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CdSe/CdS/ZnS core-shell-shell quantum dots (QDs) were synthesized by using a solution process. High-resolution transmission electron microscopy images and energy dispersive spectroscopy profiles confirmed that stoichiometric CdSe/CdS/ZnS core-shell-shell QDs were formed. Ultraviolet-visible absorption and photoluminescence (PL) spectra of CdSe/CdS/ZnS core-shell-shell QDs showed the dominant excitonic transitions from the ground electronic subband to the ground hole subband (1S(e)-1S 3/2 (h)). The PL mechanism is suggested; the carriers generated by the exciting high-energy photons in the shell region are relaxed to the bandedge states of the core region and recombined to emit lower-energy photons. The activation energy of the carriers confined in the CdSe/CdS/ZnS core-shell-shell QDs, as obtained from temperaturedependent PL spectra, was 200 meV. The quantum efficiency of the CdSe/CdS/ZnS core-shell-shell QDs at 300 K was estimated to be approximately 57%.

X-ray photoelectron spectroscopy spectra showed that the synthesized elements of the CdSe/CdS/ ZnS QDs were Cd, Se, Zn, and S. Organic bistable devices (OBDs) containing CdSe/CdS/ZnS quantum dots (QDs) and a poly(methylmethacrylate) (PMMA) layer were fabricated on indium-tin-oxide (ITO)-deposited glass substrates. Current-voltage (I-V) curves showed that the memory margin of the Al/(CdSe/CdS/ZnS QDs) embedded in PMMA layer/ITO device at 300 K was larger than that of the device without a ZnS shell layer. The retention time of the OBDs was above 1 x 10(4) s, indicative of the stability of the device. The memory mechanisms were described by using charge trapping and tunneling processes on the basis of the energy diagram and the I-V curves.

We investigated the effective channel length (L eff. ) of a-IGZO single layer and bi-layer. In the I-V curve, the drain-induced barrier lowering (DIBL) phenomenon appeared to be severe in the single layer, while it was relatively improved in the Bi layer. Based on this, we have determined the effective channel length through transmission line method (TLM) and confirmed that the effective channel length of the Bi layer is longer. The threshold voltage variation for each design length from 3.5 to 8.5 μm was also smaller in the Bi-layer. The results of XPS analysis show that this was due to the oxygen decomposition by Ti. In the Bi-layer with Ga-rich top layer, the high conduction region due to the oxygen decomposition phenomenon was reduced.

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