Mitsuhiko Yamada

Submicrometre-pitch intercomparison between optical diffraction, scanning electron microscope and atomic force microscope

Intercomparison of pitch measurements for one-dimensional-grating standards (240 nm pitch), one of the widely used reference standards for nanometric lateral scales, was performed by three different methods, optical diffraction, critical dimension scanning electron microscopy and nanometrological atomic force microscopy. Average pitch values obtained by the three methods deviated by a maximum of only 0.67 nm with expanded uncertainties (k = 2) of less than 1.2 nm. The calculated En number, the index of measurement quality, of less than 1 indicates consistency of the measured pitch values and subsequent uncertainty analyses performed by three methods.

Mapping of multiple-quantum-well layers and structure of V defects in InGaN/GaN diodes

Cathodoluminescence mapping reveals threading defects, frequently formed by the lattice misfit between GaN and sapphire substrate, as a dark contrast connected with changes in the energy state. Multiple quantum wells, 2.5 nm In0.25Ga0.75N and 13.9 nm GaN layers, are resolved in the secondary electron image as well as in the backscattered electron image. The backscattered electron image, providing compositional mapping without surface effects such as cleaved steps, reveals the presence of V defects and confirms the thin six-walled structure of the V defect with InGaN/GaN {1011} layers. These scanning electron microscopy observations can be performed after very simple specimen preparation, namely just cleaving the sapphire substrate with the epilayers.

High-resolution scanning electron microscopy observation of GaN/AlGaN strained-layer superstructures in GaN-based violet laser diodes

Two hundred coupled layers of n-Al0.14Ga0.86N (3 nm)/n-GaN (3 nm) strained-layer superstructures (SLSs) with a n-GaN:Si layer were grown directly on a (0001) sapphire substrate by metalorganic vapor-phase epitaxy. With the aid of image processing, each SLS was definitely resolved as a bright or dark fringe 3 nm wide in the mapping of secondary electrons in a high-resolution scanning electron microscope.