A III-nitride-based light emitting device having a multiple quantum well (MQW) structure and a method for fabricating the device, wherein at least one barrier in the MQW structure is doped with magnesium (Mg). The Mg doping of the barrier is accomplished by introducing a bis(cyclopentadienyl)magnesium (Cp2Mg) flow during growth of the barrier using metalorganic chemical vapor deposition (MOCVD). The barriers of the MQW structure may be undoped, fully Mg-doped or partially Mg-doped. When the barrier is partially Mg-doped, only portions of the barrier are Mg-doped to prevent Mg diffusion into quantum wells of the MQW structure. The Mg-doped barriers preferably are high Al composition AlGaN barriers in nonpolar or semipolar devices.