An investigation of control mechanisms of the excitonic behavior in reactively sputtered ZnO on (0001) Al2O3

Abstract

Above-band-edge absorption spectra of reactively sputtered Zn- and O-rich samples exhibit free exciton and neutral acceptor bound exciton (A0X) features. It is shown that the residual acceptors which bind excitons with an energy of 75meV reside about 312meV above the valence band, according to effective mass theory. An intra-band-gap absorption feature peaking at 2.5eV shows correlation with the characteristically narrow A-free exciton peak intensity, suggesting a compensation mechanism of the centers involving oxygen vacancy (VO) related donors. In order to enhance free exciton concentration relative to competing neutral bound exciton density, relevant annealing processes are performed without disturbing the residual shallow acceptor profile which is necessary for at least background p-type conductivity.

Stimulated electroluminescence emission from n-ZnO/p-GaAs:Zn heterojunctions fabricated by electro-deposition

“…20 The calculated lattice constants of ZnO thin films grown by ECD are consistent with the standard literature value of c = 5.209 Å. 20 The decrease in the lattice constant for the sample 3 and the sample 4 may be due to decline in the amount of Zn(OH) 2 . From the XRD patterns of ZnO thin films, it is clear that ZnO particles were well crystallized and have a dominant growth trend in the (002) direction.…”

“…1 Owing to its high exciton binding energy (63 meV), 2 it is of importance for optoelectronic applications. Recently, due to its potential applications such as light emitting diodes (LEDs), 3 photodiodes, 4 gas sensors, 5 nanolasers, 6 nanowire-LEDs 7 and heterojunction solar cells, 8 ZnO material has been given much attention.…”

Influence of films thickness and structure on the photo-response of ZnO films

“…Since the O-rich samples usually have lower band gap energy, relatively more Znrich samples after annealing due to the evaporation of excess oxygen from the surface will have higher band gap energies in comparison to the as-deposited samples. On the other hand, we propose that this discrepancy might be resulted from the air annealing conditions where oxygen loss from surface is impossible so that the material may become relatively more O-rich at the annealing temperatures and has lower band gap energy after annealing [28,29]. As can be seen Figs.…”

Effect of nitrate concentration on the electrochemical growth and properties of ZnO nanostructures

“…Among various synthesis methods, electrochemical deposition represents a simple and inexpensive solutionbased method for synthesis of semiconductor nanostructures. Zinc oxide (ZnO)-based semiconductors have been investigated as promising materials for advanced electronic and optoelectronic devices due to their interesting physical and chemical properties [3,4]. It is an established fact that the electrodeposition of ZnO is a versatile growth method and various nanostructures can be easily designed by this technique.…”