Spectroscopic information may be acquired using an electron beam in a modern scanning electron microscope (SEM), exploiting the cathodoluminescence (CL) signal. CL offers several advantages over the usual optical spectroscopy. The multimode imaging capabilities of the SEM enable the correlation of optical properties (via CL) with surface morphology (secondary electron mode) at the nanometer scale and the large energy of the electrons allows the excitation of wide-bandgap materials.
Here, we present results obtained on a field emission time-resolved and continuous (CW) cathodoluminescence scanning electron microscope. The microscope can either be operated in CW mode by heating up the emitter (Schottky emission), or in time-resolved mode by illuminating the field emission gun with a femtosecond UV laser, so that ultrafast electron pulses are emitted through the photoelectric effect. In both modes, a spacial resolution around 10 nm is demonstrated. The collected cathodoluminescence signal is dispersed in a spectrometer and analyzed with a CCD camera (CW mode) or an ultrafast STREAK camera to obtain <10 ps time resolution (TR mode). Quantitative CW cathodoluminescence was first used to quickly map defects in III-V semiconductor structures. Then, time-resolved cathodoluminescence measurements were carried out on specific regions in order to measure local lifetimes and carrier diffusion within the structures.
We will also discuss the advantages of combining CL with a scanning transmission electron microscope (STEM) and introduce Attolight’s most recent developments in this field.