Abstract

The time-resolved reflectivity from a series of variously prepared GaAs interfaces has been observed. GaAs n-type wafers of 2 × 10¹⁶ cm^-3 doping density were used. The surfaces were prepared in the following ways: growth of a thermal oxide, growth of a photochemically passivated oxide, and growth of an epitaxial ZnSe overlayer using the technique of laser-assisted MOCVD. Reflectivity measurements were performed using a CPM laser (620 nm, pulsewidth <100 fsec) in a standard pump-probe geometry. The time dependence of the reflectivity within the first few picoseconds is highly dependent on surface preparation. This variation of surface treatment is linked to a variation of both the density of states present at the interface and a variation in the space-charge layer on the GaAs side of the interface. Characterization of the GaAs spacecharge layer by contactless optical probing techniques, as well as additional experiments on III–V device structures enable us to make some initial correlations between the time dependence of the optical reflectivities observed and the properties of the GaAs space-charge layer.

© 1991 Optical Society of America