The Study Of White Light Emission From ZnS/PS Composite System

The solid white light-emitting diodes (LEDs) will be the new generation of light source in the 21st century, and LEDs have attracted particular attention as backlight panels of liquid-crystal displays over the past few years. The achievement of Si-based white light emission is one of the challenging goals in the field of display and lighting technologies. In this dissertation, a new way was used to realize white light emission. According to the photoluminescence (PL) properties of porous silicon (PS) and zinc sulfide (ZnS), based on the principle of tricolor overlay, intensively white photoluminescence was obtained by combining the blue-green emission from ZnS films with the red emission from PS layers under proper excitation wavelength.ZnS films were grown by pulsed laser deposition (PLD) on PS substrates formed by electrochemical anodization of silicon wafers. X-ray diffraction (XRD) patterns showed that all the ZnS/PS samples had a diffraction peak at 28.5°corresponding to (111) direction of p-ZnS, which indicated that ZnS films were grown in preferred orientation along this direction. However, the full width at half maximum (FWHM) of the diffraction peak was large due to the special structure of the PS substrates. Due to the roughness of the PS surface, there were some voids and cracks in the ZnS films which could be seen from scanning electron microscope (SEM) images.In this dissertation, the photoluminescence properties of ZnS/PS composites were studied in detail, and the effects of excitation wavelength, porosity of PS substrate, growth temperature of ZnS films, and post-annealing on the photoluminescence properties of ZnS/PS composites were researched. At proper conditions, the luminescence of ZnS combining with the luminescence of PS, ZnS/PS composites had a broad photoluminescence band in the visible region from 450nm to 700nm, exhibiting intensively white light emission.The I-V characteristics of the ZnS/PS heterostructure exhibited the similar rectifying behavior compared with the common diodes, and an ideality factor n was calculated from the I-V plot.