O. Romanyuk

Time-Resolved In Situ Spectroscopy During Formation of the GaP/Si(100) Heterointerface.

Though III-V/Si(100) heterointerfaces are essential for future epitaxial high-performance devices, their atomic structure is an open historical question. Benchmarking of transient optical in situ spectroscopy during chemical vapor deposition to chemical analysis by X-ray photoelectron spectroscopy enables us to distinguish between formation of surfaces and of the heterointerface. A terrace-related optical anisotropy signal evolves during pulsed GaP nucleation on single-domain Si(100) surfaces. This dielectric anisotropy agrees well with the one calculated for buried GaP/Si(100) interfaces from differently thick GaP epilayers. X-ray photoelectron spectroscopy reveals a chemically shifted contribution of the P and Si emission lines, which quantitatively corresponds to one monolayer and establishes simultaneously with the nucleation-related optical in situ signal. We attribute that contribution to the existence of Si-P bonds at the buried heterointerface. During further pulsing and annealing in phosphorus ambient, dielectric anisotropies known from atomically well-ordered GaP(100) surfaces superimpose the nucleation-related optical in situ spectra.

Dielectric response functions of the (0001¯), (101¯3) GaN single crystalline and disordered surfaces studied by reflection electron energy loss spectroscopy

Polar GaN(0001¯) (1×1), semipolar GaN(101¯3) surfaces prepared in NH3 vapor, and their disordered counterparts are investigated by reflection electron energy loss spectroscopy (REELS) and low-energy electron diffraction. The REELS spectra are measured in a range of polar angles at electron kinetic energies of 200 and 1000 eV. The electron energy loss function is determined from the REELS within the framework of the semiclassical approach. Good agreement between experimental and theoretical functions is achieved at all angles for the disordered GaN surfaces and for the ordered surfaces measured at a kinetic energy of 1000 eV. The agreement is worse for the crystals measured at 200 eV, which is explained by the coherent scattering contributions at low energies. The optical constants of the GaN surfaces are derived from the computed dielectric functions: the optical properties of the (0001¯) and (101¯3) surfaces are similar, except for differences in bandgap values, which may be due to observed steps on the ...

Polarity of semipolar wurtzite crystals: X-ray photoelectron diffraction from GaN{101¯1} and GaN{202¯1} surfaces

Polarity of semipolar GaN(101¯1) (101¯1¯) and GaN(202¯1) (202¯1¯) surfaces was determined with X-ray photoelectron diffraction (XPD) using a standard MgKα source. The photoelectron emission from N 1s core level measured in the a-plane of the crystals shows significant differences for the two crystal orientations within the polar angle range of 80–100° from the 〈0001〉 normal. It was demonstrated that XPD polar plots recorded in the a-plane are similar for each polarity of the GaN{101¯1} and GaN{202¯1} crystals if referred to 〈0001〉 crystal axes. For polarity determinations of all important GaN{h0h¯l} semipolar surfaces, the above given polar angle range is suitable.

An experimental-theoretical atomic-scale study - in situ analysis of III–V on Si(100) growth for hybrid solar cells

We consider GaP/Si(100) as quasi-substrate for III-V-on-silicon growth targeting solar energy exploration in dual junction devices for both photovoltaics as well as photoelectrochemical tandem diodes with optimum bandgaps. We prepare Si(100) surfaces with majority domains of either type, grow thin GaP layers free of anti-phase disorder, find that abrupt Si-P interfaces are favored over abrupt Si-Ga interfaces and, finally, observe an RAS signal attributed to N incorporation in GaPN/Si(100). Combining in situ reflection anisotropy spectroscopy during metalorganic vapor phase epitaxy with UHV-based surface techniques and ab initio DFT calculations, we aim to understand the interface formation at the atomic scale.