A comparative study of the chemical passivation of GaAs(100) using alkanethiols (R-SH, R=CnH2n+1) with different carbon chain lengths (n=3-18) was performed using spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and water contact angle. The time required to reoxidize the surface when exposed to the ambient scaled with the length of the chain. A threshold of about 12 C atoms was necessary for minimal protection. 1-octadecanethiol (OT-18C) containing 18 C atoms prevented reoxidation for 3 min. The OT-18C self-assembled into a monolayer containing closely packed molecules at a tilt angle from the surface normal of about 28°. The crystalline structure presented a physical barrier to oxygen diffusion with a thickness of 2.2 nm. Alkanethiols could offer ease of deposition and removal with protective properties to enable the use of III-V materials in high volume manufacturing.
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