II-VI semiconductor quantum dots

Recently, II-VI direct band-gap semiconductor materials have been studied intensively due to their potential applications in blue lasers. On the other hand, the electrical and optical properties of low dimensional semiconductor microstructures have been investigated for two decades because of their ultra-fast electrical and optical properties and enhancement of light emission in indirect band-gap materials. Therefore, to improve the understanding of the low dimensional semiconductor microstructures is useful in fundamental physics and for application to optical and electrical devices. Two nanometer-scale quantum dots (QDs) of II-VI semiconductors, cut from molecular-beam-epitaxy grown ZnSTe/ZnS single quantum well heterostructures (QWs) and ZnSe/ZnSTe superlattice (SLs) by electron beam lithography and dry etching processing, were studied. They were characterized by using both temperature dependent photoluminescence (PL) from 10K to room temperature and excitation power dependent photoluminescence. The blue shift due to the quantum confinement and red shift due to the strain relaxation of the emission spectra were in reasonable agreement with the calculation results. From the temperature dependent PL spectra of free-excitons in both superlattice and quantum dots, the binding energies were determined. It is also found that even at room temperature, the deep level emission due to the Te isoelectronic centers in ZnSTe quantum dots is significantly enhanced, in comparison with that from the unprocessed region. Finally, we propose a simple concerning the surface effect to understand such enhancement of the isoelectronic related PL emission