MOVPE-grown n- and p-type (001) GaAsSb and GaSb were studied using in situ reflectance-difference spectroscopy (RDS), high-resolution X-ray diffraction and Hall measurements. We report RD spectra at 550degreesC and at room temperature, and the effects of different growth interruptions on GaAsSb RD spectra. The spectra shown a strong bulk-related feature, with a maximum at 3.9 eV (GaAsSb) and 3.7 eV (GaSb), at room temperature, GaAsSb and GaSb exhibit a linear electro-optic (LEO) effect. In both n- and p-type materials, the LEO effect results in features in the room temperature RD spectra at the energies corresponding to the E-1 and E-1 - Delta(1) critical points in the bulk band structure. (C) 2002 Elsevier Science B.V. All rights reserved.