Nanotube wires on commensurate InAs surfaces: binding energies, band alignments, and bipolar doping by the surfaces

Using first-principles methods, we study the physicochemical properties such as the binding mechanism and band offset for single-wall zigzag nanotubes on InAs. While the tubes maintain their structural and electronic integrity, binding energies as large as 0.4 eV per site are obtained. Except for semiconducting tubes on the polar surfaces, an approximate universal band alignment is also obtained. The exception is due to large surface dipoles. In fact, polar (111) and (1;1;1;) surfaces have opposite dipoles that cause autodoping of a (14,0) tube to the n and the p type, respectively, without actual dopant.