  Crystal phase semiconductor heterostructures allow for electron confinement
without uncertainties caused by chemical intermixing found in material
heterostructures and are candidates for next generation optoelectronics devices
ranging from single-photon emitters to high efficiency LEDs. While there has
been a great deal of experimental work developing fabrication processes for
these structures, theoretical calculations have been limited due to a lack of
atomistic models that are able to incorporate the zincblende and wurtzite
within the same structure. Here, we present calculations of the electronic
energies in GaAs nanowires containing various thicknesses of zincblende and
wurtzite layers using a recently developed tight-binding model for wurtzite
III-V semiconductors that is compatible with a zincblende model. By comparing
results in the flat-band and the unscreened limits, we explain the sensitivity
of experimentally observed band gaps on zincblende and wurtzite well widths.
Our calculations suggest that experiments on devices are likely near the
flat-band limit under typical operating conditions.
