Martin Hjort, Jesper Wallentin, Rainer Timm, Alexei A. Zakharov, Ulf Hakanson, Jesper N. Andersen, Edvin Lundgren, Lars Samuelson, Magnus T Borgstrom, and Anders Mikkelsen
Surface Chemistry, Structure and Electronic Properties from Microns to the Atomic Scale of Axially Doped Semiconductor Nanowires
ACS Nano 6, 9679 (2012)
Using both synchrotron based photoemission electron microscopy/spectroscopy and scanning tunneling microscopy/spectroscopy we obtain a complete picture of the surface composition, morphology and electronic structure of InP nanowires. Characterization is done at all relevant length scales from micrometer to nanometer. We investigate nanowire surfaces with native oxide and molecular adsorbates resulting from exposure to ambient air. Atomic hydrogen exposure at elevated temperatures which leads to the removal of surface oxides while leaving the crystalline part of the wire intact were also studied. We show how surface chemical composition will seriously influence nanowire electronic properties. However, opposite to for example Ge nanowires, water or sulfur molecules adsorbed on the exterior oxidized surfaces are of less relevance. Instead it is the final few atomic layers of the oxide which plays the most significant role by strongly negatively doping the surface. The InP nanowires in air are rather insensitive to their chemical surroundings in contrast to what is often assumed for nanowires. Our measurements allow us to draw a complete energy diagram depicting both band gap and differences in electron affinity across an axial nanowire pn-junction. Our findings thus gives a robust set of quantitative values relating surface chemical composition to specific electronic properties highly relevant for simulating the performance of nanoscale devices.
Link to the complete paper (if available):
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