Role of Channel Inversion in Ambient Degradation of Phosphorene FETs

Phosphorene is a potential material to replace silicon in next-generation electronic devices. However, the material is not favorable for device applications due to its gradual degradation when exposed to ambient environmental conditions. The degradation process is mainly initiated by oxygen molecules, which attacks the lone pair of phosphorus atoms. We show that in the case of phosphorene-based field-effect transistors (FETs), the channel degradation due to oxygen molecules is also influenced by the presence of channel inversion or excess (inversion) carriers. Our study reveals a unique reliability issue related to phosphorene FETs. Here, we investigate the role of channel excess holes (due to inversion) in the phosphorene degradation using the first-principles molecular dynamics computations and electrical and Raman characterization. The results show that phosphorene degrades faster under negative gate bias (excess hole) than pristine conditions (unbiased). The rapid degradation is mainly due to the enhanced chemical interaction of oxygen with the available hole in the channel. Using electrical and Raman characterization, the computational findings are experimentally verified over phosphorene FETs. The devices show a faster change in drain current and fast decay of Raman peaks in the ambient environment under negative gate bias compared to no gate bias condition. Therefore, phosphorene has an additional ambient reliability issue once exposed with negative biased during its FETs applications.