InAs nanowires are potential materials for high speed nanoelectronic devices due to their high electron mobility among the semiconductor nanostructures. One of the main challenges, however, is to obtain a p-type InAs material, since the Fermi level is usually pinned at the conduction band, leading to an intrinsic n-type behaviour. Here we show through first principles calculations that InAs nanowires, doped with Cd or Zn substitutional impurities, can behave as p-type materials. Differently from other III-V nanowires, these impurities introduce shallow acceptor levels. We show that the Zn impurity can be equally distributed along the nanowire radius, naturally compensating the surface levels. On the other hand, the Cd impurity is preferentially found in the core region, requiring a surface treatment to eliminate the surface pinning levels. These results explain the available experiments and show how and why p-type InAs nanowires can be obtained.
The one-dimensional character of the nanowires (NWs), with large surface to volume ratios, allows one to accommodate internal strains that would not be achieved in composite bulk materials with large mismatches. This opens a vast field to explore new materials with specific properties. One of the ways to efficiently exploit this characteristic feature of the NWs is through composition modulation. Using first principles calculations, we investigate the structural and electronic properties of core/shell modulated [111] zinc-blende InAs/InP NWs with different core/shell ratios and diameters (from 1.0 to 2.0 nm). Basic properties of these systems like the lattice parameter and the band gaps are seen to vary non-linearly with the core/shell ratio. The presence of an external InP shell is shown to improve the electronic mobility when compared with pure InAs NWs by eliminating the pinning of the Fermi level at InAs-derived surface states, while keeping the electron effective mass as low as in pure InAs NWs with similar diameters. We determine a type-I like band alignment, with a valence band offset depending on the core/shell ratio and a vanishing conduction band offset. We discuss the consequences of these results to the p-type conduction in the InAs core due to remote p-type doping at the InP shell region.
In this manuscript, we report a study on the removal of contaminant methylphenidate from aqueous solution, including ab initio simulations and experimental adsorption, applying graphene oxide and reduced graphene oxide as adsorbents.
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