TEM and Photoluminescence Investigations of InGaAs/GaAs Quantum Well Layers

Photoluminescence (PL) and (200) dark field TEM have been applied to investigate InGaAs SQWs grown on misoriented GaAs substrates. For such SQWs the PL FWHM is greater and the PL emission wavelength is smaller than those for the SQWs grown on exactly oriented substrates, indicating a worse interface quality and a lower In content, respectively. TEM has shown that this is due to the presence of macrosteps at the GaAs-on-InGaAs interface, as igh as 5-8 nm, along which a lateral and a vertical compositional inhomogeneity occur. The macrosteps have formed via a step bunching mechanism because of the substrate misorientation. The SQWs grown on misoriented substrates also have a smaller critical thickness than the SQWs grown on exactly oriented substrates. Strain relaxation in such SQWs starts with the generation of 1/2[110]{011} dislocations instead of the usual 1/2[110]{111} misfit ones.