Abstract
X-ray photoelectron spectroscopy (XPS) is one of the most used methods in a diverse field of materials science and engineering. The elemental core-level binding energies (BE) and core-level shifts (CLS) are determined and interpreted in the XPS. Oxidation is commonly considered to increase the BE of the core electrons of metal and semiconductor elements (i.e., positive BE shift due to O bonds), because valence electron charge density moves toward electronegative O atoms in the intuitive charge-transfer model. Here we demonstrate that this BE hypothesis is not generally valid by presenting XPS spectra and a consistent model of atomic processes occurring at HfO2/InP interface including negative In CLSs. It is shown theoretically for abrupt HfO2/InP model structures that there is no correlation between the In CLSs and the number of oxygen neighbors. However, the P CLSs can be estimated using the number of close O neighbors. First native oxide model interfaces for III-V semiconductors are introduced. The results obtained from ab initio calculations and synchrotron XPS measurements emphasize the importance of complementary analyses in various academic and industrial investigations where CLSs are at the heart of advancing knowledge.
Highlights
The x-ray photoelectron spectroscopy (XPS) is widely utilized in the characterization of the chemical composition of materials and to understand and control various scientifically and industrially interesting phenomena such as atomic layer deposition, catalysis, materials protection, operation of electronic devices, and photoelectrochemical reaction
It should be noted that I2 is not very reliable due to only slight core-level shifts (CLS) which results in large changes in intensity ratios when the shifts are varied by even +/− 0.05 eV
The presented results for HfO2/InP junctions demonstrate that the semiconductor oxidation can cause negative CLSs, in contrast to the common hypothesis that the material oxidation causes positive CLSs, which is based on the charge-transfer model and the well-understood SiO2/Si system
Summary
The x-ray photoelectron spectroscopy (XPS) is widely utilized in the characterization of the chemical composition of materials and to understand and control various scientifically and industrially interesting phenomena such as atomic layer deposition, catalysis, materials protection, operation of electronic devices, and photoelectrochemical reaction (e.g., refs[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]). The BE is increased with the number of oxygen neighbors It is much less clear, to what extent this model can be applied to other, especially more complex systems like oxide/III-V semiconductor interfaces. The CLSs depend on several factors, not just on the atomic on-site charge and different complex environments can induce similar CLSs. In this work, we report that the semiconductor oxidation can surprisingly cause negative CLSs by presenting theoretical and experimental results for the HfO2/InP junction. The oxidation-induced CLSs of a semiconductor are interpreted, which is further essential to understand phenomena like the ALD mechanisms[4] and the formation of surface defects harmful to electronics and photonics devices[10,16,17,18,19]. We focus on the CLSs of In 3d and P 2p, which are obtained with high enough resolution and surface sensitivity concerning the analysis made here, and yield well distinguishable changes as a function of photon energy and different sample treatments
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