Opto-electronic Properties Of CdS_xSe_1-x Semiconductor Nanocrystals

The paper explores the the optoelectronic properties of semiconductornanocrystals throughthe synthesis, theoretical calculations anddevices building.Colloidal chemical route was used to synthesis CdSxSe1-xnanocrystals. Theinfluence of size and Se content on the properties of CdSexS1-xnanocrystals wasstudied. CdSxSe1-xnanocrystals are water-soluble modified by ligand exchangemethod, in order to make CdSxSe1-xnanocrystals uniformly disperse in aqueoussolution. First-principles method was used to study the crystal structure andelectronic properties of CdSe together with the effect of S content on theproperties of CdSxSe1-x, which proved that the results match the experimentalresults. Successive ionic layer adsorption and reaction was used to buildphotoelectric detection unit of CdS nanocrystals, to explore the optoelectronicproperties of CdS nanocrystals.1. The synthesized colloidal CdSexS1-xsemiconductor nanocrystals are wellcrystallized and distributed uniformly in solution. The crystal structure of CdSexS1-xNCs is face-centered cubic sphalerite phase. The UV-Vis peaks of CdS nanocrystalsis435nm, showing absorption spectrum red shift along with the increase of Secontent and the decrease of the content of S. CdSxSe1-xnanocrystals arewater-soluble modified by ligands exchange method, which resulted in the changingof OA in the surface of the CdSexS1-xNCs to TGA, so CdSxSe1-xnanocrystals canuniformly disperse in aqueous solution. But UV-Vis peak intensity of Water-solubleCdSexS1-xnanocrystals decreases due to the fluorescence quenching effect.2. First-principles method was used to study the crystal structure and electronicproperties of CdSe and the effect of S content on the properties of CdSxSe1-x. Theresults show that the lattice constant decreases linearly, but barely influence thesyngony. Besides, The band gap increases with S content increasing in CdSxSe1-xternary alloy, and the peak density of states does not shift, but influence the intensityof density of states. That’s because S doping leads to charge redistribution in CdSxSe1-x ternary alloy system.3. Successive ionic layer adsorption and reaction was used to build photoelectricdetection unit of CdS nanocrystals. The electical properties of CdS are tested both atroom temperature and low temperature. Then at room temperature(296K), thedifference of CdS nanocrystals V-I characteristic curve in air and vacuumenvironments is researched.which shows that the current is reduced in the vacuumenvironment, deducing that the CdS nanocrystals are p-type semiconductor. Theinfluence of UV lights on the photoelectric detection unit of CdS nanocrystals wasstudied. It shows that the UV lights can increase the conductance of CdSnanocrystals. The asymmetry of CdS nanocrystals V-I characteristic curve can beexplained in test.