  Large-supercell tight-binding calculations are presented for
GaBi$_{x}$As$_{1-x}$/GaAs single quantum wells (QWs) with Bi fractions $x$ of
3.125% and 12.5%. Our results highlight significant distortion of the valence
band states due to the alloy disorder. A large full-width-half-maximum (FWHM)
is estimated in the ground state interband transition energy ($\approx$ 33 meV)
at 3.125% Bi, consistent with recent photovoltage measurements for similar Bi
compositions. Additionally, the alloy disorder effects are predicted to become
more pronounced as the QW width is increased. However, they are less strong at
the higher Bi composition (12.5%) required for the design of temperature-stable
lasers, with a calculated FWHM of $\approx$ 23.5 meV at $x$=12.5%.
