CAS-Croucher Joint Labs

The CAS-Croucher Funding Scheme for Joint Laboratories is the outcome of an agreement between The Chinese Academy of Sciences (CAS) and the Croucher Foundati...

Controlled synthesis and optical properties of II-VI semiconductor

Professor Shuit-tong Lee, Chair Professor of Physics and Materials Science at the City University of Hong Kong and Professor Xiaohong Zhang of the Chinese Academy of Sciences Technical Institute of Physics and Chemistry in Beijing have made significant impact in the controlled synthesis and characterisation of II-VI compound semiconductor nanostructures.

In this joint project we find the great application potential of II-VI compound semicond-uctors nanostructure devices for high-sensitivity and high-speed nanoscale devices.

Prof Shuit-tong Lee

II-VI compound semiconductors (zinc chalcogenides: ZnO, ZnS, ZnSe, ZnTe; cadmium chalcogenides: CdS, CdSe, CdTe) have outstanding optical properties. These include: direct band gap, high fluorescent yield and a large exciton binding energy, that implies a flexibility to fabricate devices such as light emitting diodes (LED) and photodetectors. 

However, despite their excellent attributes, II-VI compound semiconductors have not yet been made into practical optoelectronic devices. The main obstacle to making II-VI-based devices is largely associated with the poor material quality available from the current II-VI wafer fabrication technology. 

In this joint project, Professors Lee and Zhang's research teams utilised nanotechnology to effectively ease or overcome material difficulties. In particular, the impact made in the area of II-VI nanostructures is considerable. The researchers have been able to conduct controlled synthesis and assembly of these nanostructures as well as explore and investigate the novel optical properties in synthesized II-VI nanostructures of  the nanometer scale.

The results revealed several material advantages of II-VI compound semiconductors nanostructure over their bulk or wafer-size crystals counterparts.  Firstly, it was easier to grow nanosized crystals with low-defect density and superior optical qualities. Secondly, II-VI compound semiconductors with different chemical compositions could be integrated into one hierarchical nanostructure conveniently. Thirdly, nanostructures of II-VI compound semiconductors could be controllably doped to tailor their optical properties with ease. 

Based on the advantages of these new materials the team has achieved significantly enhanced optical properties, for example, photocurrent and photoluminescence from II-VI compound semi-conductor nanostructures.

The findings have great application potential for II-VI compound semiconductors nanostructure devices in high-sensitivity and high-speed nanoscale devices.

Lee and Zhang's research has been published in leading international journals such as Appl. Phys. Letters, Chem. Comm and Nanotechnology.