Investigation of defect characterization, formation mechanism, and effect in distributed feedback lasers

InP, which exhibits attractive physical characteristics, such as high electron mobility, high conductivity, and high bandgap width, has always been fanatically pursued in high frequency and high speed devices in recent years. However, the inherent high density defects hinder the quality of the epitaxial layer and, even worse, impede the device’s life. Here, we found a kind of defect in the distributed feedback laser layers on an InP based substrate. A focused ion beam was employed in order to dissect the defect. The formation process was characterized using a transmission electron microscope and a high-resolution transmission electron microscope. Closer analysis reveals that defects form a subsurface damage layer between the substrate and the epitaxial layer. The subsurface damage layer already has a potentially destructive lattice, including lots of dislocations and lattice distortions, which leads to anisotropy in the interface layer. As the epitaxial film thickness increases, so does this strain relax, and dislocations form.