The unique properties of transition metal dichalcogenides provide a versatile platform for scalable, room-temperature quantum devices. Their future commercialization will inevitably depend on the development of heterostructures facilitating charge injection into pre-defined areas of 2D components. We showcase here an innovative approach to accurately engineer electrically active nanoscale regions in multidimensional heterostructures made of WSe₂ layers and GaAs, thin films and one-dimensional nanostructures. The rectifying behavior of these stacks is visualized through electron-beam induced current mapping with unprecedented spatial resolution. These electrical measurements reveal local diffusive and drift charge flows through the diode. Notably, we observe a significant reduction in the effective carrier concentration in WSe2 layers thinner than 15 nm. 2D/1D ensembles exhibit in-plane confinement of the space charge region as narrow as 140 nm. This level of control over dimensionality, position, and size opens exciting avenues to achieve tunable quantum sources, one step closer to 2D-based quantum devices