Macroscopic defects in GaN/AlN multiple quantum well structures grown by MBE on GaN templates

We have used MBE to grow in AlN/GaN superlattices, with different number of periods, on 2.5-mu m-thick MOVPE-GaN templates to study the development of defects such as surface deformation due to strain. After growth the samples were studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), XRD and Fourier transform infrared spectroscopy (FT-IR). The strain increased with the number of quantum wells (QWs) and eventually caused defects such as microcracks visible by optical microscopy at four or more QW periods. High-resolution TEM images showed shallow recessions on the surface (surface deformation) indicating formation of microcracks in the MQW region. The measured intersubband (IS) absorption linewidth from a four period structure was 97 meV, which is comparable with the spectrum from a 10 period structure at an absorption energy of similar to 700 meV. This indicates that the interface quality of the MQW is not substantially affected by the presence of cracks. (C) 2008 Elsevier Ltd. All rights reserved

Nonlinear all-optical guided wave devices: operating characteristics and material trade-offs

The operating characteristics of novel all-optical integrated optics devices based on strong nonlinearities are reviewed, as are all-optical guided-wave devices which are nonlinear extensions of well-known linear integrated optics devices. A comparison of how different material systems meet the requirements for all-optical guided-wave devices is also presented