Dipole formation and band alignment at the Si(111)/CuInS2 heterojunction

Abstract

Heterojunctions between Si(111):H faces and molecular beam epitaxy grown CuInS2 thin films were investigated. The interface formation was studied by means of photoelectron spectroscopy and low energy electron diffraction. Initial sulfur exposure of the Si substrate at 750 K leads to a surface dipole of (0.61±0.10) eV. Upon subsequent CuInS2 deposition, an interface dipole of (1.0±0.2) eV is observed. The valence band offsets between Si and CuInS2 films of different [Cu]/[In] ratios were determined and an average valence band offset of (0.08±0.15) eV is obtained. Comparison with model considerations points out that the experimental values of the valence band offset are consistent with the observed interface dipole.

Computational insights into charge transfer across functionalized semiconductor surfaces

“…The dipole shift determined using impedance spectroscopy in contact with octamethylferrocene-CH 3 CN-1.0 M LiClO4 is measured as −0.4 V and −0.25 V for n and p-Si(111), respectively [33]. The dipole shift determined using photoelectron spectroscopy in contact with vacuum is measured as −0.49 eV [48,49], [86,87]. These results are summarized in Table 1 below.…”

“…must match the experimental surface when predicting surface dipoles using DFT. These findings also suggest that the effective band-edge energies of a surface can be engineered to have a specific [33] Photoelectron Spectroscopy [48,49], [86,87] wxaMPS [83] dfT & MBPT [71] −0.40 v (n-Si) −0.49 ev −0.35 ev…”

“…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].…”

Chemical and electronic characterization of methyl-terminated Si(111) surfaces by high-resolution synchrotron photoelectron spectroscopy

“…This value may be compared to other Si surface terminations as ͓Si͑111͒ :H͔ = 4.17 eV, 44,45 ͓Si͑111͒ − ͑7 ϫ 7͔͒ = 4.16 eV, 36 and ͓Si͑100͒ − ͑2 ϫ 1͔͒ = 4.21 eV. 36 Estimating the electron affinity of bulk silicon as 4.05 eV, 46 the surface dipole ␦ caused by the methyl monolayer was calculated to be ϳ−0.4 eV.…”

Thin Film Solar Cells Based on Copper-Indiumgalium Selenide (Cigs) Materials Deposited by Electrochemical Techniques.

“…The large size of the grains implies that their electronic structure is similar to that of the bulk crystal. Moreover, the alignment of the bottom of the conduction band between the absorbing chalcopyrite layer and the surrounding buffer and transparent conducting layers favors quick drift of the electrons in thin-film solar cell devices [75,76]. These chalcopyrite materials also exhibit a very large absorption coefficient of 10 5 (cm −1 ) above the absorption edge as opposed to the majority of the III−V semiconductors with absorption coefficients of 10 4 (cm −1 ) and have yielded highest conversion efficiencies among thin film technologies at laboratory scale [77,78,79].…”