Electrical resistivity peculiarities and positron lifetime in annealed CdO

Abstract

Differently heat‐treated polycrystalline cadmium oxide (CdO) samples have been studied using room temperature (RT) resistivity, positron annihilation lifetime (PAL) and ultraviolet visible (UV‐Vis) optical absorption measurements. A small increase of the resistivity for 275 °C annealing (with respect to the other samples) and a large reduction of the same for 810 °C annealing have been observed. PAL investigation shows presence of defects, presumably Cd+O divacancy (VCd+O) clusters, in all the samples. Gradual defect recovery takes place with increasing annealing temperature. A clear defect recovery stage has been found above 400 °C annealing from where drastic fall of resistivity occurs. The optical band gaps (direct and indirect) of the 125 °C annealed sample comes out to be 1.89 eV and 0.79 eV. The indirect band gaps of the samples show anomalous variation due to 275 °C annealing which is also consistent with resistivity anomaly. To our knowledge, this is the first positron spectroscopic investigation on the CdO system. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Defect analysis and microstructural characterization of zinc-substituted cadmium oxide nanocrystallites by positron annihilation and supplementary methods

“…Positrons experience a relatively lower electron density on the nanocrystallite surfaces and hence will have larger lifetimes. In our previous work [37], we had reported the positron lifetimes in two samples of CdO with I 2 < 2% and the corresponding τ 1 (= 0.135 ns) had been accepted as the lifetime of positrons in bulk CdO, consistent with the value reported by others in literature [43]. The effect of contraction of the lattice of the Zn-doped samples on the bulk lifetime is quantitatively estimated using the method proposed by de la Cruz et al [44].…”

Silicone Rubber Composites of Differently Fired Cadmium Oxide and Their Positron Lifetime Study

“…However, current decade finds use of these oxide semiconductors, with potential application in optoelectronics and high-performance electronic device applications. While ZnO, with 3.3 eV room-temperature band gap (Eg) and large exciton binding energy of 60meV, is playing the main role in many II-VI optoelectronic devices, their spectral range is being extended [3] into the visible and deep ultraviolet ranges by alloying ZnO with the smaller band-gap compound CdO [4], having room-temperature E g of ~2.2eV at the Brillouin-zone centre, and with larger band-gap compound MgO [3,5] with E g of 7.7eV, respectively. We find non-stoichiometry [6][7][8][9][10] and, hence, widely varying electrical conductivity [2] in differently heat-treated cadmium ox ide (Figure 1).…”

“…Room temperature resistivity of as-supplied E Mark (India) cadmium oxide was 97m Ωcm. Firing [4,7] at 270 °C reduce it to ~26.4 m Ω cm. Resistivity reduces, further, to ~2.1 m Ω cm after 800 °C heat treatment.…”

“…However, even the pure material is complex, exhibiting non-stoichiometry and defect structures, as a function of its preparation or heat treatment temperature. Positron annihilation spectroscopy (PAS) being a powerful tool to study defects in soft [14] and hard [4,15] condensed matter, we investigate silicone-rubber CdO complex samples by positron lifetime spectroscopy (PLS) [14,15]. There are still a few poorly understood aspects of cadmium oxide like its non-stoichiometry (Figure 2) and colour, although cadmium oxide has been well investigated experimentally and theoretically for many decades.…”