GaSb is probably the least-studied of all III-V semiconductors from the perspective of fundamental surface science. However, new areas of application have led to increased interest in this material. A critical issue is the production of high-quality gate oxides with a low defectdensity on either side of the oxide/substrate interface, the most viable approach to which involves atomic layer deposition (ALD). This talk will describe recent and on-going experimental and computational work at NRL that is aimed at understanding and optimizing oxide ALD on the GaSb (001) surface. The most stable reconstruction, the so-called a-(4x3), consists of 4 Ga-Sb adatom dimers per unit cell on the Sb termination layer, which also comprises 1 Sb-Sb dimer. This surface is non-metallic with no surface states in the band gap. Molecular adsorption of H2O via a Ga---OH2 dative bond is exothermic, but dissociation is highly unfavorable. Hence the formation, via direct dissociation of H2O, of the OH-terminated surface necessary for the initiation of ALD is problematic. An alternative is to produce (somehow) a high-quality native oxide, which will presumably form OH sites when exposed to H2O. The key issue is how to accomplish this while avoiding the well-documented problem of defective III-V/oxide interfaces.Careful measurement of the Fermi-level pinning position vs. O2 exposure shows that O2 can passivate defects as well as cause them, which is supported by recent electrical measurements performed at NRL. This in turn has led to efforts to understand the mechanism whereby O2 exposure generates GaSb surface defects. Preliminary results have revealed a process, which is apparently unique to GaSb (001), in which O2 dissociates with little or no barrier and forms sub-surface defects. A practical outcome of this work is a set of tentative suggestions for how best to form a GaSb native oxide.

GaSb (001): New adventures in III-V surface chemistry

247th National Meeting (2014)

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