in reduced dimensions. Electrons are free to move in two dimensions but are strictly confined in the third. Such confinement leads to quantized energy levels in the third dimension. These conditions are usually achieved in a quantum well (QW) or transistor-like semiconductor heterostructures and recently in atomically-thin 2D materials. At low temperatures, the mobility of a 2DEG can reach extremely high values, up to several $10^7~cm^2/Vs$ for GaAs based QWs [@Umansky2009; @Manfra2014]. Such high-quality QWs opened access to new physics, such as integer [@Klitzing1980] and fractional [@Tsui1982] quantum Hall effects, fractional statistics [@Arovas1984], and many other phenomena. In QWs made of chalcogenides, carrier mobility is generally lower than found in III-V semiconductor QWs. However, the advantage of chalcogenide QWs is that they can be doped with Mn without affecting the carrier concentration and without strongly reducing carrier mobility. Manganese is a neutral impurity in II-VI semiconductors but is an acceptor in III-V semiconductors. The exchange interaction between conduction electrons and magnetic ions give rise to a giant spin splitting. Thus, chalcogenide QWs made of diluted magnetic semiconductor (DMS) materials offer the possibility to study highly spin-polarized low-density 2DEGs [@Smorchkova1997; @Teran2002; @Jaroszynski2002]. In addition, QWs based on narrow-gap semiconductors, such as 