Novel Correlated Energy-Loss and Cathodoluminescence Spectroscopy in the Transmission Electron Microscope

Many modern semiconductor devices are based on multiple layer structures or the lateral structuring of planar layers to locate charge carriers in specific positions. These so-called quantum domain structures can have unique (opto)electronic properties, depending on the design used for carrier confinement (quantum wells, quantum wires or quantum dots for confinement in two, one or zero dimensions of space, respectively). Various forms of spectroscopy can be used to investigate such materials, however, most lack the spatial resolution necessary to study individual nanostructures. Spectroscopy in a transmission electron microscope (TEM) has the unique advantage of being able to investigate such individual nanostructures embedded below the specimen surface at nanometre-scale spatial resolution in two dimensions. This project proposes to combine the rather new method of electron spectroscopic profiling (ELSP), a hybrid imaging-spectroscopy method based on electron energy-loss spectroscopy (EELS) in a transmission electron microscope equipped with imaging energy filter, and cathodoluminescence (CL) spectroscopy. While EELS provides chemical and electronic information, CL yields optical information. Hence, the combination of both methods in the same instrument provides a unique probe of the local optoelectronic properties of light-emitting quantum domain structures. It is intended to investigate in particular quantum well and quantum dot structures of compound semiconductors with spatial dimensions of only a few nanometres in one or three dimensions, respectively, which are only really accessible using a modern analytical TEM. In order to incorporate CL detection into the narrow high-resolution pole-piece of a high-quality field-emission (scanning) TEM an existing specimen holder will be modified in order to accommodate both a newly designed highly-efficient light collecting optical cavity and a fibre optic cable. The fibre optics will allow the user to connect the specimen holder to two external spectrometers, a small Czerny-Turner type spectrometer with silicon diode array detector for the ultraviolet-visible (UV-VIS) wavelength range important for wide-bandgap nitride semiconductors or a high-resolution optical grating diffractometer installed in another laboratory with cooled germanium detector for the infrared (IR) range, relevant for the study of arsenide based semiconductors.