Band offset

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

A promising blue phosphorene/C2N van der Waals type-II heterojunction as a solar photocatalyst: a first-principles study.

Abstract: An appropriate band structure and effective carrier separation are very important for the performance of a solar photocatalyst. In this paper, based on first-principles calculations, it was predicted that blue phosphorene (BlueP) and a C2N monolayer can form a promising metal-free type-II heterojunction. The electronic structure of the BlueP/C2N heterojunction facilitated the overall water splitting reactions well. The projected band structure showed that the conduction band edge was contributed by C2N and the valence band edge was dominated by BlueP. Under the combination of the driving force of the band offset and the built-in electric field between the two layers, the photo-generated electrons and holes were transferred spontaneously to the conduction band of C2N and the valence band of BlueP, respectively. An effective carrier separation in the heterostructure was thus achieved. More notably, the obtained light absorption of the BlueP/C2N junction showed an obvious red-shift, which greatly extended the area of light adsorption to the visible light region. We further proposed that strain could also be used to modulate the band gap and the band edge positions of the heterojunction. Our results not only provide a theoretical design, but also reveal the fundamental separation mechanism of the photo-generated carriers in the BlueP/C2N heterojunction.

First principles investigation of scaling trends of zirconium silicate interface band offsets

Abstract: First principles density functional theory calculations are carried out to investigate the scaling trends of band offsets at model silicon/zirconium silicate interfaces. Owing to the d character of zirconium silicate conduction bands, the band gap and band offset are shown to decrease as the zirconium concentration is increased. Since the valence band character of silicates remains unchanged relative to SiO2, the conduction band offset alone decreases, leading to increasingly asymmetric band offsets at higher zirconium concentrations. The use of charge transfer dipoles at the interface is investigated as a possible remedy to restore the band offset symmetry by shifting the silicate bands relative to the silicon bands.

Interface instabilities and electronic properties of ZrO2 on silicon (100)

Abstract: The interface stability of Zr-based high-k dielectrics with an oxide buffer layer was explored with x-ray (hυ=1254eV) and ultraviolet (hυ=21.2eV) photoemission spectroscopy. Zirconium oxide films were grown and characterized in situ in a stepwise sequence to explore their chemical stability and electronic properties as a function of film thickness and processing conditions. The buffer layers serve to lower the interface state density and to address the high temperature instabilities of ZrO2 in direct contact with Si. This research addresses three issues: (1) the development of the band offsets and electronic structure during the low temperature (T 700°C). Annealing the as-grown films to 600°C results in an ∼2eV shift of the ZrO2-Si band alignment, giving a band offset that is, favorable to devices, in agreement wi...

Design of high speed Si/SiGe heterojunction complementary metal–oxide–semiconductor field effect transistors with reduced short-channel effects

Abstract: By taking advantages of higher carrier mobility and bandgap engineering in the Si/SiGe system, we explore the channel and source/drain (S/D) designs for Si/SiGe heterojunction complementary metal–oxide–semiconductor field effect transistors (CMOSFETs). A planar CMOS structure is proposed in which a strained SiGe layer (the hole channel) and a strained Si layer (the electron channel) grown on relaxed SiGe wells are designed for p- and n-MOSFETs, respectively, to provide better current drive capability. On the other hand, a strained-SiGe S/D heterojunction is also included in the CMOSFET device structure in that the band offset between S/D and the channel is found to be very effective in suppressing short-channel effects such as drain-induced barrier lowering/bulk punchthrough and drain leakage. With proper structure design, the near symmetrical n-MOS/p-MOS VT, enhanced current-drive capability and reduced short channel effects are achievable within the proposed planar structure.

Electronic and optical properties of two-dimensional covalent organic frameworks

Abstract: Two-dimensional covalent organic films with a macrocyclic network were recently synthesized experimentally under simple solvothermal conditions [J. W. Colson et al., Science, 2011, 332, 228], which offers immense potential for optoelectronic applications as in the case of graphene. Here we systematically investigate the electronic and optical properties of such novel covalent organic frameworks (COF-5, TP-COF and NiPc-PBBA COF) as free-standing sheets using density-functional theory. The results shed considerable light on the nature of spatial carrier confinement with band offset. COF-5 exhibits a type-II heterojunction alignment with significant valence and conduction band offsets, suggesting an effective spatial carrier separation of electrons and holes. In TP-COF, the valence offset is close to zero, related to the dispersed distribution of photoexcited holes over the entire structure, while the conduction band offset is still remarkable, indicating the effective confinement of photoexcited electrons. NiPc-PBBA COF presents a type-I heterojunction alignment where the band-edged wave functions are localized in the same region, achieving effective spatial carrier congregation. The calculated absorption peaks of the optical absorption of TP-COF and NiPc-PBBA COF frameworks are in agreement with experimental measurements, thus providing theoretical insights into experimental observed transmission spectra of these frameworks.