Morphology and composition of highly strained InGaAs and InGaAsN layers grown on GaAs substrate

We have studied the morphology and the composition of highly strained InGaAs and InGaAsN layers using 002 dark-field image contrast and the selected area electron diffraction technique. The images show the presence of two symmetrical interfacial layers around the wells. Even if their thicknesses are about 1.5 nm, a double peak-splitting is always observed around the high index spots on the electron diffraction patterns. From the position of the two extra spots, we can determine the strain of the interfacial layers as well as the strain of the middle part of the wells. The incorporation of a small amount of nitrogen (about 0.5%) in these indium-rich alloys allows the emission wavelength of 1.3 mum to be reached. However, the morphology of the quaternary alloy quantum wells deteriorates.