Investigation of polarization-induced electric field in ultrathin InAlN layers on GaN by X-ray photoelectron spectroscopy

The polarization‐induced electric field in ultrathin InxAl1‐xN (0.17 ≤ x ≤ 0.30) layers on GaN was investigated by using X‐ray photoelectron spectroscopy (XPS). The core‐level energy position, ECL, and the full width at half maximum (FWHM) of the Al2p, In4d, and In3d spectra from 2.5‐nm‐thick InAlN layers increased with the increase in the photoelectron exit angle (elevation angle). These increases were well reproduced with numerical calculations assuming polarization‐induced internal fields combined with surface Fermi level pinning. The magnitudes of the internal field decreased as the In molar fraction increased. The Ga3d spectra from the host GaN layers markedly shifted by 530 meV depending on the molar fraction of InAlN layers, which was independent of the exit angle. This indicated that the Fermi level was unpinned at the interfaces, or GaN surfaces, and shifted due to the potential drop in the InAlN layers. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)