  Semiconducting piezoelectric materials have attracted considerable interest
due to their central role in the emerging field of piezotronics, where the
development of a piezo-potential in response to stress or strain can be used to
tune the band structure of the semiconductor, and hence its electronic
properties. This coupling between piezoelectricity and semiconducting
properties can be readily exploited for force or pressure sensing using
nanowires, where the geometry and unclamped nature of nanowires render them
particularly sensitive to small forces. At the same time, piezoelectricity is
known to manifest more strongly in nanowires of certain semiconductors. Here,
we report the design and fabrication of highly sensitive piezotronic pressure
sensors based on GaAs nanowire ensemble sandwiched between two electrodes in a
back-to-back diode configuration. We analyse the current-voltage
characteristics of these nanowire-based devices in response to mechanical
loading in light of the corresponding changes to the device band structure. We
observe a high piezotronic sensitivity to pressure, of ~7800 meV/MPa. We
attribute this high sensitivity to the nanowires being fully depleted due to
the lack of doping, as well as due to geometrical pressure focusing and current
funneling through polar interfaces.
