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Silicon, being earth-abundant, inexpensive, and fully compatible with the mature
complementary metal–oxide–semiconductor (CMOS) platform, is an attractive candidate for
next-generation integrated optoelectronic devices. However, bulk crystalline silicon is
inherently limited as a light emitter due to its indirect band gap, leading to low radiative
recombination efficiency and poor photon emission. This fundamental drawback has
historically hindered the use of silicon in active light-emitting applications. On the other hand,
silicon nano-rods and nano-dots exploit quantum confinement effects, leading to altered
electronic states that enable efficient visible photoluminescence with tunable emission
properties. Though these features have the potential to effectively mitigate the limitations of
bulk silicon while offering pathways for fabricating low-cost, CMOS-compatible LEDs, the
origin of the observed luminescence became a topic of controversy from the very beginning.
Some groups believe it is due to the quantum confinement effect, while other groups
consider the oxide-related traps as responsible for the bright PL under UV excitation.
Though the omnipresent, unavoidable non-stoichiometric insulating silicon oxide layer
surrounding the quantum structures acts as a window layer for visible light, the complicated
charge transport through it hinders efficient carrier injection, limiting the Electroluminescence
efficiency well below that of its competitors with direct bandgap semiconductors. Many
groups, including ours, could reach an external quantum efficiency of only <1 % for the
devices with electrochemically grown Nano Silicon as an active layer, primarily due to this
unwanted but nearly unavoidable oxide layer.
In this background, I’ll provide an outline of different synthesis techniques that produce
quantum rods and dots of silicon. A method for distinguishing the origin of the luminescence
from these quantum structures will also be discussed. I’ll also discuss our recent observation
on the memristive properties of the devices fabricated using these quantum structures.
Finally, I’ll present an encouraging observation on efficient white light emission from an LED
device made with rGO capped Silicon quantum rods. |