Stability and electronic properties of atomic layers of GaN are investigated in the framework of the van der Waals-density functional theory. We find that the ground state of the layered GaN is a planar graphene-like configuration rather than a buckl
ed bulk-like configuration. Application of an external perpendicular electric field to the layered GaN induces distinct stacking-dependent features of the tunability of the band gap; the band gap of the monolayer does not change whereas that of the trilayer GaN is significantly reduced for the applied field of 0.4 V/ {AA}. It is suggested that such a stacking-dependent tunability of the band gap in the presence of an applied field may lead to novel applications of the devices based on the layered GaN.
The electronic conduction of a novel, three-terminal molecular architecture, analogous to a heterojunction bipolar transistor is studied. In this architecture, two diode arms consisting of donor-acceptor molecular wires fuse through a ring, while a g
ate modulating wire is a pi-conjugated wire. The calculated results show the enhancement or depletion mode of a transistor by applying a gate field along the positive or negative direction. A small gate field is required to switch on the current in the proposed architecture. The changes in the electronic conduction can be attributed to the intrinsic dipolar molecular architecture in terms of the evolution of molecular wavefunctions, specifically the one associated with the terphenyl group of the modulating wire in the presence of the gate field.
The quantum transport via a donor (D)-bridge (B)-acceptor (A) single molecule is studied using density functional theory in conjunction with the Landauer-B{u}ttiker formalism. Asymmetric electrical response for opposite biases is observed resulting i
n significant rectification in current. The intrinsic dipole moment induced by substituent side groups in the molecule leads to enhanced/reduced polarization of the system under a forward/reverse applied potential, thus asymmetry in the charge distribution and the electronic current under bias. Under a forward bias, the energy gap between the D and A frontier orbitals closes and the current increases rapidly; whereas under a reverse bias, the D-A gap widens and the current remains small.
