Ion Bombardment Effects on GaAs Using 100eV Nitrogen Ions
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ION BOMBARDMENT EFFECTS ON GaAs USING 100eV NITROGEN IONS W.M. LAU Surface Science Western, Ontario, Canada N6A 5B7
University of Western Ontario, London,
ABSTRACT The ion bombardment effects of low energy molecular nitrogen ions (100eV) on GaAs have been investigated using in-situ polar angle dependent X-ray photoelectron spectroscopy. It was found that arsenic and gallium nitrides were formed as a result of the nitrogen ion bombardment. The ion bombardment also caused a depletion of arsenic in the near surface region. For example, with a dose of 6x10 icm-2 of nitrogen molecular ions at 100eV, the surface structure can be described approximately as 1.5nm of Ga0. 6 7 As0. 3 3 N on GaAs. The ion bombardment moves the Fermi levels of both n-type and p-type GaAs to mid-gap. Heating the ion bombarded samples in a vacuum chamber to 500 C desorbs all arsenic nitrides but most of the gallium nitrides remain on the surface. The Fermi levels of both n-type and p-type are then stablized at about 0.4eV from the valence band maximum. A surface type-inversion of the n-type substrate is therefore induced by the nitrogen-ionbombardment/annealing treatment. I.
Introduction The ability to control Schottky barrier height is technologically important. However, in the past, it was generally believed that Fermi level pinning near mid-gap is inevitable upon metal deposition on GaAs, and that the control of Schottky barrier height on GaAs is difficult [1]. However, several techniques for preparing GaAs surfaces prior to metal deposition have been recently reported which promise the possibility of controlling Schottky barrier height on GaAs. The approach taken by Brillson et al. (2] is to prepare a high quality GaAs film by molecular beam epitaxy and to cap it in the same chamber with a thin overlayer of arsenic. The protective arsenic cap is then thermally desorbed in the metal deposition chamber in order to regenerate a clean and stoichiometric surface with a low defect density prior to Schottky contact formation. Another approach is to use an ultrathin sandwich-layer between the GaAs substrate and the Schottky metal in order to achieve the control of Schottky barrier height. For example, 1.5-3nm of Si [3], surface oxide [4], and adsorbed inorganic sulfide [5] have been used as the sandwich-layer for this purpose. An alternative approach similar to this sandwich-layer technique is to type invert the near surface region of the GaAs substrate before metal deposition. For example, Zhang et al. [6] reported that high temperature annealing of refractory metal nitrides on n-GaAs led to the formation of metal/p /n structures and, thereby, to an increase of Schottky barrier height. This group has also reported that nitroqen bombardment (
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Before bombardment . 405 Binding Energy (eV)
385
Fig. 1 The incorporation of nitrogen into GaAs by 100eV nitrogen ion bombardment
The incorporation of nitrogen as a function of ion bombardment time (with a current density of about 0.3gA/cm 2) is The nonlinear behavior suggests th
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