Effect of Molecule鈥揝urface Reaction Mechanism on the Electronic Characteristics and Photovoltaic Performance of Molecularly Modified Si

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• 作者：Omer Yaffe ; Tal Ely ; Rotem Har-Lavan ; David A. Egger ; Steve Johnston ; Hagai Cohen ; Leeor Kronik ; Ayelet Vilan ; David Cahen
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：October 31, 2013
• 年：2013
• 卷：117
• 期：43
• 页码：22351-22361
• 全文大小：398K
• 年卷期：v.117,no.43(October 31, 2013)
• ISSN：1932-7455

文摘

We report on the passivation properties of molecularly modified, oxide-free Si(111) surfaces. The reaction of 1-alcohol with the H-passivated Si(111) surface can follow two possible paths, nucleophilic substitution (S_N) and radical chain reaction (RCR), depending on adsorption conditions. Moderate heating leads to the S_N reaction, whereas with UV irradiation RCR dominates, with S_N as a secondary path. We show that the site-sensitive S_N reaction leads to better electrical passivation, as indicated by smaller surface band bending and a longer lifetime of minority carriers. However, the surface-insensitive RCR reaction leads to more dense monolayers and, therefore, to much better chemical stability, with lasting protection of the Si surface against oxidation. Thus, our study reveals an inherent dissonance between electrical and chemical passivation. Alkoxy monolayers, formed under UV irradiation, benefit, though, from both chemical and electronic passivation because under these conditions both S_N and RCR occur. This is reflected in longer minority carrier lifetimes, lower reverse currents in the dark, and improved photovoltaic performance, over what is obtained if only one of the mechanisms operates. These results show how chemical kinetics and reaction paths impact electronic properties at the device level. It further suggests an approach for effective passivation of other semiconductors.