  In this study, we designed and optimized the performance of pin junction
GaAs/AlGaAs heterojunction nanowire solar cell arrays. It is done by performing
coupled optoelectronic simulations to find the optimal doping for the GaAs core
and AlGaAs shell, and to see the influence of GaAs and AlGaAs shell thickness
and junction positions on the solar cell performance. Further, the impact of
different surface effects that exists at the semiconductor interface such as
surface traps, surface recombination velocities, and associated lifetime
degradation are also investigated. It has been observed that a high core and
shell doping is essential to achieve the appropriate band configuration and
carrier extraction. Further, it is observed that having a larger doping density
is more important than having a larger lifetime. The importance of the
thickness and the passivation properties of the radial and axial AlGaAs layer
is also examined and it has been observed that having a thick AlGaAs shell at
the cost of the i-GaAs region can be detrimental to the performance due to
increased local carrier generation and recombination. Finally, the effect of
having different Aluminium compositions (on the shell) on the photogeneration
inside the nanowire is examined and it was observed that having a large
Aluminium composition can confine most of the photogeneration to the inner GaAs
regions, thus potentially allowing for thicker Aluminium shells which can more
efficiently prevent surface recombination.
