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X-ray photoemission spectroscopy has been used to measure the valence band offset ΔEv for the AlN/GaN (0001) heterojunction interface. The heterojunction samples were grown by reactive molecular beam epitaxy on 6H–SiC (0001) substrates. A nested interface band alignment with ΔEv=1.36±0.07 eV is obtained (ΔEc/ΔEv=52/48).

Accurate knowledge of the band discontinuities at a heterojunction interface and the factors that affect their magnitude are of both fundamental and practical interest. The application of x-ray photoemission spectroscopy (XPS) to the direct, contactless, and quantitative measurement of the valence band discontinuity (ΔEv) at abrupt heterojunctions is discussed. The topics covered include a description of a method to achieve precise measurement, results of ΔEv measurements for many heterojunction pairs selected from the lattice-matched semiconductor series Ge, GaAs, ZnSe, CuBr, and AlAs, and a comparison of experiment to models that predict ΔEv. Examples are given to illustrate the effect on ΔEv of such preparation-dependent parameters as growth sequence and interface crystallographic orientation.