Quantum point contact due to Fermi-level pinning and doping profiles in   semiconductor nanocolumns
  We show that nanoscale doping profiles inside a nanocolumn in combination with Fermi-level pinning at the surface give rise to the formation of a saddle-point in the potential profile. Consequently, the lateral confinement inside the channel varies along the transport direction, yielding an embedded quantum point contact. An analytical estimation of the quantization energies will be given. 
K. M. Indlekofer, M. Goryll, J. Wensorra, and M. I. Lepsa