First-principles study of uniaxial strained and bent ZnO wires

Abstract

We investigated the variation of the electronic band gap of ZnO bulk and that of bent ZnO nanowires under the influence of uniaxial strain by using density functional theory. By applying a strain of about ±2% to bulk ZnO in equilibrium, we mimic the recent experimentally determined tensile and compressive strain along the c axis of ZnO microwires which results from the bending of such wires. The slope of band gap size versus tensile-compressive strain at the equilibrium gives a deformation potential parameter, the value of which ranges between −2.0 and −4.0 eV depending on the exchange correlation treatments applied in order to improve the absolute value of the band gap. We find that the local (local density approximation) and semilocal [generalized gradient approximation (GGA) and the meta-GGA] approximations to the exchange-correlation functionals give a deformation potential, which is in good agreement with experiments. It is shown that the elastic constants derived from bulk ZnO are sufficient to model the strain effects for microwires. On the other hand, nanowires, only a fewÅ in diameter, respond with stronger changes in the band gap to applied strain. This feature, however, approaches the bulk behavior as the thickness of the nanowire increases.

Band-Gap Deformation Potential and Elasticity Limit of Semiconductor Free-Standing Nanorods Characterized in Situ by Scanning Electron Microscope–Cathodoluminescence Nanospectroscopy

“…Previous a cc calculations are based on generalized gradient approximation (GGA) or projector augmented wave method (PAW), which are plotted in Figure 4b. When we calculate a cc from reported conduction band d i (i = 1, 2) and valence band C i (i = 1,2,…) deformation potentials [29][30][31][32][33] of Pikus-Bir strain Hamiltonian 31,46 for wurzite semiconductor (Γ 9v valence band symmetry), reported bulk ZnO Poisson ratio in c-axis 47 (ν c,Bulk = 0.32) is used.…”

Non-linear optical deformation potentials in uniaxially strained ZnO microwires

“…These values agree very well with those deduced from theoretical calculations, which yields D 1 ¼ À2:18 eV… À 4:14 eV and D 2 ¼ À6:7 eV… À19:2 eV, depending on the applied method. 19 From the difference between the linear deformation potential determined here and those reported previously by us with D 1 ¼ ðÀ2:0460:02Þ eV, 7 we attribute to fact that in the experiments presented here the shift of the entire near band gap emission peak was investigated whereas in our previous experiments we focus on the shift of the exciton line as a function of the strain.…”

“…This behaviour is in agreement with theoretical calculations using local density approximation (LDA) and generalized gradient approximation. 19 For the determination of the optical deformation potential of the observed energy shift, we described the change of the emission energy by a polynomial of second order through zero, i.e.…”

Lattice dynamics of twisted ZnO nanowires under generalized Born–von Karman boundary conditions

“…For example, it was shown that an axial twist could realize metal-toinsulator transition in carbon NTs (CNTs) [14,15] and graphene NRs (GNRs) [16][17][18]. On the other hand, in deformed ZnO [19,20] and other semiconductor NWs [21][22][23], their fundamental bandgaps could be also tuned to a great extent. Strain can also alter the architecture of the entire electronic spectrum of the system.…”