Detection of 2D electron g-factor sign inversion in narrow GaAs/AlGaAs quantum wells

By means of CW polarization-resolved photoluminescence spectroscopy we demonstrate the sign inversion of $g_z$-component of 2D electron g-factor with narrowing of a hosting GaAs/Al$_{0.33}$Ga$_{0.67}$As quantum well (QW). The energy splitting between spectral lines correspoding to recombination from the electron lowest Landau level and possessing opposite curcular polarization is analyzed. Due to exchange interaction, this value reveals maximum or minimum as a function of magnetic field strength in the vicinity of electron filling factor $\nu=3$. The actual type of extremum depends on the electron $g_z$-component sign. The method allows to detect the sign inversion of electron Lande g-factor with its absolute value changing by less than $\Delta g \approx 0.06$. The reversal happens at a QW width of ($65\pm 3$ \AA).