Metal - Gallium-Arsenide Interface Modification Using Ultraviolet-Laser Enhanced Surface Oxidation.

The deep ultraviolet laser enhanced oxidation of gallium-arsenide is investigated using x-ray photoelectron spectroscopy and Auger electron spectroscopy. A 2-3 monolayer oxide formed in this way is used to modify metal-GaAs contacts. The experiments are performed in an ultrahigh vacuum system to allow in situ processing and analysis. The laser enhanced room temperature oxidation of GaAs is found to be strongly wavelength dependent. Different surface reactions are found to explain the wavelength dependence and other features of the enhancement. Visible and near ultraviolet light (hv < 4.1 eV) enhance the dissociative adsorption of oxygen for 0.1-0.7 monolayer oxide coverage, but the reaction saturates near 1 monolayer of oxide coverage. Deep ultraviolet light enhances a molecular like oxygen precursor to GaAs oxidation and results in oxide coverages up to 20 or more monolayers. This enhancement is only observed after 0.7 monolayers of oxide are present on the GaAs surface. When this oxide is used to modify a wide range of metal-GaAs contacts, the resulting Schottky barrier is found to systematically show large variations from the Schottky barrier for clean GaAs. The variation is dependent on the metal work function, varying in the direction predicted by the ideal Schottky limit. A model for Schottky barrier formation is used to conclude that oxygen at the interface may be increasing the energy separation of interface acceptor donor levels. The important conclusion, however, is that the GaAs Schottky barrier has been made to vary in a wider range than is usually observed by chemically modifying the GaAs surface prior to metal deposition.