  We report electrical characterization of quantum dots formed by introducing
pairs of thin wurtzite (WZ) segments in zinc blende (ZB) InAs nanowires.
Regular Coulomb oscillations are observed over a wide gate voltage span,
indicating that WZ segments create significant barriers for electron transport.
We find a direct correlation of transport properties with quantum dot length
and corresponding growth time of the enclosed ZB segment. The correlation is
made possible by using a method to extract lengths of nanowire crystal phase
segments directly from scanning electron microscopy images, and with support
from transmission electron microscope images of typical nanowires. From
experiments on controlled filling of nearly empty dots with electrons, up to
the point where Coulomb oscillations can no longer be resolved, we estimate a
lower bound for the ZB-WZ conduction-band offset of 95 meV.
