Stabilization of Si photoanodes in aqueous electrolytes...

Details Stabilization of Si photoanodes in aqueous electrolytes... Stabilization of Si photoanodes in aqueous electrolytes...

1999-05-04

2004-07-06

Eckert, George (Department: 2815)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

Insulative material deposited upon semiconductive substrate

C438S038000, C438S765000, C438S769000, C438S778000

Reexamination Certificate

active

06759349

ABSTRACT:

BACKGROUND
Silicon is often used as a semiconductor material for many purposes. The surface of silicon is very chemically active; and easily combines with many materials, including oxygen. The “oxide” formed on the surface can impede the characteristics of the silicon.
Semiconductors having band gaps between 0.9 and 1.7 eV are often used in photoelectrochemical solar energy conversion devices. Silicon has a band gap of 1.12 eV, and is an especially attractive material for this application.
A typical way of forming a silicon semiconductor, e.g., a photodiode, is to use wet chemical etching with HF(eq), resulting in a hydrogren-terminated Si surface. This surface is electrically suitable when initially formed. However, this surface readily oxidizes in air or in water-containing ambients. An oxide on the surface introduces electrical defect states. This also forms an insulating, passivating overlayer. That overlayer can impede the semiconductor characteristics. For example, this can impede photocurrent flow through an electrochemical cell.
It is often important to stabilize Si electrodes in aqueous media. Previous art has suggested coating the surface of Si electrodes with islands or films of metal. This process creates buried Si/metal junctions on protected regions of the electrode. This can be undesirable.
SUMMARY
The present specification describes silicon surfaces derivatized with covalently-attached alkyl chains used to protect the surface. A preferred mode uses a halogenation/alkylation procedure in which the surface is treated with a halogen, e.g., chlorine, and then an alkyl-containing material. The silicon surface is preferably in contact with an aqueous Fe(CN)
6
3−/4−
. These surfaces are treated with the alkyl groups, or “derivatized.” This forms covalent Si—C linkages and these covalent Si—C linkages protect the surface against oxidation.
A preferred mode uses CH3 as the alkyl group.


REFERENCES:
Bansal, A., et al., “Alkylation of Si surfaces using a two-step halogenation/grignard route”,J. Am. Chem. Soc., 1996, vol. 118, No. 30, pp. 7225-7226.
Pomykal, K.E., et al., “Stability of n-Si/CH3OH contacts as a function of the reorganization energy of the electron donor”,J. Phys. Chem., 1995 vol. 99, pp. 8302-8310.
Rosenbluth, M.L., et al., “Kinetic studies of carrier transport and recombination at the n-silicon/methanol interface”,Journal of the American Chemical Society, vol. 108, No. 16, Aug. 6, 1986, pp. 4689-4695.
WWW.chem.ox.ac.uk/mom/derrocene.html, “Ferrocene-molecule of the month Jun. 1996” p. 1.

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