AVS 61st International Symposium & Exhibition
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuP

Paper EM-TuP2
Passivation of InSb(100) with 1-Eicosanethiol Self-Assembled Monolayers

Tuesday, November 11, 2014, 6:30 pm, Room Hall D

Session: Electronic Materials and Processing Poster Session
Presenter: Pablo Mancheno, University of Arizona
Authors: Y.D. Contreras, University of Arizona
P. Mancheno, University of Arizona
A.J. Muscat, University of Arizona
Correspondent: Click to Email
III-V semiconductors have the potential to replace Si to make faster computer processors due to their higher charge mobility. In particular, the bandgap of InSb (0.17 eV, the smallest of the III-V group) makes this semiconductor an absorber and emitter in the infrared region, suitable for infrared detectors. III-V semiconductors oxidize rapidly when exposed to air after etching, and have complex oxide layers. It has been shown that sulfur-containing molecules can passivate and enhance the electrical properties of III-V semiconductors. In this study, InSb(100) was chemically passivated for 3 min after native oxide etching by liquid-phase deposition of an alkanethiol self-assembled monolayer (SAM) on the surface of the semiconductor. The SAM contained 1-eicosanethiol (ET, 20 C atoms). The passivated surface was characterized with atomic force microscopy (AFM), spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS) and FTIR. Tapping Mode AFM images of InSb native oxide showed that the starting surface was rough (RMS 2.25 nm), which could limit the formation of a dense and ordered alkanethiol SAM. The thickness of the overlayer (both InSb oxides and ET) measured by spectroscopic ellipsometry was 35 Å immediately after passivation. XPS analysis showed that the passivation process with a 1.0 M HCl last step and 20 h passivation yielded no detectable oxygen in the Auger region for 3 min of air exposure, but the surface was completely oxidized after 4 h of exposure. As a comparison, passivation of GaAs(100) (bandgap of 1.4 eV) with an ET SAM maintained oxygen below detection limits after 30 min, but the surface still oxidized after 4 h. When the passivation of InSb(100) was performed with different preparation conditions (HCl and thiol concentrations, solvent type, and deposition time), the largest bulk InSb to Sb2O5 3d + O 1s XPS peak area ratio (minimum Sb oxidation) was achieved by using 1.0 M HCl in the oxide etching steps, 0.1 mM ET in ethanol and long thiol deposition times (~20 h). FTIR analysis of an InSb sample passivated for 20 h in 0.1 mM ET showed the presence of peaks characteristic of methyl and methylene stretches at 2963 cm-1, 2925 cm-1 and 2847 cm-1. The position and width of these peaks indicates the presence of a partially ordered alkanethiol layer. These results demonstrate that physically blocking O2 diffusion with alkyl chains is possible on the surface of a narrow band-gap semiconductor, even on a surface with a relatively high average roughness.