Abstract: Exemplary embodiments of the present invention comprise a high efficiency 3D nanostructured neutron detector. The neutron detector comprises a primary and secondary substrate, each substrate comprising an external and internal surface area, wherein one of the respective substrates comprises an n-type semiconductor material and the other substrate comprises a p-type semiconductor material. Disposed between the primary and secondary substrates is a composite structure consisting of a predetermined neutron converting material and a predetermined neutron detecting material, wherein one of the composite materials is fabricated into a nanostructure in the configuration of a stack of nanosheets, a 3D nanowire network, or as 3D nano-trees, and a pair of electrodes, wherein one electrode is disposed on the respective external surface areas of the primary and secondary substrates.