Magnetic Field Induced Spin Polarization of AlAs Two-dimensional Electrons

Two-dimensional (2D) electrons in an in-plane magnetic field become fully spin polarized above a field BP , which we can determine from the in-plane magnetoresistance. We perform such measurements in modulation-doped AlAs electron systems, and find that the field BP increases approximately linearly with 2D electron density. These results imply that the product |g∗|m∗, where g∗ is the effective g-factor and m∗ the effective mass, is a constant essentially independent of density. While the deduced |g∗|m∗ is enhanced relative to its band value by a factor of ∼ 4, we see no indication of its divergence as 2D density approaches zero. These observations are at odds with results obtained in Si-MOSFETs, but qualitatively confirm spin polarization studies of 2D GaAs carriers.