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Improving the opto-microwave performance of SiGe/Si phototransistor through edge-illuminated structure

Abstract : This paper demonstrates the experimental study of edge and top illuminated SiGe phototransistors (HPT) implemented using the existing industrial SiGe2RF Telefunken GmbH BiCMOS technology for opto-microwave (OM) applications using 850nm Multi-Mode Fibers (MMF). Its technology and structure are described. Two different optical window size HPTs with top illumination (5x5µm 2 , 10x10µm 2) and an edge illuminated HPTs having 5µm x5µm size are presented and compared. A two-step post fabrication process was used to create an optical access on the edge of the HPT for lateral illumination with a lensed MMF through simple polishing and dicing techniques. We perform Opto-microwave Scanning Near-field Optical Microscopy (OM-SNOM) analysis on edge and top illuminated HPTs in order to observe the fastest and the highest sensitive regions of the HPTs. This analysis also allows understanding the parasitic effect from the substrate, and thus draws a conclusion on the design aspect of SiGe/Si HPT. A low frequency OM responsivity of 0.45A/W and a cutoff frequency, f-3dB , of 890MHz were measured for edge illuminated HPT. Compared to the top illuminated HPT of the same size, the edge illuminated HPT improves the f-3dB by a factor of more than two and also improves the low frequency responsivity by a factor of more than four. These results demonstrate that a simple etched HPT is still enough to achieve performance improvements compared to the top illuminated HPT without requiring a complex coupling structure. Indeed, it also proves the potential of edge coupled SiGe HPT in the ultra-low-cost silicon based optoelectronics circuits with a new approach of the optical packaging and system integration to 850nm MMF.
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Submitted on : Wednesday, July 24, 2019 - 3:14:00 PM
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Zerihun Gedeb Tegegne, Carlos Viana, Jean-Luc Polleux, Marjorie Grzeskowiak, Elodie Richalot. Improving the opto-microwave performance of SiGe/Si phototransistor through edge-illuminated structure. SPIE photonics west, Feb 2016, San Francisco, United States. pp.1-10, ⟨10.1117/12.2208676⟩. ⟨hal-02193543⟩



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