Chapter 7 - Spatially Resolved Thermoluminescence in a Scanning Electron Microscope

Abstract

Abstract The capabilities of thermoluminescence (TL), performed in a scanning electron microscope (SEM), are presented using the electron beam for sample excitation. By using small beam currents in the range of a few pascals and short excitation times in the order of several seconds, a spatially resolved defect analysis on a microscopic scale is achieved. Conversely, large beam currents and prolonged excitation results in a loss of spatial resolution by means of intense cathodoluminescence, causing photoexcitation of the specimen. A spatially resolved analysis of defects down to a few microns is demonstrated for bulk crystals and an epitaxial multilayer structure. For the bulk crystals, we determine the trap parameters by fitting the TL curve. The variations of the TL peak heights, which are recorded after selective excitation of different regions of the crystal, reveal a spatially inhomogeneous distribution of the defects. For the epitaxial sample, a selective excitation of different layers is achieved by varying the primary electron energy. This results in a set of TL curves, which depict the samples depth profile. In addition, we demonstrate some enhanced methods to thermoluminescence TL, which will allow us to gain more insight into the characteristics of the traps and recombination centers. A trap with a temperature-dependent capture coefficient is identified in bulk aluminum nitride (AlN) by using different temperatures for sample excitation. Also, spectrally resolved TL was performed, which allowed to analyze the radiative recombination centers involved in the emission of TL.