Ambient-induced surface effects on InP and GaAs

The effects of gas ambient changes on the photoluminescence (PL) intensity and the conductivity of chemically cleaned (100) InP and GaAs have been investigated. The room-temperature PL intensity of n-type, p-type, and Fe-doped semi-insulating InP is found to be reversibly changed by the presence of various gases at the semiconductor surface. The resistivity of thin-film InP resistors is also found to be affected by gas ambient changes, both under illumination and in the dark. These measurements show that the surface Fermi level of InP is not tightly pinned and is reversibly changed by exposure to different ambients. The PL intensity and surface conductivity of GaAs are also found to be sensitive to the gas environment, though to a lesser degree than InP. The responses of InP and GaAs are of a different nature and suggest that the surface state densities of these materials are reversibly affected by the chemisorption of oxygen. This in turn suggests that there are adsorbate-induced surface states on InP and GaAs which arise as a result of the interaction of adsorbed oxygen with the semiconductor surface and that are not associated with intrinsic semiconductor defects.