Formation of quantum-dot quantum-well heteronanostructures with large lattice mi

2019-11-22 20:59:14

small quantum large CdS ZnS

责任者: Little, R.B.;El-Sayed, M.A.;Bryant, G.W.;Burke, S. 单位: Dept. of Chem., Florida A&M Univ., Tallahassee, FL, USA 来源出处: Journal of Chemical Physics(J. Chem. Phys. (USA)),2001/01/22,114(4):1813-22 摘要: Two-dimensional heterostructures have been exploited extensively in the synthesis of optoelectronic devices. Structures with small lattice mismatch can be synthesized readily. Large lattice mismatch in II-VI film heterostructures makes synthesis of devices with these materials more difficult. However, these large mismatch heterostructures usually have useful optical properties. One such heterostructure is the ZnS/CdS system with a large exciton binding energy and a large band gap useful for blue-green emitting devices. In this work, small II-VI nanoparticles are studied. We show that II-VI heterostructures can be made in quantum dots, despite the large bulk lattice mismatch. Two well-known techniques are combined to synthesize first very small ZnS and CdS seed nanoparticles and then do nanoepitaxy on them to produce ZnS/CdS core/shell quantum-dot quantum-well heteronanostructures. These structures are characterized by UV visible absorbance. Measured spectra are compared with electronic level structures calculated for the fabricated heteronanostructures with a tight-binding model. The consistency of the observed spectra with the predicted transitions indicates that the desired core/shell and core/shell/clad structures were grown. The metastability of the ZnS/CdS/ZnS heteronanostructures is attributed to low-temperature construction and small crystal size (<3 nm). The small particle size should produce large surface forces and ZnS core contraction. Also, the small particle size should accommodate strain, as a result of the ZnS/CdS interfacial curvature, which is not possible for planar systems. Furthermore, this new structure is kinetically stabilized against alloying by the large size difference between the Cd2+ ion and Zn2+ ions. We suggest that all of these factors contribute to the formation of quantum-dot quantum-well ZnS/CdS/ZnS heteronanostructures 关键词: cadmium compounds;energy gap;epitaxial growth;excitons;II-VI semiconductors;interface states;interface structure;nanostructured materials;semiconductor growth;semiconductor heterojunctions;semiconductor quantum dots;semiconductor quantum wells;tight-binding calculations;ultraviolet spectra;visible spectra;zinc compounds;quantum-dot quantum-well heteronanostructures;large lattice mismatch;ZnS/CdS/ZnS;two-dimensional heterostructures;II-VI film heterostructures;optical properties;exciton binding energy;large band gap;small II-VI nanoparticles;seed nanoparticles;nanoepitaxy;ZnS/CdS core/shell quantum-dot quantum-well heteronanostructures;UV visible absorbance;electronic level structures;tight-binding model;core/shell/clad structures;metastability;low-temperature construction;small crystal size;ZnS/CdS interfacial curvature;alloying;ZnS-CdS-ZnS