Korte, L.; Rößler, R.; Pettenkofer, C.: Direct determination of the band offset in atomic layer deposited ZnO/hydrogenated amorphous silicon heterojunctions from X-ray photoelectroscopy valence band spectra. Journal of Applied Physics 115 (2014), p. 203715/1-7
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The chemical composition and band alignment at the heterointerface between ALD-grown zinc oxide (ZnO) and hydrogenated amorphous silicon (a-Si:H) is investigated using monochromatized X-ray photoelectron spectroscopy. A new approach for obtaining the valence band offset DeltaEV is developed, which consists in fitting the valence band (VB) spectrum obtained for a-Si:H with a thin ZnO overlayer as the sum of experimentally obtained VB spectra of a bulk a-Si:H film and a thick ZnO film. This approach allows obtaining DeltaEV = 2.71±0.15 eV with a minimum of assumptions, and also yields information on the change in band bending of both substrate and ZnO film. The band offset results are compared to values obtained using the usual approach of comparing valence band edge-to-core level energy differences, DeltaEB,CL – DeltaEB,VB. Furthermore, a theoretical value for the VB offset is calculated from the concept of charge neutrality level line-up, using literature data for the CNLs and the experimentally determined ZnO/a-Si:H interface dipole. The thus obtained value of DeltaEVCNL = 2.65±0.3 eV agrees well with the experimental DeltaEV.