Hanging Keys, Vacancy Defects And Doping Carbon Chain, Gallium Nitride Nanotubes With First Principles Study Of The Nature Of Particular Average

Bulk GaN has been investigated intensively both experimentally and theoretically due to its wide direct band gap of3.4eV at room temperature and it being an ideal material for the fabrication of blue and ultraviolet light-emitting diodes and high temperature/power electronic devices. GaN with low-dimensional nanostructure is considered to have great potential for testing and understanding the fundamental concepts about how dimensionality and size affect physical properties, and also to play a key role in novel nano-technological applications. In addition, with the development of the quantum mechanics theory and the computer technology as well as the increasing power of computer performance, the use of computer simulation to study the structure and properties of low-dimensional materials are complementarily useful. Under the generalized gradient approximation (GGA), we explore the structural, electronic and magnetic properties of GaNNRs with different edge modifications (dangling bond), a single vacancy effect and a single C chain doped are investigated by using the first-principles projector augmented wave (PAW) potential within the density function theory (DFT) framework.Though GaN nanoribbons (GaNNRs) with H atoms terminating both edges are nonmagnetic semiconductors, the extra dangling bond bands around the Fermi level lead to a transition from semiconducting to metallic, except for the armchair edge GaNNRs (AGaNNRs) with bare N and Ga edges, which are still nonmagnetic semiconductors due to the strong coupling of the dangling bonds of dimeric N and Ga atoms at the same edge. The larger difference in the charge density (pup-pdown) for edge bare N atoms and decaying for N sub-lattices away from the edge, as well as the smaller difference in the charge density for edge bare Ga atoms and without decaying for Ga sub-lattices away from the edge is consistent with the magnetic moment of a GaNNR with bare N edge being larger than that of a GaNNR with bare Ga edge. The magnetic moment of a zigzag edge GaNNR (ZGaNNR) with bare N (Ga) edge has nearly half the value of the magnetic moment of a AGaNNR with bare N (Ga) edge. Such a relationship also exists in the number of extra dangling bond states appearing around the Fermi level in the band structures. For ZGaNNRs, the magnetic moment of bare N and Ga edges is larger than either bare N edge or bare Ga edge, but smaller than their sum, implying that there exists an interaction between the dangling bonds at both edges of bare N and Ga edges.The formation energies of GaNNR show that the formation of the N vacancy is easier than that of the Ga vacancy at each equivalent geometrical site and both of them are endothermic. A single non-edge Ga vacancy makes either GaNNR a semi-metal and thus yields complete (100%) spin polarization and the charge transport is totally dominated by minority spin electrons, as well as a significant magnetic moment. Hence a single non-edge Ga vacancy defect GaNNR can be used to construct efficient spin-polarized transport devices. A single non-edge N vacancy is still nonmagnetic, but makes GaNNR have metal character. The GaNNR with a single edge N or G vacancy is still semiconducting and leading to a smaller band gap, except for a single edge N vacancy in GaNNR. A single edge N vacancy is still nonmagnetic but a single edge Ga vacancy induces a magnetic moment in GaNNR.In perfect GaN nanoribbon with7zigzag Ga-N chain across the ribbon width7-ZGaNNR, the LUCB and HOVB at zone boundary of Z are edge state whose chargers are localized at edge Ga and N atom, respectively. A singly C chain changing its position lead to the HOVB and LUCB getting closer with each other. Similar to the edge states existing in perfect GaNNRs, the flat dispersion border states also exist in a singly C chain decorated ZGaNNR, but their charges are localized at border C-N and C-Ga for LUCB and HOVB, respectively. A single C chain decorated ZGaNNR is always semiconducting independent of the position of the C chain in the ribbon. The gap energy decreases monotonically and theshifts down near the Fermi level successively except n=l. For Nz-ZGaNNR-C(n) with ribbon width Nz=3,4,5,6,7and10, the band gap decreases successively for C chain position n from2to3,4,5,6,7and10, respectively. The Nz-ZGaNNR-C(1) and Nz-ZGaNNR-C(2) have nearly identical the minimum band gap of0.117eV and nearly identical the maximum band gap of1.01eV, respectively. Only Nz-ZGaNNR-C(1) has a direct band gap, while the other Nz-ZGaNNR-C(n) has an indirect band gap.