Abstract
The Raman microprobe is used for characterising chemically revealed defects in as-grown GaAs. Different microstructures were scanned with 1 mu m spatial resolution. Emphasis is paid to the breaking down of the Raman-backscattering selection rules. Precipitates and twins are studied in semi-insulating GaAs. Coupled phonon-plasmon modes are analysed in Te-doped GaAs (ND-NA approximately=1017 cm-3); dislocation grain boundaries and hillocks are scanned by the Raman microprobe, revealing misorientation and free carrier effects.