  Polarization dependent photocurrent spectra are measured on a (001)
$\beta$-Ga$_{2}$O$_{3}$ Schottky photodetector, where the linear polarization
of light is rotated within the ab plane. Three spectral peaks at 4.92 eV, 5.15
eV, and 5.44 eV are observed that vary in intensity with the optical
polarization direction. The peak transition energies are consistent with
excitons previously reported in $\beta$-Ga$_{2}$O$_{3}$ due to interband
transitions modified by the valence band p-orbital anisotropy and the
electron-hole Coulombic attraction. The measured polarization-dependence of the
photocurrent matches our predictions based on electromagnetic simulations of
anisotropic absorption using the complex dielectric function tensor extracted
from previous ellipsometry studies. These results illustrate the dominance of
excitonic absorption and photocurrent in $\beta$-Ga$_{2}$O$_{3}$ both below and
above the band gap, demonstrate a combined theoretical/experimental
understanding of anisotropic photocarrier generation, and validate previous
atomistic band structure calculations in this low-symmetry ultra-wide band gap
semiconductor.
