Chemical Surface Composition of Sputtered ZnO Films

Examples of XPS spectra recorded from in situ sputter-deposited ZnO and ZnO Al films are shown in Fig. 4.6. Absence of contaminations is evident from the survey spectra, which show only emissions from Zn and O. Aluminium-doped ZnO films, deposited from a target with a nominal Al concentration of 2 wt%, also show a small Al signal. Detailed spectra of the Zn 2p3/2, O Is, Zn LMM Auger, and valence band emissions for largely different deposition conditions are given in the lower half of Fig. 4.6. 

The chemical composition of the surface can be evaluated from the integrated intensities of the core-level emissions [31]. Unfortunately, the accuracy of quantitative analysis with photoelectron spectroscopy is generally limited to a few percent even when good standards are available [31]. Therefore, even from a large number of measured samples it was not possible to observe a 

2 Oxygen-Related Surface Species and Initial Growth of ZnO Films 

The O Is spectra in Fig. 4.6 show an additional small emission at higher binding energies. The energy difference between the ZnO-related emission at 530-531 eV and the high binding energy component amounts to 1.6-1.8 eV. Such a species is always observed on ZnO surfaces. In literature, it is mostly attributed to adsorbed species. These include water and hydroxides 

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