High Aspect Ratio Ternary Zn_1–xCd_xO Nanowires by Electrodeposition for Light-Emitting Diode Applications

Abstract

We present a combined experimental and computational approach to study Zn 1Àx Cd x O nanowires (NWs) and their integration in light-emitting diode (LED) structures. Self-standing Zn 1Àx Cd x O NWs have been electrodeposited on fluorine-doped tin oxide and p-GaN substrates. The electrochemical behavior has been studied, and the reaction mechanism is discussed. Low-dimensional Zn 1Àx Cd x O structures have been obtained for CdCl 2 concentrations in the deposition bath lower than 6 μM whereas at higher concentration it is admixed with crystallized CdO and the aspect ratio of the wires is decreased. According to scanning electron microscopy observations, the Zn 1Àx Cd x O NWs have a higher aspect ratio (>30) than pure ZnO NWs (∼20) grown in similar conditions. Analyses show that the ZnO is doped with cadmium incorporated within ZnO NWs and that Cd doping increases with increasing Cd(II) content in the deposition bath. X-ray diffraction studies show increased lattice parameters in Cd-alloyed ZnO NWs. Photoluminescence studies on pure ZnO and Zn 1Àx Cd x O NWs show the near band-edge emission red shifted by 3À7 nm as a function of Cd(II) concentration (4 or 8 μM in the electrolyte). The structural and optical properties of the prepared Zn 1Àx Cd x O materials have been interpreted using density functional theory (DFT) to computationally simulate the effect of Cd substitution for Zn in the ZnO lattice. DFT calculations show that the crystal lattice parameters increase with the partial replacement of Zn atoms by Cd and that the band gap enlargement is due to the increased lattice parameters. We demonstrate the possibility to tailor the electroluminescence emission wavelength by cadmium doping in ZnO nanowires integrated in Zn 1Àx Cd x O NWs/p-GaN heterojunction based LED structures. Reported results are of great interest for the research on band gap engineering of low-dimensional zinc oxide by doping/alloying NWs and for wavelength-tunable LED applications.

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

“…concentrations (120 mM). Similar reports of increased current density observed in the electrochemical growth of doped ZnO elsewhere [33,34].…”

Electrical properties of n-Zn0.94Cd0.06O/p-SiC heterostructures

“…The XRD data of both studied films accurately correspond to that of JCPDS card No.36-1451 for hexagonal wurtzite structure of ZnO. This suggests that the introduction of cadmium atoms does not change the ZnO crystal structure [8,14]. The observed (002) peak of ZnCdO was found to be shifted towards a lower 2θ angle (by 0.23°) than that of pure bulk ZnO (see Fig.…”

“…There is an extraordinary interest in ZnCdO ternary alloy caused by (i) the possibility to change its band-gap energy in the wide range depending on the cadmium content [7,8], substrate type [9] and growth conditions [10][11]; (ii) the existence of visible luminescence covering the blue-green optical region; and (iii) the high optical transparency [12]. Many interesting phenomena like electroluminescence from n-ZnCdO/p-GaN heterojunction [6,13,14], green electroluminescence from ZnCdO multiple quantum-well lightemitting diodes [15] and luminescence enhancement effects of deuterium in ZnO/ZnCdO quantum wells [12] have already been reported. Nevertheless, the growth of Zn 1-x Cd x O alloys is complicated by the solid phase miscibility gap [16], which gives rise to a compositional inhomogeneity, and thus, local variations in the fundamental energy gap.…”

Effect of P. Murex on the properties of spin coated ZnO thin films for dye sensitized solar cell applications

“…The peak located at 336 cm -1 is observed in the film (b) and (c), respectively, which corresponds to the second order phonon of E 1H -E 2H mode [29]. The high intensive peak at 436 cm -1 is attributed to the non-polar optical phonon mode of the ZnO and higher frequency is involved due to the vibration of an Oxygen atom in E 2 (High) mode, which is well coincided with previous report [30]. The peak of E 2 (high) is slightly shifted toward lower frequency number from 436 to 431 cm -1 due to the presence of stress at C axis growth in film (b) [11].…”