Structural characterization of III-nitride materials and devices

The electron microscope provides a wide range of techniques that are very well suited for structural characterization of nanophotonic materials and devices. High-resolution electron microscopy (defect identification and strain field analysis), Z-contrast imaging in the scanning transmission electron microscope (cation distribution), convergent-beam electron diffraction (local lattice parameter and strain), and off-axis electron holography (internal electrostatic fields), represent powerful complementary approaches for distinguishing between the often-competing effects of growth conditions and compositional differences. These various TEM techniques have been used separately or in tandem in our recent collaborative studies of III-nitride heterostructures and nanostructures, where lattice mismatch, compositional inhomogeneities and phase separation were all important considerations that can possibly impair the structural quality of the final material and/or device. Representative applications that illustrate the prospects and some of the problems include the following: i) relaxed InN quantum dots; ii) deep-UV-emitting AlGaN quantum wells; iii) near-UV light-emitting diodes based on InN/GaN quantum wells; and iv) blue-green LEDs based on GaN quantum-dot superlattices.