Bandgap Modulation in ZnO by Size, Pressure, and Temperature

Abstract

The effect of crystal size, pressure, temperature, and their coupling on the bandgap (E G ) of ZnO crystals have been investigated based on the Hamiltonian perturbation, using the extended BOLS correlation theory. The functional dependence of the E G on the identities (order, nature, length, energy) of the representative bond for a specimen and the response of the bonding identities to the applied stimuli have been established. Theoretical reproduction of the measurements confirms that the E G expansion originates from the bond contraction/compression and bond strength gain due to (i) Goldschmidt-Pauling's rule of bond contraction induced by undercoordination, (ii) low-temperature enhanced stability, and (iii) mechanical energy storage. It is found that the multiple-field coupling effect dominates in the surface skin up to three atomic layers. The presented approach provides a guideline for harnessing the photoluminescence, photoabsorption, and exciton emission from ZnO and other semiconductors as well.

Strain engineering of the elasticity and the Raman shift of nanostructured TiO2

“…The trends of the T and P dependence of B and Dx are much the same to that of the T and P dependent bandgap shift in ZnO, 53 indicating the interdependence of the Raman shift, bandgap, and elastic modulus, in general.…”

“…53 In the T-dependent curves, the shoulder is related to the h D and the slope at higher temperature depends on the atomic cohesive energy, E c ¼ zE z . Matching the two sets of B(T) and the Dx(T) data will improve the reliability of the derivatives.…”

Highly monodispersed ZnO nanorods: preparation and optical properties

“…[24] Only markedly enhanced near-band-edge UV PL and rarely defect-related green emission were observed in all the temperature-dependent PL spectra, which demonstrate the high crystal quality of our products. We carry out a curve-fitting analysis of the temperature dependence of the free exciton transition energy by Varshni's formula [25,26]: E g ðT Þ ¼ E g ð0Þ À aT 2 =ðb þ T Þ, where E g ð0Þ is comparable to the bandgap energy at 0 K, a represents the T ! 1 limit of the gap entropy dE g ðT Þ=dT and b is approximately the Debye temperature at low temperature.…”

Enhancement of UV emission and optical bandgap of ZnO nanowires via doping and post-growth annealing

“…In recent years, one-dimensional nanostructures have been extensively researched on due to their wide scale potential applications [1,2]. Compared to their bulk or thin film counterparts, nanostructures have a higher surface area to volume ratio, can exhibit quantum effects, and are capable of greater modulation of their band structure [3]. Zinc oxide (ZnO), an n-type semiconductor material with a direct wide bandgap of ∼3.4 eV and a high exciton binding energy of 60 meV, has excellent optical and electrical properties [4][5][6].…”