title: Conduction Band Offset and Polarization Effects in InAs Nanowire Polytype Junctions.
abstract: Although zinc-blende (ZB) and wurtzite (WZ) structures differ only in the atomic stacking sequence, mixing of crystal phases can strongly affect the electronic properties, a problem particularly common to bottom up-grown nanostructures. A lack of understanding of the nature of electronic transport at crystal phase junctions thus severely limits our ability to develop functional nanowire devices. In this work we investigated electron transport in InAs nanowires with designed mixing of crystal structures, ZB/WZ/ZB, by temperature-dependent electrical measurements. The WZ inclusion gives rise to an energy barrier in the conduction band. Interpreting the experimental result in terms of thermionic emission and using a drift-diffusion model, we extracted values for the WZ/ZB band offset, 135 ± 10 meV, and interface sheet polarization charge density on the order of 10-3C/m2. The extracted polarization charge density is 1-2 orders of magnitude smaller than previous experimental results, but in good agreement with first principle calculation of spontaneous polarization in WZ InAs. When the WZ length is reduced below 20 nm, an effective barrier lowering is observed, indicating the increasing importance of tunneling transport. Finally, we found that band-bending at ZB/WZ junctions can lead to bound electron states within an enclosed WZ segment of sufficient length, evidenced by our observation of Coulomb blockade at low temperature. These findings provide critical input for modeling and designing the electronic properties of novel functional devices, such as nanowire transistors, where crystal polytypes are commonly found.
authors.affiliation: Solid State Physics and NanoLund and ‡Center for Analysis and Synthesis, Lund University , S-221 00 Lund, Sweden.
authors.forename: I-Ju
authors.identifier: 0000-0002-8343-8096
authors.initials: IJ
authors.lastname: Chen
authors.affiliation: Solid State Physics and NanoLund and ‡Center for Analysis and Synthesis, Lund University , S-221 00 Lund, Sweden.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Lehmann
authors.affiliation: Solid State Physics and NanoLund and ‡Center for Analysis and Synthesis, Lund University , S-221 00 Lund, Sweden.
authors.forename: Malin
authors.initials: M
authors.lastname: Nilsson
authors.affiliation: Solid State Physics and NanoLund and ‡Center for Analysis and Synthesis, Lund University , S-221 00 Lund, Sweden.
authors.forename: Pyry
authors.initials: P
authors.lastname: Kivisaari
authors.affiliation: Solid State Physics and NanoLund and ‡Center for Analysis and Synthesis, Lund University , S-221 00 Lund, Sweden.
authors.forename: Heiner
authors.initials: H
authors.lastname: Linke
authors.affiliation: Solid State Physics and NanoLund and ‡Center for Analysis and Synthesis, Lund University , S-221 00 Lund, Sweden.
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Dick
authors.affiliation: Solid State Physics and NanoLund and ‡Center for Analysis and Synthesis, Lund University , S-221 00 Lund, Sweden.
authors.forename: Claes
authors.initials: C
authors.lastname: Thelander
keywords: InAs; Nanowire; crystal structure; transport; wurtzite; zinc blende