AVS 60th International Symposium and Exhibition
    Electronic Materials and Processing Wednesday Sessions
       Session EM1-WeM

Paper EM1-WeM4
Chemical Passivation of GaAs using Alkanethiols

Wednesday, October 30, 2013, 9:00 am, Room 101 B

Session: Electrical Testing and Defects in III-V’s
Presenter: P. Mancheno-Posso, University of Arizona
Authors: P. Mancheno-Posso, University of Arizona
A.J. Muscat, University of Arizona
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III-V semiconductors are among the most promising materials for low-power and high-speed electronic devices owing to their high electron mobility and high breakdown fields. For instance, their use as channel materials would enable an increase in performance without changing the transistor density. Despite these advantages, III-V materials lack a defect-free and stable native oxide that could be used as a dielectric in metal-oxide-semiconductor field-effect transistors (MOSFET). Moreover, the most widely studied III-V semiconductor, GaAs, contains interfacial oxides that detrimentally affect its electronic performance. Etching the oxides and depositing a passivation layer that hinders oxidation is one approach to incorporate III-V materials in high volume production. Chemical passivation layers containing S have shown particular promise and were deposited using the precursors Na2S, (NH4)2S, and alkanethiols. The alkyl chain on the thiols can act as a diffusion barrier to prevent oxygen from reaching the III-V surface, if the thiol molecules can be closely packed. In this study, alkanethiols with chain lengths from 3-20 carbon atoms were deposited from the liquid phase on GaAs (100), and their effectiveness in preventing oxidation in ambient conditions was characterized using ellipsometry, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). The C 1s XPS peak showed that thiols with longer carbon chains exhibited higher surface coverages, as well as reduced surface oxidation after ambient exposure. FTIR peaks at 2918±1 and 2850±1 cm-1, corresponding to asymmetric and symmetric stretches of CH2 moieties, demonstrated the formation of a well ordered monolayer for chains with 18 and 20 carbon atoms. In addition, XPS and temperature programmed desorption confirmed the successful desorption of the carbon chains of thiols after annealing in vacuum to 750 K. Atomic layer deposition (ALD) of Al2O3 using a TMA and water process showed that film nucleation and growth was reduced by a factor of about two on the thiol-passivated surface compared to the liquid-cleaned surface. Although the initial film growth was slowed, a thiol passivation layer could broaden the use of III-V semiconductors in device manufacturing.