Passivation of Dangling Bonds in Amorphous Si and Ge by Gas Adsorption
We have used molecular-beam deposition (MBD) with a base pressure of 10–10 torr to prepare a-Si and a-Ge at relatively low substrate temperatures. The films contain voids which can adsorb gases such as H2, F2, SiF4, GeF4, O2, etc. Due to the high reactivity of the dangling bonds present, these molecules are broken down to their atomic constituents, thereby passivating the dangling bonds. Further annealing is required to form proper chemisorption and drive the passivating agents into smaller or isolated voids. Typically a decrease of dark conductivity by as much as 8 orders of magnitude is observed accompanied by the appearance of few decades of photocurrent above the dark current under (Air Mass 1) AM1. For a-Ge, using a similar procedure, fluorine is more effective as a passivating agent than hydrogen.
KeywordsSubstrate Temperature Amorphous Silicon Dangling Bond Dark Conductivity Passivating Agent
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