Modulation doping in hexagonal BN atomic-layer semiconductor

We study the stable stacking sequences and the electronic properties of hexagonal BN (h-BN) trilayers within the framework of the density functional theory. Because of its lower-symmetry geometry of the h-BN sheet than that of graphene, there appear several different stable stacking sequences in the h-BN trilayers. Interestingly, most of stable stacking sequences of trilayers are found to be different from that of the bulk phase. It is also found that spatial distributions of both the valence-band top states and the conduction-band bottom states are rather confined to a certain specific layer in stable h-BN trilayers. By utilizing this fact, we design the C-doped h-BN trilayers where carriers conduct not in the doped layer but mostly in the undoped perfect layer. These systems are therefore considered to be the ultimate modulation-doped semiconductor heterostructure where both the doped region and the conducting region are only one atomic-layer thick. We also discuss several four-layer and five-layer h-BN systems which can host further clear spatial modulation doping.