Some Aspects of Quantitative Analysis of Ternary Alloys of Group III-Nitrides by Auger Electron Spectroscopy

Abstract

In recent years, much attention has been paid to semiconductor materials based on group III nitrides and their alloys used as short wavelength light emitting materials. The properties of these materials are tightly related to their chemical composition. One of these materials is also the alloy of Al and Ga nitrides, AlxGa1−xN. To determine the elemental composition and its depth distribution, Auger electron spectroscopy (AES) is one of the most widely used techniques. Even though depth profiling using AES is already a standard process, there are still fields in which a further development is needed. One of them is accurate quantitative evaluation of Auger spectra in the case of nanometer thin film structures based on chemical compounds such as GaN, other group III/nitrides and their alloys. Whereas in the analysis of homogeneous alloys the accuracy of quantitative AES is relatively good, problems are encountered in analysis of compounds because in general the shape of Auger peaks is changed in comparison with the pure element. Hence, the quantities needed to evaluate elemental concentrations (Auger current and elemental sensitivity factors) cannot be determined from the amplitude of the Auger peaks but from the area below the peaks in N(E) spectra [1,2]. Other phenomena affecting the accuracy of quantitative analysis are the changes in morphology, structure and initial composition in the surface region caused by bombarding the surface by high energy ions used for depth profiling. To cope with this adverse fact it is necessary to know the changes induced by ions directly in the particular analysed material. These changes depend on both the parameters of the ion beam (energy, kind of ions, angle of incidence) and the analysed material itself and are the result of preferential sputtering (component sputtering yields) and other effects induced by interaction of the ion beam with the solid [3,4]. From among the various methods for determining the component sputtering yields, the most reliable quantitative results could by obtained using standard samples of comparable composition. If AES analysis involves sputtering and if the same experimental parameters are used in sputtering both the analysed and reference samples, then the experimentally determined elemental sensitivity factors account also for the component sputtering yields. For correct quantitative interpretation of spectra of chemical compounds and of their alloys it is necessary to have the relative sensitivity factors of elements and the sputtering yields measured for the material under analysis [5]. So far only scanty data have been published on these quantities for aluminium, gallium and their alloys [6] and they do not cover the required range of experimental parameters needed for wider utilization in experimental practice. The topic of this work has been experimental determination of the quantities needed for reliable and precise quantitative interpretation of the measured Auger spectra of materials based on gallium and aluminium nitrides and their ternary alloys. Relative elemental sensitivity factors and component sputtering yields have been measured of the components contained in these multicomponent materials.