Light emission from Si nanocrystals ( SiNCs ) embedded in Si oxide was studied in this work. SiNCs were fabricated by annealing a Si-rich oxide ( SRO ) deposited by a plasma-enhanced chemical vapor deposition ( PECVD ) system. The gas flow ratio between SiH4 and N2O of a precursor gas was changed by varying a N2O gas flow rate and the annealing temperature was varied from 800 to 1100°C. The highest PL intensity was obtained with a N2O flow rate of 125sccm, a SiH4 flow rate of 1400sccm and annealing temperature of 900°C. The PL wavelength was also controlled by N2O gas flow rate and annealing temperature, with blue shifting to the visible wavelengths for increasing N2O flow rate and decreasing annealing temperature. In addition, forming gas ( 4% H2 ) anneal for 1 hour, which is a common method to passivate Si surface, at 500°C to SiNCs was used to further enhance the emission intensity. To approach emission at shorter wavelength, the Si oxide with SiNCs / SiO2 multi layer structure ( MLS ) was also fabricated by similar methods. The SiO2 layer was used as a diffusion barrier to extra Si on vertical direction during the annealing process. Such a barrier can effectively reduce the diameter of SiNCs and shift the emission peak to shorter wavelength. A blue shift from PL was clearly observed as the thickness of Si oxide layer with SiNCs in MLS reduces. Finally, the PIN light emitting diode which consisted of n-type poly-Si / Si oxide with SiNCs / p-type poly-Si structure was also fabricated to study the electroluminescence ( EL ) of SiNCs. The current under the forward bias was about 10 times higher than under the reverse bias. The carrier injection mechanism assumed that Poole-Frenkel type conduction or hopping conduction dominates under a low electric field and Fowler-Nordheim tunneling dominates under a high electric field. EL was obtained with a forward bias voltage of around 6V and EL emission efficiency was proportional to the current density.
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Ishikawa, S., Cheng, SL., Gong, Y. et al. Optimization of Light emission from Silicon nanocrystals grown by PECVD. MRS Online Proceedings Library 1257, 305 (2010). https://doi.org/10.1557/PROC-1257-O03-05