| AVS 60th International Symposium and Exhibition | |
| Applied Surface Science | Tuesday Sessions |
| Session AS-TuM |
| Session: | Developments in Electron Spectroscopies for Non-Ideal Samples |
| Presenter: | A. Barlow, NEXUS, Newcastle University, UK |
| Authors: | A. Barlow, NEXUS, Newcastle University, UK P. Cumpson, NEXUS, Newcastle University, UK |
| Correspondent: | Click to Email |
There is an ever-present need to characterise surfaces and interfaces with increasing sensitivity and precision. One frequently-used tool to do this is the "Relative Depth Plot" (RDP) that can be derived very easily from Angle-Resolved XPS spectra. Despite the name, this does not plot relative depth, but relative attenuation of the signal electrons. For peaks widely-separated in energy this will lead to errors, so that even the order of layers, not just their depth, is incorrect. This may be obvious to XPS practitioners, but to those collaborating with them, or those new to XPS such as many of our clients, the name "Relative Depth Plot" plot can be extremely misleading.
Compound semiconductors are a class of specimen that is ideal for illustrating these issues. Available in good quality they have known compositions, low roughness and have a high degree of homogeneity, so that the composition as a function of depth is well-known. We have analysed a wide range of compound semiconductors including ZnSe, InAs, InSb, GaAs, GaP and CdTe using our parallel acquisition Angle-Resolved XPS instrument, using an argon gas cluster ion beam (GCIB) to clean these surfaces without damage. We present the results of applying RDP, Stratification[1], and some variants of these methods.
We develop a very simple correction factor that greatly improves (but does not completely eliminate) the RDP problem and which can be applied automatically. This is particularly valuable for many semiconductor materials that are of industrial significance. Understanding the nature of the surface of an active material, or the interface between two active materials, such as in a junction or at the surface of a photo-active sensor, is crucial for novel device development and advancement. It is even more important to interpret Angle-Resolved XPS spectra correctly in cases where layer order is genuinely unknown, as is often the case in biological problems, for example.
Finally, some investigations of sputter depth profiling of these materials using novel ion beam technology, argon gas clusters, will be discussed.
[1] M P Seah et al, Surf and Interface Anal. 21 (1994) 336–341