BELOW BAND-GAP ELECTROABSORPTION IN BULK SEMIINSULATING GAAS

Electroabsorption measurements of bulk semi-insulating GaAs using a pulsed applied voltage are presented for the wavelength range 890-920 nm and compared with results of the same measurement using a dc applied voltage. In the latter case, field inhomogeneities in the GaAs gives a spatially dependent absorption which thwarts extraction of the absorption coefficient versus electric field. We circumvent this problem by transiently measuring the absorption during a pulsed bias voltage when the field in the sample is nearly uniform.