Measurement of the Band Bending and Surface Dipole at Chemically Functionalized Si(111)/Vacuum Interfaces

Abstract

The core-level energy shifts observed using X-ray photoelectron spectroscopy (XPS) have been used to determine the band bending at Si(111) surfaces terminated with Si–Br, Si–H, and Si–CH3 groups, respectively. The surface termination influenced the band bending, with the Si 2p3/2 binding energy affected more by the surface chemistry than by the dopant type. The highest binding energies were measured on Si(111)–Br (whose Fermi level was positioned near the conduction band at the surface), followed by Si(111)–H, followed by Si(111)–CH3 (whose Fermi level was positioned near midgap at the surface). Si(111)–CH3 surfaces exposed to Br2(g) yielded the lowest binding energies, with the Fermi level positioned between midgap and the valence band. The Fermi level position of Br2(g)-exposed Si­(111)–CH3 was consistent with the presence of negatively charged bromine-containing ions on such surfaces. The binding energies of all of the species detected on the surface (C, O, Br) shifted with the band bending, illustrating the importance of isolating the effects of band bending when measuring chemical shifts on semiconductor surfaces. The influence of band bending was confirmed by surface photovoltage (SPV) measurements, which showed that the core levels shifted toward their flat-band values upon illumination. Where applicable, the contribution from the X-ray source to the SPV was isolated and quantified. Work functions were measured by ultraviolet photoelectron spectroscopy (UPS), allowing for calculation of the sign and magnitude of the surface dipole in such systems. The values of the surface dipoles were in good agreement with previous measurements as well as with electronegativity considerations. The binding energies of the adventitious carbon signals were affected by band bending as well as by the surface dipole. A model of band bending in which charged surface states are located exterior to the surface dipole is consistent with the XPS and UPS behavior of the chemically functionalized Si(111) surfaces investigated herein.

Photo-assisted electrodeposition of MoSxfrom ionic liquids on organic-functionalized silicon photoelectrodes for H2generation

“…Fig. 11,12,45,46 In this work, it was reported that the greatest extent of band bending occurred on the p-Si(111)|H electrodes as compared with other surface moieties ( Table 2). As shown in Fig.…”

Combined soft and hard X-ray ambient pressure photoelectron spectroscopy studies of semiconductor/electrolyte interfaces

“…A common assumption is that core-level binding energy shifts mirror the shifts in the valence band maximum induced by band bending. As a result, PES has been successfully used to correlate semiconductor band edge positions and band bending with the chemical composition of their surfaces [19,20]. Such an approach has been recently used to study band alignment at the solid-solid interface formed between silicon and TiO 2 protection layers for photoelectrochemical applications [21].…”

Computational insights into charge transfer across functionalized semiconductor surfaces

“…For an n-type semiconductor the behavior is reversed and a molecule with a negative dipole increases the V oc by increasing the barrier height and depletion width at the surface. The surface dipole (δ) is defined as the difference between the electron affinity at the surface (χ s ) and the electron affinity in the bulk (χ B ) of the semiconductor χ s can be expressed in terms of the work function at the surface (Φ s ), band gap of the semiconductor (E g ), and the absolute energy difference between the valence band edge and the Fermi level (|E v −E F | s ) at the surface resulting in an expression for the surface dipole as Equation (4) allows for a direct determination of the surface dipole because the values of E g and χ B can be found in literature while the magnitude of Φ S and |E v −E F | s can be measured from ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy data (XPS), respectively [47][48][49].…”