Photoemission study and band alignment of GaN passivation layers on GaInP heterointerface

III-V semiconductor-based photoelectrochemical (PEC) devices show the highest solar-to-electricity or solar-to-fuel conversion efficiencies. GaInP is a relevant top photoabsorber layer or a charge-selective contact in PEC for integrated and direct solar fuel production, due to its tunable lattice constant, electronic band structure, and favorable optical properties. To enhance the stability of its surface against chemical corrosion which leads to decomposition, we deposit a GaN protection and passivation layer. The n-doped GaInP(100) epitaxial layers were grown by metalorganic chemical vapor deposition on top of GaAs(100) substrate. Subsequently, thin 1-20 nm GaN films were grown on top of the oxidized GaInP surfaces by atomic layer deposition. We studied the band alignment of these multi-junction heterostructures by X-ray and ultraviolet photoelectron spectroscopy. Due to the limited emission depth of photoelectrons, we determined the band alignment by a series of separate measurements in which we either modified the GaInP(100) surface termination or the film thickness of the grown GaN on GaInP(100) buffer layers. On n-GaInP(100) surfaces prepared with the well-known phosphorus-rich (2x2)/c(4x2) reconstruction we found up-ward surface band bending (BB) of 0.34 eV, and Fermi level pinning due to the present surface states. Upon oxidation, the surface states are partially passivated resulting in a reduction of BB to 0.12 eV and a valence band offset (VBO) between GaInP and oxide bands of 2.0 eV. Between the GaInP(100) buffer layer and the GaN passivation layer, we identified a VBO of 1.8 eV. The corresponding conduction band offset of -0.2 eV is found to be rather small. Therefore, we evaluate the application of the GaN passivation layer as a promising technological step not only to reduce surface states but also to increase the stability of the surfaces of photoelectrochemical devices

Atomic surface structure of MOVPE-prepared GaP(1 1 1)B

Controlling the surface formation of the group-V face of (1 1 1)-oriented III-V semiconductors is crucial for subsequent successful growth of III-V nanowires for electronic and optoelectronic applications. With a view to preparing GaP/Si(1 1 1) virtual substrates, we investigate the atomic structure of the MOVPE (metalorganic vapor phase epitaxy)-prepared GaP(1 1 1)B surface (phosphorus face). We find that upon high-temperature annealing in the H2-based MOVPE process ambience, the surface is phosphorus-depleted, as evidenced by X-ray photoemission spectroscopy (XPS). However, a combination of density functional theory calculations and scanning tunneling microscopy (STM) suggests the formation of a partially H-terminated phosphorus surface, where the STM contrast is due to electrons tunneling from non-terminated dangling bonds of the phosphorus face. Atomic force microscopy (AFM) reveals that a high proportion of the surface is covered by islands, which are confirmed as Ga-rich by Auger electron spectroscopy (AES). We conclude that the STM images of the samples after high-temperature annealing only reflect the flat regions of the partially H-terminated phosphorus face, whereas an increasing coverage with Ga-rich islands, as detected by AFM and AES, forms upon annealing and underlies the higher proportion of Ga in the XPS measurements

Combining advanced photoelectron spectroscopy approaches to analyse deeply buried GaP(As)/Si(1 0 0) interfaces: Interfacial chemical states and complete band energy diagrams

The epitaxial growth of the polar GaP(1 0 0) on the nonpolar Si(1 0 0) substrate suffers from inevitable defects at the antiphase domain boundaries (APDs), resulting from mono-atomic steps on the Si(1 0 0) surface. Stabilization of Si(1 0 0) substrate surfaces with As is a promising technological step enabling the preparation of Si substrates with double atomic steps and reduced density of the APDs. In this paper, 4–50-nm-thick GaP epitaxial films were grown on As-terminated Si(1 0 0) substrates with different types of doping, miscuts, and As-surface termination by metalorganic vapor phase epitaxy (MOVPE). The GaP(As)/Si(1 0 0) heterostructures were investigated by X-ray photoelectron spectroscopy (XPS) combined with gas cluster ion beam (GCIB) sputtering and by hard X-ray photoelectron spectroscopy (HAXPES). We found residuals of As atoms in the GaP lattice (∼0.2–0.3 at.%) and a localization of As atoms at the GaP(As)/Si(1 0 0) interface (∼1 at.%). Deconvolution of core level peaks revealed interface core level shifts. In As core levels, chemical shifts between 0.5 and 0.8 eV were measured and identified by angle-resolved XPS measurements. Similar valence band offset (VBO) values of 0.6 eV were obtained, regardless of the doping type of Si substrate, Si substrate miscut or type of As-terminated Si substrate surface. The band alignment diagram of the GaP(As)/Si(1 0 0) heterostructure was deduced

Combining advanced photoelectron spectroscopy approaches to analyse deeply buried GaP As Si 1 0 0 interfaces Interfacial chemical states and complete band energy diagrams

The epitaxial growth of the polar GaP 1 0 0 on the nonpolar Si 1 0 0 substrate suffers from inevitable defects at the antiphase domain boundaries APDs , resulting from mono atomic steps on the Si 1 0 0 surface. Stabilization of Si 1 0 0 substrate surfaces with As is a promising technological step enabling the preparation of Si substrates with double atomic steps and reduced density of the APDs. In this paper, 4 50 nm thick GaP epitaxial films were grown on As terminated Si 1 0 0 substrates with different types of doping, miscuts, and As surface termination by metalorganic vapor phase epitaxy MOVPE . The GaP As Si 1 0 0 heterostructures were investigated by X ray photoelectron spectroscopy XPS combined with gas cluster ion beam GCIB sputtering and by hard X ray photoelectron spectroscopy HAXPES . We found residuals of As atoms in the GaP lattice amp; 8764;0.2 0.3 at. and a localization of As atoms at the GaP As Si 1 0 0 interface amp; 8764;1 at. . Deconvolution of core level peaks revealed interface core level shifts. In As core levels, chemical shifts between 0.5 and 0.8 eV were measured and identified by angle resolved XPS measurements. Similar valence band offset VBO values of 0.6 eV were obtained, regardless of the doping type of Si substrate, Si substrate miscut or type of As terminated Si substrate surface. The band alignment diagram of the GaP As Si 1 0 0 heterostructure was deduce

Band bending at heterovalent interfaces Hard X ray photoelectron spectroscopy of GaP Si 001 heterostructures

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 Sisingle bondP 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 amp; 9651;EV 1.1 0.2 eV SD samples and amp; 9651;EV 0.8 0.2 eV TD samples at GaP Si 0 0 1 interface