Band offset

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

ZnS/ZnSe strained-layer superlattices under pressure.

Abstract: First-principles density-functional calculations of the electronic properties of ZnS/ZnSe (001) strained-layer superlattices are used to investigate the influence of hydrostatic pressure on the valence-band offset (VBO). Three different strain modes corresponding to various values of the relative thicknesses of the two types of layers are considered. The pressure coefficients of the VBO's are found to be very sensitive to the strain mode. A I→II type conversion associated with the conduction-band crossover between the ZnSe well layers and ZnS barrier layers is found, in agreement with recent experimental data. The pressure behavior of the key quantities (VBO's, bulk moduli, energy gaps) is discussed for various strain modes

Band offset determination of the GaAs/GaAsN interface using the DFT method

Abstract: The GaAs/GaAsN interface band offset is calculated from first principles. The electrostatic potential at the core regions of the atoms is used to estimate the interface potential and align the band structures obtained from respective bulk calculations. First, it is shown that the present method performs well on the well-known conventional/conventional AlAs/GaAs (001) superlattice system. Then the method is applied to a more challenging nonconventional/conventional GaAsN/GaAs (001) system, and consequently type I band lineup and valence-band offset of about 35 meV is obtained for nitrogen concentration of about 3 %, in agreement with the recent experiments. We also investigate the effect of strain on the band lineup. For the GaAsN layer longitudinally strained to the GaAs lattice constant, the type II lineup with a nearly vanishing band offset is found, suggesting that the anisotropic strain along the interface is the principal cause for the often observed type I lineup.

A unique photoemission method to measure semiconductor heterojunction band offsets

Abstract: We report a unique way to measure the energy band offset of a heterojunction by exploiting the light absorption profile in the heterojunction under visible-ultraviolet internal photoemission. This method was used to determine the band alignment of W/Al2O3/n+InAs/p+Al0.45Ga0.55Sb heterojunctions that are of interest for tunnel field-effect transistors. The barrier heights from the InAs and Al0.45Ga0.55Sb valence band maxima to the Al2O3 conduction band minimum are found to be 3.24 eV± 0.05 eV and 2.79 eV± 0.05 eV, respectively, yielding a 0.4 eV± 0.1 eV offset at the InAs/AlGaSb interface. This approach can readily be applied to characterize a wide range of other semiconductor heterojunctions.

Effect of an Al interlayer on the GaAs/Ge(100) heterojunction formation

Abstract: The chemistry, structure, and growth kinetics of epitaxial GaAs/Ge heterojunctions are controllably modified using an Al interlayer of one to two monolayers in thickness. Photoemission spectroscopy is used to investigate the interface formation with and without the Al interlayer. Although the valence-band and core-level spectra indicate dramatic changes of the chemistry and structure caused by the Al (deposited on the substrates both at room temperature and at 340 \ifmmode^\circ\else\textdegree\fi{}C) at the interface, the band-structure lineup is not affected. The Fermi level in the gaps is influenced by both the presence of the Al interlayer and the deposition temperature. The Fermi level moves toward the valence band by 0.15 and 0.3 eV (relative to the GaAs c(4\ifmmode\times\else\texttimes\fi{}4)/Ge degenerate n-type interface) for room-temperature and 340 \ifmmode^\circ\else\textdegree\fi{}C deposition, respectively. The Fermi-level position is simply related to the amount of As diffusion into the Ge layer and its role as an n-type dopant. The results support the conclusion that the band offset is primarily an intrinsic (bulk) property which is insensitive to interfacial charge distribution or chemistry to within \ifmmode\pm\else\textpm\fi{}0.05 eV.

The impact of bandgap offset distribution between conduction and valence bands in Si-based graded bandgap HBT's

Abstract: This work examines the impact of bandgap offset distribution between conduction and valence bands in Si-based graded bandgap HBT's using dc and ac simulation. For a fixed total bandgap offset, a conduction band pushed up by the total offset, together with a valence band pushed up by 2× the total offset gives the best ac performance, and allows the highest operational current for high frequency applications in an n–p–n HBT. A retrograded mole fraction profile, when properly optimized, can produce nearly identical ac performance for different bandgap offset distributions. These suggest that contrary to popular belief, applying careful optimization can yield excellent transistor performance for any arbitrary band alignment for both n–p–n and p–n–p graded bandgap HBT's.