Infrared luminescence from spark-processed silicon and erbium-doped spark-processed silicon

Spark-processed silicon has substantial potential as an optical material. In the past 15 years, our group has investigated a multitude of properties of this unique material, concentrating mostly on the visible and near UV spectral region.The present study expands our endeavors to infrared photoluminescence (PL) of undoped spark-processed silicon. A broad infrared photoluminescence peak at around 945 nm under Ar ion laser excitation was observed at room temperature when investigating a spark-processed layer on a silicon wafer. This light emission is interpreted to be the result of energy transfers between certain energy levels involving the spark-processed silicon matrix. The infrared PL intensity of spark-processed silicon was found to be proportional to the excitation energy.However, telecommunication requires presently a light emission near 1.54 mum (because fiber-optics "conductors" have a minimum in absorption at this wavelength). This cannot be achieved with pure spark-processed silicon. Therefore spark-processed silicon needs to be doped with a rare-earth element such as erbium to shift the emission to longer wavelengths. It is known that erbium has a light emission from intrashell energy transition, that is, from 4I13/2 &rarr4I15/2. Erbium was deposited on a silicon wafer followed by spark-processing, which enables diffusion of some erbium into the SiOx matrix, thus achieving opto-electronically active spark-processed silicon. Rapid thermal annealing enhances the 1.54 mum wavelength intensity from erbium-doped spark-processed silicon. The processing conditions that result in the most efficient photoluminescence have been established and will be presented in this dissertation. In contrast to erbium-doped crystalline silicon, whose light emission is highly affected by temperature (103 times reduction in intensity when heating from 12 K to 150 K), the intensity of erbium-doped spark-processed silicon decreases by only a factor of 4 when heated from 15 K to room temperature.Based on the most efficient photoluminescence conditions, an erbium-doped spark-processed silicon electroluminescence (EL) device was prepared. The devices studied have metal contacts on top and bottom of the substrate. A window through the metallization at the bottom was formed by masking which enabled the light emission. The electroluminescence spectrum has a peak at around 1.55 mum with an output/input power efficiency of about 0.01%. The device works even at elevated temperatures.The experimental findings are interpreted by postulating a photoluminescence mechanism with energy transfer from spark-processed silicon to the Er 3+ ions. Furthermore, a hot electron tunneling-induced electroluminescence mechanism is considered.