Different Infrared Responses from the Stacked Channels and Parasitic Channel of Stacked GeSn Channel Transistors

An optical non-destructive method to check the existence of the parasitic Ge0.94Si0.06 channel underneath vertically stacked Ge0.91 Sn0.09 channels by infrared illumination is investigated. The 1310-nm and 1550-nm infrared light excite the electron-hole pairs in both the stacked floating channels and parasitic channel. On the other hand, the 2000-nm infrared light generates photo-excited carriers in the floating GeSn channels, but not in the parasitic GeSi channel since the photon energy is lower than the bandgap of Ge0.94 Si0.06. The main infrared responses of the floating channels and parasitic channel are the threshold voltage shift and the photocurrent, respectively. In addition, the distinct photoresponses of the stacked channels and parasitic channel are further confirmed by transistors without floating channels. The mechanisms behind the infrared responses are proposed. The existence of the parasitic channel can be detected by the infrared response for the advanced technology nodes, where the presence of the parasitic channel is not desired for performance enhancement and power reduction. ? 2019 IEEE.