Important aspects of investigating optical excitations in semiconductors using a scanning transmission electron microscope

Since semiconductor structures are becoming smaller and smaller, the examination methods must also take this development into account. Optical methods have long reached their limits here, but small dimensions are also a challenge for electron beam techniques, especially when it comes to determining optical properties. In this paper, electron microscopic methods of investigating optical properties are discussed. Special attention is given to the physical limits and how to deal with them. We will cover electron energy loss spectrometry as well as cathodoluminescence spectrometry. We pay special attention to inelastic delocalisation, radiation damage, the Cerenkov effect, interference effects of optical excitations and higher diffraction orders on a grating analyser for the cathodoluminescence signal. As semiconductor components continue to evolve, they are shrinking in size. Transistors, the fundamental building blocks of microchips, now measure as small as several nanometres wide. This miniaturisation trend impacts their performance. The investigation of dielectric properties of such building blocks in miniaturised semiconductor devices is best accomplished using electron beam techniques. Thus, one can explore phenomena such as optical properties, bandgap energies and quantum confinement effects. But electron beam techniques also have their physical limitations in terms of spatial resolution, spurious relativistic and interference effects, which are topic of the present work. We utilise the spectroscopic investigation of the probe electrons as well as the emitted light of the electron-sample interaction. We touch topics like delocalisation of the electron-sample interaction, the Cerenkov effect, beam damage and higher-order diffraction at blazed grating analysers.