Direct Imaging of p–n Junction in Core–Shell GaN Wires

While core–shell wire-based devices offer a promising path toward improved optoelectronic applications, their development is hampered by the present uncertainty about essential semiconductor properties along the three-dimensional (3D) buried p–n junction. Thanks to a cross-sectional approach, scanning electron beam probing techniques were employed here to obtain a nanoscale spatially resolved analysis of GaN core–shell wire p–n junctions grown by catalyst-free metal–organic vapor phase epitaxy on GaN and Si substrates. Both electron beam induced current (EBIC) and secondary electron voltage constrast (VC) were demonstrated to delineate the radial and axial junction existing in the 3D structure. The Mg dopant activation process in p-GaN shell was dynamically controlled by the ebeam exposure conditions and visualized thanks to EBIC mapping. EBIC measurements were shown to yield local minority carrier/exciton diffusion lengths on the p-side (∼57 nm) and the n-side (∼15 nm) as well as depletion width in the range 40–50 nm. Under reverse bias conditions, VC imaging provided electrostatic potential maps in the vicinity of the 3D junction from which acceptor <i>N</i>_a and donor <i>N</i>_d doping levels were locally determined to be <i>N</i>_a = 3 × 10¹⁸ cm^–3 and <i>N</i>_d = 3.5 × 10¹⁸ cm^–3 in both the axial and the radial junction. Results from EBIC and VC are in good agreement. This nanoscale approach provides essential guidance to the further development of core–shell wire devices

Characterisation of Semiconductor Nanowires by Electron Beam Induced Microscopy and Cathodoluminescence

International audienceNowadays the realization of market-competitive devices based on nanomaterials is a major challenge. Optimization of the device performance requires deep understanding of the physical phenomena at the nanoscale. In this context, electron beambased techniques become indispensable. Several instruments have been developed in the past decades to provide versatile diagnostic solutions for improving materials, designs and device fabrication. These characterization techniques applied to nanostructured semiconductors can help filling the gap between material science and engineering by bringing in light important physical parameters. In this Chapter, the family of electron beam-based techniques is briefly introduced. First, the electron beam/matter interaction is described both in physical and operational terms. In particular, different phenomena occurring when a flux of electron collides with a semiconductor material are discussed. Then, two main electron beam scanning techniques are discussed in the following sections: electron beam induced current microscopy and cathodoluminescence. After a short description of the fundamentals, for each technique a bibliographic review is presented to illustrate its applications to analyses of semiconductor nanowires