) by the blue and red curves, respectively, calculated after modifying the doping parameters according to the results of secondary ion mass spectrometry (SIMS) measurements
The use of silicon-on-insulator substrate for Si/Ge uni-traveling carrier (UTC) photodiodes offers advantages in reflecting the transmission light to increase the absorption efficiency of the input optical signal, and improving the lattice quality of Ge epitaxial layer to increase the efficiency of photon generated carrier collection
Summary
The responsivity of this device at 1550 nm was as low as 0.12 A/W with a 0.8-μm-thick Ge absorption layer [24] Such a low responsivity could seriously increase power dissipation and limit high-output applications. The large difference in refractive index between the buried oxide layer (BOX) and the Si is beneficial in recycling transmission light back to the absorption layer, which is equivalent to extending the absorption length This allows the absorption efficiency of the photodiodes to be increased without sacrificing the response speed. We report a high-speed, high responsivity vertical-illumination Si/Ge UTC-PD based on a silicon-on-insulator (SOI) substrate. The silicon-on-insulator substrate was used to reflect transmission light for high absorption efficiency, and to improve the lattice quality of the Ge epitaxial layer to increase the efficiency of photon-generated carrier collection. The responsivity of the photodiodes at 1550 nm was improved to 0.18 A/W
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