Sequential vs. Simultaneous Trust

We examine theoretically and experimentally the implications of trust arising under sequential and simultaneous designs, where one player makes an investment choice, and another player decides whether to share the investment gains. We show analytically that in some cases the sequential design may be outperformed by the simultaneous design. In an experiment we find that the investment levels and sharing rates are higher in the sequential design, but there are no corresponding differences in beliefs. We conjecture that this happens because in the sequential design substantially more trust is necessary to induce cooperation. Our data strongly support this conjecture

Electron affinity and surface states of GaN m -plane facets: Implication for electronic self-passivation

The electron affinity and surface states are of utmost importance for designing the potential landscape within (heterojunction) nanowires and hence for tuning conductivity and carrier lifetimes. Therefore, we determined for stoichiometric nonpolar GaN(10¯10) m-plane facets, i.e., the dominating sidewalls of GaN nanowires, the electron affinity to 4.06±0.07eV and the energy of the empty Ga-derived surface state in the band gap to 0.99±0.08eV below the conduction band minimum using scanning tunneling spectroscopy. These values imply that the potential landscape within GaN nanowires is defined by a surface state-induced Fermi-level pinning, creating an upward band bending at the sidewall facets, which provides an electronic passivation

Polarity-dependent pinning of a surface state

We illustrate a polarity-dependent Fermi level pinning at semiconductor surfaces with chargeable surface states within the fundamental band gap. Scanning tunneling spectroscopy of the GaN(101¯0) surface shows that the intrinsic surface state within the band gap pins the Fermi energy only at positive voltages, but not at negative ones. This polarity dependence is attributed to arise from limited electron transfer from the conduction band to the surface state due to quantum mechanically prohibited direct transitions. Thus, a chargeable intrinsic surface state in the band gap may not pin the Fermi level or only at one polarity, depending on the band to surface state transition rates

Atomically resolved study of initial stages of hydrogen etching and adsorption on GaAs(110)

The initial stages of hydrogen adsorption on GaAs(110) surfaces at room temperature are investigated by atomically resolved scanning tunneling microscopy and spectroscopy. Two effects are found to occur simultaneously: On the one hand a surface phase separation occurs, creating 1×1 reconstructed fully hydrogen-covered areas while leaving the surface in between completely hydrogen free. In the fully hydrogen-covered areas, hydrogen bonds equally to As- and Ga-derived dangling bonds, unbuckling and passivating the surface. On the other hand, hydrogen-induced point defects are formed with increasing density. The dominating defects consist of As vacancy–hydrogen defect complexes, formed by preferential hydrogen etching of As. Using a defect-molecule model the Ga-H bridge bonds and double-occupied Ga dangling bonds are suggested to be at the origin of the observed surface Fermi level pinning 0.25 to 0.3 eV above the valence band edge, identical within error margins for p- and n-doped GaAs(110)

Morphologic and electronic changes induced by thermally supported hydrogen cleaning of GaAs(110) facets

Hydrogen exposure and annealing at 400 °C leads to a layer-by-layer etching of the n-doped GaAs(110) cleavage surface removing islands and forming preferentially step edge sections with [001] normal vector. In addition, a large density of negatively charged point defects is formed, leading to a Fermi level pinning in the lower part of the bandgap. Their charge transfer level is in line with that of Ga vacancies only, suggesting that adatoms desorb preferentially due to hydrogen bonding and subsequent Ga–H desorption. The results obtained on cleavage surfaces imply that the morphology of nanowire sidewall facets obtained by hydrogen cleaning is that of an etched surface, but not of the initial growth surface. Likewise, the hydrogen-cleaned etched surface does not reveal the intrinsic electronic properties of the initially grown nanowires

Meandering of overgrown v-shaped defects in epitaxial GaN layers

The meandering of v-shaped defects in GaN(0001) epitaxial layers is investigated by cross-sectional scanning tunneling microscopy. The spatial position of v-shaped defects is mapped on (101¯0) cleavage planes using a dopant modulation, which traces the overgrown growth front. Strong lateral displacements of the apex of the v-shaped defects are observed. The lateral displacements are suggested to be induced by the meandering of threading dislocations present in the v-shaped defects. The meandering of the dislocation is attributed to interactions with inhomogeneous strain fields