Experimental Investigations of Quantum Confined Silicon Nanoparticle Light Emitting Devices

Rebekah K. Ligman (ECE)

Advisors: Stephen A. Campbell (ECE), Uwe R. Kortshagen (ME)

As the demands on our worlds energy resources continue to grow, alternative high efficiency materials such as quantum confined silicon nanoparticles (Si nps) are desirable for their potential low cost application in general white light illumination, in optical displays and in on-chip optical interconnects. Many fabrication and passivation techniques have been developed that produce Si nps with high photogenerated quantum yield. However, high electrically generated Si np quantum efficiency has eluded our society. Predominantly due to the lack of a stable surface passivation and a device fabrication technique that preserves the Si np optical properties. To amend these deficiencies, the passivation and subsequent device fabrication around Si nps are being investigated with the end goal of generating electroluminescence (EL) from Si nps.

The nonthermal plasma fabricated Si nps are first passivated with a surface oxide grown under UV exposure. Although the oxide is not desirable for high energy Si nps emission, the surface oxidized Si np (Si/SiO₂) surface chemistry is composed predominately of SiO₂, readily controlled using the Si np concentration and UV exposure, and stable in various chemical environments. Therefore the Si/SiO₂ nps are suitable for the purpose of demonstrating Si np EL.

EL from Si nps has been previously demonstrated by incorporating Si nps in various dielectric matrices. However, these devices have low Si np quantum efficiencies as they are inherently limited by the poor carrier transport properties of the dielectric matrix. It is instead desirable to incorporate Si nps into organic light emitting diode (OLED) devices. Such hybrid devices are the most promising candidates for the generation of high efficiency Si np EL as they utilize conductive organic materials. Therefore, such hybrid devices should vastly improve carrier transport to the Si nps, thereby enhancing Si np EL.

Two approaches for constructing hybrid OLED devices around nonthermal plasma fabricated Si nps will be investigated: (1) multilayer devices, composed of a nonthermal plasma fabricated Si np layer embedded between a hole and electron transporting layer and (2) single layer polymer(Si/SiO₂) hybrid devices, composed of nps randomly dispersed within an extrinsic conductive polymer. In the multilayer device, the hole and the electron transport layers are selected to form a type II heterojunction with the Si/SiO₂ nps, thereby improving carrier transport to and trapping within the np layer. In the single layer device, the polymer will be selected to form a type I heterojunction with the Si/SiO₂ nps, such that the nps act as a radiative recombination center within the polymer host.