Structural, Optical and Electrical Properties of Cobalt Doped ZnO Quantum Dots

Abstract

In this study we investigated the optical and electronic properties of cobalt doped Zinc Oxide (ZnO) nanoparticles (quantum dots) fabricated by a precipitation method. We observed significant reduction in ZnO nanoparticle diameter as we increased the percentage of cobalt. UV-VIS absorption measurement show a systematic increase in bandgap from 3.40 eV to 3.69 eV as the cobalt percentage is increased from 0 to 15%. This increase in bandgap is consistent with the confinement effects observed in quantum dots. Photoluminescence studies show a blue shift in near band absorption as the cobalt doping percentage is increased from 0% to 15%. Fluorescence life time measurements of the doped and undoped ZnO samples show a reduction in radiative life time as the cobalt percentage is increased. Electrical properties of doped and undoped samples show that the series resistance in a Cole-Cole plot decreases systematically with higher doping percentage. We will discuss the quantitative changes observed in structural, optical and electrical properties of ZnO quantum dots as the doping percentage is varied from 0 -15%.

A Comparative Study of Structural, Optical and Electrical Properties of Fe-ZnO Nanoparticles Synthesized by Precipitation and Microwave Method for Photovoltaic Applications

“…On the other hand, for samples prepared with microwave method A, the NBE peak shifted towards a longer wavelength, resulting in a redshifted from 384.5 nm to 387.6 nm and an increase in the full width at half maxima (FWHM) with the increase in iron concentration as shown in Figure 6 (d). This increase in FWHM was also observed in cobalt-doped ZnO quantum dots and is attributed to the simultaneous effect of Coulomb interaction, quantum size effects, vacancies, and defects effects [3]. The shifts in NBE peaks in PL in the samples could be due to several effects present in quantum particles such as the creation of vacancies and defects, and variation in the size of nanoparticles during the growth process and doping.…”

“…These results are consistent with the reduction and increment of grain size prepared from precipitation and microwave method (B and A) respectively. Since the capacitance is directly proportional to the diameter of a spherical capacitor, the capacitance of nanoparticles also decreases [3] in nanoparticles as the size decreases.…”

“…Recently, ZnO nanoparticles have received significant attention due to the wide range of morphologies they exhibit and potential applications to spintronics [1]. In recent years, transition metal-doped ZnO has been extensively investigated because of its chemical, mechanical, electrical, optical, and magnetic properties [2,3]. A wide range of techniques has been used to synthesize ZnO, such as sol-gel [4], laser-assisted chemical vapor deposition [5], solvothermal [6], hydrothermal [7], and microwaveassisted method [8].…”