The generation of high density 2D hole gases is crucial for further progress in the electronic and optoelectronic nitride devices. In this paper, we present systematic theoretical studies of Mg-doped GaN/AlGaN gated heterostructures and superlattices. Our calculations are based on a self-consistent solution of the multiband k.p Schrodinger and Poisson equation and reveal that the hole 2D sheet density is mainly determined by the polarization induced interface charges. For an aluminium concentration of 30%, the induced hole density in the heterostructure can reach values up to 1.5 x 10(13) cm(-2). In the GaN/AlGaN superlattices, the hole sheet density increases with the superlattice period and saturates for a period of 40 nm at a value of 1.5 x 10(13) cm(-2).