Elemental Distribution Profiling of Thin Films for Solar Cells

Abstract

The present chapter will give an overview about the techniques glow discharge-optical emission (GD-OES) and glow discharge-mass spectroscopy (GD-MS), secondary ion mass spectroscopy (SIMS) and sputtered neutral mass spectroscopy (SNMS), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS), which are methods broadly available for depth-resolved information about the matrix and trace element concentrations in multilayer stacks as those used for thin-film solar cells. In addition, also energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope may be applied on fractured cross-section specimens of these multilayer stacks, providing a quick way of analyzing the spatial distribution of the matrix elements, which is why this technique is also included in this chapter.AES, XPS, SIMS, and SNMS have a good lateral resolution, and depth-resolved information may be obtained by the investigation either of cross-section specimens or (most simply) of a fractured surface (see Section 16.6.3.1). All of these methods are in general performed in combination with a sputtering process when aiming for depth-resolved elemental distribution analysis. Thereby, ions are accelerated toward the surface of the sample and collide with the atoms in the region near the surface. The resulting collision cascade leads to the emission of sample material from the surface and forms a more or less flat crater. While AES and XPS only use this process to expose the region of interest, SIMS and SNMS analyze the sputtered material. Because of practical reasons, different sputtering rates are employed at times, that is, fast sputtering for removing sample material and slow sputtering during the analysis.XPS, AES, and SIMS work under ultrahigh vacuum conditions and must be performed at high-acceleration voltages in order to obtain high sputtering yields. These techniques make use of a scanning ion beam for sputtering, which allows the discrimination of crater edge effects. For the SIMS analysis, only an electronically gated area is used for the analysis. Similarly, in AES and XPS measurements, only

Glow Discharge Mass Spectrometry

“…(Source: Cornel Venzago. )Figure 13.25 Trace and matrix concentrations of a Si layer system on a SiC substrate (C concentration scaled by the right axis) 136. …”