Comparison of different X‐ray‐based scanning electron microscopy methods to detect sub‐nanometre ultra‐thin InAs layers deposited on top of GaAs

We compare three different methods of X‐ray analysis in a scanning electron microscope (SEM): energy‐dispersive X‐ray spectroscopy (EDX), wavelength‐dispersive X‐ray spectroscopy (WDX) and micro X‐ray fluorescence (μXRF). These methods are all applied to the same gallium arsenide (GaAs) wafer with a 0.8 nm layer of indium arsenide (InAs) on top. All methods allow detection and quantification of the indium L‐line intensity from the thin InAs layer. EDX is the easiest to perform, WDX is the most sensitive and μXRF a novel technique where a poly‐capillary optics is used to focus an X‐ray beam from a high‐voltage X‐ray tube onto a small spot several micrometres wide and the characteristic X‐rays produced are detected by a solid‐state silicon detector similar to that used in EDX. It is to our knowledge the first time a sub‐nanometre layer is reliably detected and analysed using μXRF in an SEM.