High-absorbance resonant-cavity-enhanced free-standing Ge photodetector for infrared detection at 1550 nm wavelength

Abstract

A novel free-standing resonant-cavity-enhanced (RCE) Ge thin-film absorber is designed with a bottom distributed Bragg reflector (DBR) for infrared photodetection at 1550 nm wavelength based on a Si substrate. The free-standing structure offers a high degree of freedom in optimizing the number of periods, the layer arrangement, and the thickness of each layer of the DBR. A SiO2/Si DBR that is compatible with Si processing technology is used on the bottom of the Ge thin film to construct the RCE structure. Based on our theoretical study, the SiO2 low-index layer must be placed next to the Ge layer to utilize the large difference in the refractive indices between SiO2 and Ge to achieve high reflectance for the DBR. In this design, the structure can reach an absorbance of 85.90% with a DBR of three periods on the bottom and an antireflective oxide layer on the top surface of the Ge layer. Without the antireflective oxide layer, the absorbance is increased to 99.17%. The design paves the way for high-responsivity Ge infrared photodetectors in Si-based photonic systems.

High-Performance Ge PIN Photodiodes on a 200 mm Insulator with a Resonant Cavity Structure and Monolayer Graphene Absorber for SWIR Detection

“…The main advantages of poly-Si over single-crystalline Si were its slightly higher refractive index and simpler manufacturing process, indicating that poly-Si/ SiO 2 DBR mirror offers higher reflectivity than that of Si/SiO 2 DBR mirror. 68 In addition, we demonstrated the high responsivity and low dark current Ge PIN photodetectors on the two periods of poly-Si/SiO 2 DBR mirror, 69 which is realized by the wafer bonding process. Experimental result shows that the responsivity at 1550 nm was improved from 0.49 to 0.67 A/W due to the RCE structure and the presence of a graphene cap layer.…”