1ST STEP OF DEGRADATION MECHANISMS IN ALGAAS GAAS LASER-LIKE STRUCTURES

We analyse the first step of artificial degradation experiments performed on Al0.4Ga0.6As/GaAs/Al0.17Ga0.83As samples. Aluminium content fluctuations in the AlGaAs layer deposited on the GaAs were deduced, in regions sensitive to laser damage, from local scanning transmission electron microscopy cathodoluminescence spectra recorded at 30 K. No fluctuation could be detected in areas where degradation could not be initiated. Even if the lattice mismatch is very low for such epitaxial layers, such composition fluctuations can be seen as being one possible origin of the first step of degradation mechanisms of optical devices. The fluctuations induce stress variations of the order of 1 MPa, which are large enough to induce photoplastic glide of dislocations. The optical contribution to dislocation glide is roughly estimated to be 0.9 eV. It is much more likely to correspond to electronic transitions at a dislocation reconstruction defect than to transitions related to dislocation intrinsic bands.