  III-V solar cells dominate the high efficiency charts, but with significantly
higher cost than other solar cells. Ultrathin III-V solar cells can exhibit
lower production costs and immunity to short carrier diffusion lengths caused
by radiation damage, dislocations, or native defects. Nevertheless, solving the
incomplete optical absorption of sub-micron layers presents a challenge for
light-trapping structures. Simple photonic crystals have high diffractive
efficiencies, which are excellent for narrow-band applications. Random
structures a broadband response instead but suffer from low diffraction
efficiencies. Quasirandom (hyperuniform) structures lie in between providing
high diffractive efficiency over a target wavelength range, broader than simple
photonic crystals, but narrower than a random structure. In this work, we
present a design method to evolve a simple photonic crystal into a quasirandom
structure by modifying the spatial-Fourier space in a controlled manner. We
apply these structures to an ultrathin GaAs solar cell of only 100 nm. We
predict a photocurrent for the tested quasirandom structure of 25.3 mA/cm$^2$,
while a planar structure would be limited to 16.1 mA/cm$^2$. The modified
spatial-Fourier space in the quasirandom structure increases the amount of
resonances, with a progression from discrete number of peaks to a continuum in
the absorption. The enhancement in photocurrent is stable under angle
variations because of this continuum. We also explore the robustness against
changes in the real-space distribution of the quasirandom structures using
different numerical seeds, simulating variations in a self-assembly method.
