  We investigate the effects of an in-plane magnetic field on the weak
antilocalization signature of near-surface quantum wells lacking bulk and
inversion symmetry. The measured magnetoconductivity exhibits a strong
anisotropy with respect to the direction of the in-plane magnetic field. The
two-fold symmetry of the observed magneto-anisotropy originates from the
competition between Rashba and Dresselhaus spin-orbit couplings. The high
sensitivity of the weak antilocalization to the spin texture produced by the
combined Zeeman and spin-orbit fields results in very large anisotropy ratios,
reaching 100%. Using a semiclassical universal model in quantitative agreement
with the experimental data, we uniquely determine the values of the Dresselhaus
and Rashba parameters as well as the effective in-plane g-factor of the
electrons. Understanding these parameters provides new prospects for novel
applications ranging from spintronics to topological quantum computing.
