Deep-level emission in ZnO nanowires and bulk crystals: Excitation-intensity dependence versus crystalline quality

Abstract

The excitation-intensity dependence of the excitonic near-band-edge emission (NBE) and deep-level related emission (DLE) bands in ZnO nanowires and bulk crystals is studied, which show distinctly different power laws. The behavior can be well explained with a rate-equation model taking into account deep donor and acceptor levels with certain capture cross sections for electrons from the conduction band and different radiative lifetimes. In addition, a further crucial ingredient of this model is the background n-type doping concentration inherent in almost all ZnO single crystals. The interplay of the deep defects and the background free-electron concentration in the conduction band at room temperature reproduces the experimental results well over a wide range of excitation intensities (almost five orders of magnitude). The results demonstrate that for many ZnO bulk samples and nanostructures, the relative intensity R = INBE/IDLE can be adjusted over a wide range by varying the excitation intensity, thus, showing that R should not be taken as an indicator for the crystalline quality of ZnO samples unless absolute photoluminescence intensities under calibrated excitation conditions are compared. On the other hand, the results establish an all-optical technique to determine the relative doping levels in different ZnO samples by measuring the excitation-intensity dependence of the UV and visible luminescence bands.

Enhancement of the Sub-Band-Gap Photoconductivity in ZnO Nanowires through Surface Functionalization with Carbon Nanodots

“…However, this cannot be conclusively attributed to an increased density of defect levels in the functionalized device. This is because the ratio between the DLE and the NBE in ZnO depends, among other factors, also on the excitation intensity, − which was adjusted at significantly different values for the PL measurements on the pristine and the functionalized devices.…”

“…The electronic transitions corresponding to main absorption peaks are indicated. The photoluminescence spectrum was measured under laser excitation at 3.81 eV and an intensity of 110 mW / cm 2 .depends, among other factors, also on the excitation intensity[29,30,31], which was adjusted at significantly different values for the PL measurements on the pristine and the functionalized devices.The Current-Voltage (I-V) measurements on the pristine and the functionalized devices in dark are shownFigure 4 (a). The I-V characteristics are linear in both devices over a large voltage range, indicating the formation of Ohmic contacts.…”

Growth of 18 O isotopically enriched ZnO nanorods by two novel VPT methods

“…O-enriched ZnO nanorods were then synthesized using a VLS method with an Au catalyst. The method used was based on previous work on VPT by direct oxidation[31,32].The setup shows some similarities to that described previously, albeit also with some notable differences. This furnace contained two alumina tubes, one inside the other.…”

Local atomic environment of the Cu-related defect in zinc oxide

“…ZnO nanorods were then grown using this source powder in a VLS process using Au as a catalyst, based on previous work. [42,43] The Au coating melts and forms droplets on the substrate, which act as energetically favourable nucleation sites. The furnace then cooled overnight before the samples were removed.…”