Optimization of Light Emission from Silicon Nanocrystals Grown by PECVD

<jats:title>Abstract</jats:title><jats:p>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 SiH<jats:sub>4</jats:sub> and N<jats:sub>2</jats:sub>O of a precursor gas was changed by varying a N<jats:sub>2</jats:sub>O gas flow rate and the annealing temperature was varied from 800 to 1100°C. The highest PL intensity was obtained with a N<jats:sub>2</jats:sub>O flow rate of 125sccm, a SiH<jats:sub>4</jats:sub> flow rate of 1400sccm and annealing temperature of 900°C. The PL wavelength was also controlled by N<jats:sub>2</jats:sub>O gas flow rate and annealing temperature, with blue shifting to the visible wavelengths for increasing N<jats:sub>2</jats:sub>O flow rate and decreasing annealing temperature. In addition, forming gas ( 4% H<jats:sub>2</jats:sub> ) 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 / SiO<jats:sub>2</jats:sub> multi layer structure ( MLS ) was also fabricated by similar methods. The SiO<jats:sub>2</jats:sub> 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.</jats:p>