Structural and optical properties of high In and N content GaInNAs quantum wells

We have analysed by Transmission Electron Microscopy and Photoluminescence (PL) the structural and optical properties of Ga1-xInxNyAs1-y quantum wells with Indium and Nitrogen contents in the range 0.20<x<0.35 and 0.013<y<0.023, respectively. Our results have shown that a degradation of the structural quality of the wells when increasing the In content takes part in two distinct steps. In the first one, an undulation of the surface of the wells on raising the In content from 20% to 25% has been observed. This is accompanied by the appearance of a high density of extrinsic dislocation loops, probably due to a high local stress concentration in the material. For these samples the PL spectra show intense and narrow emission peaks at 1.1-1.2 μm, therefore the existence of dislocation loops seems not to affect considerably the optical efficiency of the material at this stage. In a second step, on increasing the In composition to 35%, the PL emission efficiency of the wells is severely degraded and the samples show the appearance of threading dislocations. An unfaulting of the dislocation loops as a consequence of a coalesce reaction with two Shockley partials is proposed as the mechanism for the formation of the observed threading dislocations