Structural defects characterisation of GaInNAs MQWs by TEM and PL

The authors´ work is focused on the structural and optical properties of GaInNAs/GaAs(001) QWs with In and N contents in the ranges 0.20-0.35 and 0.013-0.023, respectively, studied by transmission electron microscopy and photoluminescence. An undulation of the wells was observed when increasing the In content to 25% and the N content to 1.6%. This induces the appearance of extrinsic Frank dislocation loops, which are most likely formed because of local stress accumulation in the structure. The PL spectra show intense peaks at 1.1 μm and 1.2 μm for samples with In compositions of 20% and 25%, respectively, representing therefore structures with and without loops. Consequently, the existence of these structural defects seems not to affect the optical efficiency of this alloy. On increasing the In content to 35%, a considerable decrease in the PL peak intensity, related to the existence of threading dislocations observed by TEM, has been found. The unfaulting of dislocation loops by means of the reaction with two Shockley partial dislocations is proposed as the mechanism of formation of these threading dislocations.