Can silicon be used as an emissive layer in white light emitting diode?

Pure silicon for white light led is not a suitable emissive material. The band gap of silicon corresponds to emission in the infra red and red regions of light. For the light to be white the emission centers must radiate higher energy wavelengths. Greens and blues. This is not possible with silicon alone.

But because silicon is such an abundant material that is already widely used in electronic industry and as such has a great deal of tooling created around it , there is immense interest in making silicon based white light emitting(wle) diodes work.

While silicon alone is insufficient for wle its compounds can work. Silicon carbide has already shown its ability to emit in blue, green and yellow regions(infact it was the first led ever made). Now research is being conducted into silicon oxycarbide which has shown some promising initial results.

The paper "White light emission from amorphous silicon oxycarbide a-SiCxOy thin films: Role of composition and postdeposition annealing" by Himani Suhag and others discusses this in detail

https://www.researchgate.net/publication/234956109

“Development of a light source for intense and efficient white light is of interest. It is attractive to fabricate white- light emitters based on silicon using microelectronics technologies for applications in flat-panel display and tele- communication. There are many reports on red to near-infrared - NIR luminescence from Si-based dielectrics. For one, Si-rich silicon oxide - SRSO films, containing Si nanoclusters - Si- ncs in SiO2, reportedly emit red to NIR luminescence due to quantum confinement effect of Si-nc. However, unlike the observed red to NIR luminescence, luminescence at shorter wavelengths from SRSO is difficult due to the interplay be- tween defects and quantum confinement effects, even though Si-ncs could be made smaller than 2 nm with a band gap exceeding 2.5 eV.

The effects of carbon and postdeposition annealing on white luminescence are studied in amorphous silicon oxycarbide - a-SiCxOy films grown by chemical vapor deposition. The films showed strong room-temperature luminescence in a broad spectral range from blue-violet to near infrared, depending on excitation energy. Photoluminescence - PL intensity exhibited good correlation with Si-O-C bond concentration. At low C - - 5%, matrix PL was completely quenched after annealing in O2 even at 500°C. PL was unaffected by O2 annealing at higher C, and could be enhanced when excited by an ultraviolet laser. These findings are correlated to C- and Si-related O defect centers as luminescence sources in a-SiCxOy.

#engineering #materials #light

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