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GaP is a preferred candidate for the transition between Si and heterogeneous III-V epilayers as it is nearly lattice-matched to Si. Here, we scrutinize the atomic structure and electronic properties of GaP/Si(0 0 1) heterointerfaces utilizing hard X-ray photoelectron spectroscopy (HAXPES). GaP(0 0 1) epitaxial films with thicknesses between 4 and 50 nm are prepared by metalorganic vapor phase epitaxy on either predominantly single-domain (SD) or two-domain (TD) Si(0 0 1) surfaces. The antiphase domain content in the GaP films is in situ controlled, employing reflection anisotropy spectroscopy. Via the analysis of core level photoelectron intensities, we reveal core level shifts of the P 2p and Si 2p peaks near the interface as well as core level shifts in the Ga 3d peaks near the surface. We suggest an Inter-Diffused Layer (IDL) model of the GaP/Si(0 0 1) interfacial structure with Si P bonds at the heterointerface and residual P atoms in the Si substrate. Using a newly developed Parametrized Polynomial Function (PPF) approach, we derive a non-monotonic band bending profile in the heterostructures, correct experimental valence band offsets implying interfacial electronic barriers, and determine valence band discontinuities of Δ E V = 1.1 ± 0.2 eV (SD samples) and Δ E V = 0.8 ± 0.2 eV (TD samples) at GaP/Si(0 0 1) interfaces.

Growth of GaN quantum dots (QDs) on polar and semipolar GaN substrates is a promising technology for efficient nitride-based light emitting diodes (LED). The QDs crystal orientation typically repeats the polarity of the substrate. In case of non-polar or semipolar substrates, the polarity of QDs is not obvious. In this article, the polarity of GaN QDs and of underlying layers was investigated nondestructively by X-ray photoelectron diffraction (XPD). Polar and semipolar GaN/Al0.5Ga0.5N heterostructures were grown on the sapphire substrates with (0001) and ( 1 1 ¯ 00 ) orientations by molecular beam epitaxy (MBE). Polar angle dependence of N 1s core-level photoelectron intensities were measured from GaN QDs and compared with the corresponding experimental curves from free-standing GaN crystals. It is confirmed experimentally, that the crystalline orientation of polar (0001) GaN QDs follows the orientation of the (0001) sapphire substrate. In case of semipolar GaN QDs grown on ( 1 1 ¯ 00 ) sapphire substrate, the ( 11 2 ¯ 2 ) polarity of QDs was determined.

The study of the chemical composition of buried interfaces by X-ray photoelectron spectroscopy (XPS) is limited by the inelastic mean free path of emitted photoelectrons (PE). Soft X-ray sources (AlKα) are generally suitable for careful probing of surfaces or very thin films. Here we applied gas cluster ion beam sputtering in combination with in-situ XPS (GCIB-XPS) to analyze buried GaP/Si(0 0 1) heterointerfaces. The GCIB method was used to dig a crater into the 20 nm thick GaP(0 0 1) film. We found optimal parameters for GCIB sputtering and achieved interface layers without severe damage. Destructive effects, i.e. broadening of core level peaks, could not be completely avoided, however, and the formation of metallic Ga on the GaP surface was observed. PE spectra of the sputtered heterostructures were compared with corresponding reference spectra of sputtered bulk crystals. Interface contributions to the intensity of phosphorus and sillicon core level peaks were revealed: interface components are shifted to high binding energies of P 2p Si 2p core levels. Similar results were obtained on 4 nm thick GaP/Si(0 0 1) by XPS. Finally, a top-to-bottom concept for buried semiconductor interfaces studies by GCIB-XPS is demonstrated.

Photoelectron diffraction is proposed to determine nondestructively the polarity of wurtzite crystals with polar surfaces (c-plane). Small segments of polar plots of photoemission from anion core levels in the ( 1 0 1 ¯ 0 ) azimuthal plane are qualitatively different for two polarities around the polar angle 20°. The magnitude of the ratio of electron photoemission intensities at two polar angles I20/I23 can be utilized as a simple criterion determining the crystal polarity.