Silicon light emitting materials, structures and devices

The overall objective of this work combines a study of the fundamental mechanisms of light emission from porous silicon with the development of techniques fabricating porous Si-based light emitting structures and devices, and ultimately with the fabrication of porous silicon light emitting nanostructures and diodes.; Incubation time of porous silicon formation using pure chemical etching (stain-etching) in HF:HNO{dollar}sb3{dollar}:H{dollar}sb2{dollar}O was studied in detail and a strong dependence of the incubation time on the substrate doping type and concentration was consequently observed. Scanning electron microscopy study of the stain-etched porous silicon revealed the existence of a wide variety of surface morphology which is primarily affected by the substrate doping. No significant doping effect on the photoluminescence itself was observed. Utilizing the incubation time difference and Ga{dollar}sp+{dollar} focused ion beam implantation a process was successfully developed to fabricate selective light emitting silicon patterns and nanostructures embedded in a conventional silicon substrate with sub-micron resolution being achieved for the first time.; Luminescent porous polycrystalline silicon films were obtained by stain-etching poly-Si films on both oxidized silicon and quartz substrates deposited by low pressure chemical vapor deposition. Uniform light emission was achieved from patterned poly-Si films on oxidized Si with both sub-micron features and large area which offers potential application in porous-silicon-based flat panel display devices. Porous silicon from stain-etched Si thin films deposited on oxidized Si substrates at temperatures ranging from 540 to 640{dollar}spcirc{dollar}C, designed to provide varying levels of crystallinity, was systematically studied by x-ray diffraction, photoluminescence and infrared transmission spectroscopy. It was observed that a minimum level of crystallinity in the as-deposited Si film is required for the subsequent porous silicon layer to exhibit visible photoluminescence, and it appears that there exists a unique correlation between the level of crystallinity of the starting Si film, and the presence of surface oxyhydrides and photoluminescence after stain-etching.; Visible light emitting diodes (LED) using stain-etched porous silicon thin films have been fabricated and characterized. The porous silicon film used in this work of only about 200 nm is the thinnest ever reported for a porous silicon LED. The devices have superior electrical characteristics and achieved the best ideality factor, the highest rectifying ratio and the lowest EL onset current reported to date along with improved EL linearity. Since the stain-etch process is much simpler than anodization and can be used to form sub-micron luminescent porous silicon patterns and to produce luminescing poly-porous silicon films on quartz and glass, these results demonstrate a very promising and advantageous technique for fabrication of porous-silicon-based LED's and poly-porous-silicon-based electroluminescent devices.