Abstract
Amorphous Ga2O3 thin films were deposited on p-type (111) and (100) surfaces of silicon and (100) germanium by atomic layer deposition (ALD). X-ray photoelectron spectroscopy (XPS) was used to investigate the band alignments at the interfaces using the Kraut Method. The valence band offsets were determined to be 3.49± 0.08 eV and 3.47± 0.08 eV with Si(111) and Si(100) respectively and 3.51eV± 0.08 eV with Ge(100). Inverse photoemission spectroscopy (IPES) was used to investigate the conduction band of a thick Ga2O3 film and the band gap of the film was determined to be 4.63±0.14 eV. The conduction band offsets were found to be 0.03 eV and 0.05eV with Si(111) and Si(100) respectively, and 0.45eV with Ge(100). The results indicate that the heterojunctions of Ga2O3 with Si(100), Si(111) and Ge(100) are all type I heterojunctions.
Highlights
Ga2O3 is a wide band gap material with the largest band gap of the transparent conducting oxides, at ≈4.8 eV
The band alignment of β-Ga2O3 with Si has previously been reported by Guo et al.[9] using the electron affinity rule,[11] this disagrees with the alignment obtained by Chen et al.,[12] where the alignment is measured by photoelectron spectroscopy
The interpretation of the alignment obtained by Chen et al is complicated by a number of issues: Firstly, the authors use a non-monochromatic x-ray source, resulting in the presence of x-ray satellites, which are problematic for finding the valence band maximum (VBM) of the Ga2O3 sample; secondly, the interfacial sample is produced by Ar+ ion etching, the interfacial sample clearly shows two Ga species in the Ga 2p spectrum, indicative of the preferential removal of oxygen, leaving a sub-stoichiometric oxide or elemental Ga; their discussion on the formation of an interfacial SiO2-x layer is limited by the issues raised above
Summary
Ga2O3 is a wide band gap material with the largest band gap of the transparent conducting oxides, at ≈4.8 eV. We describe the use of the Kraut method[16] to investigate the band alignments of Ga2O3 with Si(111), Si(100) and Ge(100) substrates. As the Kraut method requires a thick, bulklike sample, a thin, interfacial sample, where the core-levels of the substrate can be observed and a clean substrate, thick (31 nm) and thin (3 nm) Ga2O3 layers were synthesized on the aforementioned substrates.
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