Physics and Chemistry of Silicon Surface Passivation

accumulation;inversion;methanol;recombination;silicon;surface passivation

Michalak, David Jason ; Lewis, Nathan Saul

University:California Institute of Technology

Department:Chemistry and Chemical Engineering

关键词: accumulation;    inversion;    methanol;    recombination;    silicon;    surface passivation;   

Others  :  https://thesis.library.caltech.edu/1679/1/ThesisMasterFinal.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

Low interfacial electron-hole recombination rates are essential for low-noise electronic devices and high-efficiency solar energy converters. This recombination rate is dependent on both the surface electrical trap state density, NT,s, and the surface concentrations of electrons, ns, and holes, ps.A reduction in NT,s is often accomplished through surface chemistry, and lower recombination rates, through lower NT,s values, have been demonstrated in this work for surfaces chemically treated to produce methoxylated, Si-O-CH3, overlayers.The H-Si(111) surfaces can react with methanol quickly in the presence of an oxidant or slowly in neat anhydrous methanol.Mechanisms have been proposed for both reactions.

Low recombination rates can also be achieved through control of the surface physics; a large ns or ps can lower recombination rates.To date, low recombination rates have often been attributed only to a reduction in NT,s, without a direct measurement of ns and ps, partly because the importance of ns and ps has not been fully recognized and partly because an accurate evaluation of ns and ps can be very difficult. Surface recombination rates of silicon immersed in liquids containing various redox species (e.g., Fc+/0, I2, Me10Fc+/0, or CoCp2+/0) were studied using an rf photoconductivity decay apparatus and compared with ns and ps values obtained from Mott-Schottky and other analysis techniques.The results demonstrate that the observed recombination rates can only be correlated with NT,s values when ns [approx.] ps.In all other cases, the recombination rate was low due to a large ns or ps even for surfaces with large NT,s values.

The full impact of this work was further realized through a study of the recombination rates of H-Si immersed in solutions of 48% HF, 40% NH4F, and buffered HF (BHF), because such measurements are often performed for in situ monitoring of the surface quality during wafer processing steps.Our results demonstrate that only HF contacts can be used for in situ monitoring because ns [approx.] ps.For NH4F or BHF contacts, low recombination rates were observed only because ns » ps, and NT,s cannot be inferred from these measurements.