Band offset

About: Band offset is a research topic. Over the lifetime, 2446 publications have been published within this topic receiving 53450 citations.

Band alignment in visible-light photo-active CoO/SrTiO3 (001) heterostructures

Abstract: Epitaxial oxide heterostructures are of fundamental interest in a number of problems ranging from oxide electronics to model catalysts. The epitaxial CoO/SrTiO3 (001) heterostructure on Si(001) has been recently studied as a model oxide catalyst for water splitting under visible light irradiation (Ngo et al., J. Appl. Phys. 114, 084901 (2013)). We use density functional theory to investigate the valence band offset at the CoO/SrTiO3 (001) interface. We examine the mechanism of charge transfer and dielectric screening at the interface and demonstrate that charge transfer is mediated by the metal-induced gap states in SrTiO3, while the dielectric screening at the interface is largely governed by the ionic polarization of under-coordinated oxygen. Based on this finding, we argue that strain relaxation in CoO plays a critical role in determining the band offset. We find that the offsets of 1.36–1.10 eV, calculated in the Schottky-limit are in excellent agreement with the experimental value of 1.20 eV. In addition, we investigate the effect of the Hubbard correction, applied on the Co 3d states, on the dipole layer and potential shift at the interface.

Band offset at TiO2/MDMO PPV and TiO2/PEDOT PSS interfaces studied using photoelectron spectroscopy

Abstract: We report band alignment and band offset studies across the interfaces of hetero-structures of TiO2 with poly[2-methoxy-5-(3′,7′-dimethyl-octyloxy)-p-phenylene vinylene] (MDMO PPV) and poly(styrenesulfonate) doped poly(3,4-ethylenedioxythiophene) (PEDOT PSS) using photoelectron spectroscopy. In both the cases the band alignment was found to be type II with significant band bending in the range 0.2 to 0.3 eV. In the case of the TiO2/MDMO PPV hetero-structure, the valance band offset (VBO)/conduction band offset (CBO) were found to be 2.68 ± 0.1 eV/1.68 ± 0.1 eV, while the TiO2/PEDOT PSS hetero-structure exhibited VBO/CBO as 2.3 ± 0.1 eV/0.7 ± 0.1 respectively. Based on these results, schematic band diagrams for these organic/inorganic hetero-structures were proposed. Our studies are important for the optimum design of various photovoltaic devices based on these organic/inorganic hetero-junctions.

Electron band alignment at the interface of (100)InSb with atomic-layer deposited Al2O3

Abstract: From experiments on internal photoemission of electrons at the (100)InSb/Al2O3 interface, the top of the InSb valence band is found to be 3.05 ± 0.10 eV below the oxide conduction band and corresponds to a conduction band offset of 2.9 ± 0.1 eV. These results indicate that the top of valence band in InSb lies energetically at the same level as in GaSb and above the valence bands in InxGa1−xAs (0 ≤ x ≤ 0.53) or InP, suggesting that variation of the group III cation has no significant impact on the energy of the semiconductor valence band top and, therefore, it mostly affects the conduction band bottom edge.

Design of InGaN-ZnSnN2 quantum wells for high-efficiency amber light emitting diodes

Abstract: InGaN-ZnSnN2 based quantum wells (QWs) structure is proposed and studied as an active region for high efficiency amber (λ ∼ 600 nm) light emitting diodes (LEDs), which remains a great challenge in pure InGaN based LEDs. In the proposed InGaN-ZnSnN2 QW heterostructure, the thin ZnSnN2 layer serves as a confinement layer for the hole wavefunction utilizing the large band offset at the InGaN-ZnSnN2 interface in the valence band. The barrier layer is composed of GaN or AlGaN/GaN in which the thin AlGaN layer is used for a better confinement of the electron wavefunction in the conduction band. Utilizing the properties of band offsets between ZnSnN2 and InGaN, the design of InGaN-ZnSnN2 QW allows us to use much lower In-content (∼10%) to reach peak emission wavelength at 600 nm, which is unachievable in conventional InGaN QW LEDs. Furthermore, the electron-hole wavefunction overlap (Γe-h) for the InGaN-ZnSnN2 QW design is significantly increased to 60% vs. 8% from that of the conventional InGaN QW emitting at the same wavelength. The tremendous enhancement in electron-hole wavefunction overlap results in ∼225× increase in the spontaneous emission radiative recombination rate of the proposed QW as compared to that of the conventional one using much higher In-content. The InGaN-ZnSnN2 QW structure design provides a promising route to achieve high efficiency amber LEDs.InGaN-ZnSnN2 based quantum wells (QWs) structure is proposed and studied as an active region for high efficiency amber (λ ∼ 600 nm) light emitting diodes (LEDs), which remains a great challenge in pure InGaN based LEDs. In the proposed InGaN-ZnSnN2 QW heterostructure, the thin ZnSnN2 layer serves as a confinement layer for the hole wavefunction utilizing the large band offset at the InGaN-ZnSnN2 interface in the valence band. The barrier layer is composed of GaN or AlGaN/GaN in which the thin AlGaN layer is used for a better confinement of the electron wavefunction in the conduction band. Utilizing the properties of band offsets between ZnSnN2 and InGaN, the design of InGaN-ZnSnN2 QW allows us to use much lower In-content (∼10%) to reach peak emission wavelength at 600 nm, which is unachievable in conventional InGaN QW LEDs. Furthermore, the electron-hole wavefunction overlap (Γe-h) for the InGaN-ZnSnN2 QW design is significantly increased to 60% vs. 8% from that of the conventional InGaN QW emitting at t...

Dopant incorporation, Fermi-level movement, and band offset at the Ge/GaAs(001) interface

Abstract: We have used high-energy Auger electron diffraction and x-ray photoelectron diffraction to obtain a direct structural determination of $n$-type dopant atoms coevaporated with ultrathin Ge epilayers on GaAs(001). Angular distributions of photoelectron intensity from the isovalent dopant atoms P and Sb establish that P atoms uniformly incorporate into the epilayer and occupy lattice sites, whereas Sb atoms surface segregate. These structural results are strongly correlated with Fermi-level movement at the interface. The Fermi-level energy within the band gap is critically dependent on overlayer structure. However, the valence-band offset remains constant at 0.60\ifmmode\pm\else\textpm\fi{}0.05 eV, independent of dopant kind, quantity, and spatial distribution in the epilayer. Significant Schottky-barrier-height reduction (0.4-0.5 eV) occurs only when dopant atoms occupy Ge lattice sites.